h'J^ ' -s^ .0 sV HARVARD UNIVERSITY LIBRARY OF THE Museum of Comparative Zoology JAN 1 1929 MEMOIRS OF THE MUSEUM OF COMPARATIVE ZO(»LO(,'y AT HARVARD COLLEGE. VOL. LI. CAMBRIDGE, MASS., U. S. A. printeb for tbe /iDuseum. 1928. JAU 101923 MEMOIRS OF THE MUSEUM OF (JOMPARATIVE ZOOLOUY AT HARVARD COLLt:GE. VOL. LI. CAMBRIDGE, MASS., U. S. A. pvinteD fov the /IDuscum. 1928. printed by The Cosmos Press, Incorporated Cambridge, Mass. ADemotrs of tbe /IDuseum of Comparative Zoology AT HARVARD COLLEGE. Vol. LI. REPORTS ON THE SCIENTIFIC RESULTS OF THE EXPEDITION TO THE EAST- ERN TROPICAL PACIFIC, IN CHARGE OF ALEXANDER AGASSIZ, BY THE U. S. FISH COMMISSION STEAMER " ALBATROSS," FROM OCTOBER, 1904, TO MARCH, 1905, LIEUT.-COMMANDER L. M. GARRETT, U.S.N., COM- MANDING. XXXV. THE DINOFLAGELLATA: THE DINOPHYSOIDAE. By CHARLES ATWOOD KOFOID AND TAGE SKOGSBERG. WITH THIRTY-ONE PLATES. [Published by permission of Henry O'Mallet, U. S. Fish Commissioner]. CAMBRIDGE, U. S. A. IPrinteO for tbe flDuseum. December, 1928. CONTENTS. REPORTS on the scientific results of the expedition to the Eastern Tropical Pacific, in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer "Albatross," from October, 1904, to March, 1905, Lieut. -Commander L. M. Garrett, U. S. N., commanding. XXXV. The Dinoflagellata; The Dinophysoidae. By Charles A. Kofoid and Tage Skogsberg. 766 pp., 31 plates. December, 1928. CONTENTS Page PART I. Introduction and Collections 13 Acknowledgments ............. 15 Methods of collecting ' .... 16 Distribution of collections 18 Examination of collections 19 Number of genera and species 21 Orthogenesis and convergence 23 Procedure used in the accounts of genera and species 26 PART II. Systematic Account 29 Classification 29 Dinophysoidae Kofoid, 1926 30 Diagnosis 30 Derivation. Subdivisions. Relationships among the families .... 30 1. Dinophysidae Stein, 1883 : 32 Diagnosis 32 Subdivisions. Relationships among the genera ...... 32 Distribution 35 Key to the genera 35 Heteroschisma, gen. nov. 36 Diagnosis 36 Distribution 36 H. aequale, sp. nov. 36 H. inaequale, sp. nov 38 Phalacroma Stein 40 Diagnosis 40 Organology 40 Reproduction . 51 Distribution ........... 53 Historical discussion and systematica 58 Adaptive and systematic value of the characters. Principles used in description of the species ........ 63 Subdivisions. Relationships among the species 66 Discussion of species groups 68 1. Contractum group 83 P. contractum, sp. nov. ........ 83 2. Rotundatum group 85 P. parvulum (Schiitt) Jorgensen 85 P. lativelatum, sp. nov. ........ 89 P. lens, sp. nov 91 P. porosum Kofoid & Michener 93 p. lenticula Kofoid 96 CONTENTS. Page 3. Argus group 98 P. porodictyum Stein .... 98 P. argus Stein ..... . 104 P. apicatum, .sp. uov. .... 111 P. circunicinctuin Kofoid & Michener 114 P. ovum Scliiitt lis P. pyriforme, sp. nov. . 122 4. Cuneus group . 124 P. cuneus Schiitt .... . 124 P. striatum Kofoid .... . i;ii P. gigantcuni Kofoid & Michener . 136 5. Rapa group . 139 P. rapa Stein . 139 P. favus Kofoid & ^Michener . 146 P. hindmarchi Murray & Wliitting . 150 6. E.xpulsum group .... . 1.5.-) P. protuherans, sp. nov. 155 P. e.xpulsum (Kofoid & Michener) . 157 7. Limbatum group .... . 161 P. Iinil)atum Kofoid & Michener . 162 P. bipartitum, sp. nov. . 166 P. pulchrum Kofoid & JNIichener . 168 S. Doryphorum group .... . 172 P. niucronatum, sp. now . 172 P. doryphorum Stein .... 175 P. circunisutum Karsten 182 P. cuneolus, sp. nov. .... 186 9. Praetextum group .... 188 P. praetextum Kofoid & Michener 189 10. Reticulum group .... 192 P. fimbriatum Kofoid & Michener 192 P. reticulatum Kofoid 195 P. turbineuin Kofoid & Michener 198 Dinofurcula, gen. no\- 201 Diagnosis 201 Distribution 202 D. ultima (Kofoid) 203 D. ventralis, sp. nov. 205 I )inophysis Ehrenberg . 207 Diagnosis .... 207 Organology 207 Reproduction 218 Distribution 219 Historical discussion and systematics 224 .\daptive and systematic value of the characters. Principles used n the description of the species .... 233 Sulxlivisions. Relationships among the species . 235 1. Acuta group 239 D. exigua, sp. nov. . . . . 239 CONTENTS. f. nov D. sphaerica Stein .... D. similis, sp. nov D. okamurai, sp. nov. D. fortii Pavillard .... D. norvegica Claparede & Lachmann [?] D. schrtideri Pavillard 2. Hastata group I), hastata Stein ..... D. uracantha Stein .... D. urceolus, sp. nov. .... D. monacantha, sp. nov. D. trapezium, sp. nov. D. swezyi, sp. nov. .... D. collaris Kofoid & Michener D. schiitti Murray & Whitting D. nias Karsten D. jnrgenseni, sp. nov. L). triacantha Kofoid .... 3. Caudata group D. caudata Saville-Kent D. caudata Saville-Kent f. acutiformis, noni Histiophysis, gen. nov Diagnosis ....... H. rugosa (Kofoid & Michener) 2. Amphisolenidae, fam. nov Diagnosis ........ Subdivisions. Relationships between the genera Distribution Key to the genera ...... Amphisolenia Stein Diagnosis Organology ...... Reproduction ...... Distribution Historical discussion ..... Adaptive and systematic value of the characters. P the description of the species . Subdivisions. Relationships among the species Key to the species of Amphisolenia . 1 . Species of uncertain or more or less isolated A. inflata Murray & Whitting A. laticincta Kofoid .... A. brevicauda Kofoid .... A. schauinslandi Lemmerniann A. rectangulata Kofoid A. astragalus Kofoid & Michener 2. Extensa group ..... A. extensa Kofoid .... A. elongata, sp. nov posi ncipli es US' ed ii Page 241 247 250 253 256 257 261 261 273 281 283 286 289 292 296 303 307 312 314 314 330 333 333 334 335 335 336 339 340 340 340 340 347 349 353 355 360 365 366 366 369 372 374 378 380 382 383 386 10 CONTENTS. Page 3. Globifera group 388 A. globifera Stein 388 A. quadrispina Kofoifl 393 4. Bispinosa group . . . 395 A. bispinosa Kofoid 395 A. curvata Kofoid 398 5. Schroderi group ...... 400 A. schroderi Kofoid 400 A. clavipes Kofoid 402 A. complanata, sp. nov 404 A. truncata Kofoid & Michener .... 406 6. Palmata group 409 A. bidentata Schroder 409 A. lemmermanni Kofoid ..... 419 A. pahnata Stein 422 .\. palaeotheroide.s Kofoid ..... 427 A. asymmetrica Kofoid 429 7. Bifurcata group 432 A. bifurcata Murray & \Vhitting 432 A. projecta Kofoid 436 A. thrinax Schiitt 438 A. quadricauda Kofoid & Miciieucr 444 A. quinquecauda Kofoid ..... 445 Triposolenia Kofoid ....... 446 Diagnosis ......... 446 Organology 447 Reproduction ........ 453 Distribution ........ 454 Historical discussion ....... 459 Adaptive and systematic value of the characters. Principles used in thf descriptions of the species ..... 45!) Subdivisions. Relationships between the subgenera and among th( species . ; 461 Key to the species of Triposolenia .... 462 Subgenus 1. Triposolenia, nom. subgen. nov. 463 T. truncata Kofoid 463 T. depressa Kofoid 468 T. bicornis Kofoid ...... 473 T. intermedia, sp. no\ . ..... 477 T. longicornis Kofoid ...... 479 T. fatula Kofoid 483 T. ambulatrix Kofoid 486 Subgenus 2. Ramiciformia Kofoid .... 48!) T. ramiciformis Kofoid 489 3. Ornithocercidae, fam. nov. ...... 494 Diagnosis 494 Subdivisions. Relationships among the genera 494 Distribution 495 Key to the genera 496 CONTENTS. 11 Ornithocercus Stein Diagnosis .... Organology .... Reproduction .... Distribvition .... Historical discussion and systematics Adaptive and systematic \-alue of the characters. Prir description of the species . . vSubdivisions. Relationships among the species Key to the species of Ornithocercus 1. Splendidus group .... 0. heteroporus Kofoid O. splendidus Schiitt .... 2. Magnificus group .... O. magnificus Stein, s. str. Schiitt O. thurni (Schmidt) .... 0. steini Schiitt, s. str. 0. orbiculatus Kofoid & Michener O. quadratus Schiitt .... O. carolinae Kofoid .... 3. Formosus group .... O. formosus Kofoid & Michener . Specimens of Ornithocercus of ([uestionable specific a Parahistioneis, gen. nov. .... Diagnosis Organology Distribution Historical discussion ..... Subdivisions. Relationships among the species Key to the species of Parahistioneis . 1 . Species of uncertain generic allocation P. rotundata (Kofoid & Michener) 2. Garretti group P. garretti (Kofoid) .... P. paraforniis, sp. nov. P. para (Murray & Whitting) 3. Reticulata group .... P. karsteni (Kofoid & Michener) P. reticulata (Kofoid) P. diomedeae (Kofoid & Michener) Histioneis Stein ...... Diagnosis ....... Organology Distribution Historical discussion and systematics Aflaptive and systematic value of the characters. Princ description of the species .... Subdivisions. Relationships among the species Key to the species of Histioneis . pies used : the I turn plesi in tht Page 496 496 496 .501 .503 .509 512 515 516 517 517 521 528 529 540 551 559 561 572 577 577 580 582 582 583 588 589 590 592 592 593 596 596 598 601 603 603 605 60S 611 611 611 625 629 631 634 645 12 CONTENTS. atefl speci es of soniewhiit 1. Primitive species and higlily clitt'erent isolated positions H. costata Kofoid & Michener H. pauiseni Kofoid H. inciinata Kofoid & Michener H. inornata Kofoid & Michener H. reginelhi Kofoid & Michener H. panaria, sp. nov. 2. Remora group H. elongata Kofoid & Michener H. carinata Kofoid H. navicula Kofdid 3. Biremis group H. biremis Stein . H. highleyi Murray & Whittiiig 4. Longicollis group H. longicollis Kofoid H. hyalina Kofoid & Michener H. pacifica, sp. nuv. 5. Pulchra group H. gubernans Schiitt H. striata Kofoid & Micliencr H. pulchra Kofoid H. niitchellana Murray & Wliitting H. panda Kofoid & Michener 6. Dolon group H. helenae Murray & Wliitting H. milneri Murray & Whitting H. dolon Murray & Whitting H. hippoperoides Kofoid & INIicl H. josephinae Kofoid 4. Citharistidae, fani. nov. . Diagnosis ...... Citharistes Stein .... Diagnosis ..... Distribution .... Historical discussion . C. regius Stein C. apsteini Schiitt . PART III. Distribution of I )inophvsoidae .\t the Stations of the Expeditio.v Bibliography Index. I. Names of systematic units higlier tluin species .... II. Specific and subspecific names ...... Page 647 647 650 652 654 656 659 661 6(il 663 667 669 669 673 676 677 679 681 683 684 684 686 690 694 696 696 697 698 701 704 707 707 707 707 708 708 709 712 717 739 759 760 I. INTRODUCTION AND COLLECTIONS This report deals with the pelagic Dinophysoidae, a tribe of the subclass Dinoflagellata, taken by the U. S. Fish Commission Steamer Albatross during an expedition to the Eastern Tropical Pacific, from October, 1904, to March, 1905, under the leadership of the late Alexander Agassiz. The Mastigophora or Flagellata are represented in the plankton of all seas, and especially in the tropics, by three main groups, called orders in Doflein's (1916) system, namely, the Chrysomonaduia, the Dinoflagellata, and the Cysto- flagellata. The first-named group is represented by two divergent families, the Silieoflagellidae and the Coccolithophoridae. Owmg to their minute size, the Silicoflagellidae are not taken in numbers in the net plankton even with the finest of silk bolting cloths. One must turn to the centrifuge or filter as an effective means of determining the relative abundance of these representatives of the nannoplankton. The natural filters of Salpa and other feeders upon the nanno- plankton also offer remarkalale resources for observing this group. The calca- reous internal skeletal elements of the Coccolithophoridae formed the coccoliths of the mythical "Bathybius" of the reputed primordial slime discovered by the Challenger Expedition. They are retained m calcareous oozes, but the flagel- lates which produce them, owing to their small sizes, must also be sought in the nannoplankton or in the digestive tracts of animals feeding thereon. The Dinoflagellata, on the other hand, are of much larger size and are to be found m great numbers in the plankton taken in silk nets, even as coarse as number 12. They are very numerous in most plankton collections, vying with the diatoms for preeminence in numbers and variety. In northern waters the species are less numerous, but the individuals are at times extraordinarily abundant, the total production massive, and their predominance extreme. In the tropics, on the other hand, the number of individuals of any one species is quite generally snmll, but the number of species is greatly increased and the processes of differentiation reach here their highest expressions. The Chrysomonadina and the Dinoflagellata are both included in the Phytomastigina, but the Dinoflagellata contain many holozoic genera and species, notably among the Gymnodinioidae. In this tribe also cell-organs such as 14 THE DINOPHYSOIDAE. ocelli, nematocysts, and tentacles have arisen. Because of these facts and also because of the size and differentiation within the group Kofoid and Swezy (1921) have treated the Dinoflagellata as a subclass coordinate with the Phytomastigina and the Zoomastigina. The third main group of Flagellata represented in the plankton of the ocean is the Cystoflagellata, containing the widely known genus Noctiluca. This, however, as Kofoid (1919) has shown, is only a highly specialized form of a gym- nodinioid dinoflagellate. Since the other representatives of the Cystoflagellata are probably either highly modified dinoflage Hates or radiolarians, this group should ultimately disappear from the scheme of classification of the Mastigophora. The Dinoflagellata are of special interest to the observer of marine life be- cause of their extraordinary power of luminescence. This appears upon stimu- lation by contact, shock, or chemical irritation, at night only, as shown by experiment. The extent to which luminescence is present among the various dinoflagellates is unknown. It occurs, however, in the Gymnodinioidae in Nocti- luca, in the Peridinioidae in Gonyaulax, Ceratium, Blepharocysta, and Peridin- ium. No critical records of this phenomenon in the Dinophysoidae are known to us, but its occurrence among them is highly probable. Much more remains to be done in relation to the occurrence, location, duration, cause, and nature of the light thus produced in Dinoflagellata generally. These flagellates are also the cause of the notorious outbreaks of "red water" in tropical and warm-tem- perate seas (Torrey, 1902, and Kofoid, 1911) m which the enormous numbers present give a reddish, brownish, or yellowish discoloration to the surface waters, often for long distances along shore, or in great areas of the off-shore tropical currents. The collections of the Expedition have been found to contain 132 species of Dinophysoidae, including 82 new species and four new genera. All but one of the known genera are represented or occur in the area traversed by the Expedition and 132 of the 198 known species, or 66.7%, occur in the Expedition material. The species not recorded are mainly those restricted to colder regions or they are \'ery rare tropical forms. The report upon the tribes Gymnodinioidae and the Peridinioidae of this Expedition is in the course of preparation. The Dinophysoidae are marine and widely distributed in the plankton of coastal waters and in the uppermost 300 fathoms of the illumined zone of the high seas in all latitudes. The species of this group are remarkable for their diversity, for their occasional brilliant coloring, and for the extraordinary evolu- tion of organs of flotation in the form of processes of the body or in the form of INTRODUCTION AND COLLECTIONS. 15 lists differentiated as parachutes, sails, wings, or rudders. The thecal wall or cuirass which forms the surface of the body retains throughout the whole group the structural simplicity in the matter of the numbers of its constituent plates found in the simplest and most primitive members. It is bivalved and each valve contains three elements, an epithecal, a cingular, and a hypothecal plate. In certain genera such as Dinofurcula, Amphisolenia, Triposolenia, and in a few of the more divergent tropical species of Dinophysis, the body, while retaining its bivalved simpUcity of component parts, undergoes a remarkable evolutionary flare of elongation, bifurcation, multiple branching, and distal twisting into asymmetrical form, all of which serve the function of flotation. In this assem- blage of species in which the body proper undergoes these extensive diversifica- tions in form, there is very little evolution of the lists of the girdle and the sulcus. Since the Dinophysoidae are predominantly, if not wholly, either photo- synthetic, or associated with commensal photosynthetic phaeosomes, they find their optimum conditions of life within the lighted zone in the upper levels of the sea. Adaptations to flotation and to hydrostatic adjustments thus loom large in their structural evolution. The structural expansions of the surface lend them- selves to regulatory control by resorption, especially at binary fission, and to extension by renewed outgrowth to meet diverse conditions of the environment. Acknowledgments No investigation involving so extensive collections, so prolonged search of the diversified constituents of the tropical marine plankton, so much drawing and sketching for purposes of record and comparisons, and the use and clerical analysis of so widelj' scattered a literature, can be brought to completion without the collaboration of several workers. During the Cruise the senior author made daily observations and notes on the plankton as collected, and throughout the work has continued in close collabo- ration in the microscopical, morphological, and systematic analysis of the mate- rial. He has resolved the structure of the individuals utilized in the elaborately finished drawings, and supervised the completion of the illustrations. He is responsible for the plan of the work, of the method of treatment of species, and jointly with Dr. Skogsberg for the morphological analysis and systematic arrange- ment of the text. The manuscript of Part II of the work has in the main been prepared by Dr. Skogsberg, with the continuous collaboration and joint analysis of all moot points with the senior author. 16 THE DINOPHYSOIDAE. The original drawings and records of occurrences based on the painstaking examination of the plankton collections are the work of Mrs. Michener from May 1905 to June 1908, and from June 1909 to July 1910. Her sketches have been utilized in the text figures and her detailed drawings, finished in pencil, have been transferred and prepared for reproduction on Ross board by Mr. A. B. Streedain. His skill in portraying contour and detail by this method has con- tributed much to the accuracy and beauty of the plates. We are indebted to the late Dr. Alice Robertson for assistance in organizing the multitudinous details of several of the genera. For grants in aid of the work we are also indebted primaril,y to Alexander Agassiz, who after the close of the Cruise continued to manifest a deep interest in the progress of the work; and to the Carnegie Institution of Washington, through the late Dr. Alfred G. Mayor, Director of the Department of Marine Biology, for a grant for assistance in the preparation of tlie manuscript. The work could not have been completed except for substantial grants made bj' the Board of Research of the University tif California for the past four years. Methods of Collecting The plankton collections were made, in the main, by the following methods : — Under normal conditions, except on the Manga Reva-Acapulco line, a collection was made each evening at 8 p.m. with number 12 and number 20 silk nets towed from the port boom on either side of the large 000 plankton net. The depth at which these nets fished was generally within the uppermost fathom. The nets were out for about twenty minutes. The same nets were used in the morning collections at 8 a.m., but at this time sufficient cable was payed out to lower them to a depth of 300 fathoms. They were towed for twenty minutes, steaming slowly, and were then hauled in. They were open and fishing during Ixith descent and ascent and the catch there- fore represented the plankton from all knels traversed by the nets, but mainly from the level at which they were towed for twenty minutes, since the total time of lowering and hoisting was not more than one third of the time of towing at the lower level. As a rule the number 12 and number 20 nets were attached to the cable when hj'drographic samples were taken at a depth of 800 fathoms. These catches are thus from a vertical column of water from this depth to the surface. On the line from San Francisco to Panama collections were made in vertical INTRODUCTIOX AND COLLECTIONS. 17 hauls with the number 12 and number 20 nets attached in series to a vertical bar lashed to the cable. This method was abandoned after leaving Panama. The plankton nets used in these collections were of the Kofoid (1898) type, of number 12 and number 20 Dufour silk bolting cloth respectively, fourteen inches in diameter at the top, five feet in length, with a brass bucket at the lower end. Two such nets may be cut readily from two yards of silk and are of a size convenient to handle. They have a surface for filtration of such proportions to the opening that the coefficient of filtration is low. These plankton collections made regularly in course of the routine of the Cruise were supplemented from time to time by wing-net catches taken in small nets (four inches in diameter) tied to the upper bars of the runners of the trawl when trawhng. These catches contain samples of plankton from bottom to surface, since they were so suspended as to fish during both descent and ascent as well as while trawling. An attempt was also made to utilize a silk filter connected with the ship's circulating system near the intake and running continuously during the Cruise. A number 20 silk net with a fourteen-inch opening was suspended in a vertical cylinder with suitable overflow for the filtered water. This net received a con- tinuous stream from a pipe tapped into the circulating system within twenty feet of the intake. It functioned satisfactorily for the first fortnight, but its efficiency was destroyed by the accumulation of attached plankton-feeding organisms, principally barnacles, as shown by their faeces and remnants, which grew along the pipe fine and so reduced the plankton in amount as to render the catches of little significance. Iron rust and the cjuick disintegration of the silk net in the warm waters of the tropical seas also added to the ineflficiency of this method. Catches were made by this method for over half of the Cruise, but their contents are meager and add nothing of value to the material. Local surface and a few short vertical hauls with the number 12 and number 20 nets were made in the harbors at Panama, Manga Reva, and Acapulco. Con- ditions at Callao, at Chatham Island in the Galapagos, and at Easter Island re- spectively were so similar to those of the environing ocean that local collections at these points were of no great significance. In the main these local collections added little to the material of the Dinophj-soidae, since they were remarkably poor in organisms of this group except for a few of the hardier types which were invariably found also in the coastal waters. As will be seen in the station lists our main resources were in the regular hauls from the surface and from 300-0 fathoms, especially in the latter, which, 18 THE DINOPHYSOIDAE. as a rule, have a wider range of species since they contain the contributions from practically all zones in which dinoflagellates normally live. The catches of the wing-nets from the greatest depth and those at the hydrographic stations from 800 fathoms contained no additional Dinophysoidae not found in hauls from 300 fathoms and no noticeable change in the proportionate representation of the species. Distribution of Collections The collections were taken at 127 stations on the Cruise. A list will be found in Part III, together with the pertinent data. A fuller accoimt appeared in the General Report of the Cruise by Mr. Agassiz (1906). Their distribution on the six lines of the Expedition is shown in Plate 24. Stations 4571 to 4627 are on the San Francisco-Panama line, 4631-4671 on the Panama-Callao line, 4673- 4692 on the Callao-Easter Island line, 4694-4716 on the Easter Island-Galapagos line, 4717-4739 on the Galapagos-Manga Reva line, and 4740-4746 on the Manga Reva-Acapulco line. The collections at regular stations number 225. Of these eighty-three are from the surface, twenty-four more from Salpa stomachs treated as from the surface, ninety-four from 300-0 fathoms, twenty from 800-0 fathoms, and four from various other depths to the surface. The surface hauls, those from Salpa, and those from deeper levels are distributed on the six lines of the Expedition as follows: — on the (first) San Francisco-Panama line, 19, 2, and 19; on the (second) Panama-Callao line, 21, 5, and 29; on the (third) Callao-Easter Island line, 11, 2, and 15; on the (fourth) Easter Island-Galapagos line, 13, 6, and 19; on the (fifth) Galapagos-Gambier fine, 9, 6, and 31 ; and on the (sixth) Gambier- Acapulco line, 10, 3, and 5, respectively. In addition to these from the surface, from Salpa, and from the deeper levels there were incidental plankton collections at the anchorages at Panama, off Easter Island, and in the harbor at Acapulco, Mexico. These are, however, utilized only incidentally and are not treated as regular stations of the Cruise. The few collections made with the Chun plankton closing net are also omitted as they add nothing of systematic significance to the Dinoflagellata from the other collections. The distribution of the pelagic stations in the several oceanic currents is shown in detail in the following table : — INTRODUCTION AND COLLECTIONS. 19 DISTRIBUTION OF PELAGIC STATIONS Total number Surface end Surface Total of Total of of stations vertical oniy vertical surface California Current 4 4 4 4 Mexican Current 13 1 8 5 9 Panamic Area 17 2 11 6 13 Peruvian Current 27' 15 5' 22 201 Easter Island Eddy 10 5 5 5 Galapagos Eddy 4 2 2 2 South Equatorial Drift 45 1 22 23 23 South Equatorial Current 3 2 1 2 Equatorial Counter Current 2 2 2 North Equatorial Current 2 2 2 127 23 59 68 82 ' One of these is from Salpa only. Examination of Collections The plankton catch, as soon as it arrived on board ship, was released from the bucket into glass sorting dishes, treated with chloretone for anaesthetizing the larger organisms, and promptly fixed in 10% formalin. The plankton con- sisted of the fine sedimented residues remaining after the larger organisms such as the Coelenterata, larger Copepoda, Amphipoda, pelagic MoUusca, Tunicata, and larval fishes were removed. Small amounts were occasionally preserved in various fixing agents. This Report is, however, based on the formalin material since formalin, far better than any other fluid, preserves and reveals the skeletal structures upon which in final analysis the systematic relationships are based, and in which individual variations are revealed. The collections were examined in the original sea-water and formalin without other treatment than replacing the loss by evaporation with distilled water in some cases. It is thus often possible to roll the organisms about under the cover- glass and to secure diverse views in many cases of the same individual, and some- times also to shatter it into its constituent plates when this is necessary. The method has the disadvantage of not making it possible to reexamine the same individual with certainty a second time. There is, unfortunately, no safe and certain method of sealing permanent microscopical mounts in formalin. When- ever it was desired to isolate some special individual organism, the material under the cover-slip was washed carefully into a vial instead of into the general catch. The type specimens and cotypes are thus preserved. After a sufficient knowledge of the more abundant species had been acquired, each catch was searched by use of the mechanical stage until no additional species 20 THE DIXOPHYSOIDAE. were detected. The lists of occurrences at the record stations were thus made up. The station hsts (Part III) incorporate these data as modified by all later more critical revision. In order to have at least a quasi-quantitative record of relative frequency in individuals of the component species of each catch, records were made during the search of each collection of the number of individuals seen of each species, up to the total of the first one hundred individuals seen. Thereafter each additional species detected at that station was merely recorded as "also present." The number of individuals recorded is thus the percentage frequency at that station. These numbers ha^■e been used in mapping the local distribution of the genera. The numbers are recorded in Roman numerals at the ends of the radii from the circles marking the locations of stations on the route (Plate 24). The records of relative frequency used in the discussions of the distribution of each species, thus refer solely to the relative numbers of the different species in the one catch and give no indication of relative numbers of the species in question in different catches. The data thus accumulated have involved certain difficulties and discrepan- cies, especially in those cases in which a species, originally conceived in the wider sense, was later in the preparation of the manuscript broken up into several species by the withdrawal of divergent groups. In all such cases only those individuals which had Ijeen drawn were perforce included in the groups thus segregated off. All others recorded in the original analysis wei'e left under the original specific name in the later restricted sense. The concept of each species in the inception of the work of necessity rested upon previously published figures or upon the characters of the first individual whose structures were analyzed and from which the first figures were made. As the allocating of the individuals to definite species progressed, our concept was widened or modified by the detection of variants from the figure of the type individual. To meet this condition and to make available for purposes of com- parison the structure of individuals of the same species from different localities, it became necessary to sketch the outline of the most apparent and easily de- termined parts of an ever-increasing number of individuals. This was especially true in most cases of the more abundant and generally more w idely varying com- plexes. These groups of sketches constituted the great mass of data on which the manuscript has been based, and they form the sources of the text figures which illustrate the range of \'ariability and the aberrant types which are included within our concept of the several species. INTRODUCTION AND COLLECTIONS. 21 The fact should be noted that these habitus sketches represent the range of variation observed and not the normal distribution within that range. The constant tendency quite naturally in the premises was to make graphic record of all the aberrant individuals e\'en though these constituted only a very small pro- portion of the total representatives of the species. It thus follows that the di- versity in the few individuals within the species is emphasized rather than the uniformity among the many. Number of Genera and Species The microplankton of the Expedition contains a total of 132 species of Dinophysoidae. No less than eighty-eight new species have been established in connection with this Report. Of these new species thirty-two were described by Kofoid (1907a), twenty-nine by Kofoid and Michener (1911), and twenty- seven are described in the present paper. Of these twenty-seven species, twenty- six were found in the material of the Expedition; one {Phalacroma paulscni, p. 60) was based on a figure published previously (Paulsen, 1911b, p. 305, fig. 2). The following is a list of the new species found in the material of the Expedition : Described in Kofoid {1907a) Phalacroma lemmermanni Ornithocercus lentirula palaeotheroides carolinae reticulatum projecta heteroporus striatum quadrispina Parahistioneis Dinophysis quinquecauda (: as Histioneis) triacantha rectangulata garret ti Amphisolenia sohroderi reticulata asymmetrica Dinofiircula Histioneis bispinosa (as Phalacroma) carinata brevicauda ultima josephinae clavipes Triposolenia longicollis curvata longicornis navicula extensa fatula paulseni laticincta ambulatrix pulchra In Kofoid and Michener {1911) Phalacroma Histiophysis karsteni circumcinctum (as Dinophysis) rotundata expulsum (as Dinophysis) rugosa Hii ?tioneis favus Am|5hisolenia costata fimbriatum astragalus elongata giganteum quadricauda hippoperoides limbatum truncata hyalina porosum Ornithocercus inclinata praetextum truncata inornata pulchrum orbiculatus panda turbineum Parahistioneis reginella Dinophysis (as Histioneis) striata coUaris diomedeae 22 THE DINOPHYSOIDAE. Described in this Report Heteroschisma aequale inaequale Phalacroma apicatum bipartitum contractum cuneolus lativelatum lens mucronatum protuberans pyriforme Dinofurcula ventralis Dinophysis exigiia jorgenseni monacantha okamurai similis swezyi trapezium urceolus Amphisolenia complanata elongata Triposolenia intermedia Parahistioneis paraformis Histioneis pacilica panaria Besides the new species mentioned above, the following new specific and subspecific names are introduced in this Report: — Dinophysis baltica (p. 229) for D. ovum Schiitt var. baltica Paulsen (1908) Dinophysis caudala f. acutijormis (p. 227) for D. homunculus var. ventricosa Pavillard (1916) Dinophysis reciirva (p. 228) for D. lenlicida Pavillard (1916) Dinophysis renijormis (p. 228) for D. pavillardi Schroder (1906a) As shown in the following table there are in all fourteen genera, of which five are new. Total iiiimber of Bpecific and sub- speciHr namefi estab- lished in litpralurp Number of valid species and subspecies Number of new 8perie.s and sub- species described in connection with this Report Total number of species and sub- species found by the Expedition Theradinium, gen. nov. 2 2 Pseudophalacroma 1 1 Oxyphysis 1 1 Heteroschisma, gen. nov. 2 2 2 2 Phalacroma 73 50 23 31 Dinofurcula, gen. nov. 2 2 2 2 Dinophysis 123 52 10 20 Histiophysis, gen. nov. 1 1 1 1 Amphisolenia 32 31 19 26 Triposolenia 9 9 4 8 Ornithocercus 16 8 4 9 Parahistioneis, gen. nov. 9 9 6 7 Histioneis 45 28 17 24 C'itharistes 2 2 2 Totals 31S 198 88 132 Of the five new genera, four — viz., Heteroschisma, Dinofurcula, Histiophy- sis, and Parahistioneis — are based on species found in the material of the Expedi- tion; one, Thccadinium (p. 32), was founded on two previously described species, Amphidinmm kofoidi var. pelasalwn Herdman (1922, p. 26) and Phalacroma ebriola Herdman (1924, p. 34). INTRODUCTION AND COLLECTIONS. 23 Up to April 1, 1926, there have been described 318 species and subspecies in the Dinophysoidae. Of these only 198 are regarded as valid. Of the 198 valid species 132 or 66.7% of the known species were found in the collections of the Expedition. The eighty-seven new species constitute 65.9% of the total number (132) found on the Expedition, and an increase of 80% to the 111 species previ- ously known. This has resulted from the large representation of the rich tropical fauna in the collections and from the intensive search of the richer plankton collections and of the contents of Salpa stomachs for the rare and often minuter species. The accompanying table records under each genus the number of species and subspecies in literature, the numbers of these which in our opinion, with some reservations, are to be considered valid, the numbers of new species established in connection with this Report, and the total numbers of species found in each of fourteen genera. Orthogenesis and Convergence The species are arranged within the genera according to their structural resemblances, upon the assumption that the degrees of structural resemblances are indications of commensurate degrees of genetic relationship. It is fully realized that such resemblances may, however, not be accurate quantitative measures of the degrees of genetic relationship, or unequivocal demonstrations of genetic . origins. Nevertheless they are the only evidences of the nature and results of the evolutionary process in this highly diversified group, and while their quantitative value may well be quite hypothetical, their qualitative significance is undoubtedly of high value in showing the method, direction, and trend of the evolutionary process in the group. The record is all the more definite and clear because of the fact that it is registered in the non-mobile exoskeleton or theca of the body and its outgrowths. While it is true that the more superficial structures such as lists, fins, and sails are subject to regulatory modifications and to considerable individual variation, we nevertheless find beneath such variation the more basic similarities and differ- ences, which may serve as guides in the establishment of genetically related groups. The groups of species thus established within the genera exhibit relationships in structure among themselves which make feasible their grouping in a dendritic, diverging fashion, suggestive of phylogenetic descent. Within the subgenera or other secondary groups of several of the genera, the known species, even though there be but a few, may usually be arranged in 24 THE DINOPHYSOIDAE. something of an orthogenetic fashion according to the degree of specialization of one or more structural features, in ascending series from the simpler to the more complex. These series, which are not always equally spaced, are ortho- genetic, since they appear to exhibit progressive (or regressive) movements in their evolution or speciation. The orthogenetic tendencies within these lines may be summarized as (1) increase in size; (2) increase in relative length, especially in Amphisolcnia and Triposolenia; (3) branching or extensions of the body, as in Amphisolcnia and Dinofurcula; (4) increase in the development of the reticulations on the surface of the theca, often by heavier ribbing and larger size of the reticulations; (5) ex- tension and ribbing of the anterior and posterior cLngular lists about the girdle culminating in Ornilhocercus splendidus and Histioneis josephinae; {6) extension and structural modifications of the right and left sulcal lists, as in Histioneis; and (7) the progressive elaboration of the phaeosome chamber in Ornithocercus, Histioneis, Parahistioneis, and Citharistes. The net result of our analysis of the process of speciation in the Dinophy- soidae has been a growing conviction that there is in this group a more or less orderly divergence from primitive species with a small, spheroidal body, with a smooth undifferentiated surface, low, simple cingular and sulcal lists, and no phaeosome chamber, toward the more elaborate types along a number of diver- gent lines. Furthermore the progress of this process of evolutionary divergence is marked to a surprising degree by an orthogenetic aspect. The evolutionary steps seem to be represented in living Dinophysoidae, at least to such a degree that the path presumably followed in the process is still indicated by them. It may be that they represent only laterals along this path, but these still-existing types have seemingly remamed near enough to their levels of divergence from the main paths to mark their courses. A striking feature is that the process of speciation has proceeded in this group to a marked degree of specialization in the seeming absence of sexual reproduc- tion. There is as yet no evidence of the occurrence of this mode of reproduction in the Dinophysoidae. Another striking feature of the evolution of the Dinoflagellata is the fact that there is no evidence of closely related species being isolated from each other either geographically or bathymctrically. Both the most primitive and the most diver- gent and highly specialized genera and species occur together in the same region, and very closely related forms are not infrequently recorded in the same surface catch or from the same Salpa stomach. Specific adaptations to zones of illumi- I IXTRODITTIOX AND COLLECTIONS. 25 nation and temperature undoubtedly exist, but di;u-nal migrations in heliotropic responses to the rhythm of solar energy and to other crsniic and meteorological factors may be expected to produce some vertical extension of the zones inhabited by each species, and to vary these extensions with changing conditions. Save for the larger differences due to latitude and depth, areal distribution affords little aid in the solution of evolutionary problems. Along broad lines the species are widely distributed in all seas in waters of comparable temperatures and illuminations. The ecologic niche which each fills is in reality a wide shelf girdling the tropical seas and extending to a considerable depth. Moreover, many of these areas of distribution appear to be to a large degree coincident, even within the species of a single orthogenetic line. The factor of geographical isolation, so significant among birds and mammals in which feeding range and sexual behavior so immediately affect the genetic processes and evolutionary progress, sinks into relative insignificance, if indeed it ever had any considerable part, in the process of speciation among the Dinophysoidae. It is also interesting to note that the most highly specialized genera such as Citharistes and Histioneis and the most highly specialized species within the genera, are, in the main, relatively rare in individuals. The development of adaptive structures of a highly specialized type is not in many instances accom- panied by a corresponding reproductive vigor or ec^ual enlargement of survival value. Attention may also be invited to another phenomenon of evolutionary significance which has emerged in the analysis of the Dinophysoidae, namely, the appearance in Heteroschisma and Pseudophalacroma of a structural character identical in location and morphological relations with a fundamental structural feature of the Peridinioidae. This character in Heteroschisma is the marking out by structural lines ofan area corresponding to plate 1 of the postcingular series of the latter tribe. The Peridinioidae differ from the Dinophysoidae in the facts that the skeletal elements of the former are {1} in five (or six) instead of three horizontal zones and (2) that the pre- and postcingular zones have five instead of two plates or elementary subdivisions. It is a striking fact that the postcingular zone of Heteroschisma has developed the structural features of the first plate of the post- cingular series next to the flagellar pore, sulcus, and blepharoplast (see Hall, 1925). This is illustrated in detail in the discussion of Heteroschisma acquale and inaequale (Plate 1). In the genus Pseudophalacroma there are evidences of a comparable emergence of a structural field homologous in morphological re la- 26 THE DINOPHYSOIDAE. tions with plate 1 of the precingular series and also located near the flagellar pore. Both of these genera are among the less specialized members of the tribe, although the species of Heteroschisma have a somewhat advanced development of the surface. The phenomenon here observed is of the same category as that described by Kofoid (1926) in Oxyphysis oxytoxoides, in which a rather highly specialized genus, Oxyphysis, of the Dinophysoidae, has the facies of Oxytoxum, of the Peridinioidae. In the cases of Heteroschisma ^and Pseudophalacroma the con- vergence of characters is found in a single one of the plates or unitary elements of the skeleton. In the case of Oxyphysis it appears in the external form of the body as determined by the total skeleton, the location of the girdle and sulcus, and the shaping of the two apices. These three instances of convergent features of structure between the Dinophysoidae and the Peridinioidae lead strongly to the inference that the structure of the species or larger systematic category, as well as that of the individual, may not wholly reveal its genetic potentialities. The Dinophysoidae appear to carry potentialities of producing in the course of their evolution, in these three genera only, so far as is known, certain structural features which belong primarily in the tribe Peridinioidae and are characteristic of it, in the case of the plate of Heteroschisma and Pseudophalacroma, or of a single genus in the tribe, as in the case of Oxyphj'sis. Pkocedure used in the Accounts of Genera and Species Nearly all the descriptions of genera, species, and subspecies published up to the present time are short and incomplete, with but few data concerning the nature and amplitude of variation. Ours is the first attempt at a more or less exhaustive treatment of the various systematic units. A consequence of this is that we have had to elaborate a new technique of description and treatment. Our basic principle is to keep everything that implies comparisons as stereotyped as possible in order to obtain the greatest possible perspicuity and ease of com- parison and reference. A usual shortcoming of current taxonomic papers is that the various systematic descriptions are not treated in a consistent arrangement and manner. Frequently it is necessary to traverse a mass of facts in order to find the one that is desired. In short papers this defect may be more or less inconsequential, in large monographs and in genera with numerous species it creates almost insuperable difficulties and an annoying loss of time. In the present paper each character has the same relative place in all of the diagnoses and descriptions and in so far as possible is discussed in the same phraseology. INTRODUCTION AND COLLECTIONS. 27 The families have been treated under the following headings: — (1) Diag- nosis; (^) Subdivisions. Relationships among the genera; (3) Distribution; (4) Key to the genera. In the case of the genera the following arrangement has been adopted: — (1) Synonyms; (2) Diagnosis; (3) Organology; (4) Reproduction; (5) Distribu- tion; (6) Historical discussion; (7) Adaptive and systematic value of the charac- ters. Principles used in the descriptions of the species; (5) Subdivisions. Rela- tionships among the species; {9) Key to the species. These are the subheadings under each species: — (/) Synonyms; {£) Diag- nosis; (S) Description; (4) Dimensions; (5) Variations; (6) Comparisons; (7) Synonymy; (8) Occurrence. On account of the fact that the various genera are quite decidedly different morphologically, it is impossible to apply the same procedure of description to all of them. The differences in descriptive technique are, however, not very great and inside each genus the treatment conforms to the type established. In the general account of most genera a diagrammatic figure elucidates our term- inology and methods of measuring proportions and angles. At the end of the description of each species information is given as to the number of specimens, the proportions of which were measured. With the ex- ception of the length of the body, all statements as to proportions and dimensions refer to these specimens only. The following random example : — "the posterior cingular list is 0.50 (0.49-0.53) the length of the body from the apex" should be understood as follows: — the figures inside the parenthesis indicate the range of variation; the figure in front of the parenthesis, the average. This average is not weighted and based on random sampling, but is the average of the drawings which are based on selected specimens, some of which were "typical," others more or less extreme and selected because of their departure from the norm. In describing curves: — gently, moderately, and strongly (or boldly) convex or concave indicates an increasing degree of convexity or concavity (quantita- tive) ; in order to express an increasing uniformity of curvature, the terms irregu- larly, somewhat irregularly, subuniformly, and uniformly convex or concave (qualitative) are used. In recording the species all the samples from the same depth are counted as a single record; for instance, if a species is found at one station in two or more samples from 300 fathoms to the surface, all these records are considered as one. In the accounts of the distribution of the species, according to previously pub- lished literature, the material is arranged geographically. Beginning with the 28 THE DIXOPHYSOIDAE. data from the northern Atlantic Ocean we proceed south to the Antarctic Ocean; then the data from the Mediterranean, proceeding from the west to the east; from the eastern Mediterranean we proceed through the Red Sea, the Gulf of Arabia, the Indian Ocean, Antarctic Ocean, Malay Archipelago, Australian waters, Chinese and Japanese waters, and finally in an easterly direction across the Pacific Ocean. J II. SYSTEMATIC ACCOUNT Classification Phylum 1. Protozoa Goldfuss Superclass 1. Plasmodroma Doflein Class 1. Mastigophora Diesing Subclass 1. Dinoflagellata Biitschli Order 1. Adiiiiferidea Kofoid and Swezy Tribe 1. Athecatoidae Kofoid and Swezy Tribe 2. Thecatoidae Kofoid and Swezy Order 2. Diniferidea Delage and Herouard emend. Tribe 3. Gymnodinioidae Poche emend. Tribe 4. Amphilothoidae Kofoid and Swezy Tribe 5. Peridinioidae Poche emend. Tribe 6. Dinophysoidae Kofoid Family 1 . Dinophysidae Stein emend. Genus 1. Thecadinium, gen. nov. 2. Pseudophalacroma Jorgensen 3. Oxyphysis Kofoid 4. Heteroschisma, gen. nov. 5. Phalacroma Stein 6. Dinofurcula, gen. nov. 7.^ Dinophysis Ehrenberg 8. Histiophysis, gen. nov. Family 2. Amphisolenidae, fam. nov. Genus 9. Amphisolenia Stein 10. Triposolenia Kofoid Family 3. Ornithocercidae, fam. nov. Genus 11. Ornithocercus Stein 12. Parahistioneis, gen. nov. 13. Histioneis Stein Family 4. Citharistidae, fam. nov. Genus 14. Citharistes Stein DINOPHYSOIDAE "der Dinophysiden" Stein, 1883, p. 23. Dinophysida Butschli, 1885, p. 1009. Dinophyseae Schutt, 1896, p. 20. Dinophysidae Doflein, 1909, p. 464; 1911, p. 530; 1910, p 436; Kofoid & Michener, 1911, p. 268; Lebouh, 1925, p. 75. Dinophysiaceae Pavill.^rd, 1916, p. 44; Jorgensen, 1923, p. 3. Dinophysaceae Oltmanns, 1922, p. 54. Dinophy.soidae Kofoid, 1926, p. 215. Diagnosis: — Dinoflagellata with well-developed girdle and sulcus, with permanent longitudinal and transverse flagella located respectively in sulcus and girdle, with a single flagellar pore located in sulcus, and with body surrounded by theca composed of two subequal halves joined approximately in sagittal plane and, as a rule, made up of but three plates, epithecal, cingular, and hypothecal. Girdle usually anterior in position. Exclusively marine. Derivation. Subdivisions. Relationships among the Families While several investigators have united the dinophysids and the peridiniids {e.g., Lebour, 1925), we have adopted Kofoid's (192G) decision that they form two separate tribes, viz., Dinophysoidae and Peridinioidae, and have done so on account of the fundamental structural differences and because of the fact that all available evidence appears to support the opinion expressed in the pedi- grees of the dinoflagellates constructed by Butschli (1885, p. 1016) and Kofoid and Swezy (1921, p. 84), viz., that these groups have evolved independently from the tribe Gymnodinioidae. In all the discussions of the hiterrelationships of the various taxonomic units of Dinophysoidae, we have (contrary to Kofoid and Swezy, 1921, p. 84) adopted the viewpoint that this tribe evolved from ancestral forms very closely resembling Gymnodiniuyn ovulum Kofoid and Swezy (1921, pi. 5, fig. 58). These ancestral forms might be characterized briefly in the following manner: — (1) body small and spheroidal, its length, depth, and width subequal; (:2) girdle subequatorial, its distal portion not displaced; (3) sulcus short on both epitheca and hypotheca; (4) cingular and sulcal lists small and structurally undifferen- tiated; (5) without accessory lists or sails. Small size and subrotund shape of body are features characteristic of the simply organized members of most of the genera of Dinophysoidae, e.g., Heteroschisma, Phalacroma, Dinophysis, Orni- thocercus, Parahistioneis, and Histioneis. It is an almost universal rule in this SYSTEMATIC ACCOUNT. 31 tribe that the increase in structural complexity is accompanied by an increase in size. The distal portion of the girdle is displaced only in one of the known species of Dinophysoidae, viz., in Dinofurcula ultima (Plate 5, fig. 4, 6). The shortness of the hypothecal sulcus is a characteristic of most genera, and its anterior prolongation occurs but seldom and only in genera (Pseudophalacroma, Oxyphysis) which show other indications of primitiveness. There is within most of the large genera a distinct tendency for the cingular and sulcal Usts to increase in size and structural complexity; and accessory lists and sails occur only in a few genera and very seldom in the simply organized members of these. The assumption that the girdle originally was equatorial in position is somewhat more uncertain than the others. In C5ymnodinioidae this structure has no fixed position but may be found anywhere between the apex and the antapex; in Amphidinium it is anterior, in Gymnodinium more or less equatorial, and in Torodinium posterior. In Dinophysoidae, on the other hand, it is either sub- equatorial or more or less anterior. The reasons for assuming the equatorial position as the most primitive in Dinophysoidae are as follows: — {1) the gu'dle is anterior in all the more or less highly differentiated families, viz., in Amphiso- lenidae, Ornithocercidae, and Citharistidae, and Histioneis, the most complex of all the genera of this tribe, is characterized by a smaller epitheca than any other genus; {2) in the Dinophysidae the epitheca is small in the two most differ- entiated genera, viz., Dinophysis and Histiophysis, and relatively large in most of the more or less primitive genera, Pseudophalacroma, Oxyphj-sis, Hetero- schisma, and Phalacroma. The onlj' strikmg exception to this rule is Theca- dinium, and this genus is of uncertain systematic position and probably did not develop from the same ancestral forms as the rest of the family, but from Axnphi- dinium-like forms. The genera of the tribe, Dinophysoidae are assigned to one of the four fami- lies, viz., Dinophysidae, Amphisolenidae, Ornithocercidae, and Citharistidae, all of which are either new or emended. As to the interrelationships of these four families but little can be said with any degree of certainty. The Dinophysidae comprises the structurally simplest members and presumably evolved directly from Gymnodinioidae. Amphisolenidae may have sprung from the same ancestral forms of Dinophysis which evolved into Dinophysis caudata and D. miles and which were characterized by the tendencies toward elongation, atten- uation, and posterior bifurcation. Ornithocercidae presumably evolved from some ancestral forms closely related to Phalacroma, Dinophysis, and Histiophysis. Citharistes approaches Dinophysis in the shape and size of the anterior cingular 32 THE DIXOPHYSOIDAE. and the sulcal lists. It differs strikingly from this genus in the differentiation of the dorsal portion of the girdle into the large phaeosome chamber. This chamber probably originated by a gradual increase in the dorsal width and concavity of the transverse furrow, such as can be seen in the genus Parahistioneis (cf. for instance, P. reticulata, Plate 19, fig. 7). 1. DINOPHYSIDAE Stein, 1883, emend. Diagnosis: — Body of diverse shapes; ratio between length and depth usually somewhere between 1.0:1 and 1.7:1. Epitheca small, disk-like to large, some- times even as large as hypotheca. Transverse furrow narrow and, as a rule, about as wide dorsally as ventrally; its dorsal width less than 0.30 the greatest depth of body. Cingular lists, when present, subhorizontal or inclined anteriorly, narrow or of moderate width, usually less than 0.30 the greatest depth of body. Phaeosomes occur only in one genus. Length of body, 21-148 fi. Marine, usually eupelagic, in all seas. Subdivisions. Relationships among the Genera Dinophysis Ehrenberg (1840a), the type genus of Dinophysidae, was the first genus of the family to be established. Later Phalacroma was introduced by Stein (1883), Pseudophalacroma by Jorgensen (1923), and Oxyphysis by Kofoid (192G); and in the present paper four new genera, viz., Heteroschisma, Dino- furcula, Histiophysis, anil Thecadinium, are described. Of these eight genera, Phalacroma and Dinophysis are by far the largest, the former comprising fortj'- seven, the latter forty-one presumably \alid species. Pseudophalacroma was founded on a single species previously assigned by Stein (1883) to Phalacroma. Oxyphj'sis also comprises but one species, 0. oxyioxoides Kofoid (192G). Of the four new genera, Heteroschisma is based on two new species; Dinofurcula on two species, one of which is new, the other previously described and figured by Kofoid (1907a) under the generic name of Phalacroma; and Histiophysis on one species previously (Kofoid and Michener, 1911) referred to Dinophysis. Theca- dinium comprises two species, viz., T. petasalum and T. ebriolum. Of these, the first was described and figured by Herdman (1922, p. 26) under the name of Amphidiinum kofoidi var. petasatu7n and later (Herdman, 1923, p. 34) trans- ferred to Phalacroma as P. kofoidi. The second species was introduced by Herdman (1924, p. 34) as Phalacroma ebriola. The members of Thecadiniinn are, on the whole, the most primitive represen- tatives of this family. Indeed, even their assignment to the tribe Dinophysoidae SYSTEMATIC ACCOUNT. 33 must be considered as uncertain. It is true that they are characterized by a distinct theca (Lebour, 1925, pi. 11, fig. Ic, d), but the thickness of the pelUcle in Gynmodinioidae is variable, and it appears probable that there are stages intermediate between unarmored forms with exceedingly thin and flexible pellicle and armored ones, i.e., forms in which the pellicle has become more resistant and inelastic. If the theca is left out of consideration, the two species of Thecadinium are structurally much closer to Amphidinium than to any of the genera of Dino- physoidae. They evidently lack cingular lists and the left sulcal list is very narrow or absent. Furthermore, their longitudinal furrow appears to be deep, while in all the other members of this tribe it is flat or but slightly impressed. The close structural similarity between Amphidinium and Thecadinium indicates that the latter genus evolved directly from the former. It may be noted in this connection that the anterior position of the girdle is considered as secondary; in other words, in this respect these two genera are more advanced than some of the highly differentiated members of Phalacroma (e.g., P. limhatum, Plate 3, fig. 5). Next to Thecadinium, Pseudophalacroma and Oxyphysis appear to be the most primitive. This assumption is based on the following structural features : — (1) the longitudinal furrow continues anteriorly beyond the anterior cingular list (Stein, 1883, pi. 18, fig. 1 ; Kofoid, 1926, pi. 18, fig. 1) ; this peculiarity is found in a great number of the representatives of Gymnodinioidae, but in no other mem- bers of Dinophysoidae (Jorgensen, 1923, p. 4); {2) the epitheca is comparatively high and deep; (3) the cingular lists are very narrow and lack structural differen- tiation; (4) the sulcal lists are small, and the left of them lacks the three ribs and the posterior angularity characteristic of most of the members of the higher genera, viz., Phalacroma and Dinophysis. Pseudophalacroma appears to be very close to the evolutionary line that led to the development of Phalacroma and Dinophysis. Oxyphysis, on the other hand, forms an aberrant and in many respects highly differentiated branch that split off at a very early stage. It embodies many of the tendencies inherent in the peculiar genus Oxytoxum uf the tribe Peridinioidae and furnishes one of the most striking examples of conver- gence known among the Protozoa (Kofoid, 1926). The genus Heteroschisma is characterized especially by two structural features: — {1) the entire left sulcal list belongs to the right \alve, its fission rib being located at the level of the posterior cingular list; (2) the left valve of the hypotheca has a triangular postcingular plate on the ventral side. The behavior of the left sulcal list in binary fission is not known in Thecadinium, Pseudophala- croma, and Oxyphysis. On the other hand, in the highly organized genera of 34 THE DINOPHYSOIDAE. Dinophysidae, viz., Phalacroma, Dinophysis, and Histiophysis, the fission rib of this Ust is displaced posteriorly; in other words, the anterior portion of this list belongs to the left valve and the posterior to the right. Although there are no proofs in support of this assumption, Heteroschisma is considered primitive in this respect. Except in Heteroschisma, a triangular postcingular plate is not known to occur in any of the members of this tribe (with the possible exception of Phalacroma fimhriatum, Plate 2, fig. 1). For these reasons and because of the rounded outline of the body, the large size of the epitheca, and the simple struc- ture of the left sulcal list, Heteroschisma is considered an independent evolu- tionary branch that split off at a very early stage. Furthermore, the entire organization of Heteroschisma, when compared with that of Thecadinium, Pseudophalacroma, Oxj'physis, and Phalacroma, indicates that this genus is much more closely related to Phalacroma and Pseudophalacroma than to The- cadinium and Oxyphysis. Dinofurcula recalls Phalacroma in the great depth of the epitheca and in the moderate width, subhorizontal position, and ribbed structure of the cingular lists. On the other hand, it differs very strikingly from this genus in having the hypo- theca bifurcate posteriorly. Another peculiarity of Dinofurcula ultima (Plate 5, fig. 4, 6) is the posterior displacement of the distal portion of the girdle, a feature not found in any other member of Dinophysoidae, but frequent in Gymno- dinioidae and Peridinioidae. Dinofurcula, like Pseudophalacroma and Hetero- schisma, represents an independent branch near the base of the evolutionary line that led to the differentiation of Phalacroma. Of the three remaining genera of Dinophysidae, viz., Phalacroma, Dinoph}'- sis, and Histiophysis, all of which are structurally very closely related, the first is, on the whole, the most primitive. This is indicated by the following features : — {1) the body is frequently subrotund in lateral outline; {2) the epitheca is very large and the girdle is subhorizontal not only in some of the primitive, but also in some of the highly advanced species; (S) the cingular lists are relatively narrow. Phalacroma and Dinophysis embody several common tendencies, e.g., the tend- ency to develop accessory sails and lists, and even their generic separation "seems ... to be somewhat arbitrary'" (Jdrgensen, 1923, p. 5). It is very difficult to allocate generically not only several of their primitive but also some of their advanced members. Histiophysis, which is structurally more closely related to Dinophysis than to Phalacroma, shows certain similarities to Parahistioneis. For instance, its epitheca is very small, its anterior cingular list is unusually high, has a pronounced funnel shape, and simplified ribbing, its posterior cingular list SYSTEMATIC ACCOUNT. 35 is reticulated instead of ribbed as in Phalacroma and Dinophysis, and it has phaeosomes in the girdle. The highly developed structure of the sulcal lists and the lack of a posterior main rib in the left sulcal list should also be taken into account when the systematic position of Histiophysis is under consideration. In short, of the eight genera, six, viz., Pseudophalacroma, Heteroschisma, Dinofurcula, Phalacroma, Dinophysis, and Histiophysis, are structurally quite closely related, while the two remaining, viz., Thecadinium and Oxyphj^sis, occupy rather isolated positions. Thecadinium is still on the borderland to Gymno- dinioidae, and Oxyphysis is a highly differentiated genus that branched off at a very early stage from the evolutionary line that led to the differentiation of the first six genera. Of Pseudophalacroma, Heteroschisma, and Dinofurcula, which also split off very early, the last is in some respects very aberrant, while the others are still, on the whole, quite primitive (see also Hensen, 1891, pi. 2). Distribution: — The Dinophysidae are very widely distributed, exclusively marine, and all the genera are eupelagic, except Thecadinium which is found on sandy beaches. Most of the species occur exclusivelj^ or almost so, in tropical, subtropical, and warm-temperate seas, but some of them are endogenetic in the Arctic and the Antarctic Oceans, where no representatives of the other families of this tribe are to be found. Most species appear to be rare, but some have been recorded as rather frequent. The optimum habitat is the lower levels of photo- synthesis. Key to the Genera 1. Cingular lists absent Thecadiniuin, gen. nov. 1. Cingular lists present 2. 2. Sulcus continues anteriorly beyond anterior cingular list 3. 2. Sulcus does not continue anteriorl}' beyond anterior cingular list 4. 3. Epitheca narrow, cone-shaped Oxyphysis Kofoid. 3. Epitheca rounded, dome-shaped Pseudophalacroma Jorgensen. 4. Body niolariforni in lateral outline Dinofurcula, gen. nov. 4. Body not molariform in lateral outline 5. 5. Entire left sulcal list belongs to right valve Heteroschisma, gen. nov. 5. Entire left sulcal list does not belong to right valve 6. 6. Posterior cingular list finely reticulated Histiophysis, gen. nov. 6. Posterior cingular hst not finely reticulated Dinophysis Ehrenberg and Phalacroma Stein. 36 THE DINOPHYSOIDAE. Heteroschisma, gen. nov. Diagnosis: — Body subcircular to broadly subobovate in lateral outline. Epitheca large, but slightly narrower than hypotheca. Transverse furrow nar- row, of subuniform width throughout, 0.43-0.70 the greatest height of epitheca. Posterior cingailar list 0.36-0.46 the length of body from apex. Left hypotheca characterized by a triangular postcingular plate, occupying its ventroanterior corner; this plate is somewhat deeper than high, and its ventral height is 1.5-3.0 the width of the transverse furrow. Cingular lists subhorizontal and subequal, slightly wider to slightly narrower than transverse furrow; without structural differentiation except dorsally and ventrally, where they may have a few ribs. Right sulcal list about 0.33-0.45 as long as body, with a maximum width 0.66- 0.75 the width of transverse furrow. The most important feature of the left sulcal hst is that it belongs to the left valve in its entire extension; i.e., that it crosses over from the left to the right valve at the le\'el of the posterior cingular list. Other characteristics of this list are: — it is 0.53-€.67 as long as body, of subuniform width throughout the greater portion of its length, its average width being subequal to width of transverse furrow, forms a round to ear-shaped lobe posteriorly, and either lacks structural differentiation or has but a single rib near the posterior end. Type. — Heteroschisma inaequale, sp. nov. Distribution: — Heteroschisma has never been found outside the area ui- vestigated by the Expedition; and by the Expedition it was taken at five stations only. Two of these five stations (4665, 4671) are in the Peruvian Current; one (4699) is in the Easter Island Eddy; and two (4701, 4721) are in the South Equatorial Drift. All records refer to hauls from 300-0 fathoms except one (Station 4699) which refers to a specimen from the stomach of a Salpa taken in surface waters. The frequency is less than 1 % at all the five record stations. Heteroschisma aequale, sp. nov. Plate 1, fig. 7, 8. P'igure 1 :1, 2 Diagnosis: — Body subcircular in lateral outline, deepest near the middle; in dorsoventral view obovate, widest at girdle. Posterior cing-ular list 0.45-0.46 the length of body from apex. Ventral margin of right sulcal list strongly sig- moid, concave anteriorly and convex posteriorly. Left sulcal list 0.53 the length of bod}', of subuniform width throughout the greater portion of its length; its I SYSTEMATIC ACCOUNT. 37 average width subequal to width of transverse furrow; postmargin of list pro- tracted into narrow, ear-shaped lobe ; without ribs or other structural differentia- tion.. Theca finely and faintly reticulate. Length, 43.2-51.0 m- Eastern tropical and subtropical Pacific. Description: — Body subcircular in lateral outline and deepest near the middle. The margins are confluent and subuniformly convex, and the epitheca, which is highest in the center, is about as broadly rounded as the posterior portion of the body. The longitudinal axis is about perpendicular to the girdle. The transverse furrow is flat or gently con\ex, and its width is about 0.43-0.44 the greatest height of the epitheca. The posterior cingular list is about 0.45-0.46 the length of the body from the apex. The ventral height of the triangular field is about 1.5 times the width of the transverse furrow. In dorsoventral view the body is obovate and widest at the girdle. Figure 1. — 1, 2, Heleroschifwa aequale, gen. et sp. nov. 1, right lateral view of type specimen, Station 4671 (300-0 fathoms); 2, ventral view, Station 4701 (300-0 fathoms); 3, Heteroschisma inaequale, gen. etsp. nov., right lateral view of type specimen, Station 4665 (300-0 fathoms), x 430. The cingular lists are subhorizontal and subequal, about as wide as the transverse furrow or slightly narrower or wider, and, as far as the records go, without structure. The right sulcal list is 0.33-0.40 as long as the body; its ventral margin is strongly sigmoid, concave anteriorlj', convex posteriorly; its maximum width is about 0.75 the width of the transverse furrow. The left sulcal list is about 0.53 the length of the body and of subuniform width throughout the greater portion of its length; its average width is subequal to the width of the transverse furrow ; its greatest width is located in or somewhat behind the middle ; its ventral margin is gently sigmoid, slightly concave or almost straight anteriorly, convex in the middle, and slightly concave posteriorly; its postmargin is pro- tracted into a narrow, ear-shaped lobe at an angle of about 50°; there are no ribs or other structural differentiations. The thecal wall is finely and faintly reticu- late; the meshes are of subuniform size and polygonal; pores were not seen. Only megacytic stages were recorded. Two specimens had exceedingly wide intercalary zones. 38 THE DINOPHYSOIDAE. Dimensions: — The dimensions of two specimens were : — Length of body, 43.2-51.0 /J (type, 51.0 yu). Total length of megacytic specimens, 54.0-55.4 m- Variations: — Judging by the few specimens available, this species appears to be quite constant in shape and structure and fairly variable in size. Co7nj)arisons: — The description of the shape of the body is somewhat un- certain, since all the specimens examined are megacytic with very broad inter- calary zones. The simplicity of the structure of the thecal wall seems to indicate that Heteroschisma aequale is more primiti\'e than H. inaequale. Occurrence: — Heteroschisma aequale is recorded at four of the 127 stations. There are 0, 1 , 0, 2, 1, and stations on the six lines of the Expedition. Of these four stations, one (4671), the type locaUty, is in the Peruvian Current; one (4699) is in the Easter Island Eddy; and two (4701, 4721) are in the South Equatorial Drift. At one station (4699, Salpa stomach) the species was taken in surface waters. The remaining records refer to hauls from 300-0 fathoms. The temperature range of these four stations at the surface is 66°-75°; the average was 72°. At Station 4699 the surface temperature was 75°. The frequency in all the cases is less than 1 r/ Heteroschisma inaequale, sp. nov. Plate 1, fig. 1, 2. Figure 1 : 3 Diagnosis: — Body broadly subobovate in lateral outline, deepest at girdle. In dorsoventral view subbiconical, widest at girdle, side contours of epitheca and hypotheca almost straight or even slightly concave, except posteriorly where they are convex. Posterior cingiilar list 0.36 the length of body from apex. Ventral margin of right sulcal list almost straight anteriorly, gently convex posteriorly. Left sulcal list 0.67 the length of body, of subuniform width throughout; its average width subequal to width of transverse furrow; with rounded postero- ventral lobe; with short posterior rib that ends at middle of postmargin. Wall of left hypotheca, except triangular field, has fine and rather faint reticulation; remaining portion of theca with well-developed and rather wide-meshed reticu- lation. Length, 51.0 ;u. Eastern tropical Pacific. Description: — Body broadly subobovate in lateral outline and deepest at the girdle. The margins are subuniformly convex and confluent, and the epi- theca, A\lii(h is highest somewhat ventrally to the center, is somewhat more SYSTEMATIC ACCOUNT. 39 broadly rounded than the posterior portion of the body. The longitudinal axis is about perpendicular to the girdle. The transverse furrow is shghtly concave, and its width is about 0.70 the greatest height of the epitheca. The posterior cingular list is about 0.36 the length of the body from the apex. The ventral height of the triangular field is about three times the width of the transverse furrow. In dorsoventral view the body is subbiconical and widest at the girdle ; in the type specimen (megacytic) the ratio between the length and width is 1.20: 1 ; the side contours of the epitheca and hypotheca are almost straight or even shghtly concave, except at the posterior end of the body where they are more or less convex. The cingular lists are subhorizontal and subequal, about as wide as the trans- verse furrow or somewhat narrower, and without structural differentiation except dorsally and ventrally where a few (1-4) ribs are to be found. The right sulcal hst is about 0.45 as long as the body, of subuniform width throughout the greater portion of its length, and with a maximum width about 0.66 the width of the transverse furrow; its ventral margin is almost straight anteriorly and gently convex posteriorly. The left sulcal list is about 0.67 as long as the body, of subuniform width throughout its entire length, and its average width is subequal to the width of the transverse furrow ; it is characterized by a rounded postero- ventral lobe and has no structural differentiation, with the exception of a short posterior rib that ends at the middle of the postmargin of the list and has a pos- terior inclination of about 80°. The thecal wall of the right \'alve and of the epitheca, the transverse furrow, and the triangular field of the left valve have a well-developed reticulum of rather large polygonal meshes. The meshes of the epitheca and of the right hypotheca are subuniform in size; and about twenty meshes border the girdle posteriorly on the right valve. In the entire triangular field about sixteen meshes are to be found. The polygons of the transverse furrow are arranged in two rows; on each valve there are about sixteen or seventeen polygons in each row. Except in the triangular field the wall of the left hypotheca is characterized by a fine and rather faint reticulation resembling the one found in Heteroschisma aequale. Scattered pores are to be found. The only specimen examined was megacytic. Dimensions: — Length of body, 51.0 fi. Total length of megacytic specimen (including intercalary zone), 54.8 m- Comparisons: — The description of the shape of the body is somewhat uncertain since the only specimen examined is megacytic. 40 THE DIXOPHYSOIDAE. ' This species is easily distinguished from Heteroschisma nequale by the well- developed and comparatively wide-meshed reticulation of its theca. Occurrence: — Heleroschisma inaequale is recorded at only one (4665) of the 127 stations, on the second line of the Expedition, in the Peruvian Current, from a depth of 300-0 fathoms, and at a surface temperature of 68°. The frequency is less than 1% (one specimen). Phalacroma Stein Phalacroma Stein, 1883, p. 23. Butschli, 188.5, p. 940, 1009. DsL.'iGE & Herouard, 1896, p. 385. ScHtiTT, 1896, p. 26. Paulsen, 1908, p. 19. Lebodr, 1925, p. 75. Phalarocoma Daday, 1888, p. 99 {lapsus pennae). Phalacromo Nathansohn, 1908, p. 601 (typ. err.). Diagnosis: — Body usually subcircular, subellipsoidal, subobovate, subbi- conical, subcuneate, or fig-shaped in lateral outline, distinctly longer than deep (length: depth, 0.86-1.84: 1), and more or less compressed bilaterally. Epitheca usually large (ratio between its depth and depth of hypotheca in most species somewhere between 0.8:1 and 1.0:1, sometimes as low as 0.54: 1), either high, even as high as hypotheca, or more or less flattened. Transverse furrow narrow, of subuniform width throughout, flat or but slightly convex or concave; its width, 0.07-0.12 the length of body. Cingular lists usually subhorizontal and subequal, slightly wider to slightly narrower than transverse furrow, with or without ribs; sometimes somewhat inclined anteriorly. Right sulcal list usually somewhat narrower than the left and ends somewhere between Rj and R3 of left. Left sulcal list usually subtrapeziform, somewhat wider posteriorly than anteriorly, with pronounced posteroventral angle, and with three main ribs, one (Ri) in front, and one (R3) behind fission rib (R2) ; R2 somewhat behind girdle ; sometimes this list extends to antapex, sometimes its length is only 0.33 the length of hy- potheca; R . and R3 at most 0.22 and 0.55 the greatest depth of body, respectively ; margin may be rounded posteroventrally. Sometimes with accessory lists and sails. Type. — Phalacroma porodictyum Stein. Organology: — The body (theca) in Phalacroma is simple in structure, but diverse in shape. When seen laterally, it usually is somewhat asymmetrical, but symmetrical species also have been found {e.g., P. oinwi, Figure 11:4). In dorsal or ventral ^•iew it appears always to be syminetrical. In many species the longitudinal a.ris {a. I., Figure 29) has maintained its original position, i.e., it is perpendicular to the girdle; frequently, however, it is more or less deflected posteroventrally. In the two species with the most pronounced posteroventral SYSTEMATIC ACCOUNT. 41 deflection of this axis, viz., P. porodictyum and P. expulsum, an inclination of l°-20° and 5°-15°, respectively, was found. The only species in which this axis has a slight (2°) posterodorsal inclination is P. circumcinctum (Plate 1, fig. 5). WTien seen laterally, the hodij usually is distmctly longer than deep, only seldom is it deeper than long. In the most elongated species (P. iurbineum, Plate 2, fig. 3) the ratio between the length and the depth is 1.84: 1 ; in the species with the relatively deepest body [P. giganleum, Figure 14: 1) the corresponding ratio is 0.86: 1; in most species it is between 1.1: 1 and 1.3: 1. Sometimes the body is deepest in or near the middle, but usually the greatest depth has shifted to the anterior third of the body. As a rule, the body is deepest at or just behind the girdle. No species with the greatest depth located anterior to the girdle has been found. Usually the body, seen in lateral view, is circular or subcircular {Phalacroma lalivelalum, Figure 3:2, 3), ellipsoidal or subellipsoidal {P. parindiwi, Figure 3: 4-6), obovate or subobovate (P. circumsulum, P. doryphorum, Figure 23). Of these shapes the last two are by far the most common. Although the circular shape is the most primitive, it is found not only in some of the primitive but also in some of the highly differentiated members of the genus (Plate 3, fig. 5). The following shapes of body, seen laterally, have also been found : — subcircular, with a shght (P. lens, Figure 4:3) or striking (P. contractum, Figure 3: 1) con- striction at the girdle ; subcircular, with the anterior end subtruncate (P. porosiim, Plate 1, fig. 6; P. pulchrum, Plate 3, fig. 6); rounded subbiconical (P. praetexlum , Plate 4, fig. 6); subbiconical, with well-rounded apices (P. fimhriatum, Plate 4, fig. 4); biconical, top-shaped, narrowly to fairly broadly rounded anteriorly, subacute posteriorly (P. reticulatuni, Plate 4, fig. 3; P. turbineum, Plate 2, fig. 3); irregularly obovate, with strikingly conical epitheca, or sublozenge-shaped (P. apicatimi, Figure 10); sac-like, truncate anteriorly, with a dorsal shoulder-like constriction at the girdle (P. expulsum, Figure 20: 1) ; subobovate, with a broadly rounded angle at the posterior end of the left sulcal list (P. acutinn, Schiitt, 1895, pi. 3, fig. 17:1); cuneate, with a very broadly rounded epitheca (P. cuneus, Figure 12); subcuneate, with the posterior margin strikingly sigmoid, convex anteriorly, concave posteriorly (P. wrtim, Schiitt, 1895, pi. 4, fig. 18: 1) ; subcuneate, very broadly rounded to nearly flat anteriorly, narrowly rounded to subacute but not mammilliform posteriorly, and with the ventral margin strikingly angular at the posterior main rib of the left sulcal list (P. rapa, Figin-e 16); subcuneate, broadly rounded anteriorly, constricted, mammilliform posteriorly, and with the ventral margin more or less angular at the posterior main rib of the left sulcal list 42 THE DINOPHYSOIDAE. (P. favus, Plate 2, fig. 7); inverted fig-shaped (P. hindmarchi, Figure 18). A peculiarity worth mentioning is that species with ovoidal body have not been found as yet in Phalacroma, although this shape is fairly common in the closely related genus Dinophysis. Generally the body is more or less compressed bilaterally ; only a few species (e.g., Phalacroma globulus, Schiitt, 1895, pi. 2, fig. 12: 1; P.fimbriatum, Plate 4, fig. 4; P. giganieum, Plate 2, fig. 1) have the dorsoventral and transverse diameters subequal. It may also be mentioned that in the type specimen of P. turbineum (Plate 2, fig. 3; Plate 4, fig. 1) the transdiameter even exceeded the dorsoventral diameter, but this specimen possibly was megacytic (see p. 200). In the .species with the most pronounced bilateral compression (P. lens, Figure 4: 1-3) the ratio between the length and the transdiameter is 2.38-2.66: 1, while the ratio between the length and the dorsoventral diameter is 1.05-1.11: 1. When seen in dorsoventral view, the body generally is obovate (P. pulchrum, Plate 3, fig. 1), eUipsoidal (P. mucronatum, Figure 22:6), or lenticular (P. limbatum, Plate 3, fig. 3). In all the species with ellipsoidal or lenticular outline and in some of the species with obovate outline, the body is widest in or near the middle ; in the remaining species with obovate outline the greatest width is located in the anterior third of the body, often near the girdle. The following shapes of body, seen dorsoventrally, have also been found: — subcircular (P. globulus, 't^Qh.uii, 1895, pi. 2, fig. 12: 1, in which the body approaches the fundamental, spherical form); biconical, with more or less narrowly rounded apices (P. apicatum, Figure 10: 2; P. circumcincium , Plate 1, fig. 4); biconical, with acute or subacute apices (P. fimbriatum, Plate 2, fig, 1 ; P. reticulatum, Plate 4, fig. 5) ; cuneate, broadly rounded anteriorly, narrowly rounded or subacute posteriorly ; and with the side contours of the hypotheca straight, or evenly and gently convex or concave (P. cuneolus, Figure 22: 7), or more or less undulating (P. expulsum, Figiu-e 20: 2, 5; P. favus. Figure 14:2); inverted pyriform (P. pyrijorme, Figure 4:4); inverted fig-shaped (P. hindmarchi) . One of the most characteristic features of Phalacroma is the relatively large size of the epitheca (epi., Figure 29). In lateral as well as in dorsoventral view^ the epitheca usually is about as deep as or but slightly narrower than the hypo- theca. In most species the ratio between the depth of the epitheca and that of the hypotheca is somewhere between 0.8: 1 and 1.0: 1 ; in the species with the relatively smallest epitheca (P. expulsum, Figure 20: 1, 3) the corresponding ratio is 0.60 (0.54-0.66): 1. Only in exceptional cases (P. reticulatum, Plate 4, fig. 3) is the epitheca slightly deeper than the hypotheca. In the ancestral forms of SYSTEMATIC ACCOUNT. 43 this genus the epitheca and the hypotheca presumably were subequal in size, and this condition is still found in some of the recent species, e.g., in P. limhatum (Plate 3, fig. 5), P. praeiextum (Plate 4, fig. 6), and P. circumcindum (Plate 1, fig. 5). However, in most of the recent forms the height of the epitheca has been more or less reduced without a corresponding reduction in depth. In some species this reduction in height has proceeded so far that the epitheca has the shape of a large and but slightly vaulted disk {P. porosum, Plate 1, fig. 6; P. giganteum, Plate 2, fig. 2; Plate 3, fig. 2). Only in a few of the known species (P. expulsuw, Figure 20: 3) has this reduction in height been accompanied by a decided decrease in depth. Phalacroma expulsum, which in several respects is intermediate between Phalacroma and Dinophysis, is also the only representative of its genus in which the epitheca in lateral view is not at all or but slightly visible above the anterior cingular list. As a rule, the epitheca is highest in or near the center, and only in a few species has its greatest height shifted dorsally or ven- trally (Figiu-e 20). In some species {Phalacroma praetextum, Plate 4, fig. 6; P. limhatum, Plate 3, fig. 5) the transverse furrow {tr. /., Figure 29) has maintained its original equa- torial position, but usually it is distinctly nearer to the anterior than to the pos- terior end of the body. Sometimes (P. porosum, Plate 1, fig. 6) it is even so close to the apex that its width exceeds the greatest height of the epitheca. Its distal portion is not displaced posteriorly, i.e., it does not form a spiral about the body. It usually crosses the lateral faces of the body in an almost straight line, but in P. porosum (Plate 1, fig. 6) it forms a gentle, sigmoid ciu"ve. Its width is subject to but slight variations; in obovoidal and subcuneate species the width is about 0.07-0.09, in subrotund species about 0.11-0.12 the length of the body. Its floor usually is flat or but slightly concave or convex, and only in a few species (P. coutra.ctum, Figure 3:1) is the concavity pronounced; this character appears to be fairly variable even within the species. The longitudinal furrow usually is about half as long as the hypotheca but may be somewhat longer or shorter; e.g., in Phalacroma porosum (Plate 1, fig. 3, 6) it is about 0.63 and in P. turhineum (Plate 4, fig. 1) about 0.26 the length of the hypotheca. Anteriorly it does not extend beyond the girdle, i.e., into the epi- theca. It is at most but slightly impressed. The lists of the furroios are not excessively developed. They arise from low and narrow basal ridges (Plate 3, fig. 1, 6) and are hyaline and usually exceed- ingly delicate. In almost all the species the cingular lists {ant. cing. I., post. cing. I., Figure 44 THE DINOPHYSOIDAE. 29) are subhorizontal, subequal, of subuniform width throughout, and about as wide as or shghtly wider or narrower than the transverse furrow. The anterior appears usually to be closed, but may be open ventrally in some species (Plate 2, fig. 1; Plate 1, fig. 5, of Phalacroma fimbriatum and P. circumdnctuni) . The posterior is always open ventrally. Only in exceptional cases are these lists strikingly inclined anteriorlj^; in P. expulsum (Plate 6, fig. 1) and P. pulchrwn (Plate 3, fig. 6), which have this anterior incUnation better developed than any other members of the genus, these Usts are inclined at about 30°-45° and 20°-40°, respectively. It should be remembered, however, that the pressure of t he co\er- glass is likely to change the inclination of these lists. In the species with the widest cingular lists (P. protuherans, Figure 20:8), these are about 1.7-2.3 times wider than the transverse furrow; in P. canlraclum (Figure 3:1) and P. lenticula (Figure 3:7), which form the opposite extreme, they are only about half as wide as the transverse furrow. In the most primiti\e as well as in some of the highly developed species {P. circumcinclum , Plate 1, fig. 5; P. pnlchrum, Plate 3, fig. 6), the cingular lists appear to lack structural differentiation, except for one or two ribs dorsally and ventrally on each valve near the sagittal suture. In the remain- ing species both these lists are ribbed. The ribs usually are rather strong, straight, simple, and nearly equidistant; but they may be fairly irregular (P. striatum, Plate 2, fig. 5), or they may even anastomose into a reticulum (P. cuneiis, Schutt, 1895, pi. 3, fig. 14: 2; P. striatum, Jorgensen, 1923, fig. 12). The number of ribs in the anterior list is either subequal to or somewhat larger than that in the posterior. In some species (P. turhineum, Plate 2, fig. 3) these lists have only a few ribs, but in others the number is fairly large; for instance, in P. giganteum (Plate 2, fig. 2), each of these lists has, on each valve, as many as seventy-five ribs. The sidcal lists, which form a direct continuation of the posterior cingular list, run about parallel to each other on either side of the longitudinal furrow. While the entire right sulcal list belongs to the right valve, the anterior portion of the left list belongs to the left valve and the posterior portion to the right. The right sulcal list {r. sulc. I., Figure 29) is fairly \-ariable in size and shape even within the species. It always is smaller than the left. In some species {Phalacroma porosum, Plate 1, fig. 6; P. famts, Plate 2, fig. 7) it extends to or slightly beyond the posterior main rib of the left sulcal list; in others (P. striatum, Plate 2, fig. 8) it ends at a point somewhere between the fission rib and the poste- rior main rib of the last-mentioned Ust; only exceptionally (P. expulsum, Plate 5, fig. 1) does it end at or even in front of the fission rib. Usually, it either (P. limhatum, Plate 3, fig. 5) is subtriangular to rounded triangular, about as wide as SYSTEMATIC ACCOUNT. 45 the transverse furrow anteriorly, and decreasing gradually in width posteriorly; or [P. favus, Plate 2, fig. 7) of subuniform width throughout the greater portion of its length, fairly strongly rounded posteriorly, and about as wide as the trans- verse furrow anteriorly. The following shapes have also been found : — crescent shape, wider in the middle than anteriorly and posteriorly (P. porosum, Plate 1, fig. 6) ; the anterior half to two thirds of the free margin is more or less concave and forms a distinct angle with the posterior portion of the margin which is either straight iP. fimhriatum, Plate 4, fig. 4) or more or less convex (P. striatum, Plate 2, fig. 8) ; the free margin is sigmoid, concave anteriorly and con\'ex poste- riorly (P. giganteum, Plate 2, fig. 2). Usually this list lacks structural differentia- tion, but sometimes it has a marginal rib (P. striatum, Plate 2, fig. 8; P. argus, Figure 8: 1), a T-shaped rib (P. turhineum, Plate 4, fig. 1), or a more or less de- veloped reticulation (P. striaiurn, Plate 2, fig. 8; P. circurncinctum, Plate 1, fig. 5); the reticulation is always first developed along the base of the list. The ventral margin is always free. The left sulcal list (/. sulc. /., Figure 29) is also strikingly variable in size and shape. It usually is about half as long as the hypotheca or slightly longer, but sometimes {Plialacroma turbineum, Plate 2, fig. 3) it is only about 0.33-0.39 as long as the hypotheca, or (P. striatuin, Plate 2, fig. 8) it may extend as far as to the antapex. In most species it is subtrapeziform, somewhat wider posteriorly than anteriorly, with a pronounced postero ventral angle, and with the ventral and posterior margins straight, or gently concave, convex, or sigmoid; in some of the species of this category (P. porosum, Plate 1, fig. 6) the ventral margin may be very broadly angular near the middle. The posteroventral angle frequently is between 80° and 95°, but sometimes this portion of the Ust is more or less acuminate (P. bipartitum. Figure 21 : 2; P. circumsutum, Figure 23: 6), or it shows intermediate stages between an angular and a rounded outline. In some species (P. apicatum. Figure 10:4) the entire free margin of the list is almost evenly rounded, in others (P. argus. Figure 8:1) it is more or less sigmoid, concave an- teriorly and convex posteriorly. It also should be mentioned that in one species, viz., P. praetextum (Plate 4, fig. 6), this list is subtriangular, decreasing gradually in width posteriorlj'. In nearly all the species this list has three well-developed cross-ribs, which in the present paper have been named the anterior main rib, the fission rib, and the posterior main rib. The anterior main rib (a«/. m.r., Figure 29) is located anteriorly, at the junction of this Ust and the posterior cingular list; the fission rib (/. r., Figure 29), at the place where the list is divided in binary fission, i.e., at the sagittal suture and usually somewhat in front of the 46 THE DINOPHYSOIDAE. middle of the list; the posterior main rib {post. m. r., Figure 29), near the posterior end of the list. Usually the anterior main rib and the fission rib are subequal, or either of them is slightly longer than the other; and the posterior main rib, as a rule, is between 1.5 and 2.5 times longer than the fission rib. The relative length of the posterior main rib is more variable than that of either of the two anterior ribs. Sometimes {P. doryphonwi, Figure 23; P. ovum, Figure 11) this rib is as much as 2.8-3.5 times longer than the fission rib, sometimes (P. giganteum, Figure 14: 1 ; P. argus, Figure 8: 1, 2) it is more or less reduced in length or even absent (P. expulsum, Plate 6, fig. 1). When the posterior main rib is well de- veloped, the posteroventral margin of the list is angular, and the rib ends at or near the vertex of the angle ; when the length of this rib is more or less reduced or when this rib is absent, the posteroventral margin of the list is rounded (P. giganteum, Figure 14: 1) or almost straight (P. praetextum, Plate 4, fig. 6). When compared to the depth of the body, the maximum length of the fission rib and the posterior main rib is about 0.22: 1 and 0.55: 1 (P. circumsutum. Figure 23: 6). The minimum length of the fission rib, expressed in the same manner, is about 0.07: 1 (P. argus, Figure 8:1). The main ribs always are unbranched, straight or but slightly curved, and usually of moderate strength, and tapering distally. The fission rib frequently (always?) is double, i.e., there is one rib on either side of the suture (P. porosum, Plate 1, fig. 3, G); and it may be T-shaped, in which case it is divided distally in two branches, which form a marginal rib along the anterior half of the list (P. circumcinctum , Plate 1, fig. 5). The posterior main rib, which sometimes is more or less club-shaped distally (P. doryphorum, Figure 23: 1 ; P. hindmarchi. Figure 18:3), generally has a posterior inclination of about 45° and may be directed straight back (P. slriatmn, Plate 2, fig. 8). In all the primitive and in many of the more or less highly differentiated species this list appears to lack structural differentiation except for the main ribs; in others it may have a number of short, secondary ribs (P. f aims, Plate 2, fig. 7), or a more or less de- veloped reticulation (P. striatuvi, Plate 2, fig. 8; P. hindmarchi. Figure 18:3). It also should be mentioned that in P. Kmbaturn (Plate 3, fig. 5) and P. pulchrum (Jorgensen, 1923, fig. 18) this list has a fine rib just behind the posterior main rib that extends to the margin of the list. The left sulcal list of P. turhineum (Plate 2, fig. 3) is of an exceptional type; its length is, as previously mentioned, only 0.38-0.39 the length of the hypotheca; and its greatest width is 0.12-0.13 the greatest depth of the body; its free margin is gently and evenly convex; it has a weak cross-rib somewhat in front of its middle and a submarginal rib along its entire length; with the exception of these two ribs, this list appears to lack struc- SYSTEMATIC ACCOUNT. 47 tural differentiation. With regard to this list in P. fimbriatum, see p. 192. In most species this hst ends a very short distance behind the posterior rib, but in some {P. f aims, Figure 14: 4, 5) it is more or less decurrent. The last condition is, in a sense, an initial step in the development of a parasagittal list (see P. cuneolus, Figure 22:1-3). The primitive species have no lists except the cingular and sulcal lists. On the other hand, in many of the more or less highly evolved forms, accessory lists are developed. As an example of a highly differentiated and, if we may say so, almost schematical system of accessory lists, these lists in Phalacroma limbatum (Plate 3, fig. 3, 5) may first be described. In this species two lists, the para- sagittal lists {par. I., Figure 29), encircle the body, one on either side of the sagittal suture ; however, in the transverse furrow parasagittal lists never are developed, and the left list ends at or near the posterior end of the longitudinal furrow. The left parasagittal list is of subuniform width throughout its entu-e length, has a maximum width which is subequal to or somewhat less than the width of the transverse furrow, and is furnished with a moderate number of simple, free or anastomosing, incomplete riblets. The right parasagittal list, which directly continues the left sulcal list, resembles the left, but forms on the antapex an acute, wedge-shaped process, the posterior sail (post, s., Figure 29), directed posteriorly. When fully developed, the posterior sail is 0.15-0.27 the greatest depth of the body in length and has a central rib, the proximal half of which might form a more or less complex reticulum; the angle at its tip is 35°-50°. Of this fundamental system there are a great number of variants, the most important of which will now be described. In P. fimbriatum (Plate 4, fig. 4; Plate 2, fig. 1) the two parasagittal lists also encircle the whole body. On the epitheca both lists are of about the same width and structure; from the apex, where their width about equals 0.09 the greatest depth of the body, they slightly decrease in width toward the girdle ; each of them has about twenty almost equidistant ribs, a few of which are branched. On the hypotheca the left list is very narrow, at most about half as wide as the transverse furrow. The right is much wider than the left, lacks a posterior sail, and merges so completely in the left sulcal list that the boundary between these two lists cannot be estabUshed with certainty. From the posterior main rib of the left sulcal list to the antapex, the right parasagittal list is of nearly subuniform width, about 0.14-0.20 the greatest depth of the body; anterodorsally to the antapex this list gradually becomes narrower, and its average width on the dorsal side of the hypotheca is only about 0.07 the greatest depth of the body. The right parasagittal Ust of the hypotheca has about 48 THE DINOPHYSOIDAE. twenty-six fairly strong and almost equidistant ribs, most of which are simple and almost straight, a few irregulai- or iri-egular and branched. The structure of the left list is unknown. As a last example of a species with the two para- sagittal lists extending around the whole body, P. turhineum (Plate 2, fig. 3; Plate 4, fig. 1, 2) may be mentioned. In this species the right parasagittal list forms a direct continuation of the left sulcal list and lacks a posterior sail. On the average both the parasagittal lists are about twice as wide on the posterior half of the body as on the anterior half, and their maximum width is about 0.08- 0.09 the greatest depth of the body. Each of them has a moderate number of short, simple ribs, approximately six on the epitheca and eighteen on the hypo- theca. In most species the parasagittal hsts are less developed than in the examples mentioned above. Generally speaking, the phylogenetic development of these Usts appears to have proceeded from the posterior end of the body to the anterior, and the development of the right list seems to have preceded that of the left. In order to illustrate this statement, a few examples will be given. P. pulchrum (Plate 3, fig. 6) has two parasagittal lists on the hypotheca, but none on the epitheca. The left one of these two lists extends, on the dorsal side of the body, from the posterior cingular list to the antapex; it is very narrow, its maxi- mum width being less than the width of the transverse furrow ; and it is furnished with a few cross-ribs; in some specimens it may even be absent. The right para- sagittal list forms a direct continuation of the left sulcal list and either extends to the posterior cingular list or is absent from the dorsal side of the hypotheca; dorsally it is of about the same type as the left list; posteriorly and postero- ventrally of about the same type as the corresponding list in P. Umbatuin, onlj^ as a rule, somewhat wider and with a slightly different structural differentiation. In P. bipartitum (Figure 21:2) only the right parasagittal hst is present; it is restricted to the posterior half of the hypotheca, but still is connected with the left sulcal list. A peculiar feature of this species is that there are two posterior sails of about the same type as the corresponding structures in P. limbatum, one on each side of the antapex. In a fairly great number of species (P. doryphorum, Figiu'e 23) only the posterior sail of the right parasagittal list is developed. This sail is subtriangular or wedge-shaped and is either situated on the antapex and directed posteriorly or slightly displaced ventrally and inclined posteroventrall}'. When fully developed, its length usually is about 0.20-0.40 the greatest depth of the body, and it is about as wide at the base as it is long or more or less decidedly narrower {P. pugiunculus, Jorgensen, 1923, fig. 19). Sometimes this sail has a central rib, sometimes it is more or less reticulated, especially in its central SYSTEMATIC ACCOUNT. 49 portion; sometimes both the central rib and the reticulation are developed; sometimes no structure can be distinguished. Only in a few of these species (P. circumsutum, Figure 23:6; P. cuneolus, Figure 22: 1, 2) a connection is de- veloped between the posterior sail and the left sulcal list. The flagellar pore (/. p., Figure 29) is a fairly large opening^ located in the longitudinal furrow, i.e., on the right valve, and just behind or about a girdle width behind the posterior cingular list. Its shape usually is subcircular or slightly elongated, in exceptional cases subtriangular (Phakicroma porosum, Plate 1, fig. 3) or slightly irregular. It is variable in size, but its greatest diame- ter appears never to exceed the width of the transverse furrow. Other pores to be mentioned in this connection are as follows: — in P. praetextum (Plate 4, fig. 7) there is a fairly small pore on the ventral side of the left valve, near the sagittal suture, and just behind the anterior cingular list. In P. pulchrum, P. giganteum, and P. striatum (Plate 3, fig. 1, 2; Plate 2, fig. 5) there are one to three fairly small pores on the ventral side of the left \alve, near the sagittal suture, and just in front of the anterior cingular list. Although pores of the last-men- tioned kind have been observed only in a comparatively small number of species, it is not impossible that they are characteristic of the genus as a whole. Their significance is not apparent. "Boih flagella arise in the flagellar pore and are well developed. The trans- verse flagellum (Schiitt, 1895, pi. 2, fig. 11 : 2) lies in the girdle and encircles the body from the left around to the right. The longitudinal flagellum (Schiitt, 1895, pi. 2, fig. 13: 6), which is about as long as the body or slightly longer or shorter, passes posteriorly between the sulcal lists. The structure of the thecal mdl is very different in the various species and affords important systematic characteristics. In most species there is a varying number of pores and poroids (Schiitt, 1895, p. 21, 22) moi-e or less uniformly scattered all over the theca. Sometimes (Phalacroma fimhriatum, Plate 4, fig. 4) these structures are numerous, sometimes (P. ttirhineum, Plate 4, fig. 1, 2) they are few, sometimes (P. praetextum, Plate 4, fig. 0, 7) they appear even to be absent. In P. lurhineum they seem to be restricted to the transverse furrow and only about fifteen in number. In some species the theca appears to lack struc- tural differentiation except for the pores and poroids, but usually it is charac- terized either by areolation or by reticulation. The areoles, which are small, rounded pits and usually more or less closely set (P. circumcinctum, Plate 1, fig. 5), resemble the poroids, with which they are connected by transitional structures (Schiitt, 1895, p. 22). The meshes of the reticulation usually are 50 THE DINOPHYSOIDAE. fairly uniform in size within the species, but show a wide range of variation within the genus as a whole. In P. striatum (Plate 2, fig. 8), which is charac- terized by meshes of moderate size, twenty-five to thirty-five meshes on each valve border the posterior margin of the transverse furrow; in P. f aims (Plate 2, fig. 7) the corresponding value is twenty to twenty-five ; in P. praetextum (Plate 4, fig. 6), about fifteen; in P. fimbriatum (Plate 4, fig. 4), about ten; and in P. turhineurn (Plate 2, fig. 3), five. In the last species the meshes are relatively larger than in any other known species. The ridges between the meshes some- times are so fine that the reticulation hardly can be distinguished, sometimes (P. fimbriatum, Plate 4, fig. 4) they are rather heavy. It should be remembered in this connection that the degree of structural differentiation varies with age. The new valve of a recently divided specimen is thin and almost without struc- ture; in old specimens the thecal wall is more or less heavy and its structural peculiarities are well developed. In most species the areolation or reticulation covers the whole thecal surface, in others {P. limbatum, Plate 3, fig. 4, 5) the regions nearest to the sagittal suture remain more or less undifferentiated. In P. cuneus (Figure 12) and related species a spine-like process projects into the cytoplasm from a point near the middle of the right sulcal list. P. praetextum (Plate 4, fig. 6, 7) is especially characterized by a dumbbell-shaped area, located on the ventral side of the hypotheca, just to the left of the sulcus, and extending on both sides of the sagittal suture from the posterior cingular list to the antapex. This area, which has a maximum width of about 0.33 the dorsoventral diameter of the body, is characterized by a structure quite different from that of the remaining portion of the theca. It has a faint reticulum of very small meshes, and in the middle of each or at any rate of most of these meshes there is an ex- ceedingly fine pore. In other words, this area has the structure of a cribriform plate. Presumably it is a permanent structure; i.e., it appears not to correspond to the intercalary zones of megacytic specimens (see p. 189). With regard to the shape and structure of the intercalary zones of the mega- cytic specimens, see p. 51. The sagittal suture of the two valves appears always to be finely serrated (Plate 2, fig. 1, 4). The three plates, epithecal, cingular, and hypothecal, of each valve very seldom are found separated. In one specimen of Phalacroma giganteum, the epithecal was detached from the cingular by means of the pressure of the cover-glass. The protoplasmic contents are coarsely alveolar and hyaline, or may be of a pale rose or brownish color. The nucleus, which usually is located on the dorsal SYSTEMATIC ACCOUNT. 51 side of the hypotheca (Schiitt, 1895, pi. 2, fig. 11 : 1, 2; 13: 3, 6), is rather large, ellipsoidal, ovoidal, or spherical, and has a moniliform chromatin reticulum. Probably in all species there are one or two, usually two, large pusules, which open by short and slender canals into the flagellar pore (Schiitt, 1895, pi. 2, fig. 11:2). In many species chromatophores are absent ; when present, these structures appear usually to be small, rod-shaped, and yellowish (Schiitt, 1895, p. 64, pi. 3, fig. 16: 4; 17: 2). A characteristic feature of many species is the presence of rod-like or thread-like rhabdo&omes, which in most cases are arranged radially (Schiitt, 1895, pi. 2, fig. 11: 2; 13: 3). Metaplasmic inclusions of different kinds, e.g., globules of fats and oils, also have been found. See also Schiitt (1895) and Biitschli (1885). The cell sometimes {Phalacroma pidchdhi, Lebour, 1922, p. 817) is "full of large refractive bodies." The length of the body is very variable within the species as well as within the genus. For the genus as a whole the range of variation in length thus far estab- lished is from 21 ix {Phalacroma pulchellum) to 148 /j. {P. giganteum). Reproduction: — The only mode of reproduction known in Phalacrcma is binary fission of the free-swimming individuals. The line of fission or, in other words, the sagittal suture lies in the sagittal plane except in the region of the sulcus. Probably in most species the whole flagellar pore and the entire longi- tudinal furrow belong to the right valve (Schiitt, 1895, pi. 3, fig. 16:3). It is possible, however, that sometimes the portion of the longitudinal furrow that is in front of this pore belongs to the left valve, as in the specimen of Dinophysis jorgenseni (Plate 5, fig. 3). Since in all species the flagellar pore is located near the junction of the sulcus and the cingulum, by far the larger poi'ticn of the longitudinal furrow always belongs to the right valve. The whole right sulcal list belongs to the right valve. The left sulcal list is divided at the fission rib, which probably is always double (Plate 1, fig. G) although, when seen in lateral view, it usually appears to be single. The portion of this list which is in front of the fission rib belongs to the left valve, the portion behind this rib to the right valve. The right parasagittal list and the posterior sail or sails belong exclu- sively to the right valve, the left parasagittal list exclusively to the left valve. Neither the cingular and sulcal lists nor the parasagittal lists and the pos- terior sails are resorbed in binary fission (Schiitt, 1895, pi. 2, fig. 10). Whether or not the flagella (of the right valve) are shed is not known. The flagella of the left valve are fairly well developed before the detachment of the two schizonts (Schiitt, 1895, pi. 3, fig. 16: 4), and so the dividing specimens probably continue their active swimming during the fission processes. 52 THE DINOPHYSOIDAE. The growth of the cingular and sulcal lists and the development of the thecal wall in the new halves of the two schizonts probably take place fairly rapidly. This is indicated by the fact that one rather seldom finds specimens in which these structures are not completely developed. Furthermore, judging by Schiitt's figure (1895, pi. 3, fig. 16: 3), the cingular lists are fairly well developed even before the schizonts separate; see, however, Meunier (1910, p. 59). On the other hand, the development of the parasagittal lists and of the posterior sails, which pre- sumably are phylogenetically rather young structures, appears to be rather slow. In any case, the posterior sails of the specimens of P/io/ocrowa doryphorum, etc., examined were found to be very variable in size, and in species with parasagittal lists many specimens lacked these structures or had them \'erj' incompletely developed. For a better understanding of the value of the last-mentioned struc- tures in the differentiation of species, their post-fission development should be submitted to a careful study. Double specimens or groups of specimens resulting from fission or repeated fissions, such as have been found in Dinophysis caudata and D. rniles, are unknown in Phalacroma. A phenomenon that possibly may be characteristic of the genus as a whole (Pavillard, 1916, p. 47) is the pronounced increase in size that precedes binary fission and that is accompanied by the development of the so-called intercalary bands (Stein, 1883, p. 23) along the sagittal margins of the two valves. Speci- mens with intercalary zones or, according to Pavillard's (1915a) terminology, megacytic specunens, have been found in twenty-one of the forty-seven presum- ably valid species of this genus, viz., Phalacroma acutum (by Pavillard, 1916), P. argus (by Jorgensen, 1923), P. cuneolus (by us), P. cuneus (by Pavillard, 1915a, 1916; and by us), P. doryphoruvi (by Pavillard, 1915a, 1916; Jorgensen, 1913; and by us), P.j'avus (by Jorgensen, 1923), P.fimbriatum (by us), P. giganteurn (by us), P. globulus (by Schiitt, 1895), P. hindinarchi (by us), P. mitra (by Pavillard, 1915a, 1916), P. mucronatum (by us), P. otmm (by us), P. paulseni (by Paulsen, 1911b), P. porodictyum (by Stein, 1883; Schiitt, 1895), P. porosum (by us), P. pulchellum (by Lebour, 1922), P. rapa (by Stein, 1883; Pavillard, 1915a, 1916), P. rotundaium (by Meunier, 1910), P. rudgei (by Murray and ^\^litting, 1899), and P. vastuni (by Schiitt, 1895) ; see also p. 198. The intercalary zone, which appears to be of varying width in the different species, is relatively wide on the dorsal side of the body and decreases gradually in width toward the ventral side; in the region of the sulcus it appears usually to be very narrow or not developed at all. Sometimes, as in Phalacroma mitra SYSTEMATIC ACCOUNT. 53 (Pavillard, 1916, p. 49), it has about the same structure as the thecal valves. In most cases, however, its structure is strikinglj' faint. In some species, e.g., in P. doryphorum (Pavillard, 1916, fig. 12), this zone under low magnification ap- pears to have closely set fine transverse striation; under higher magnifications each of the striae proves to be a row of closelj' set minute areoles. The mtercalary bands are transitory structures. When the new vahe is formed in binary fission its sagittal margin is attached to the premegacytic sagittal margin of the old ^'ah'e, and the intercalary band soon disappears; pre- sumably it is resorbed. For further discussion of this interesting phenomenon, see Pa\'illard (1915a, 1916), who was the first to submit it to a careful study. Finally, it may be mentioned that Bergh (1881b, p. 226) recorded a specimen of Dinophysis laevis [= Phalacroma rotundatum (Clap, and Lach.) var. laevis (Claparede and Lachmann) Jorgensen] in a restmg condition ("im Ruhezustand, zu einer Kugel innerhalb der Schale zusammengezogen"). The significance of this observation must be regarded as uncertain (see Blitschli, 1885, p. 1020), since encystment has not been investigated or definitely known to occur in the Dinophysoidae. Distribution: — The rather extensive data on the distribution of Phalacroma published at the present writing show that this genus is marine, almost exclusively eupelagic, of general oceanic distribution, but that the great majority of its species are limited to waters of tropical, subtropical, or warm-temperate nature or origin. The great difficulties implied in the determination of several of the species of this genus, the broad concept of species held by many of the inves- tigators in this field, and the fact that but relatively few of the data are accom- pamed by figures or descriptions by means of which the determinations of species may be checked (see p. 58) make the general distribution of many of the species rather uncertain. The distribution of the genus as a whole, on the other hand, may be regarded as fairly well established. Phalacroma rotundatum, P. omtuni, P. paulseni, P. rotundatum var. laevis, P. minutum, and P. rudgei are known to occur in the cold waters of the far north. Phalacroma rotundatum has been found along the whole coast of Norway, off Greenland, and in the .4i"ctic Ocean; P. ovnium, on the west coast of Norway and off Greenland; P. paulseni, oE Greenland; P. rotundatum var. laevis, on the west coast of Norway; and P. minutum. and P. rudgei, in the Atlantic Ocean between lat. 58° N. and lat. 60° N. Of these species, P. rotundatum, P. ovatum, P. paulseni, and P. rotundatum var. laeins are endogenetic in the northern waters, while P. minutum and P. rudgei are probably southern forms, occasionally carried to the 54 THE DIXOPHYSOIDAE. far north by the Gulf Stream. In the Antarctic Ocean P. rotundatum var. laevis has been found by Karsten (1905) as far to the south as lat. 63° S. It is a striking fact that all these species are small, rotund, and simply organized. The more or less luxuriant species appear to be restricted to warm-water regions (Schiitt, 1893, p. 269). The only species of this genus known to be endogenetic in brackish waters is P. rotundatum, which has been recorded repeatedly from the less saline regions of the Baltic Sea. Phalacroma is found in surface waters, but its optimum habitat seems to be the deeper levels of photosynthesis (Karsten, 1907, p. 442, 444). Some species, possibly sapruzoic, ha\e been found almost if not quite below the photic zone. It should be remembered, however, that the vertical distribution of this genus is very incompletely known, since 1/ut few records based on catches made with closing nets are available. The following from Karsten's (1905, 1906, 1907) reports on the phytoplankton of the Valdivia Expedition are the only published records. Phalacroma rotundatum var. laevis was found at Station 132, 400- 300 m.; Station 151, 200-100 m.; P. operculatum at Station 170, 200-100 m.; Station 229, 200-20 m.; and Station 268, 63-46 m. Phalacroma doryphorum was taken at the following stations: — Station 227, 1000-800 m.; Station 228, 420- 350 m.; Station 229, 1600-1400 m.; Station 239, 120-105 m.; Station 268, 105- 88 m. and 63-46 m. All the specimens recorded were reported as "living." The specimens of P. doryphorum taken at great depths were found to be without chromatophores. Although many of the species are widely distributed, none of them has been found to be abundant or even common. Indeed, most of these species appear to be rare, some even very rare. Representatives of Phalacroma were found at 100 (78.7%) out of the 127 stations of the Expedition from which dinoflagellates were recorded. These 100 stations are distributed over the whole area covered by the Expedition as shown in the following table and Plate 24: — Number and Number of Stiitions and Occurrences % of Occurrences % Cabfornia Current 4571,4.574,4.580,4.583 4 4 100 Mexican Current 4.587, 4588, 4590, 4592, 4594, 4596, 4598, 4r>(IO, 41)04, 4605, 4607, 4.545, 4546 13 13 100 Pan.amic Area 4609, 4611, 4613, 4615, 4617, 4619, 4621, 4631, 46:34, 46.3.5,4637,46:38,4640,4644 /4 17 82.3 Peruvian Current 4646, 4647, 4648, 46.50, 4651, 4652, 4655, 4657, 46.59, 4660, 4661, 4662, 4663, 4664, 4665, 4666, 4667, 4668, 4669, 4670, 4671, 4673, 4675, 4676, 4678 Easter Island Eddy 46S9, 4691, 4(i92, 4695, 4697, 4699 Galapagos Eddy 4713, 4715 25 27 92.6 6 10 60 2 A 50 Number and % of Occurrences % 30 4.5 66.6 3 3 100 2 2 100 1 2 50 SYSTEMATIC ACCOUNT. 55 Number of Stations and Occurrences South Equatorial Drift 4679, 4680, 4681, 4683, 4685, 4687, 4701, 4705, 4706, 4707, 4709, 4711, 4717, 4719, 4720, 4721, 4722, 4724, 4725, 4728, 4730, 4731, 4732, 4733, 4734, 4736, 4737. 4739, 4740, 4741. South Equatorial Current 4540, 4742, 4743 Equatorial Counter Current 4541, 4.542 North Equatorial Current 4543 At sixty-seven of these 100 stations Phalacroma was taken in vertical hauls and at forty-five in surface hauls. Most of the records from vertical hauls are from 300-0 fathoms, some are from 800, 400, 150, 100-0 fathoms. Vertical hauls were made at sixty-eight out of the 127 stations. The genus thus was found at not less than 98.5% of the stations at which vertical hauls were made; it was absent from one station only, 4574 in the California Current, at which it was found in a surface haul. Surface catches and Salpa stomachs of specimens taken in surface waters (eighty-one surface catches and twenty-four samples of Salpa stomachs) were examined from eighty-two stations. The genus, as previously mentioned, was taken in surface hauls at forty-five stations, i.e., at 54.9% of all the surface sta- tions. Taking into consideration the surface stations only, these forty-five record stations are distributed in the following manner: — Number of Stations and Occurrences California Current 4574, 4583 Mexican Current 4588, 4590, 4592, 4596, 4600, 4604, 4607, 4545, 4546 Panamic Area 4611, 4615, 4617, 4619, 4624, 4631, 4635, 4640, 4644 Peruvian Current 4648, 46.50, 4657, 4660, 4661, 4664, 4666, 4669, 4675, 4676, 4678 Easter Island Eddy 4692 Galapagos Eddy South Equatorial Drift 4680, 4706, 4709, 4720, 4725, 4731, 4733, 4741 South Equatorial Current 4743, 4540 Equatorial Counter Current 4541, 4542 North Equatorial Current 4543 On account of the prevalence of Phalacroma in deeper waters, the distribu- tion and the frequency of the record stations at which vertical hauls were made should be used as an indicator of the horizontal distribution of this genus in the area investigated by the Expedition. These records show that the genus is almost evenly distributed throughout this area; indeed, it was found at not less than 98.5% of the stations at which vertical hauls were made. Furthermore, the even distribution of this genus is also evident when the distribution and fre- quency of the records of species are considered (Plate 24). The only region in Number and % of Occurrences % 2 4 50 9 9 100 9 13 69.2 n 20 55 1 5 20 2 8 23 34.7 2 2 100 2 2 100 1 2 50 56 THE DINOPHYSOID.\E. which Phalacroma was found tci be represented rather sparingly was the CaU- fornia Current ; north of Point San Lucas there were only four records of species, viz., three records of P. parvuluin and one record of P. rapa. This scarcity pos- sibly may be due to the fact that the California Current comes from the north, in other words, from a region where this genus is less abinidant than within the tropics and subtropics. Of the eight most frequent species, P. argus, P. cuneus, P. doryphorum, P. porodidyum, and P. rapa (Figure 9, 13, 24, 7, 17) were found to be almost evenly distributed throughout the area investigated; P. reticulaturn (Figure 26) was not fountl nortli of the equator; P. striatum (Figiu-e 15) was not found in the California, Mexican, and Peruvian Currents; and P. hindmarchi (Figure 19) was restricted to the southwestern portion of this area, in other words, it had the same pecuUar distribution as Amphisolenia schauinslandi (Figure 51) and A. thrinax (Figure 59). The surface record-stations of Phalacroma are very unevenly distributed. ^^^lile this genus was found at twenty-nine (69.0%) out of the fortj^-two surface stations in the Mexican Current, the Panamic Area, and the Peruvian Current, it did not occur at more than nine (30.0%) out of the thirty surface stations in the South Equatorial Drift, the Easter Island Eddy, and the Galapagos Eddy. The causes of this uneven distribution may lie in the greater influence of vertical circulation in the regions nearer to the western shores of the continents. It should also be mentioned that there is no surface species of this genus prevalent in the coastal regions as in the case of Dinophysis (D. caudata). There are 309 records of species of Phalacroma from vertical catches. Out of these 309 records 1(0.3%; Station 4664) showed a frequency of 40%; 1(0.3%; Station 4663) 10%; 2(0.6%; Stations 4613, 4666) 6%; 2(0.6%,; Stations 4663, 4709) 5%; 2(0.6%c); Stations 4590, 4662) 4%,; 8(2.5%; Stations 4598, 4664, 4667, 4671, 4695, 4713, 4715, 4742) 3%; 11(3.6%; Stations 4609, 4634, 4638, 4675, 4681, 4689 [2 records], 4697, 4699, 4713, 4740) 2%o; 62(20.1%; Stations 4580, 4590, 4594, 4598 [2 records], 4605, 4613 [2 records], 4617, 4634 [2 records], 4637, 4638 [2 records], 4647, 4648 [3 records], 4650, 4651 [2 records], 4655, 4657 [2 records], 4665, 4667, 4671, 4676 [2 records], 4679 [2 records], 4681 [3 records], 4689 [3 records], 4691 [2 records], 4695, 4697, 4699 [3 records], 4701 [3 records], 4705, 4719 [2 records], 4721 [2 records], 4722, 4730, 4732 [2 records], 4734, 4737, 4739 [3 records], 4742) 1 %; 220(71.2%) showed a frequency of less than 1 %. There are seventy-four records of species of this genus from surface catches. Out of these seventj'-four records 1(1.4%; Station 4546) showed a frequency of 7%; 1(1.4%; Station 4619) 5%; 1(1.4%; Station 4669) 4%; 3(4.1%; Stations SYSTEMATIC ACCOUNT. 57 4604, 4542, 4545) 3%; 6(8.1%; Stations 4615, 4624, 4650, 4669, 4675 [2 records]) 2%; 19(25.7%; Stations 4574, 4600 [2 records], 4604, 4617, 4619 [2 records], 4635, 4657, 4664, 4666, 4720, 4731, 4743, 4540, 4541, 4542, 4543, 4545) 1%; 43(58.2%) a frequency of less than 1% or did not have the frequency estabUshed. Coincident occurrence of difTerent species of Phalacroma in catches from 300 (800, 400, 150, 100)-0 fathoms is recorded at the following of the sixty-seven stations mentioned above: — 15 species occurred coincidently at 1 station (1.5%; Station 4730) ; 12 species at 1 station (1.5%,; Station 4681) ; 11 specie-s at 1 station (1.5%; Station 4734); 10 species at 2 stations (3.0%; Stations 4699, 4701); 9 species at 1 station (1.5%; Station 4740) ; 8 species at 3 stations (4.5%; Stations, 4713, 4732, 4737) ; 7 species at 6 stations (9.0%; Stations 4679, 4697, 4705, 4711, 4734, 4742); 6 species at 7 stations (10.4%,; Stations 4587, 4637, 4691, 4695, 4709, 4721, 4739) ; 5 species at 6 stations (9.0%; Stations 4590, 4613, 4634, 4689, 4719, 4722); 4 species at 12 stations (17.9%; Stations 4594, 4598, 4605, 4617, 4638, 4655, 4662, 4664, 4665, 4676, 4683, 4717); 3 species at 9 stations (13.4%; Stations 4583, 4609, 4648, 4650, 4667, 4671, 4707, 4715, 4736); 2 species at 11 stations (16.4%; Stations 4580, 4647, 4651, 4652, 4657, 4661, 4663, 4666, 4675, 4685, 4728). Coincident occurrence of different species in surface catches is recorded at the following of the forty-five surface stations mentioned above : — 3 species occurred coincidently at 7 stations (15.6%; Stations 4604, 4617, 4619, 4743, 4540, 4542, 4545); 2 species at 15 stations (33.3%; Stations 4592, 4596, 4600, 4635, 4644, 4660, 4664, 4669, 4675, 4676, 4678, 4720, 4731, 4741, 4541). At the forty-five surface stations just mentioned, there are records of only nine of the thirty-one species found in the material of the Expedition. The number of surface records of each of these nine species is as follows: Phalacroma doryphorum, 26 records, 4 of which are from Salpa stomachs; P. rapa, 22 records, 2 of which are from Salpa stomachs; P. cuneus, 13 records, 2 of which are from Salpa stomachs; P. f aims, 6 records, 1 of which is from a Salpa stomach; P. argus, 2 records, 1 of which is from a Salpa stomach; P. parvulum, 2 records; P. hind- marchi, 1 record; P. expulsum, 1 record (Salpa stomach); P. lalirelatum, 1 record (Salpa stomach). Thus not less than sixty-one (82.5%) out of the seventy-four surface records refer to three species only. These three species are evenly dis- tributed over the whole area investigated by the Expedition (see p. 55, on the distribution of the surface stations). It may also be mentioned that P. poro- dictyum was taken in a surface haul in Acapulco Harbor, a station not included in the 127 discussed above. 58 THE DINOPHYSOIDAE. The fact that Phalacroma was found to be evenly distributed throughout the area investigated makes it highly plausible that this genus is fairly evenly distributed throughout all the tropical and subtropical seas. Finally, it may be mentioned that not less than sixteen out of the forty-seven presumably valid species have not been found except in the material of the Expedition. Historical Discussion and Systematics Stein (1883, p. 23), who estabhshed Phalacroma, gave no diagnoses but confined himself to a few words of comparisons and to the figuring of six new species, viz., P. nasutum, P. operculatum, P. porodictyum, P. argns, P. doryphnrum, and P. rapa. Diagnoses of this genus have been published by Biitschli (1885, p. 1009), Delage and Hcrouard (1896, p. 385), Schiitt (1896, p. 26), Paulsen (1908, p. 19), and Lebour (1925, p. 75). Of these diagnoses the one by Schiitt (1896) is by far the most nearly complete and satisfactory. No extensive descrip- tion and discussion of this genus have been published. Besides the sLx specific names established by Stem (1883), the following specific and subspecific names are to be found in the literature: P. armatwn Hensen (1895) P. haslatum Hensen (1895) P. operculoides Schiitt (1895) P. glnbiilvs Schiitt (1895) P. porodictyum Stein var. parvula Schiitt (1895) P. cunem Schiitt (1895) P. vasltim Schiitt (1895) P. vastum var. aciila Schiitt (1895) P. milra Schiitt (1895) P. jourdani (Gourret) Schutt (1895) P. ovum Schiitt (1895) P. hhckmani Murray & Whitting (1899) P. hivdmarcbi Murray & Whitting (1899) P. doHchopleriigium Murray & Whitting (1899) P. rudgci Murray & Whitting (1899) P. ynirtulum Cleve (1900c) P. cerntncorys Entz (1902a) P. cernlocorys var. tride7itata{Dadny) Entz (1902a) P. acuminatum (Claparede & Lachmann) Zacharias (1906) P. spliaericum (Stein) Zacharias (1906) P. knlicuJn Kofoid (1907a) P. reticulntum Kofoid (1907a) P. Mrintum Kofoid (1907a) P. ultimum Kofoid (1907a) P. circumnutum Karsten (1907) P. hastatum Pavillard (1909) P. CU71C11S Stuwe (1909) P. circtimcinclum Kofoid & Michener (1911) P.favuis Kofoid & Michener (1911) P. fimbriatum Kofoid & Michener (1911) P. giganleum Kofoid & Michener (1911) limbatum Kofoid & Michener (1911) porosum Kofoid & Michener (1911) praetextum Kofoid & Michener (1911) pulchrum Kofoid & Michener (1911) rotundatiim (Claparede & Lachmann) Kofoid & Michener (1911) turbineum Kofoid & Michener (1911) arcuatum Hensen (1911) P. argn Hensen (1911) P. cuter Hensen (1911) nblrquum Hensen (1911) propuhans Hensen (1911) rotundntum Hensen (1911) acrilum (Schiitt) Pavillard (1916) pulchellum Lebour (1922) kofoiiU Herdman (192.3) rotundatum (Claparede & Lachmann) var. tncpis (Claparede & Lachmann) .lorgensen (1923) P. ovntum (Claparede & Lachmann) Jorgensen (1923) P. parrulum (Schiitt) Jorgensen (1923) P. ehngatum Jorgensen (1923) P. stetiopterygiiim Jorgensen (1923) P. simulans Jorgensen (1923) P. pugiuncului Jorgensen (1923) P. ebriola Herdman (1924) P. irregulare Lebour (1925) SYSTEMATIC ACCOUNT. 59 In the present paper the following new specific names have been estab- lished: — P. apicatum, P. hipartitum, P. contradum, P. cuneolus, P. lativelatum, P. lens, P. rnucronaium, P. pavlseni, P. protuberans, and P. pyriforme; and two previously described species, Dinnphysis galea Pouchet (1883) and D. expulsa Kofoid and INIichener (1911), have been transferred to this genus. Several of the species mentioned in the last two paragraphs ha\'e been trans- ferred to other genera. Schiitt's (1895) transfer of Dinophysis jourdani Gourret to Phalacroma and Entz's (1902a) allocation, under the name of Phalacroma ccra- tocorys, are incorrect. This species belongs to Ceratocorys of the tribe Peridioni- oidae, as has been shown by Kofoid (1910a, p. 183) and by Jorgensen (1911, p. 147). Ceratocorys tridentata Daday (1888), which was treated by Entz (1902a) under the name of Phalacroma ceratocorys var. tridentata (Daday), is so inade- quately described and figured that its generic allocation must be considered as uncertain. Zacharias's (1906, p. 536, 530) use of Phalacroma for Dinophysis in designating Dinophysis acuminata Claparede and Lachmann and D. sphaerica Stein was probably due to slips of the pen, since at the remaining several places in his paper he maintained the original generic allocation of these two species. In any case, it is erroneous; both these species are typical representatives of Dinophysis. Herdman's (1923, p. 34) transfer of Amphidinium kofoidi var. petasatum Herdman (1922) to Phalacroma, under the name of P. kofoidi, is incorrect, since this species has a very small epitheca and since its transverse and longitudinal furrows are very deep and without distinct lists (see the Dinc- physidae, p. 32). It may also be mentioned that if this variety is given the status of a species, then its name must be petasatum and not kofoidi. For the same reasons Phalacroma ebriola Herdman (1924) does not belong to this genus; (see the family Dinophysidae, p. 32). The transfer to the genus Phalacroma of Dinophysis rotundata Claparede and Lachmann (by Kofoid and Michener, 1911), of D. ovata Claparede and Lachmann (by Jorgensen, 1923), and of D. laevis Claparede and Lachmann (by Jorgensen, 1923) probably is justified. These primitive forms are on the borderland between Phalacroma and Dinophysis, but they appear to be somewhat more closely related to the former than to the latter. It should be remembered, however, that these two genera merge into each other, and that their separation is almost arbitrary. As to whether Dino- physis laevis should be treated as a distinct species or as a variety of Phalacroma rotundatum is a question of its own that cannot be settled as yet. Phalacroma hastatum Pavillard (1909), although fairly highly differentiated, is of uncertain generic assignment. In the present paper we have followed Jorgensen's (1923, 60 THE DINOPHYSOIDAE. p. 31) suggestion and have referred it to Dinophysis hastata Stein (see p. 269). Apparently with full justification, Jorgensen (1923, p. 3) has made Phalacroma nasutum Stein (1883) the type of a new genus, Pseudophalacroma. Phalacroma ullimum Kofoid (1907a) has in the present paper been made the type of another new genus, Dinofurcula. The elevation to the rank of species of Phalacroma porodictyum Stein var. parvula Schiitt (1895) (by Jorgensen, 1923) and of P. vasium var. acuta Schiitt (1895) (by Pavillard, 1916) probably is justified. Phalacroma arcuatum, P. argo, P. arnudum, P. enter, P. hastalum, P. obliquum P. propulsans, and P. roiundatum Hensen (1895, 1911) are nomina nuda. The identity in the arrangement of the species in the two tables given by Hensen (1911, p. 166, 167) and the great similarity in the names indicate that the new names P. arcuatum and P. argo were intended for P. armatum and P. argus. Phalacroma rotundatum Hensen (1911) does not refer to P. rotundatum (Clapa- rede and Lachmann), since Hensen (1895, 1911) records the latter as Dinophysis rotundata. P. cxmcus Stiiwe (1909), which also is a nomen nudum, evidently is due to a typographical error and stands for P. cxmeus. Phalacroma simulans Jorgensen (1923) is a synonym of P.famis Kofoid and Michener (1911); and P. stenopterygiu7n Jorgensen (1923) is a synonym of P. expulsum (Kofoid and Michener, 1911). Jorgensen (1923, p. 5) suggests that P. rudgei Murray and Whitting (1899) "is perhaps only a thick megacytical stage of Phalacroma rotundatum ^'ar. laevis." However, on account of our scant knowledge of the small and rotund species of this genus, it is advisable to treat P. rudgei, preliminarily, as a valid species. With regard to P. ovum Schiitt (1895) and P. operculoides Schiitt (1895) see p. 118. With regard to P. galea (Pouchet, 1883) see p. 121. Phalacroma irregulare Lebour (1925) is based exclu- sively on fission stages with incomplete lists and with the intercalary border not yet absorbed. It must be regarded as too insufficiently known for certainty of specific identification. Finally, Paulsen (1911b, p. 305, fig. 2) figured a specimen, under the name of Dinophysis rotundata, which is referable to Phalacroma but not to any of the species known at the present time. For this form we suggest the name Phalacroma paulsenl, sp. nov. Under the designation of Phalacroma sp., four specimens have been figured, viz., by van Breemen (1906, pi. 1, fig. 4a, b), by Okamura (1907, pi. 4, fig. 26 and pi. 5, fig. 42), and by Lindemann (1923, fig. 13). P. sp. van Breemen (1906) possibly may be referable to P. rudgei, as suggested by Paulsen (1908, p. 19). P. sp. Okamura (1907, pi. 4, fig. 26) has been allocated to P. apicatum (p. 111). SYSTEMATIC ACCOUxNT. 61 P. sp. Okamura (1907, pi. 5, fig. 42) probably belongs to P. mitra Schutt (see Okamura, 1912, p. 18), and not to P. elongatum as suggested by Jorgensen (1923, p. 11). P. sp. Lindemann (1923) cannot be identified at the present time. As will be seen from the previous paragraphs, there are at present forty-seven presumably valid species and one variety of Phalacroma, as follows : — P. acutum (Schutt) Pavillard (1916) P. apicatum, sp. nov. P. argus Stein (1883) P. bipartitum, sp. nov. P. blackniani Murray & VVhitting (1899) P. circumcinctum Kofoid & Michener (1911) P. circumsutum Karsten (1907) P. contractuni, sp. nov. P. cuneolus, sp. nov. P. cuneus Schutt (1895) P. dolichopterygiiun Murray & Whitting (1899) P. doryphorum Stein (1883) P. elongatum Jorgensen (1923) P. expulsum (Kofoid & Michener) nobis P. favus Kofoid & Michener (1911) P. fimbriatum Kofoid & Michener (1911) P. giganteum Kofoid & Michener (1911) P. globulus Schutt (1895) P. hindmarchi Murray & Whitting (1899) P. lativelatum, sp. nov. P. lens, sp. nov. P. lenticula Kofoid (1907a) P. limbatum Kofoid & Michener (1911) P. niinutum Cleve (1900c) P. mitra Schtitt (1895) P. mucronatum, sp, nov. P. operculatum Stein (1883) P. operculoides Schutt (1895) P. ovatum (Claparede & Lachmann) Jorgensen (1923) P. ovum Schutt (1895) P. parvulum (Schutt) Jorgensen (1923) P. paulseni, sp. nov. P. porodictyum Stein (1883) P. porosum Kofoid & Michener (1911) P. praetextum Kofoid & Michener (1911) P. protuberans, sp. nov. P. pugiunculus Jorgen.sen (1923) P. pulchellum Lebour (1922) P. pulchrum Kofoid & Michener (19il) P. pyriforme, sp. nov. P. rapa Stein (1883) P. retieulatum Kofoid (1907a) P. rotundatum (Claparede & Lachmann) Kofoid and Michener (1911) P. rotundatum (Claparede & Lachmann) var. laevis (Claparede & Lachmann) P. rudgei Murray & Whitting (1899) P. striatum Kofoid (1907a) P. turbineum Kofoid & Michener (1911) P. vastum Schutt (1895) Besides these forty-seven valid species, we have Phalacroma galea (Pouchet, 1883), which may be identical with either P. doryphorum or P. circumsutum, and P. irregulare. All the published descriptions of the species are short and incomplete and have no or but few data of variation for consideration. The descriptions of Kofoid (1907a) and of Kofoitl and Michener (1911) are preliminary and based on the same material as those of the present paper. Some of the forty-se\-en species mentioned above, e.g., Phalacroma globulus Schutt and P. minutum Cleve, are so incompletely known that their certain specific identification will cause considerable difficulty. Furthermore, the synonymies of some of these species, e.g., those of P. rolundatum (Claparede and Lachmann) and of the other species occurring in northern European waters, are so exceedingly complicated that it appears more than doubtful whether anybody will be capable of unravel- ling them in a satisfactory way. Finally, a few of these species, as conceived in the present paper, are so variable that there are reasons to beUeve that future 62 THE DIXOPHYSOIDAE. investigators with adequate material at their disposal will find it necessary and feasible to undertake a further systematic subdivision. The first investigator to attempt a subdivision of Phalacroma (Jorgensen, 1923) divides the genus into six sections, viz., Paradinophysis, Euphalacroma, Cuneus, Argus, Podophalacroma, and Urophalacroma. The species included in these sections are as follows: — Paradinophysis: — P. rotundatum, P. rolunda- tum var. laevis, P. rudgei, P. ovatum, and P. parvulum. Euphalacroma: — P. ovum, P. porodictyum , P. operculatum, P. acutum, and P. elongahwi. Cuneus: — P. expulsum, P. cuneus, P. hlackmani, and P. striatum. Argus: — P. argus. Podophalacroma: — P. rapa, P. dolichopterygium, P. mitra, P. favus, and P. hindmarchi. Urophalacroma: — P. doryphorurn, P. circumsutwn, P. pugiunculus, and P. pulchrum. Using Jorgensen's system as a basis, Pavillard (192.3a) suggested a division of the genus into two subgenera, Euphalacroma and Para- dinophysis. To the first of these he referred four of Jorgensen's sections, viz., Oblongata (nom. nov.), Cuneus, Argus, Podophalacroma. To the second sub- genus he referred the remaining two of Jorgensen's sections, viz., Rotundati (nom. nov.) and Urophalacroma. The situation of the sulcal lists relative to the thecal valves was unknown even to Stein (1883, p. 23). This problem was settled by studies on the closely related genus Dinophysis (see p. 224). Biitschli (1885) and Schutt (1895, 1899) have given fairly extensive accounts of the structure and organization of the thecal wall and of the cell contents. With regard to the morphological changes that take place in the theca pre- ceding binary fission, it may be mentioned that megacytic specimens were figured by several investigators, e.g., by Stein (1883), Schutt (1895), Murray and Whitting (1899), and Meunier (1910) before Pavillard (1915a, 191(i) dis- cussed at length and correctly interpreted this phenomenon. Schutt (1895, p. 148) misunderstood the significance of the intercalary zones, while Meunier (1910, p. 59) gave a short l)ut correct account of these structures. It may also be mentioned in this connection that Pouchet (1894) interpreted megacytic specimens in the genus Dinophysis as prefission stages. Contributions to our knowledge of the distribution of Phalacroma are to be found in the following papers, not specifying those previously mentioned in this section:— Cleve (1899c, 1900b, 1901a, c, 1902b, 1903b), Daday (1888), Entz (1902b, 1904, 1905), Forti (1922), Graf (1909), Gran (1912b, 1915), Karsten (1905, 1906, 1907), Lemmermann (1899a, 1901a, 1904, 1905a), Lindemann (1924, 1925), Lloyd (1925), Lohmann (1902, 1908a, 1920), Mangin (1912, 1915), Nathansohn SYSTEMATIC ACCOUNT. 63 (1908, 1909, 1910a), Ostenfeld (1898a, 1906, 1915, 1916b), Ostenfeld and Paulsen (1904), Ostenfeld and Schmidt (1901), Paulsen (1904), Pavillard (1905, 1912), Rauschenplat (1900), Schiller (1911a, b, c, 1912), Schmidt (1901), Schroder (1900a, 1906a, 1911), Stuwe (1909), and Whitelegge (1891). None of these papers contains original figures by means of which the correctness of the de- terminations may be checked. Forti (1922) gives reproductions of previously published figures of the species recorded. Due to the great difficulties implied in the determination of several of the species of Phalacroma and to the broad concept of species held by many of the investigators, much of the data on the distribution of this genus should be accepted tentatively. References to Phalacroma or minor contributions to our knowledge of this genus are found also in Balbiani (1884c), Bergh (1884), Calkins (1902), Chun (1903), Doflein (1909, 1911, 1916), Forti and Issel (1923, 1924), Hensen (1891), Kofoid (1906c), Lindemann (1923a), Nathansohn (1910b), Oltmanns (1922), Schutt (1893, 1900a), Steuer (1910, 1911), Walther (1893), and Willey and Hickson (1909). Pavillard (1923a) gives a critical review of Jorgensen's (1923) important paper on this group. Adaptive and Systematic Value of the Characters. Principles used IN the Description of the Species Although Phalacroma is limited largely to tropical, subtropical, and warm- temperate waters of relatively low buoyancy, it is characterized by the fact that the body (theca) is simple in shape, viz., subspheroidal (Schutt, 1895, pi. 2, fig. 12: 1), lenticular (Plate 3, fig. 3, 5), cuneate (Plate 2, fig. 5, 8), inversed fig-shaped (Plate 2, fig. 7), subbiconical (Plate 4, fig. 1-7), or bilaterally flattened ellipsoidal (Figure 3:6) and subobovoidal (Figure 11). In no species does the body show adaptations to flotation in the form of pronounced elongation or protuberances as in Amphisolenia, Triposolenia, and certain species of Dino- physis; they maintain themselves in their optimum habitat, i.e., in the upper strata of the sea mainly as follows: — (1) they are fairly active swimmers; (2) most of them are relatively small; (3) their protoplasm contains large pusules (Schutt, 1895, pi. 4, fig. 19:2) and inclusions of low specific gravity, such as fats and oils (Schutt, 1895, p. 82-86), and they thus have a specific gravity approaching that of the surrounding medium; (4) in many of them the surface friction is increased by structural differentiations of the outer surface of the theca (Plate 4, fig. 1-7) ; (5) some of them have relatively large cingular, sulcal, or para- 64 THE DINOPHYSOIDAE. sagittal lists (Plate 2, fig. 8; Plate 1, fig. 6; Plate 4, fig. 4; Plate 3, fig. 5; P'igure 23:6). The most important of these five points probably is the third one, i.e., the lowering of the specific gravity of the body. Without stressing the first point, it is known that the species of Phalacroma are fairly active swimmers, but, on the other hand, there are no data as yet on the question as to how their swimming capacity compares with that of the members of such genera as Amphisolenia and Triposolenia in which the body is highly adapted for flotation. As to the second point, i.e., the relatively small size of the body, it may be mentioned that the largest of all the known species of Phalacroma, P. giganteurn, is characterized by its thin and fragile theca, while its close relative, the comparatively small P. cuncus, has a rather heavy theca. The reduced thickness of the thecal wall in P. giganteurn may be interpreted as an adaptation to flotation; the decrease in the weight of the theca at least to some extent counterbalances the reduction in the relati^'e surface of resistance caused by the increase in the \'olume of the body. When the adaptive value of the lists is considered, it should be remem- bered that these structures are relatively small in all the species of the genus occurring in cold waters (viz., P. rolundatum and its variety laens, P. ovatuni, P. paulseni, P. minutum, and P. rudgei), and that they reach their highest de- velopment in waters of low buoyancy. A thorough understanding of the func- tions of each of the three different kinds of lists present in this genus, viz., the cingular, sulcal, and parasagittal lists, will require a careful analysis from the viewpoints of mechanics and hydrodynamics. Such an analysis is outside the scope of the present paper. The following summary statements must suffice. The cingular lists, although small, undoubtedly act as parachutes when the body is suspended with the apex uppermost. The nearly symmetrically de- veloped parasagittal lists of some species, e.g., of P. Umbatum and P. fimhrialum (Plate 3, fig. 5; Plate 4, fig. 4), act as parachutes when the organism is turned upon one of its lateral faces. The asymmetrical parasagittal lists of some species, e.g., of P. pulchnini (Plate 3, fig. 6), and the asymmetrical left sulcal hst increase the surface of resistance and cause the organism to sink in a descending zigzag or spiral path whenever it rests on one of its lateral faces. They also function as keels and rudders, thus stabilizing the progressive spiral swimming character- istic of Phalacroma {cf. Kofoid, 190Ge, p. 129). Noteworthy in this connection are the small size of the right sulcal list, when compared to the left, and the fact that the left sulcal list is somewhat obhque in positit)n, passing from the left valve to the right, and often somewhat spiral-shaped (Plate 2, fig. 1, of Phala- SYSTEMATIC ACCOUNT. 65 croma fimhriatum; Plate 5, fig. 3, of Dinophysis jorgenseni). Finally, it may be added that the inclination of the longitudinal axis of the body found in several species of Phalacroma may be connected with the spiral mode of swimming. With regard to the significance of the spiral swimming, see Jennings (1901). Although in the present paper all the external characters have been taken into account in the establishment and characterization of species, some of the specific separations in Phalacroma should be regarded as tentative. This is due partly to the simple organization of many of these species and partly to the fact that all the species characters are subject to variations of the fluctuating kind, in varying degree of amplitude. The characters which are most variable within the species are the size and shape of the bodj^ (theca), the relative height of the epitheca, the shape of the left sulcal list, and the development and structure of the accessory lists and sails. These are also the characters which have been most profoundly modified within the genus as a whole, and it is largely upon them that the subdivisions of the genus have been founded. The variations in the development of the parasagittal lists appear at least in part to be due to the comparative!}' slow formation of these structures following binarj^ fission. WTien not otherwise stated, the following principles have been apphed in the descriptions of species of this genus : — {1) All characteristics refer to specimens in lateral view. (2) Diagnoses and descriptions refer to premegacytic specimens only; when only megacytic specimens were available, descriptions and measurements were made from valves exclusive of the mtercalary zone. (S) The terms length and depth of bod}', and symmetrical and asymmetrical species refer to body (theca) exclusive of Usts. (4) When the cingular lists have only the two ribs near the dorsal sagittal suture, they are said to be without ribs. (5) The right sulcal list is without structural differentiations. If not otherwise stated in the diagnosis, the species is characterized by the following features : — (1) The body is subsymmetrical, and its longitudinal axis is perpendicular to the girdle. (2) The thecal wall has scattered pores. (3) In the case of the species figured with the body viewed dorsoventrally, the flagellar pore is located about a girdle-width behind the posterior cingular list. (4) The epitheca is visible above the anterior cingular list. (5) The cmgular Usts are ribbed, subequal, about as wide as the transverse 66 THE DIXOPHYSOIDAE. furrow, subhorizontal or with but slight anterior incUnation, and run in an almost straight line across the body. Their ribs are complete or almost so, i.e., they reach the free edge of the list, equidistant, straight, and simple or almost so. (6) The right sulcal list is subtriangular, and extends to Rj or to R3 of the left sulcal list or to a point somewhere between these two ribs. (7) Left sulcal list: the ventral and posterior margins, which are straight or but slightly convex, concave, or sigmoid, form together a distinct angle. The three main ribs are present, of moderate strength, almost straight, and not club- shaped or otherwise modified; and the list has no structural differentiation besides the main ribs. (S) Accessory Usts and sails are absent, or, when present, they lack structural differentiations. The methods of measuring lengths, angles, and proportions utilized are shown in Figure 29. Subdivisions. Relationships among the Species Although Phalacroma is one of the most primitive genera of Dinophy- soidae, it exhibits a marked structural diversity. Of all the known species, P. pulchellum is considered to be, on the whole, structurally the most primitive, resembling the simple ancestors from which this genus originated. This assump- tion is based on the small size (length, 21 fi) of this species, on its approach to the fundamental spherical form, its large and high epitheca (the posterior cingular list is located about 0.40 the length of the body from the apex), the slight develop- ment of its cingular and sulcal lists, its lack of accessory lists and sails, and on the areolation and porulation of its thecal wall. A fundamental feature of the structural difTerentiation within the genus is that it nearly always has been ac- companied by an increase in size. Although the body shows a great variety of shapes, it is never characterized by extreme elongation or by processes; on the other hand, bilateral compression is a nearly universal phenomenon. The gLrdle is supposed to have been originally nearly equatorial in position (see p. 30). From the equatorial position, which still is found in some of the primitive as well as in some of the advanced species (P. lenticula, Figure 3:7; P. limbatum, Plate 3, fig. 5), the girdle has migrated anteriorly; or a reduction in the height of the epitheca has taken place. The cingular lists show increase in size and structural complexity, but remain comparatively small and simple. A somewhat greater diversity in size and structure is exhibited by the left sulcal list. Just as in Orni- thocercus and Histioneis, it is largely the portion of this list behind the fission SYSTEMATIC ACCOUXT. 67 rib that has increased in size and structural complexity. The phylogenetic de- velopment of the accessory lists and sails appears to have proceeded from the posterior end of the left sulcal list anteriorly along the dorsal side of the body, and from the right valve to the left. The structure of the thecal wall seems to have developed in most cases from areolation to reticulation; ami there seems to have been an inherent tendency for the meshes of the reticulum to become progres- sively larger. Sometimes, however, a differentiation of the thecal structure appears to have taken place (e.g., P. giganteum). In most cases the progress witliin the several groups, which have been established in speciation, is from the less to the greater diversity and specializa- tion in structural detail. This increase in complexity is expressed in several, though not often in all the characters, of tlie individual species. It is interesting to note how the structural features utilized in speciation in this genus seem to be pervaded by the aspect of factors such as those with which the geneticist deals. In some groups the speciation might be conceived as a series, partially realized, of permutations of factors with intergradations due to multiple factors giving results which simulate seriation. In other groups we find more or less clearly defined orthogenetic series of intermediate and progressively differentiated species. The factorial analyses of genetics do not compel the assumptions that the individual links in these series have originated chronologically, i.e., that they are genetically sequential, although the conventional conception of the evolu- tionary process inclines us to this interpretation. Nuclear reorganizations equiva- lent, or related to those which ensue in gametogenesis or endomixis would ap- pear to be an essential cytological basis for the distribution of genes which the kind of speciation outlined above seems to suggest. However, such reorganiza- tions are as j-et unknown in this genus. 1 . CoNTRACTUM group : — p. conlracluw, sp. nov. Figure 3:1. 2. RoTUNDATUM group: — p. jjulcliellum Lebour (1922, fig. 1-4). P. paruuluiii (Schtitt) J6rgen.sen. Figure 3: 4-6. P. ylubuhts Schutt {lS9r,, pi. 2, fig. 12). P. operculoides .Schiitt (1895, pi. 2, fig. 11: 1). P. Ttuigei Murray & Whitting (1899, pi. 31, fig. 6). P. rotundatum (Clapar«le & Lachmann) Jorgeiisen (1923, fig. 2). P. rotundatum (Claparede & Lachmann) var. laeiis (Claparede & Lachmann) ( 18.58, pi. 20, fig. 13). P. irregulare Lebour (1925, pi. 11, fig. 4). P. laiivelatum, sp. nov. Figure 3: 2, 3. P. paulseni, sp. nov. Paulsen (1911b, fig. 2). P. umtuin (Claparede & Lachmann). Jorgensen (1923, fig. 3). P. lens, sp. nov. Figure 4: 1-3. P. porosum Kofoid & Michener. I-'igure 5. P. lenticula Kofoid. Figure 3: 7. 68 THE DINOPHYSOIDAE. 3. Ahgus group: — P. porodictyum Stein. Figure C. P. vastum Schiitt (1895, pi. 3, fig. 16: 3). P. argus Stein. Figure 8:1,2. P. apicalum, sp. nov. Figure 10. P. operculatum Stein s. str. (1883, pi. 18, fig. 8). P. cirmincuictum Kofoid & Michener. Figure 8; 3. P. mniiit Schiitt. Figure 11. P. elongatum Jorgensen (1923, fig. 9). P. pyrifoTme, sp. nov. Figure 4: 4, 5. 4. CuNEUS group: — P. cuiieus Schiitt. Figure 12. P. blackmani Murray & Whitting (1899, pi. 31, fig. 4). P. striatum Kofoid. Figure 14: 3. P. gi(7a?i/e««i Kofoid & Michener. Figure 14: 1. 5. Rapa group: — p. acutuin (Schiitt) Pavillard. Schiitt (1895. pi. 3, fig. 17: 7). P. minutwn Cleve (1900c, pi. 8, fig. 10, 11). P. dolichoplerygium Murray & Whitting (1899, pi. 31, fig. 8). P. mitra Schutt (1895, pi. 4, fig. 18). P. rapa Stein. Figure 10. P. farm Kofoid & Michener. Figure 14: 2, 4, 5. P. hindmarchi Murray & Whitting. Figure 18. 6. ExPULSUM group: — P. protuberaiis, sp. nov. Figure 20: 1-5. P. expulsum (Kofoid & Michener). Figure 20: 6-9. 7. LiMBATUM group: — P. limbatwn Kofoid & Michener. Figure 21: 1. P. bipartitum, sp. nov. Figure 21 : 2. P. pulchrum Kofoid & Michener. Figure 21: 3. 8. DoRYPHORUM group : — P. mucroiiatum, sp. nov. Figure 22: 4, 6, 8. P. doryphuTum Stein. Figure 23: 1-5. P. circumsutum Karsten. Figure 23: 6. P. cviieotus, sp. nov. Figure 23: 1-3, 5, 7. P. pugiuiiculus Jorgensen (1923, fig. 19). 9. Praetextum group: — P. praetextum Kofoid & Michener. Figure 25: 4, 5. 10. Reticulum group: — p. fimbriatuin Kofoid & Michener. Figure 25: 1. P. reticulatum Kofoid. Figure 25: 2. P. turhineum Kofoid & Michener. Figure 25: 3. Discussion of Species Groups 1. CoNTRACTUM group (Figure 3:1). The sole member of this group is of uncertain generic assignment. The small size and subrotund shape of the body, the fairly large size of the epitheca, the small size and the shape of the cingular SYSTEMATIC ACCOUNT. 69 and sulcal lists, and the lack of ribs in the left sulcal list affiliate it with Pseudo- phalacroma nasuhim. The latter species is characterized especially by an anterior prolongation of the longitudinal furrow, extending two thirds the dis- tance from the girdle to the apex. This prolongation, which presumably is a primitive feature of great taxonomic significance, is not indicated in our drawing of Phalacroma contraclujn but may have been overlooked. The small size and simple structure of the cingular and sulcal lists indicate that this species is on a lower evolutionary level than the members of the Rotundatum group. 2. Rotundatum group (Lebour, 1922, fig. 1-4; Figure 3:4-6; Schlitt, 1895, pi. 2, fig. 12, 11 : 1 ; Murray & Whitting, 1899, pi. 31, fig. 6 ; Jorgensen, 1923, Argus Rapa Cuneus Limbatuni Reticulatu m Praetextum Contractum Figure 2. — Graphical representation of the relationships of the groups of species in Phalacroma. fig. 2; Claparede iu pennae). Phalacnmut opercuhihim ^CHij'n,\S95,p. 93, pi. 2, fig. 10: 1-3. Hensen, 1911, partim, p. 166, 167, tab. 15. Phalacroma porndirliim ScHRiiDEB, 1900a, p. 9, 11, 19 (/o/wk pennae); 1906a, p. 322,32.5, 327; 1911, p. 21, 37. IPhahuroma poroJictijwn Ok.\m0r.\, 1912 (non 1907, p. 134), p. IS, pi. .5, fig. 83. Diagnosis: — Body obovate or subellipsoidal in lateral outline, deepest at or somewhat behind girdle, usually somewhat deeper anteriorly than posterior^; length: depth, 1.11-1.23: 1 ; longitudinal axis deflected posteroventrally at 0°-20°. In dorsal view obovate, 1.60-1.80 times longer than wide. Posterior cingular list 0.37-0.50 the length of body from ajiex. Cingular lists without, or with but faintly indicated ribs. Right sulcal list with angular margin, concave anteriorly, and convex or straight posteriorly. Left sulcal list 0.37-0.53 the length of body; distance between Ri and R3 is 0.33-€.40 the length f)f body; R2 is 0.09-O.13, and R3 is 0.10-0.21 the greatest depth of body; margin forms angle of 75°-100° at R3: R3 inclined posteriorly at 15°-45°. Theca finely and closely areolate. Length, 72.5-81.5 M. Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, the body of which is obovate or sub- ellipsoidal in lateral outline, deepest at or somewhat behind the girdle, and 1.11- 1.23 times longer than deep. Li the Expedition specimens the ratio between the length and the depth is 1.18 (1.14-1.23): 1; in Stein's (1883, pi. 18, fig. 11), 1.14: 1 ; in Schutt's (1895, pi. 2, fig. 10: 2; 13:3), 1.11-1.15: 1 ; and in Jorgensen's (1923, fig. 6), 1.13: 1. The longitudinal axis of the body either is perpendicular to the transverse furrow, as in Stehi's (1883) specimen and in some of the Expedition specimens, or it is deflected posteroventrally at an angle of l°-20°; in the Expedi- tion specimens this deflection does not exceed 8°; in Schutt's (1895, pi. 2, fig. IO2) it is about 20°, and in Jorgeiisen's (1923) about 12°. The epitheca is 0.97 (0.96-0.98) as deep as the hypotheca, strongly and al- most evenly convex, in some specimens slightly flattened ventrally or both ventrally and dorsally (Figure 6: 1), dome-shaped, highest at or in some speci- mens slightly dorsal to the center, and ^•ery prominent above the anterior cingular list. The transverse furrow is flat or slightly convex, and its width is 0.20-0.30 the greatest height of the epitheca. The posterior cingular list is 0.37-0.50 the length of the body from the apex; in the Expedition specimens this ratio is 0.47 (0.44-0.50) : 1 ; in Stein's (1883), 0.37: 1; in Schutt's (1895, pi. 2, fig. 10:2, and 13: 3), 0.38-0.50: 1 ; and in Jorgensen's (1923), 0.37: 1. The hypotheca is some- times symmetrical, as in Stein's (1883) specimen and in Figure 6: 1, but usually 100 THE DINOPHYSOIDAE. it has a more or less pronounced post ero ventral inclination (see p. 99). Its dorsal, posterior, and ventral margins are well and evenly convex and confluent. Its posterior portion, which is rather broad in some specimens and rather narrow in others, is nearly always somewhat narrower than the anterior portion of the body. In dorsoventral view (Stein, 1883, pi. 18, fig. 13) the body is regularly obovate, about 1.60-1.80 times longer than wide, and widest at or somewhat be- hind the girdle; its anterior portion is broadly, its posterior narrowly convex; and its side contours are evenly convex. The cingular lists are subhorizontal and subequal; they are about as wide as, or slightly wider or narrower than, the transverse furrow, and are "without or with faintly indicated ribs" (Jorgensen, 1923, p. 9). The right sulcal list usually ends at or somewhat behind a point midway between the fission rib and the posterior main rib of the left sulcal list; .sometimes it extends even to the last- mentioned rib; in some specimens its ventral margin, even in the widest region, does not quite extend to the ventral margin of the left sulcal list, but in most specimens it does. The anterior half to two thirds of the free margin of this list is more or less concave and sometimes strengthened by a marginal rib ; the poste- rior portion of this margin, which forms a distinct angle with the anterior portion, is more or less convex or almost straight. The greatest width of this list is located just behind the concave portion. The left sulcal list is 0.37-0.53 as long as the body; in the Expedition specimens this ratio is 0.40 (0.44-0.53): 1; in Stein's (1883), 0.40: 1; in Schiitt's (1895, pi. 2, fig. ISs), 0.39: 1; in Jorgensen's (1923), 0.37: 1. The distance between the anterior and posterior main ribs is 0.36 (0.33-0.40) the length of the body. The anterior main rib, when present, is 0.10-0.17, the fission rib 0.08-0.13, and the posterior main rib 0.10-0.21 the greatest depth of the body; in the Expedition specimens these three ratios are 0.12 (0.10-0.13) : 1, 0.10 (0.08-0.13) : 1, and 0.17 (0.14-0.21) : 1 ; behind the poste- rior main rib the list decreases suddenlj' in width. Between the anterior and posterior main ribs the free margin of this list usually is slightly sigmoid, concave anteriorly and convex posteriorly; sometimes it is nearly straight, or gently con- cave or convex, or it may be slightly angular at the fission rib (Jorgensen, 1923, fig. G) ; at the posterior main rib it forms an angle of 75°-100°; in the Expedition specimens this angle is 93° (90°-100°); in Stein's (1883) about 75°; behind the last-mentioned rib it is almost straight or slightly concave or convex. The main ribs of this list are of moderate strength, straight or nearly so, and not club- shaped or otherwise modified. The distance between the anterior main rib and the fission rib is 0.35 (0.25-0.45) the distance between the anterior and posterior SYSTEMATIC ACCOUNT. 101 main ribs. The posterior main rib has a posterior inclination of 30° (15°-45°). Sometimes this Hst has a faint reticulation (Stein, 1883; Jorgensen, 1923). There are no accessory lists or sails. The thecal wall is finely, closely, and usually rather faintly areolate, and has scattered pores. In the transverse furrow there are two rows of pores. Megacytic stages have been seen by Stein (1883) and Schiitt (1895). The proportions of eight of the Expedition specimens and of those figured by Stein (1883, pi. 18, fig. 11), Schiitt (1895. pi. 2, fig. 10: 2, and 13: 3) and Jor- gensen (1923, fig. 6) were measured. Figure 6. — 1-5, Phnhcroma porodictinim Stein, right lateral view. Porulation indi- cated only on small portion of theca in 4 and 5. X 430. 1, 2, 3, 5, from Station 4737 (300-0 fathoms); 4, from Station 4739 (300-0 fathoms). Dimensions: — Expedition specimens: Length of body, 74.8-8.15// (average, 77.5 yu). Greatest depth of body, 62.2-69.8 m (average, 65.8 ^l). The size of the type specimen (Stein, 1883, pi. 18, fig. 11) is unknown. According to Stein's (1883) information about the magnifications of his figui'es, this specimen was somewhere between 73 ^ and 112 ju long. The specimens represented by Schiitt (1895, pi. 2, fig. 10: 2, and 13: 3) are about 76-78 n long. The length of Jorgen- sen's (1923, fig. 6) specimen is about 72 /j. According to Lohmann (1902, p. 53), the length varies between 58 ^ and 76.5 fi. This statement, which implies a striking variability in size, has been disregarded in the present paper, since Lohmann does not give any figiu'es or description by means of which his con- ception of the species might be checked. Variations: — The variability of this species, as conceived here and by Jorgensen (1923), is rather striking. However, there seems to be but little doubt 102 THE DINOPHYSOIDAE. that we are dealing with a natural systematic unit. The different fnrms repre- sented by Figure 6 and by the figures of previous investigators appear to be con- nected by continuous series of intermediate forms and are probably modifications. The size of the body, the inclination of the longitudinal axis of the l)ody, the relati\'e height and the shajie of the epitheca and of the hypotheca, and the shape and size of the left sulcal Ust are the most variable characters. Comparisons: — None of the specimens found in the material of the Expedi- tion and determined as Phalacroina porodictyum agrees completely with the type specimen of this species as figured by Stein (1883, pi. 18, fig. 11). However, some of these specimens (Figure 6:1) approach the type so closely that their assign- ment can be regarded as certain. They differ from the type mainly in having the epitheca somewhat higher relatively and the left sulcal list somewhat longer. Other specimens (Figiu'e 6:3) are rather similar to Schiitt's (1895, fig. 10:2) and to Jorgensen's (1923, fig. 6) but we have not seen any specimens that show a complete agreement with any of the figures of these two authors. Plialncromn porodictyum is proliably most closely related to P. arc/us. This relationship is indicated l\y the close resemblance in the size and shape of the body, and in the shape and structure of the right sulcal list. The first species differs from the last mainly in the angularity of its left sulcal list and in the areolate structure of its thecal wall. In both these characters it probably is the more primitive. For further discussion, see p. 107. Phalacroma porodictyum is certainly specifically distinct from P. parvidum, a form which Schtitt (1895) first figured as a variety of P. porodictyum, and which Jorgensen (1923, p. 7) established as a distinct species. .S;/''0" //'".'/-■ The spofiniens figured as Pluildcmmn njiirculriluin Stein l)y Scluitt (1S0.5, pi. 2. fi^- 10) prnhahly are referable to P. porodictyum. The sjiecinien represented by Okamura (1007, pi. 4, fig. 26) under the de.^iRnation P. sp. . . . Phalacroma imrodich/um Stein? tnidonbtedly belongs to P. apiralum nob. Phalacroma porndicliiiiiii Okamura (1912, fig. S3) is probably not identical with /'. poroilirli/um Stein, since the specimen figured is very small, about 47 ^ long, and has a left sulcal list which is more than twice as wide at the posterior main rib as it is anteriorly. Henscn (191 1, p. 166) writes that he has partly confused Phalacroma porodictyum and /'. opcrculatum. These two species probably have been confused by several investigators, but the extent of this confusion cannot be established, since only a few authors give figures or descriptions. It may be mentioned in this connection that C'leve never recorded /'. porodictyum, although he carried out extensive investigations on the plankton of the seas from which this species has been recorded repeatedly. On the other hand, Clevc has numerous records of P. opcrcnlatiwi. Occurrence: — Pludarroma porodiclytnn is recorded at twenty-nine of the 127 stations. There are 5, 5, 6, 5, 8, and stations on the six lines of the Expedi- tion. Of these twenty-nine stations, four (4587, 4590, 4598, 4605) are in the Mexican Current ; three (4613, 4634, 4637) in the Panamic .\rea; five (4648, 4(562, 4666, 4673, 4676) in the Peruvian Current; four (4689, 4691, 4697, 4699) in the SYSTEMATIC ACCOUNT. 103 Easter Island Eddy; one (4713) in the Galapagos Eddy; and twelve (4679, 4681, 4701, 4705, 4719, 4721, 4724, 4730, 4732, 4734, 4737, 4739) in the South Equa- torial Drift. At one station (4713) the species is recorded from 150-0 fathoms; at two stations (4662, 4666) from 800-0 fathoms. All the remaining records refer to hauls from 300-0 fathoms. The species is also recorded from surface waters in Acapulco Harbor, off the Mexican Current. This station is not included in the 127 stations mentioned above. Figure 7. — Occurrence of Pbalncroma porodicti/um Stein. Large, solid circles indicate records from vertical hauls; squares, records from surface hauls; small, solid circles, stations at which this species was not found; small, open circles, stations from which no plankton catches were examined. The temperature range of these twenty-nine stations at the surface was 67°-85°; the average was 75.5°. At Acapulco the surface temperature was 83°. The frequency is 1% at seven stations (4634, 4648, 4679, 4681, 4689, 4699, 4719). At the remaining stations it is less than 1 %. The species was first recorded by Stein (1883) "aus dem Atlantischen Meer und der Siidsee." The specimens of this species drawn by Schiitt (1895) prob- ably were taken either at Naples, or in the tropical or subtropical regions of the Atlantic. In the Atlantic it was found by the following investigators:- — Jorgensen (1923), in the Bay of Cadiz; Murray and WTiitting (1899), at lat. 37° 44' N., long. 30° 55' W.; Ostenfeld (1898a), at lat. 35° 44' N., long. 38° 03' W.; Stiiwe (1909), at lat. 28° 30' N., long. 40° 16' W.; Karsten (1906), at lat. 0° 9' S., 104 THE DIXOPHYSOIDAE. long. 8° 29' W.; Hensen (1911), localities not specified. From the Mediterranean it is recorded by Pavillard (1905, 1916), in the Gulf of Lyons; Forti (1922), in the Ligurian 8ea; Daday (1888) and Schroder (1900a), at Naples; Schroder (1906a), in the Ionian Sea; Entz (1902b, 1905) and Schriider (1911), in the Adriatic Sea; Jorgensen (1923), "throughout the entire Mediterranean." In the Red Sea it was found by Ostenfeld and Schmidt (1901); in the CUilf of Aden by Ostenfeld and Schmidt (1901) and Schroder (1906a); in the Arabian Sea by Ostenfeld and Schmidt (1901) and Schroder (1906a); off the coast of Celebes by Ostenfeld (1915); in the Peruvian Current by Lemmermann (1899a). With regard to Olcamura's (1912) records from Japanese waters, see p. 102. The species was found in waters of tlic following temperatures: — 74° (Murray and Whitting, 1899), 77.0°-80.3° (Ostenfeld and Schmidt, 1901), and 75.2° (Stiiwe, 1909). Of the investigators who ha\e contributed to a Icnowledge of the distribution of this species only Stein (1883), Forti (1922), and Jorgensen (1923) give descrip- tions or drawings of this form by means of which their determinations may be checked. Phalacroma porodiclyum is eupelagic and evidently widely distributed in tropical, subtropical, and warm-temperate seas. In the area investigated by the Expedition it appears to be of almost uniform occurrence. Its optimum habitat according to the records is in deeper waters, within the levels of photosynthesis. It was found at the surface at only one Expedition station, viz., Acapulco. Phalacroma argus Stein Figure 8: 1,2; 9 Phalacroma argxis Stein, 1883, p. 18, fig. 15-17. Schutt, 1895, p. 13, 83, pi. 3, fig. 15: 1-3. Lemmermann, 1899, p. 372; 19nia, p. 372. Cleve, 1901ii, p. Ui. Ostenfeld & Schmidt, 1901, p. 175. Entz, 1902b, p. 94; 1905, p. 111. Schroder, 190(in, p. 324, 327. K.\rsten, 1907, p. 235. P.vvillard, 1909, p. 283; 1916, 1). .52. HEN.SKN, 1911, p. 166, 167, tab. 15. Joroensen, 1923, p. 13, fig. 13. I'hahicrnina urgo Hensen, 1911, p. 167 {Uijifiti pcniiac). Diagnosis: — Body slightly obovate in lateral view, deepest at or somewhat behind girdle; length: depth, 1.15-1.48:1; longitudinal axis deflected postero- \entrally at 0°-12°. In ventral view obovate, widest somewhat behind girdle; length: width, 1.75: 1. Posterior cingular list 0.28-0.45 the length of body from apex. Cingular lists usually without ribs. Right sulcal list with angular margin, concave anteriorly and convex posteriorly. Left sulcal list 0.45-0.59 the length of body; distance between Ri and R3 is 0.33-0.43 the length of body; R2 is 0.07- 0.14 and R3 is 0.09-0.11 the greatest depth of body; margin gently sigmoid, con- SYSTEMATIC ACCOUNT. 105 cave anteriorly, convex posteriorly, seldom evenly convex throughout; R3 in- clined posteriorly at 25°-50°. Theca usually reticulate; 15-20 polygons border girdle posteriorly. Length, 83.5-110.5 11. Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized or rather large species, the body of which is obovate in lateral view, deepest at or in most specimens somewhat behind the girdle and 1.15-1.48 times longer than deep. In the Expedition specimens the ratio between the length and the depth of the body is 1.17-1.25: 1; in Stein's (1883, pi. 18, fig. 15, 16), 1.32-1.48: 1; in Schiitt's (1895, pi. 3, fig. 15: 1), 1.15: 1; and in Jorgensen's (1923, fig. 13), 1.21: 1. The longitudinal axis either is per- pendicular to the transverse furrow, as in Stein's (1883) and in some of the Expedition specimens, or it is deflected posteroventrally at an angle of 1°-12''; in none of the Expedition specimens is it deflected more than at 4°; in those figured by Schiitt (1895) and Jorgensen (1923) the deflection is 8°-12°. The epitheca is 0.87-0.96 as deep as the hypotheca, strongly and almost evenly convex, dome-shaped, highest at or just dorsal to the center, and very prominent above the anterior cingular list. The transverse furrow is flat or slightly convex; and its width is 0.22-0.35 the greatest height of the epitheca. The posterior cingular list is 0.28-0.45 the length of the body from the apex; in the Expedition specimens the corresponding figures are 0.43-0.45; in Stein's (1883), 0.28-0.32; in Schiitt's (1895), 0.32; and in Jorgensen's (1923), 0.37. The hypotheca is sometimes .symmetrical, as in Stein's (1883) specimens and in Figure 8:2; but usually it has a more or less pronounced postero ventral inclina- tion (see above). Its dorsal, posterior, and ventral margins are well and evenly convex and confluent. The posterior end of the body is nearly always somewhat narrower than the anterior. In the specimens represented by Stein (1883, pi. 18, fig. 15) and Schiitt (1895, pi. 3, fig. 15: 1) the anterior and the posterior portions of the body are of about the same width. In dorsoventral view (Stein, 1883, pi. 18, fig. 17) the body is regularly obovate, al)out 1.75 times longer than wide, and widest at or somewhat behind the girdle; its anterior end is broadly, its posterior end narrowly, convex; and its side contours are evenly convex. The cingular lists are subhorizontal and subequal; their width usually about equals or shghtly exceeds the width of the transverse furrow; occasionally it is somewhat less. In most specimens these lists appear to lack ribs, but in speci- mens of well-developed thecal reticulation, they have basally "irregular, coarse and short radial beams, finally anastomosing into an incomplete, wide-meshed reticulation" (Jorgensen, 1923, p. 13). The right sulcal list extends to or some- 106 THE DINOPHYSOIDAE. what beyond a point midway between the fission rib and the posterior main rib of the left sulcal hst; in some specimens its ventral margin, even in the widest region, does not quite extend to the ventral margin of the left sulcal list, but in others it does. The anterior half to two thirds of the free margin of this list is more or less concave and, at least in some specimens, is strengthened by a marginal rib; the posterior portion of this margin, which forms a distinct angle with the anterior portion, is more or less convex or, seldom, almost straight. The greatest width of this list is located just behind the concave portion. The left sulcal list is 0.45-0.59 as long as the body; in the Expedition specimens this ratio is 0.45-0.53: 1; in Stein's (1883), 0.51-0.50:1; in Schiitt's (1895), 0..54: 1; in Jorgensen's (1923), 0.45 : 1 . The distance between the anterior and the posterior main ribs is 0.33-0.43 the length of the body. The anterior main rib, when present, is 0.07-0.14, the fission rib 0.07-0.14, and the posterior main rib 0.09-0.11 the greatest depth of the body; in the Expedition specimens these three ratios are 0.09-0.14:1; 0.08- 0.09: 1; and 0.09-0.11: 1. The greatest width of this list, which in most speci- mens is located about midway between the fission rib and the posterior main rib, is 0.10-0.15 the greatest depth of the body. The free margin of this list is gently sigmoid, concave anteriorly and convex posteriorly, seldom gently and evenly convex throughout (Stein, 1883, pi. 18, fig. 15, 16); in other words, it is not angular posteriorly as in most species of the genus, but gently and evenly convex. The main ribs of this list are straight and comparatively weak, and not club- shaped or otherwise modified. The distance between the anterior mam rib and the fission rib is 0.32-0.45 the distance from the anterior to the posterior main rib; in the Expedition specimens this ratio is 0.41-0.42: 1. The posterior main rib has a posterior inclination of 25°-50° ; this angle in the Expedition specimens is 30°-35°; in Stein's (1883), 40°; in Schutt's (1895), 25°; and in Jorgensen's (1923), 50°. There are no ribs except the three main ribs, but sometimes the list appears to be delicately reticulate. There are no accessory Hsts or sails. The thecal wall has a polygonate, sometimes but slightly developed, reticula- tion. There are fifteen to twenty polygons on each valve bordering the posterior margin of the girdle. Each polygon has a central pore. In the transverse fur- row there are two rows of pores (and polygons, if present), each row with fifteen to twenty pores on each valve. Megacytic stages have been found by Jorgenscn (1923, p. 13). The dimensions of two of the Expedition specimens and of the f^pecimens drawn by Stein (1883, pi. 18, fig. 15, 16), Schiitt (1895, pi. 3, fig. 15), and Jor- gensen (1923, fig. 13) were measured. SYSTEMATIC ACCOUNT. 107 Dimensions: — Expedition specimens: Length of body, 83.5-86.2 n. Greatest depth of bodj', 66.9-73.5 /i. We do not know the size of the two specimens figured by Stein (1883, pi. IS, fig. 15, 16), one of which is the type. According to Stein's information about the magnifications of his figures, these specimens were some- where between 80 ^ and 145 ^ long; the tj'pe specimen (Stein, 1883, pi. 18, fig. 16) was somewhere between 94 n and 145 /i long. The specimen represented by Schiitt (1895, pi. 3, fig. 15) is about 110.5 yu long and 96.1 /i deep; the one figure by Jorgensen (1923, fig. 13) is about 91.2 fx long and 75.7 m deep; i.e., these speci- mens are slightly larger than those found by the Expedition in the Pacific Ocean. Variations: — Phalacronia argus is rather strikuigly variable in the following characters: — the size of the body, the inclination of the longitudinal axis of the body, the relati\"e depth of the bod.y, the relative height of the epitheca, and the Fkjure 8. — 1, 2, Phalacroma argus Stein, right lateral view. Surface markings, faint reticu- lation, and ponilation, indicated only on small portion of theca in 1. X 430. 1, from Station 47.30 (300-0 fathoms); 2, from Station 4724 (300-0 fathoms). 3, Phalacroma circumcinctutn Kofoid and Michener, right lateral view of type specimen, slightly tilted. X 430. Station 4671 (300-0 fathoms). shape of the sulcal lists. The variations in the inclination of the longitudinal axis of the body are probably exaggerated due to the tilting of some of the speci- mens examined. Cotnparisons: — Stein (1883, pi. 18, fig. 15, 16) figures two specimens of Phalacroma argus, one relatively small and dorsoventrally narrow, the other relatively large and deep. The specimens in the material of the Expedition agree rather closely with the last -mentioned specimen (Stein, 1883, fig. 16). They differ mainly in the following respects: — (1) the epitheca is relatively higher; (2) the ventral margin of the left sulcal list is not evenly convex but sigmoid, being gently concave anteriorly and convex posteriorly. In most of the Expedition specimens the longitudinal axis of the body is deflected somewhat posteroventrally, while in Stein's specimen the body is symmetrical. The differences, however, are too small to be considered as specific. Moreover, it should be noted that the relative 108 THE DINOPHYSOIDAE. height of the epitheca, the shape of the ventral margin of the left sulcal list, and the inclination of the longitudinal axis of the body are characters subject to rather striking variabihty in the species of the Argus group (P. apicatum, Figure 10). The specimens of Phalacroma argns figured by Schiitt (1895, pi. 3, fig. 15) and by Jorgensen (1923, fig. 13) agree very closely with most of the Albatross specimens of this species. They differ mainly in having the longitudinal axis of the body deflected somewhat more posteroventrally, at 8°-12° as compared with l°-4°; they agree fairly closely with the specimen represented by Stein (1883, pi. 18, fig. 16). This specimen therefore should be regarded as the type of Phalacroma argns. The question as to whether or not the two forms represented by Stein (1883) under this name are different genetically cannot be settled as yet. Preliminarily, Jorgensen's (1923) broad conception of this species is adopted. Judging by the great similarities in the shape and structure of the cingular and sulcal lists and in the structural differentiation of the thecal wall, Phalacroma argus is probably more closely related to P. apicatum than to any other known member of the genus. Indeed, these two forms are so similar that even their specific separation is questionable, and the solution suggested should be regarded as tentative. Phalacroma argus differs from P. apicatum mainly in having rela- tively lower, well-rounded, and dome-shaped epitheca. Phalacroma porodictyum Stein, as conceived in the present paper and by Schutt (1895) and Jorgensen (1923), is probably, next to P. apicatum, the nearest- known relative of P. argus. This relationship is indicated by the close resem- blance in the size and shape of the body and in the shape and structure of the right sulcal list. Phalacroma- porodictyum is easily distinguished from P. argus and P. apicatum by the angularity of the posterior portion of its left sulcal list and by the structure of its thecal wall. Probably another close relative of Phalacroma argus is P. striatum. This species, which is a member of the rather highly differentiated Cuneus group, resembles P. argus in the following respects: — {1) The longitudinal axis of the body is deflected posteroventrally. (2) The free margin of the right sulcal list is concave anteriorly and convex posteriorly. Its concave anterior portion, which forms a distinct angle with the posterior portion, is strengthened by a marginal rib. (3) The left sulcal list is delicately reticulated. Its free margin is well rounded posteriori}', and not angular at the posterior main rib as in most of the species of this genus. (4) The thecal wall has a polygonate reticulation. The polygons are of moderate size and each of them has a central pore. Phalacroma SYSTEMATIC ACCOUNT. 109 striatum is easily distinguished from P. argus by its low epitheca, its broad, some- what wedge-shaped hypotheca, and its exceptionally large left sulcal list. The CuNEUS group probably originated from an ancestral form of about the same habitus as P. argus, just as this last species probably originated frcm a form re- sembling P. porodictyu7n. From the comparatively simple structure of Phalacroma argus, it seems probable that its closest relatives, next to P. apicatum, P. porodictyum, and P. striatum, should be sought among those members of the genus which are pre- FiGURE 9. — Occurrence of Phalacroma argus Stein. Large, solid circles indicate records from verti- cal hauls; squares, records from surface hauls; small, solid circles, stations at which this species was not found; small, open circles, stations from which no plankton catches were examined. sumably the most primitive. The following species are mentioned in this con- nection: — P. operculatum Stein s. str., P. onim Schiitt, P. operculoides Schiitt s. str. However, the degree of relationship between each of these simple species and P. argus is not known ; in other words, which of them is more closely related to this species than the others. Phalacroma argus is readily distinguished from these species by the shape and structure of its sulcal lists. See also p. 113. Occurrence: — Phalacroma argus is recorded at eighteen of the 127 stations. There are 1, 4, 4, 3, 4, and 2 stations on the six lines of the Expedition. Of these eighteen stations, one (4583) is in the California Current; one (4637) in the Panamic Area; three (4652, 4655, 4664) in the Peruvian Current; two (4691, no THE DINOPHYSOIDAE. 4695) in the Easter Island Eddy; ten (4679, 4681, 4683, 4701, 4705, 4722, 4724, 4725, 4730, 4740) in the South Equatorial Drift; one (4540) in the South Equa- torial Current. At two stations (4725 [Salpa], 4540), the species was taken at the surface; at one station (4052) in a haul frcnn 100-0 fathoms, and at one sta- tion (4701) in a haul from 800-0 fathoms as well as in a haul from 300-0 fathoms. All the other records refer to catches from 300-0 fathoms only. The temperature range of these eighteen stations at the surface was ()5°-83°; and the average was 73.7°. At Stations 4725 and 4540, where the species was taken at the surface, the surface temperature was 77° and 79°, respectively. At one station (4681) the frequency is 2%; at two stations (4655, 4691) it is 1%; at the remaining stations it is less than 1%. The species was first recorded by Stein (1883) "aus dem Atlantischen Meer und der Siidsee." Hensen (1911) found it at a very great number of stations throughout the tropical, subtropical, and warm-temperate regions of the Atlantic. "P. argus tritt schon im Floridastrom auf, ist im westlichen Teil der Sargossosee gut vertreten und kommt sonst ziemlich gleichmassig, aber llickenhaft vor " (Hensen, 1911, p. 167). The specimens drawn by Schiitt (1895) were probably taken either in the tropical, subtropical, or warm-temperate regions of the Atlantic or in the Ciulf of Naples. Jorgcnsen (1923, p. 13, 14), who states that this species is "known from many places in the warmer Atlantic, including the Florida Cur- rent," reports it from the Bay of Cadiz; Pavillard (1909, 1916) from the C.ulf of Lyons; Entz (1902b, 1905) from the Adriatic Sea ; Jorgensen (1923) from "through- out the whole of the Mediterranean (at fourteen out of thirty-seven statit)ns), everywhere in single specimens." In the Red Sea it has been found by Schroder (1900a); in the Ciulf of Aden by Ostenfeld and Schmidt (1901); in the Arabian Sea by Ostenfeld and Schmidt (1901), Cleve (1901a), and Schroder (1906a); in the Indian Ocean by Cleve (1901a) and Karsten (1907). 0.stenfeld and Schmidt (1901) found it in surface waters and at a depth of twenty feet; Karsten (1907) in a catch from 100 meters. Most of the remaining records mentioned in this para- graj^h probably refer to surface catches. Ostenfeld and Schmidt (1901) found the species in waters of 79.5° and 82.4°. Only Stein (1883) and Jorgensen (1923) give drawings by means of which the accuracy of their determinations may be judged. This is a eupelagic species occurring in ti'opical, subtropical, and warm- temperate regions of all seas. The Expedition records reveal an almost even distribution throughout the area investigated, with an oi)tinium habitat in deeper rather than surface waters, within the le\-els of photosynthesis. S^^TEMATIC ACCOUNT. Ill Phalacroma apicatum, sp. nov. Figure 10 Phalacroma sp. Okamura, 1907, p. 134, pi. 4, fig. 26a and b. Diagnosis: — Body irregularly obovate or sublozenge-shaped in lateral out- line, with subconical epitheca; deepest at or just behind girdle; length: depth, 1.24-1.30: 1; longitudinal axis deflected posteroventrally at 0°-10°. In ventral view subbiconical, with rounded apices, widest at girdle, 1.40 times longer than wide. Posterior cingular list 0.49-0.53 the length of body from apex. Lists resemble those of Phalacroma argits. Of the main ribs of left sulcal list R2 is Figure 10. — Phalacroma apicatum, sp. nov. 1, 3, 4, .5, in right lateral view; 2, in ventral view. Left sulcal list with traces of reticulation in specimen represented by 3; surface markings indicated only on small ])ortion of theca in 3. X 430. 1, 2, from type specimen, Station 4737 (300-0 fathoms); 3, from Station 4730 (300-0 fathoms); 4, from Station 4737 (300-0 fathoms); 5, from Station 4734 (300-0 fathoms). 0.09-0.17 and R3 is 0.12-0.17 the greatest depth of body. Surface markings of theca as in P. argus; sometimes apparently absent. Length, 91.8-102.2 /j. Tropical and subtropical Pacific. Description: — A rather large species with the body irregularly obovate or sublozenge-shaped in lateral outline, with subconical epitheca, deepest at or just behind the girdle, and 1.27 (1.24-1.30) times longer than deep. The longitudinal axis of the body is either perpendicular to the transverse furrow (Figure 10: 3), or it is deflected posteroventrally at an angle of 1°-10°. 112 THE DIXOPHYSOIDAE. The epitheca is subconical, about as deep as the hypotheca, the ratio being 0.99 (0.95-1.00): 1, highest in or just dorsally to the center and very prominent above the anterior cingular list; it has gently convex, almost straight or even slightly concave side contours, which are nearly perpendicular to each other, and rounded apex. The transverse furrow is flat or somewhat convex; and its width is 0.10 (0.14-0.19) the greatest height of the epitheca. The posterior cingular list is 0.50 (0.49-0.53) the length of the body from the apex. The hypotheca is sometimes almost symmetrical (Figure 10:3), but in most specimens it has a more or less pronounced postcroventral inclination (see above). It is somewhat irregularly, seldom regularly, ovoidal. The dorsal margin is evenly and gently convex. The ventral margin sometimes has about the same curvature as the dorsal, but in nearly all the specimens it is somewhat more strongly curved; in some, however, (Figure 10: 5) it forms a broadly rounded corner at the posterior end of the left sulcal list, in which case its anterior portion is but slightly convex. The posterior end of the body is broadly convex and always distinctly broader than the anterior. In \entral view (Figure 10: 2) the body is subbiconical, about 1.40 times longer than wide and widest at the transverse furrow; the side con- tours of the epitheca and of the hypotheca are slightly convex or almost straight ; and the anterior and posterior ends are rounded, the anterioi- slightly narrower than the posterior. The cingTilar hsts are as in PJwlacroma argus. The sulcus is about half as long as the hypotheca. The flagellar pore is about a girdle-width behind the junction of the cingulum and the sulcus. On the ventral side of the left valve a small pore is found near the sagittal suture, just in front of the anterior cingular list. The right sulcal list resembles that of P. argus, but it sometimes (Figure 10: 1) extends to the posterior main rib of the left sulcal list. The left sulcal list also resembles that of P. argus but is, on the average, somewhat wider. The ratios between the main ribs of this list and the greatest depth of the body are as follows: — anterior main rib, 0.13 (0.10-0.15): 1; fission rib, 0.12 (0.09-0.17): 1; posterior main rib, 0.14 (0.12-0.17): 1. Sometimes (Figure 10: 3) this list has a faint and irregular reticulation; and in some specimens its free margin is evenly convex throughout the whole length (Figure 10:4). The distance between the anterior main rib and the fission rib is 0.40 (0.33-0.50) the distance from the an- terior to the posterior main rib. The posterior main rib has a posterior inclina- tion of 42° (30°-50°). There are no accessory lists or sails. The surface markings of the thecal wall are the same as m Phalacroma argus; sometimes the reticulation seems to be absent. SYSTEMATIC ACCOUNT. 113 Megacytic stages have not been seen. The proportions of five of the Expedition specimens and of that drawn by Okamura (1907, fig. 26b) were measured. Dimensions: — Expedition specimens : Length of body, 91.8-102.2 ^ (average, 96.2 m; type, 101.5 m)- Greatest depth of body, 71.5-81.3 ^ (average, 75.5 m; type, 77.8 fx). Olcamm-a's (1907, fig. 26b) specimen: Length of body, 101 p. Greatest depth of body, 76 n. Variations: — This species is rather variable in the inclination of the longi- tudinal axis of the body, in the shape and relative height of the epitheca and of the hypotheca, in the shape of the right sulcal list, in the shape and structure of the left sulcal list, and in the surface markings of the thecal wall. The variations in the inclination of the longitudinal axis of the body and in the shape of the body probably are partly apparent and due to the tilting of some of the specimens examined. The epitheca generally is pronouncedly subconical, but sometimes specimens are found which in the shape of the epitheca approach, more or less, Phalacroma argus (Figure 10:5). The ventral margin of the left sulcal list is gently sigmoid in most specimens; in exceptional cases it is evenly convex (Fig- ure 10:4). Comparisons: — The structurally nearest species io Phalacroma apicatum is P. argus, from which it differs in its more contracted epitheca. For further dis- cussion, see p. 107. Phalacroma circumcinctum, which shows a rather striking resemblance to P. apicatum in the shape of the body, especially in dorsoventral view, differs in having the longitudinal axis of the body deflected posterodorsally, in having a parasagittal list, in the shape and structure of the sulcal lists, and in the surface markings of the thecal wall. The cjuestion as to whether or not these two species are closely related must be left open. The distinguishing characteristic of Phalacroma apicatnm, when compared with P. argus, i.e., the subconical shape of the epitheca, is found also in P. opercn- latum Stein s. str. (Stein, 1883, pi. 18, fig. 8), in one of the two specimens figured by Schiitt (1895, pi. 3, fig. 17: 2) under the name of P. vaslum var. acuta, in the rather highly differentiated P. turhinenm (Plate 2, fig. 3) and in P. reticulatum (Plate 4, fig. 3). In the case of P. operculatum and P. rastmn var. acuta {= P. acutum Pavillard), this similarity may be considered a sign of close relationship, i.e., as an expression of an inherent "tendency." On the other hand, the rela- tionships of P. turbineum and P. reticulatum to P. apicatum are uncertain. See also p. 191. 114 THE DINOPHYSOIDAE. Synonymy: — Okamura (1907, p. 134, fig. 26) suggested that his Phalacroma 8p. might represent P. porodictyum Stein. According to the size and the magni- fication of the drawing, this specimen was 101 /^ long. Occurrence: — Phalacroma apicatum is recorded at five of the 127 stations. There are 0, 0, 0, 1, 4, and stations on the six lines of the Expedition. Of these five stations one (4G97) is in the Easter Island Eddy, and four (4730, 4732, 4734, 4737, type locality) are in the South Equatorial Drift. All the records refer to hauls from 300-0 fathoms. The temperatiu-e range of these five stations at the surface was 75.0°-81.5°; the average was 79.1°. The frequency in every case is less than 1 %. The species, which previously was known from Japanese waters, is probably eupelagic and widely distributed in tropical and subtropical seas. In the material of the Expedition it is limited to the Easter Island Eddy and the western portion of the South Equatorial Drift ; in other words, it has about the same distribution as Amphisolenia schauinslandi and A. thrinax and several other warm-water forms. Its average temperature is exceptionally high, 79.1°. Phalacroma circumcinctiim Kofoid and Michener Plate 1, fig. 4, 5. Figure 8: 3 Phalacroma circumcincta Kofoid & Michener, 1911, p. 288, 291. Diagnosis: — Body subovate in lateral view, deepest at girdle; length: depth, 1.25: 1; epitheca with slight ventral inclination, hypotheca almost symmetrical. In ventral view subbiconical, 1.54 tunes longer than wide, widest at girdle, with narrowly rounded apices. Posterior cingular list 0.46 the length of body from apex. Cingular lists without ribs. Right sulcal list reticulate. Left sulcal list : distance between posterior cingular list and Rs is 0.38 the length of body; Ro is 0.07 and Ra is 0.15 the greatest depth of body ; at R3 margin forms rounded corner at 90°; Ri is absent; R2 is T-shaped; R3 inclined posteriorly at 80°-85°. On right valve of epitheca and hypotheca there is an apparently structureless parasagittal list forming a direct continuation of left sulcal list; its maximum width but slightly exceeds half the width of transverse furrow. Theca densely areolate; 30-35 areoles border girdle posteriorly. Length 86.5 n. Eastern subtropical Pacific. Description: — A medium-sized species, with body subovate in lateral out- line, deepest at the girdle, and about 1.25 times longer than deep. The longi- SYSTEMATIC ACCOUNT. 115 tudinal axis of the body is deflected anteroventrally at an angle of about 2°, due to the ventral inclination of the epitheca. The epitheca is about as deep as the hypotheca and very prominent above the anterior cingidar list; it is inclined slightly ventrally; in other words, it is highest slightly ventrally to the center. Its ^•entral, anterior, and dorsal margins are confluent; the ventral and anterior are rather strongly convex; the dorsal is gently convex, somewhat flattened. The transverse furrow is slightly concave, and its width is about 0.26 the greatest height of the epitheca. The posterior cingular list is about 0.46 the length of the body from the apex. The hypotheca is almost symmetrical; its ventral, posterior, and dorsal margins are confluent; the posterior margin is somewhat more strongly convex than the \'entral and the dorsal. The posterior end of the body is somewhat narrower than the an- terior. In dorsoventral view the body is subbiconical, widest at the girdle, and about 1.54 times longer than wide; the side contours of the epitheca and of the hypotheca are gently concave or almost straight ; the anterior and posterior ends of the body are narrowly rounded or subtruncate, and of about the same width. The cingular lists are subhorizontal and subequal ; their width about ecjuals the width of the transverse furrow; and they appear to lack ribs. The sulcus is about half as long as the hypotheca. The flagellar pore is about a girdle-width behind the junction of the cingulum and the sulcus. On the ventral side of the left valve a small pore is found a short distance from the sagittal suture and just in front of the anterior cingular list. The right sulcal list extends to a point somewhat behind the fission rib of the left sulcal list; even in the widest region its ventral margin does not extend to the ventral margin of the left sulcal list; it is of almost equal width throughout the greater portion of its length; its free margin is gently sigmoid, being concave anteriorly and convex posteriorly. The whole list is reticulated, with two longitudinal rows of meshes, 6-8 meshes in each row. The left sulcal list is comparatively long and narrow; the distance from the posterior cingular list to the posterior main rib is 0.38 the length of the body; at the place of the anterior main rib the width of the list is about 0.10 the greatest depth of the body; the fission rib is about 0.07, the posterior main rib about 0.15 the greatest depth of the body; behind the posterior main rib the list decreases suddenlj' in width. The ventral margin of this list is gently sigmoid, being con- cave anteriorly and convex posteriorly; at the posterior main rib the margin forms a rounded corner at an angle of about 90°. The posterior margin of this list is almost straight. The anterior main rib of this list was not developed in the type specimen. The fission rib is T-shaped, being divided distally into two 116 THE DINOPHYSOIDAE. branches which form a marginal rib along the anterior half of the Ust. The posterior main rib is gently concave posteriorly and not club-shaped; it has a posterior inclination of about 80°-85°. The distance from the posterior cingular list to the fission rib is about 0.33 the distance between the posterior cingular list and the posterior main rib. With the exception of the main ribs, the left sulcal list appears to lack structural differentiation. On the right \'alve there is an apparently structureless parasagittal list. This list extends from the left sulcal list, of which it is a direct continuation, to the girdle, and along the anterior and ventral margins of the epitheca. On the epitheca the width of this list is some- what more than half the width of the transverse furrow; on the hypotheca the maximum width about ecjuals half the width of the transverse furrow. The thecal wall is areolate, and the areoles are of almost uniform size and evenly distributed. There are from thirty to thirty-five areoles on each valve bordering the posterior margin of the girdle. In the transverse furrow there are three irregular rows of areoles. Megacytic stages have not been seen. The proportions of the type were measured. Dimensions: — Length of body, 86. 5 ju. Greatest depth of body, 08.9 )u. Comparisons: — The above description is made from the oi'iginal drawings of the type specimen. The long, irregular, hyaline appendage of this specimen (Plate 1, fig. 5), apparently issuing from the sagittal suture near the posterior main rib of the left sulcal list, is of unknown nature and significance. Presum- ably it is a temporary structure, and it may be connected with reorganizing processes either independent of, or following binary fission; compare Kofoid (1908). This structure has not been considered of any systematic importance and thus has been omitted from the description of the species and disregarded in the discussion of the relationships of this form. The shape and the lack of struc- ture of the parasagittal list also appear to indicate that this specimen was taken while still in a process of skeletal reorganization (see Plate 3, fig. 4). This species has a somewhat uncertain position within the genus. It re- sembles P. apicatum in the somewhat elongate and, in dorsoventral view, sub- biconical shape of its body. Other features in which these two species agree are the subequatorial position of the girdle and the width and inclination of the cingular list; however, since these species presumably are relatively primitive in these respects, these similarities are of less importance in this connection. P. circumcincium is easily distinguishetl from P. apicatum by the following charac- ters: — {1) the epitheca is inclined ventrally instead of dorsally; (2) the right SYSTEMATIC ACCOUNT. 117 sulcal list is reticulate, and its free margin is gentlj- sigmoid and not angular; (3) the margin of the left sulcal list is angular at the posterior main rib; (4) the theca is areolate and not reticulate ; (.5) on the right valve of the epitheca as well as of the hj'potheca there is a well-developed parasagittal list. The differences be- tween these two species, therefore, appear to be more profound than the similari- ties. However, in spite of this, P. circumcinctum is probably rather closely related to P. apicatum and, preliminarily, should be placed in the Aegus group. Most of the characters of P. circumcinctum which are different from those of P. apicatum either have maintained a comparatively primitive type or they are expressions of "tendencies" inherent in the Argus group but not developed morphologically in most of the members of this group. For example, the angu- larity of the margin of the left sulcal list and the areolation of the thecal wall in P. circumcinctum probably are relatively primitive features; they are found also in P. porodictyum which is closely related to P. apicatum and P. argus. A para- sagittal list on the right valve also is characteristic of P. hlackmani, which un- doubtedly is a very close relative of P. striatum and thus also of P. apicatum and P. argus (see p. 107). The T-shaped fission rib of the left sulcal list is a character that is known only in Phalacroma circumcinctum and P. ovum. These two species resemble each other also in the width, structure, and inclination of the cingular lists, in the size and shape of the right sulcal list, and m the surface markings of the theca; they differ in the relative height of the epitheca, in the shape of the epitheca and of the hypotheca in dorsoventral view, in the relati^•e length and the inclination of the posterior main rib of the left sulcal list, and in the presence or absence of a parasagittal list. It also should be noted in this connection that Phalacrovm circumcinctum resembles P. limhalum in the subequatorial position of the girdle, in having a parasagittal list on the right valve of both the epitheca and the hypotheca, in the subbiconical shape of the body in dorsoventral view, and in the structure of the sulcus and of the adjacent regions (compare Plate 1, fig. 4, and Plate 3, fig. 3). Phalacroma limbatmn is easily distinguished from P. circumcinctum in the sub- circular shape of its body in lateral view, in the high structural differentiation of its right parasagittal list, in having two parasagittal lists, in the size and shape of its left sulcal list, in the structure of its theca, and in the narrowness of its body in dorsoventral view. Occurrence: — Phalacroma circumcincturn is recorded at only one (4671) of the 127 stations, on the second line of the Expedition and in the Peruvian Cur- 118 THE DINOPHYSOIDAE. rent, from 800-0 fathomi?, in a surface temperature of 66°, with a frequency of less than 1% (one specimen). Phalacroma ovum Schiitt Figure 11 Phalacroma ovum Schutt, 1895, p. 90. ^Phalacroma operculatum. Stein, 1883, partim, pi. 18, fig. 7. VFokti, 1922, ixirlim, p. 105, 190, 208, pi. 7, fig. 111. non Schutt, 1895, p. 93, pi. 2, fig. 10: 1-3. »io?( Jorcensen, 1923, p. 9, 10, fig. 7. Phalacroma opercvloides Schutt, 1895, partim, pi. 2, fig. 11:2. Okamura, 1912, p. 18, fig. 81, 82. JoR- GENSEN, 1923, p. 8, 9, 45, fig. 5. non Cleve, 1899(_:, p. -10. non Lohmann, 1902, p. 53. non Forti, 1922, p. 106, 190, 208, pi. 7, fig. 111. Diagnosis: — Body obovate in hit oral outhne, deepest at or somewhat behind girdle; length: depth, 1.20-1.31:1; longitudinal axis deflected posteroventrally at 0°-4°. In dorsal view narrowly oljovate, 1.59-1.64 times longer than wide. Posterior cingular list 0.28-0.36 the length of body from apex. C'ingular lists probably without ribs. Left sulcal list 0.43-0.53 the length of body; distance between Ri and R3 is 0.33-0.37 the length of body ; R, is 0.10-0.13, R3 is 0.30-0.37 the greatest depth of body; margin forms angle of 60°-90° at R3; R2 is T-shaped; R3 usually club-shaped and inclined posteriorly at about 30°. Theca finely and closely areolate. Length, 58.2-76.1 m- Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, the body of which is obovate in lateral view, deepest at, or, in most specimens, somewhat behind the girdle, and about 1.26 (1.20-1.31) times longer than deep. The longitudinal axis of the body either is perpendicular to the girdle, or it is slightly (l°-4°) deflected postero- ventrally. The epitheca is 0.93 (0.91-0.96) as deep as the hypotheca, and moderately elevated or very prominent above the anterior cingular list; sometimes (Figure 11: 1) it is strongly and evenly convex, dome-shaped, sometimes (Figure 11 : 3, 2) of moderate convexity or rather fiat ; in most cases it is highest in the center, but in some specimens (Figure 11:6) somewhat dorsally to the center. The trans- verse furrow is flat or slightly convex, and its width is 0.37 (0.26-0.42) the great- est height of the epitheca. The posterior cingular list is 0.32 (0.28-0.36) the length of the body from the apex. The hypotheca sometimes is sj^mmetrical, sometimes it has a slight posteroventral mclination (see above); sometimes (Figure 11:4) it is of an oval wedge shape, with rather flat dorsal and ventral margins; sometimes (Figure 11: 1) it is regularly oval, with well or moderately rounded dorsal and \'entral margins ; its posterior margin is strongly convex and confluent with the dorsal and ventral margins. The posterior portion of the SYSTEMATIC ACCOUNT. 119 body is strikingly narrower than the anterior. In dorsoventral view the body is narrowly and regularly obovate, 1.59-1.64 times longer than wide, and widest at the girdle. The cingular lists are siibhorizontal, subequal, and about as wide as the transverse furrow; they appear to be without structural differentiation. The right sulcal list extends to a point midway between the fission rib and the poste- rior main rib of the left sulcal list, or it is slightly longer or shorter; in some specimens it is subtriangular, decreasing gradually in width posteriorly; in others it is subequal in width throughout its anterior half or even throughout the greater FiGUBE 11. — • Phalacroma ovum Schiitt. 1, 2, 3, iii right lateral view; 4, 6, in left lateral view; 5, in dorsal view. 2, from a megaoytic specimen; surface markings omitted. X 430. 1, from Station 4737 (300-0 fathoms); 2, from Station 4709 (300-0 fathoms); 3, from Station 4721 (300-0 fathoms); 4, 5, from Station 4681 (300-0 fathoms); 6, from Station 4709 (300-0 fathoms). portion of its length; anteriorly it is about as wide as the transverse furrow. The left sulcal list is of moderate length, narrow anteriorly and wide posteriorly. Its length is 0.50 (0.43-0.53) the length of the body, and the distance between the anterior and posterior main ribs is 0.35 (0.33-0.37) the length of the body. The anterior main rib, when present, is 0.12 (0.10-0.14), the fission rib 0.12 (0.10- 0.13), and the posterior main rib 0.33 (0.30-0.37) the greatest depth of the body. Behind the last-mentioned rib this Ust decreases suddenly in width. Between the anterior and posterior main ribs the free margin of this list sometimes is al- most straight or gently concave, sometimes it is gently sigmoid, concave anteri- orly and convex posteriorly; at the posterior main rib it forms an angle of 75° (60°-90°) ; behind the last-mentioned rib it is almost straight, or gently concave 120 THE DINOPHYSOIDAE. or convex. The fission rib is T-shaped, being divided distally into two branches, which form a marginal rib along the anterior third or half of the list; this marginal rib is sometimes more or less irregular. The posterior main rib is straight, or but slightly concave posteriorly, and in most cases somewhat club-shaped distally; it has a posterior inclination of 30° (25°-32°). Sometimes this list appears to have a faint reticulation (Stein, 1883, pi. 18, fig. 7). There are no accessory lists or sails. The thecal wall is finely and closely areolate and has scattered pores; the areoles are of about the same size as the pores (Jorgensen, 1923, fig. 5). Megacytic stages have been seen (Figure 11:2). Sometimes the megacytic specimen has the transdiameter subequal to the length of the body. The proportions of six Expedition specimens, antl of the specimens figured by Schiitt (1895) and Jorgensen (1923) were measured. Dimensions: — Expedition specimens: Length of body, 66.9-76.1 n (average, 71.4 n). Greatest depth of body, 55.0-58.9 ix (average, 56.9 ii). The type speci- men as figured by Schiitt (1895, pi. 2, fig. 11: 2) was 61 m long and 46 ^ deep; Jorgensen's (1923), 60-66 y. long. According to the given magnifications, the specimens figured by Okaniura (1912, pi. 5, fig. 81, 82) were about 58 y. and 34 n long, respectively (see p. 120). Varialions: — Judging by the available figures, this species appears to be rather constant. The most variable features are the size of the body, the relative height and the shape of the epitheca, and the shape of the two posterior main ribs of the left sulcal list. With regard to the porulation of the theca, see Phala- croma opcrculoidcs and P. opcrculaiu77i Jorgensen (1923, p. 8, 9). Comparisons: — Most of the Expedition specimens agree closely with the type specimen as figured by Schiitt (1895, pi. 2, fig. 11:2). They differ in having the fission rib of the left sulcal list T-shaped and the posterior main rib of this list club-shaped. It should be mentioned, however, that in some of these specimens the last-mentioned rib was not club-shaped. The specimen figured by Jorgensen (1923, fig. 5) under the name of Phala- croma operculoides shows also a close agreement with the type. Those figured by Okamura (1912, pi. 5, fig. 81, 82) are comparatively small; according to the magnifications given, they are only 58 ix and 34 n long, respectively. The last measurement may be erroneous, and due to a mistake in the magnification; it has been disregarded in the diagnosis. Judging by the simplicity of its structure, Phalacroma ovum probably is fairly closely related to the comparatively primitive members of this genus, e.g., SYSTEMATIC ACCOUNT. 121 P. porodidyum Stein, P. nperculoidcs Schiitt s. sir., P. operculalum (Stein) Jorgensen, and P. argus Stein. Due to the (simplicity of their organization, the interrelationships of these species are very difficult to establish. Ho\vc\er, it seems rather plausible that P. ovum is more closely related to P. porodidyum than to any other known species. Phalacroma ovum is most easily distinguished from all these species by the shape and structure of its left sulcal list. Phalacroma circumcindum, which differs very strikingly from P. ovum in the subequatorial position of its girdle, has the fission rib of the left sulcal list T- shaped in the same way as the last species. Judging by the great similarities in the size and shape of the body and in the shape and structure of the left sulcal list, Phalacroma ovum and P. doryphorum probably are rather closely related. The last species differs strikingly from the first in having a large, triangular posterior sail. Si/noni/my: — The sj-nonyniy of this species is complicated to such an extent that it is difficult, if not impossible, to unravel it. Stein (1883, pi. 18, fig. 7-10) figures, under the name of Phalacroma nperculaluvi, two forms which probably are specifically distinct. Jorgen.sen (1923, p. 9), the first to point out this fact, applies the name operculalum to the specimen represented by Stein (pi. 18, fig. 8). This specimen there- fore becomes the type of a species which should be named P. operculalum (Stein) Jorgensen. The speci- mens represented by Stein (i)l. 18, fig. 7, 9, 10) are assigned by Jorgensen (1923, p. 9) to P. porodidyum Stein. However, on account of the almost conijilete agreement between the specimen represented by Figure 11:1 and Stein's Plate IS, fig. 7, with regard to the shape of the body and the position of the girdle, it seems more plausible that these specimens of Stein belong to the species described and figured above under the name of P. arum Schiitt. The uncertainty of the a.ssignment is mainly due to the fact that the left sulcal li.st is incomplete (damaged ?) in Stein's Plate 18, fig. 7. The lack of porulation in the last figure probably is due to an omission; see Jorgensen (1923, p. 9). If our identification is correct, Stein (1883, pi. 18, fig. 7, 9, 10) was the first to figure a sjiecimen of P. arum, and P. operculalum Stein, parlim, is a synonym of P. arum Schiitt. Phalacroma opcrcidalum Stein is used by Daday (1888, p. 99; Phalarncoma operculalum, lapsu pcnnac), Schiitt (189.5, p. 93, pi. 2, fig. 10), Hensen "(1895, p. 190; 1911, p. 137, 138, 166, 167, .393, tab. 1.5), Leni- niermann (1899, p. 371; 1901a, p. .373; 190.5a, p. 3.5), Mvirray & Whitting (1899, p. .330, tab. 1, 2, 3, 4, .5, 6, 7, 8, 9), Schroder (1900a, p. 9, 11, 19; 1906a, p. 321, 327, 330; 1911, p. 17, 37), Rauschenplat (1900, p. 134), Cleve (1901a, p. 17; 1901c, p. 272; 1902b, p. 37; 190.3b, p. .347), Lohmann (1902, p. 53; 1920, p. 485, 492, 496, 504, 505, .507, 509, 511, 513, 515, 517, .524, 525, 529, 532, .536, .537, .544, .551, 554, 561, 572, 574, 585, 596), Entz (1902b, p. 94; 1904, p. 14; 1905. p. Ill), Pavillard (1905, p. .59, 81, 102; 1909, p. 283; 1916, p. 44, 47, 48, 49, .50, .54), Zacharias (1906, p. .509, 530, 534, 536, 544, 557), Karsten (1907, p. 236, 247, 263, 304, 349, 355, 359), Nathansohn (1908, p. 60; 1909. p. 42), Stiiwe (1909, p. 237, 252, 287), Schiller (1912, p. 27), Forti (1922, p. 105, 190, 208, pi. 7, fig. 110, 112; fig. 112 is erroneously called P. porodidyum, .and the figure representing the last species h.as no number), Jorgensen (1923, p. 9, 10, fig. 7), and Lindc- mann (1924, p. 10). Most of the investigators mentioned in this paragraph do not give any information as to which of the two forms figured by Stein (1883) under the name of P. opercidalum they refer to. Daday, Hen.sen, Ijemmermann, Murray and Whitting, Schroder, Rauschenplat, Cleve, Lohmann, Entz, Pavillard, Zacharias, Kar.sten, Nathansohn, Stiiwe, Schiller, and Lindemann have not been included in the bibliographical list of P. orum. The remaining ones give figures by means of which their determina- tions can be checked. Forti (1922) refers to both the forms figured by Stein (1883) under the name of P. operculalum. According to Jorgensen (1923, p. 8) "two apparently different species" are figured by Schiitt (1895, pi. 2, fig. 11: 1-3) under the name of Phalacroma operculoides. Jorgensen applies the name operculoidcs to the specimen represented by Schiitt (1895, pi. 2, fig. 11:2); the second figure was chosen because "un- fortimately, his [Schiitt's] first figure is uncertain, and seems to represent the same species w'hioh he notes, lower down on the same plate, as Phalacroma porodidyum var. parndum, while the second figure shows a characteristic species closely related to the foregoing [P. porodidyum], and possibly merging into the 122 THE DINOPHYSOIDAE. same" (Jorgensen, 1923, p. 8). It seems almost unquestionable that the specimens represented by Schiitt (1895, pi. 2, fig. 11: 1-3) belong to two specifically distinct forms. However, it is necessary to reject Jorgensen 's decision as to the nomenclature of these two forms, since Schiitt (1895, p. 90) refers to his Plate 2, fig. 11: 2 as P. ovum; on the other hand, except in the explanation of the plates, Schiitt never refers to this figure as representing P. npcrctdoides. The name P. operculoides therefore should be used for the species repre.seuted by Schiitt (1895, pi. 2, fig. 11:1, 3), while the name P. orum should be applied to the species represented by Plate 2, fig. 11:2. Phnlacroma operculoideK Schiitt has been used by several authors, viz., Cleve (1899c, p. 40), Lemmer- mann (1899, p. 372; 1901a, p. 373; 1905a, p. 35), Lohmann (1902, p. 53), Stiiwe (1909, p. 252, 287), Okamura (1912, p. 18, fig. 81, 82), Pavillard (1916, p. 54; 1923a, p. 879), Forti (1922, p. 106, 190, 208, pi. "7, fig. HI), and Jorgen.sen (1923, p. 8, 9, 45, fig. 5). P. operculoides Cleve (1899c) refers to P. rolunda- lutn, according to Cleve (1901c, p. 241); see also Paulsen (1908, p. 18). Lenimermann only refers to data given by other writers. The specimens referred by Lohmann (1902, p. 53) to P. npcrctdoiries were only 35 M long, which indicates that they are referable to P. npercnloidca x. xtr. Stiiwe (1909) and Pavillard (1916, 1923a) do not give any information as to which of the two forms figured by Schiitt (1895) under the name of P.opcrcidoides they refcrto. Under these circumstances these authors are not included in the bib- liography of P. ovum. Forti (1922) refers to Schiitt (1895, pi. 2, fig. 11: 1 ), not to P. ovum. P. operculoides Okamura (1912) and Jorgensen (1923) refer to P. ovum (see p. 120). Occurrence: — Phalacroma ovum is recorded at ten of the 127 stations. There are 2, 1, 1, 2, 4, and stations on the six lines of the Expedition. Of these ten stations, one (4587) is in the Mexican Current; one (4617) in the Panamic Area; one (4657) in the Peruvian Current; and seven (4681, 4709, 4711, 4721, 4724, 4730, 4737) in the South Equatorial Drift. At one station (4724) the species was taken in a haul from 800-0 fathoms. All the remaming records refer to hauls from 300-0 fathoms. The temperature range of these ten stations at the surface was 68°-82° ; the average temperature was 75.8°. At one station (4657) the frequency is 1 %, at the remaining stations it is less. Schiitt (1895) did not give any information as to the localities of his speci- mens; however, his material probably was taken either at Naples, or hi the tropical or subtropical regions of the Atlantic. Jorgensen (1923) found this species "fairly common" in the Mediterranean, and "most frequent in the inner parts" of this sea. Okamura (1912) recorded it from Japanese waters. Judging by the numerous records which possibly may refer to Phalacroma ovum (see p. 121), this species appears to be eupelagic and widely distributed in tropical, subtropical, and warm-temperate seas. The ten record stations are distributed fairly evenly over the area investigated by the Expedition. The absence of surface records is noteworthy. The species probably has its optuuum habitat in deeper waters within the levels of photosynthesis. Phalacroma pyriforme, sp. nov. Figure 4:4, 5 Diagnosis: — Body obovate in lateral outline, deepest at girdle; length: depth, 1.13: 1. In dorsal view inverted pyriform, widest at girdle, broadly SYSTEMATIC ACCOUNT. 123 rounded anteriorly, narrowly rounded posteriorly; hypotheca with concave side contours; length: width, 1.30: 1. Posterior cingular list 0.43 the length of body from apex. Cingular lists somewhat wider than transverse furrow. Left sulcal Ust relatively large; its length 0.56 the length of body; throughout its anterior half it is of uniform width, 0.25 the depth of body; posteriorly it decreases gradu- ally in width; its free margin gently and evenly convex; structure unknown. Theca finely and closely areolate. Length, 48.2 m- Eastern tropical Pacific. Description: — A small species, with the body obovate in lateral outhne, deepest at the girdle. The ratio between the length and the depth is 1.13: 1. The longitudinal axis is about perpendicular to the girdle. The epitheca is about as deep as the hypotheca, highest in the center, evenly and strongly con\-cx, dome-shaped, and \-ery prominent above the anterior cingu- lar list. The transverse furrow is gently convex, and its width is 0.45 the greatest height of the epitheca. The posterior cingular list is about 0.43 the length of the body from the apex. The hypotheca is symmetrical; its dorsal and ventral margins are evenly and moderately convex and confluent with the posterior margin, which is strongly and evenly convex. The posterior portion of the body is strikingly narrower than the anterior. In dorsoventral view the body is m- verted pyriform in outlme, widest at the girdle, broadly rounded anteriorly, nar- rowly rounded posteriorly, and with the lateral contours of the hypotheca moder- ately concave; the ratio between the length and the width is 1.30: 1. The cingular lists are subhorizontal, subequal, and somewhat wider than the transverse furrow; their structure is unknown. The right sulcal list is about half as long as the left; its anterior half is subuniform in width, and about half as wide as the transversa furrow; posteriorly it decreases gradually in width. The left sulcal list is relatively large; its length is about 0.56 the length of the body; throughout its anterior half it is of uniform width and about 0.25 the greatest depth of the body; posteriorly it decreases gradually in width; its free margin is gently and evenly convex; in other words, it is not angular posteriorly, as in most species of the genus; its structure is unknown. There are no accessory lists or sails. The thecal wall is finely and closely areolate, about as in Pbalacroma dory- phorum. Pores have not been seen. Megacytic stages were not recorded. The proportions of the type were measured. Dimensions: — Length of body, 48.2 ix. Greatest depth of body, 42.5 m. 124 THE DINOPHYSOIDAE. Comparisons: — Phalncroma pi/riformc is established on two outline draw- ings made from a specimen found in the material of the Expedition. The species appears to occupy a rather isolated position. The symmetry and small size of its bod}', and the fine and close areolation of its thecal wall are features that affiliate it with the relatively primitive members of the genus, e.g., Phalacroma parmdum, P. operculoides s. str., and P. lens. In the shape of its body in lateral view and in its relatively high epitheca, it resembles P. argus, P. porodictyum, P. ovum, and some other obovoidal species. The shape of its left sulcal list recalls P. argus, P. apicatum, and the species of the Cuneiis group. The pyriform shape of its body in dorsoventral view is unique but approaches the cuneate shape of the species of the Cuneus and Rapa groups. Occurrence: — This species is recorded at one of the 127 stations. This sta- tion (4713) is on the fourth line of the Expedition and in the Galapagos Eddy. The depth is 300-0 fathoms, the surface temperature 73°, and the frequency less than 1% (one specimen). 4. Cuneus Group. Phalacmmn hlackmani is the only species of this group that is not included in the Expedition collections. Phalacroma cuneus Schiitt Figure 12, 13 Phalacroma emeus Schutt, 1895, p. 148, pi. 3, fig. 14; 1896, p. 27, fig. 38B. Ostenfeld, 1898a, p. 428. Murray & Whitting, 1899, p. 330, tab. 4. Lemmermann, 1899a, p. 372; 1901a, p. 372. Schroder, 1900a, p. 19; 1906a, p. 322, .327, 330. Cleve, 1901a, p. 16; lOOln, p. 270; 1902b, p. 3,5; 1903b, p. 347. Ostenfeld & Schmidt, 1901, p. 175. Zacharias, 1906, p. 534. Kofoid, 1907a, p. 195. Karsten, 1907, p. .325, 3.53, 355. Pavillard, 1909, p. 283; 1915a, p. 2; 1916, p. 47, 49, 52. Stuwe, 1909, p. 287. Okamura, 1912, p. 18, pi. 5, fig. 76. JoR(iEN.«EN, 1923, p. 11, fig. 11. Phalacrntiia cunciix .Stuwe, 1909, p. 252 {Inp.iiM pcnnae). Phalacroma mi/ra Oltmanns, 1922, partim, fig. 38: 1. Diagnosis: — Body cuneate in lateral outline ; epitheca very broadly rounded; posterior portion of hypotheca fairly brcadly to rather narrowly rounded; deepest at posterior cingular list; length: depth, 0.92-1.09: 1; longitudinal axis deflected posteroventrally at 4°-5°. In dorsal view cuneate ; posterior portion of hypotheca narrowly rounded to subacute; length: width, 1.22: 1. Posterior cingular list 0.23-0.28 the length of body from apex. Of- the cingular lists the anterior is reticulated, the posterior is ribbed. Left sulcal list 0.50-0.07 the length of body; distance from R, to R, is 0.40-0.47 the length of body; Ro is 0.09-0.11, and R3 is 0.07-0.10 the greatest depth of body; widest somewhat in front of R3; its ventral margin gently convex at R3, seldom subangular; R3 inclined posteriorly at 45°- SYSTEMATIC ACCOUNT. 125 60°; irregularly and incompletely reticulate. Theca reticulate; twenty-five to thirty-five polygons border girdle posteriorly. Length, 72-88 /j. Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, the body of which is cuneate in lateral outline, with a rather low and very broadly rounded epitheca, with the posterior portion of the hypotheca fairly broadly to rather narrowly rounded, with the greatest depth at the posterior cingular list, and about as deep as long. The ratio between the length and the depth of the body is 0.98 (0.92-1.09): 1. The longitudinal axis is deflected posteroventrally at an angle of 4°-5°. The epitheca is about as deep as the hypotheca, very broadly and almost evenly convex, highest in or near the center, and moderately elevated above the anterior cingular list. The transverse furrow is flat to somewhat concave, and its width is 0.35-0.50 the gi'eatest height of the epitheca. The posterior cingular list is 0.23-0.28 the length of the body from the apex. The hypotheca tapers posteriorly and is somewhat deflected posteroventrally (see above); its dorsal margin is almost straight or slightly convex to concave; its ventral margin is nearly straight or gently convex; its postmargin is evenlj', and fairly broadly to rather narrowly convex, and confluent with the dorsal and ventral margins. In dorsoventral view the body is cuneate, with broadly rounded epitheca, and with the posterior portion of the hypotheca narrowly rounded to subacute; the side contours of the hypotheca are almost straight or slightly concave ; the ratio be- tween the length and the width is about 1.22: 1. The cingular lists are subhorizontal, subequal, and about as wide as the transverse furrow. Along the base of the anterior cingular list, there is a series of ribs anastomosing into a row of polygons, which have about the same size and shape as the polygons in the tj-ansverse furrow ; sometimes a more or less complete row of similar polygons is developed outside the basal row. The posterior cingu- lar list has a great number of straight and simple ribs (Schiitt, 1895, pi. 3, fig. 14: 2). The sulcus is about half as long as the hypotheca. The flagellar pore is about a girdle-width behind the junction of the cingulum and the sulcus. The right sulcal list is long and rather narrow; usually it ends at a point about half way between the fission rib and the posterior main rib of the left sulcal list, but sometimes it extends to the last-mentioned rib; anteriorly it is about as wide as or somewhat narrower than the transverse furrow, and posteriorly it tapers gradually. The left sulcal list is of moderate size. Its length is 0.50-0.(J7 the length of the body, and the distance between the anterior and posterior main ribs is 0.40-0.47 the length of the body. The anterior main rib, when pi'esent, is 126 THE DINOPHYSOIDAE. about 0.07-0.09, the fission rib 0.09-0.11, and the posterior main rib 0.07-0.10 the greatest depth of the bod3^ The greatest width of this list, which in most specimens is located somewhat in front of the posterior main ril), is about 0.12- 0.20 the greatest depth of tlic laody. In most specimens the free margm of this list is either gently sigmoid, concave anteriorly and convex posteriorly, or it is evenly to somewhat irregularly convex throughout; in other words, it is gently convex at the posterior main rib, and not angular as in most species of the genus. In exceptional cases (Figure 12:2) this margin is slightly convex between the anterior and posterior main ribs, and subangular at and gently concave behind the posterior main rib. Posteriorly this list either tapers more or less suddenly, or it is more or less decurrent (Figure 12: 2). The main ribs of this list are straight and rather weak; none of them is club->shaped, but the posterior sometimes is rather wide. The distance between the anterior main rib and the fission rib is 0.28-0.35 the distance between the anterior and posterior main ribs. The poste- rior main rib has a posterior inclination of 45°-(i0°. Besides the main ribs, the left sulcal list has an irregular and incomplete reticulation. At least in some specunens (Jorgensen, 1923, fig. 11), there is a very narrow parasagittal list ex- tending on the hypotheca from the left sulcal list to the posterior cingular list. The thecal wall has a reticulum of medium-sized polygons, and each polygon has a small pore in the center. Tlie polygons usually are about equal in size, and on each valve from twenty-fi\'e to thirty-five of them border the posterior margin of the girdle. In most specimens there are two rows of polygons in the transverse furrow, each row with twenty-five to thirty polygons on each valve; in other cases the two rows, partly or wholly, merge into a single row. Some of the polygons may be subdivided (Jorgensen, 1923, p. 12). From a point near the middle of the right sulcal list a spine-like process projects into the cytoplasm. Megacytic stages of this species have been seen by Pavillard (1910) and are contained in the Albatross collection. The dimensions of three specimens were measured. Dimensions: — Expedition specimens: Length of body, 80-87 /j (average, 84 fi). Greatest depth of body, 77-95 ^ (average, 86 yu). The largest of the speci- mens represented by Schiitt (1895, pi. 3, fig. 14: 1) is about 88 m long. The type specimen (Schiitt, 1895, pi. 3, fig. 14: 3) is somewhat smaller, but its length can- not be determined, since it is figiu'ctl in a tilted position. According to Jorgensen (1923, p. 11), the length is 72-88 /i. Variations: — This species appears to be rather remarkably constant in shape and in structm'e. A fairly large number of specimens from Station 4664 SYSTEMATIC ACCOUNT. 127 were submitted to a careful examination; most of these agreed very closely with the specimen represented by Figure 12; 1. The size and the shape of the body and of the sulcal lists are the most variable characters. The body sometimes is longer than deep, and sometimes deeper than long; sometimes (Figure 12: 1) the posterior portion of the hypotheca is rather broad, sometimes (Figure 12: 2) it is rather narrow; the dorsal margin of the hypotheca may be straight, or gently convex to concave. Posteriorly the left sulcal list either tapers more or less sud- denly (Figure 12: 1), or it is more or less decurrent (Figure 12: 2) ; its free margin Figure 12. — Phalacrotna cuneus Sehiitt, right lateral view. Structure of thecal wall and of left sulcal hst indicated onlj' in 1; 3 is somewhat tilted. X 430. 1, 3, from Station 4664 (300-0 fathoms); 2, from Station 4737 (300-0 fathoms). usually is gently concave anteriorly and convex posteriorly, but it maj' be ince versa. The variations probably are partly apparent, and due to the tilting of some of the specimens examined. Comparisons: — Sehiitt (1895) does not give any diagnosis or description of Phalacroma cuneus, and the specimens figured in lateral view by him are tlrawn in tilted positions. In spite of these discrepancies, the characteristics represented probably are sufficient for certainty of specific assignment. The Expedition specimens agree quite closely with these figured by Hchiitt (1895, pi. 3, fig. 14:1-8). Phalacroma cuneus is very closely related in structure to P. bluckniani, P. striatum., and P. giganteum. They all agree in the following respects: — their epitheca is rather low and very broadly rounded; their hypotheca is more or less cuneate in lateral as well as in dorsoventral y'ivw; in lateral x'ww the posterior portion of the hypotheca is fairly broadly to rather narrowly rounded, in dorso- ventral view it is narrowly rounded or even acute. The free margin of their left sulcal list is gently convex at the posterior main rib, and not angular as in most species of this genus. Without giving any reasons, Jorgensen (1923, p. 11) places Phalacroma hlackmani as a synonym of P. cuneus. Is this justifiable? According to the 128 THE DINOPHYSOIDAE. only drawing of this species available, tiz., that of the type specimen (Murray and Whitting, 1899, pi. 31, fig. 4), P. blackiiumi is about 125 m long, has a parasagittal list which extends on the hypotheca from the left sulcal list to the posterior cingu- lar list and is locally wider on the posterior portion of the hypotheca, and its left sulcal list lacks reticulation and has the main ribs concave anteriorlj'. P. cuneus has a maximum length of 88 fi, and its left sulcal list has an incomplete and iiTegu- lar reticulation and straight main ribs. At least in some specimens (Jorgensen, 1923, fig. 11), P. cuneus has, just as P. blackmani, a parasagittal list extending on the hypotheca from the left sulcal list to the posterior cingular list, but this para- sagittal list is very narrow throughout its whole length. Schroder (1906a, p. 330), Karsten (1907, p. 262, 473), and Stiiwe (1909, p. 238), who have recorded P. hlackmani, found also P. cuneus in the material examined by them. In short, according to the available descriptions and figures differences do exist between P. cuneus and P. hlackmani which appear to be of specific nature, and some in- vestigators have separated the two forms. Until further data are a\ailable, these two forms should be considered specifically distinct. Phalacroma cuneus differs from P. striatum in its smaller size (72-88 fi, as compared with 102-136 ;u) and its less developed left sulcal list. From P. giganteum it is easily distinguished by its smaller size (72-88 m, as compared with 148 ju). For further discussion about the relationships of these species, see p. 133. Synonymy: — The presence of a parasagittal list in the specimens deter- mined as P. cuneus by Jorgensen (1923) calls for a reexamination of this species to determine the prevalence of this structure which was not observed by Schiitt (1895) or by us. Occurrence: — Phalacroma cuneus is recorded at sixty-three of the 127 sta- tions. There are 9, 19, 7, 10, 11, and 7 stations on the six lines of the Expedition. Of these sixty-three stations, one (4583) is in the California Current; six (4587, 4590, 4594, 4598, 4005, 4545) in the Mexican Current; six (4009, 4013, 4017, 4634, 4637, 4038) in the Panamic Area; eighteen (4647, 4650, 4055, 4657, 4660, 4661, 4662, 4663, 4664, 4665, 4666, 4667, 4668, 4669, 4670, 4671, 4075, 4676) in the Peruvian Current; five (4689, 4691, 4695, 4697, 4699) in the Easter Island Eddy; one (4713) in the Galapagos Eddy; twenty-one (4679, 4681, 4683, 4701, 4705, 4706, 4707, 4709, 4711, 4719, 4724, 4728, 4730, 4731, 4732, 4733, 4734, 4736, 4737, 4739, 4740) in the South Equatorial Drift; three (4742, 4743, 4540) in the South Equatorial Current; two (4541, 4542) in the Equatorial Counter Current. There are thirteen records from the surface (Stations 4657, 4660 [Salpa], 4664, 4669, 4675, 4706 [Salpa], 4731, 4733, 4743, 4540, 4541, 4542, 4545); at ten of these SYSTEMATIC ACCOUNT. 129 stations the species was taken in surface hauls only; at three stations (4657, 4664, 4675) in hauls from 300-0 fathoms as well as at the surface. At one station (4737) the species is recorded from 100-0 fathoms and 300-0 fathoms; at one station (4713) from 150-0 fathoms and 300-0 fathoms; at three stations (4681, 4724, 4732) from 800-0 fathoms and 300-0 fathoms; at four stations (4G47, 4662, 4666, 4670) from 800-0 fathoms only. All the remaining records refer to hauls from 300-0 fathoms only. The species was taken also in surface waters in Acapulco Harbor, off the Mexican Current. This station is not included in the 127 stations mentioned above. The temperature range of these sLxty-three stations at the surface was 65°- 85°; the average was 74.7°. At the thirteen stations in the surface catches of which the species was found, the surface temperature ranged from 67° to 80°; the average was 74.5°. At Acapulco it was 83°. For the surface catches the following frequencies are recorded: — 4% at one station (4669); 3% at two stations (4542, 4545); 2% at one station (4675); 1% at two stations (4657, 4664) ; in the remaining cases the frequency was less than 1%. For the catches from 100, 150, 300, or 800 fathoms to the surface the rec- ords of frequency are as follows: — 40% at one station (4664); 10% at one sta- tion (4663) ; 6% at two stations (4613, 4666) ; 4% at one station (4662) ; 3% at two stations (4671, 4742); 2% at five stations (4609, 4634, 4689, 4713, 4740); 1% at twelve stations (4590, 4594, 4598, 4638, 4650, 4657, 4665, 4667, 4681, 4701, 4732, 4739) ; at the remaining stations the frequency is less than 1 %. For the catch made in Acapulco Harbor the frequency of 1 % is recorded. Schiitt (1895) does not give any information as to the type locality of Phala- croma cuneus; however, it is probably either Naples or in the Atlantic Ocean. Later investigators have shown this species to be widely distributed. The follow- ing authors have found it in the Atlantic, between lat. 40° N. and lat. 28° S. : — Ostenfeld (1898), Murray and Whitting (1899), Cleve (1901c, 1902b, 1903b), Stuwe (1909), and Jorgensen (1923). Cleve (1901c) recorded it from the Carib- bean Sea. Jorgensen (1923) found it at a fairly great number of stations tlirough- out the Mediterranean. It is also recorded from the Gulf of Lyons, Pavillard (1909, 1916). Naples, Schroder (1900a) ; Zacharias (1900). Ionian Sea, Schroder (1906a). Arabian Sea, Schroder (1906a); Cleve (1901a, 1903b); Ostenfeld and Schmidt (1901). Indian Ocean, Schroder (1906a); Cleve (1901a); Karsten (1907). Japan, Okamura (1912). According to the authors noted, tliis species occurs in waters of the following temperatures and salinities. 130 THE DINOPHYSOIDAE. Number and Number and Mean of Mean of Temperature Range Observations Salinity Range Observations Murray and Wliitting (1899) 79° Cleve (1901c) 56.8°- 28 73° 35.63- 22 36.49 81.5° 37.43 Cleve (1902b) 6 69.6° 6 36.24 Cleve (1903b) 60.3°- 6 75.7° 36.13- 6 36.40 82.0° 36.49 Stuwe (1909) 80.2° Only Schiitt (1895), Okamura (1912), and Jorgensen (1923) give figures or descriptions by means of which then- determinations of this form may be judged. FuiUHE 13. — Occurrence of PhaIacT07na ciineus Schiitt. Large, solid circles indicate records from ver- tical hauls; squares, record.s from surface hauls; triangles, records from both vertical and surface hauls; small, soHd circles, stations at which this species was not foimd; small, open circles, stations from which no plankton catches were examined. Phalacroma cuneus is eupelagic and widely distributed in tropical, sub- tropical, and warm-temperate seas. While previous writers have found it to be rare, it is one of the most abundant of the species of the genus found by the Expedition. In the Eastern Pacific it occurs throughout the whole area investi- gated. According to the records, there is a center of abundance in the relatively cool Peruvian Current . Out of the twenty-eight stations with frequencies of 1 % or more, not less than eleven are in that Current; and all the stations with fre- ciuencies of 4% or more are located there. The frequent occurrence of P. cuneus in the coolest (65°-72°) of the regions investigated is the more noteworthy, since SYSTEMATIC ACCOUNT. 131 the species has not been found as yet outside of tropical, sul)tropical, and warm- temperate waters. The relatively frequent occurrence of this species in our sur- face catches is another outstanding feature. Of the species of Phalacroma only P. doryphorum (twenty-six surface records) and P. rapa (twenty-two surface records) were found more frequently than P. cuneiis (thirteen surface records) in the surface catches of the Expedition. Of P. Jams, which next to P. cuneus was the most frequent species of this genus in the surface catches, there are only six surface records. Phalacroma striatitm Kofoid Plate 2, fig. 5, 8. Figui-e 14: 3; 15 Phalacroma slriala Kofoid, 1907a, p. 195, pi. 12, fig. 73. Kofoid & Michener, 1911, p. 289. Phalacroma striatum Jorgensen, 1923, p. 12, 43, fig. 12. Diagnosis: — Body cuneate in lateral view, with very broadly rounded epitheca, and with posterior portion of hypotheca fairly broadly rounded ; deepest at posterior cingular list; length: depth, 1.00-1.04: 1; longitudinal axis deflected posteroventrally at 6°-9°. In dorsal view cuneate; posterior portion of hypo- theca narrowly rounded to acute; length: width, 1.34-1.54: 1. Posterior cingular list 0.20-0.24 the length of body from apex. Cingular lists with numerous simple or branched ribs, or reticulate. Left sulcal list extends to or ahnost to antapex; distance from Ri to R3 is 0.57-0.63 the length of body; R2 is 0.13-0.18, and R3 is 0.06-0.16 the greatest depth of body; widest somewhat in front of R3; margin gently sigmoid, gently convex at R3; R3 inclined posteriorly at about 90°; irregu- larly and incompletely reticulate. Theca reticulate; 25-35 polygons border girdle posteriorly. Length, 102-136 p. Eastern tropical Pacific, Mediterranean, Guinea Current. Description: — This is a comparatively large species, the body of which is cuneate in lateral view, with a rather low and very broadly rounded epitheca, with the posterior portion of the hypotheca fairly broadly rounded, with the greatest depth at the posterior cingular list, and about as deep as long. The ratio between the length and the depth of the body is 1.02 (1.00-1.04) : 1. The longi- tudinal axis is deflected posteroventrally at an angle of 6°-9°. The epitheca is about as deep as the hypotheca, verj- broadly and usually almost evenly convex, highest at or somewhat dorsally to the center, and moder- ately elevated above the anterior cingular list. The transverse furrow is some- what concave, and its width is 0.35-0.50 the greatest height of the epitheca. The posterior cingular list is 0.22 (0.20-0.24) the length of the body from the apex. 132 THE DINOPHYSOIDAE. The hypotheca tapers posteriorly and is somewhat deflected posteroventrally (see p. 131); its dorsal margin is almost straight, slightly convex or concave, or slightly sigmoid, concave anteriorly and convex posteriorly; its ventral margin is almost straight, gently concave or convex, or slightly irregular (Figure 14: 3); its postmargin is evenly and fairly broadly convex, and confluent with the dorsal and ventral margins. In dorsoventral view the body is cuneate, with broadly rounded epitheca, and with the posterior portion of the hypotheca narrowly rounded to acute; the side contours of the hypotheca are gently concave in the middle, or gently sigmoid, concave anteriorly and convex posteriorly; the ratio between the length and the width is 1.34-1.54: 1. The cingular lists are subhorizontal and subequal; their width about equals or in some specimens slightly exceeds the width of the transverse furrow ; each of these lists has, on each valve, about 35^5 straight or more or less irregular ribs, which often anastomose and form a more or less regular reticulum (Jorgensen, 1923, p. 12, fig. 12). The sulcus is about 0.45-0.55 the length of the hypotheca. The flagellar pore is about a girdle-width behind the junction of the cingulum and the sulcus. On the ventral side of the left valve two or three rather small pores are found on the sagittal suture, just in front of the anterior cingular list (Plate 2, fig. 5). The right sulcal list extends to or somewhat beyond the point midwaj' between the fission rib and the posterior main rib of the left sulcal list ; in some specimens its ventral margin, even in the widest region, does not quite extend to the \'entral margin of the left sulcal hst, but in others it does. The anterior half to two thirds of the free margin of this list is fairly deeply concave and is, at least in some specimens (Plate 2, fig. 8), strengthened by a marginal rib; the posterior portion of this margin, which forms a distinct angle with the anterior portion, is more or less convex, or sometimes almost straight. The greatest height of this list is located just behind the concavity. Along the base of this list a reticulum of about the same type as that of the thecal wall may be developed. The left sulcal list is unusually large. In most specimens it extends to or almost to the antapex, and the distance between the anterior and posterior main ribs is 0.57- 0.63 the length of the body. The anterior main rib, when present, is about 0.08-0.10, the fission rib is 0.13-0.18, and the posterior main rib is O.OG-O.IG the greatest depth of the body. The greatest width of this list, which is located somewhere between the fission rib and the posterior main rib, is about 0.20-0.22 the greatest depth of the body. Anteriorly the free margin of this list is gently sigmoid, concave, or almost straight; posteriorly it is convex; in other words, this margin is gently convex at the posterior main rib, and not angular as in most SYSTEMATIC ACCOUNT. 133 species of the genus. The main ribs of this Hst are rather weak and not ckib- shaped or otherwise modified. The distance between the anterior main rib and the fission rib is 0.35-0.45 the distance between the anterior and posterior main ribs. The posterior main rib has a posterior inchnation of about 90°. Besides the main ribs, the left sulcal hst has a "more or less distinct structiu-e of incom- plete areoles, which often present the impression of irregular radial striation" (Jorgensen, 1923, p. 12). There are no accessory lists or sails. The thecal wall has a reticulum of medium-sized polygons, and each polygon has a small pore in the center; the reticulation often is "faint and thm-wallcd' (Jorgensen, 1923, p. 12). The polygons usually are about eciual in size, and on each valve about 25-35 of them border the posterior margin of the girdle. In most specimens there are two rows of polygons in the trans\erse furrow, each row with 25-30 polygons on each vahe. From a point near the middle of the right sulcal list a spine-like process projects into the cytoplasm. Megacytic stages have not been recorded. The proportions of three Expedition specimens were measured. Dimensions: — Expedition specimens: Length of body, 108-115^1 (average, 111 m; type, 108 m). Greatest depth of body, 105-114 ^ (average, 109 m; type, 109 n). Jorgensen (1923, p. 12) : "Length of cell (height) almost equal to breadth in dorso-ventral direction, or somewhat greater; the latter 102-136 yu." Variations: — Apart from variations in size, this species appears to be unusually constant. Cornparisons: — The description and figures of this species are based on the type material. Phalacroma striatum is structurally very close to P. cuneus, P. hlachmani, and P. giganteum (see P. cuneus, p. 127). It differs from P. cuneus in the larger size of its body (102-136 tx, as compared with 80-88 m), and in its larger left sulcal list. From P. blackmani it is easily distinguished by its lack of parasagittal lists, and by the large size and the structure of its left sulcal list. From P. giganteum it differs in the smaller size of its body (102-136 ju, as compared with 148 m), and in the large size and the structure of its left sulcal list. The four species mentioned in the last paragraph form a natural systematic group, the Cuneus group. The closest relative of Phalacroma striatum, outside of this group, presumably is P. argus. With regard to the characters in which the last two species resemble each other, see P. argus (p. 107). Phalacroma striatum is easily distinguished from P. argus by its low and broadly roundsd epitheca, its cuneate hypotheca, and its exceptionally large left sulcal list. The 134 THE DINOPHYSOIDAE. most striking feature of this relationship is that P. argus appears to be more closely related to P. striatum than to P. cuneus, although the latter species is smaller and has a smaller and less differentiated left sulcal list (compare, for in- stance, the directions of the posterior main ribs) and a simpler right sulcal list than P. striatum. The Cuneus group probably evolved from an ancestral form of about the same habitus as P. argus. Figure 14. — 1, I'halacronm giganitum Kofoid and Michencr, right lateral view of right valve of type specimen. X 430. Station 4734 (300-0 fathoms). 3, P/ratacroma s(riohrilra Schiitt as a .synonym of P. rapa Stein. Even though the extent of the confusion of Phalacroma rapa and P. milra by previous investigators caimot be fully established, there are reasons to assume that, with the exceptions mentioned in the last paragraph, it is not very great and that, therefore, the bibliographical list of /■*. rapa is fairly correct. This statement is ba.sed on the fact that P. rapa anil P. milra arc recorded as specifically distinct by most of the investigators, Ostenfeld and Schmidt (1901), Zacharias (190(i), Karstcn (1906, 1907), Stiiwe (1909), and Hensen (1911), who do not give any descriptions or figures by means of which their determinations may be checked. Occurrence: — Phalacroma rapa is recorded at fifty-three of the 127 stations. There are 17, 9, 10, 7, 6, and 4 stations on the six lines of the Expedition. Of these fifty-three stations, two (4580, 4583) are in the California Current; nine (4587, 4590, 4594, 4596, 4598, 4000, 4004, 4005, 4007) are in the Mexican Current; eleven (4009, 4013, 4015, 4017, 4019, 4024, 4034, 4035, 4037, 4040, 4044) hi the Panamic Area; six (4050, 4001, 4005, 4000, 4670, 4678) in the Peruvian Current; six (4689, 4691, 4692, 4695, 4697, 4099) in the Easter Island Eddy; seventeen (4079, 4680, 4081, 4083, 4085, 4701, 4705, 4709, 4711, 4719, 4721, 4722, 4724, 4737, 4739, 4740, 4741) in the South Equatorial Drift; two (4742, 4743) in the South Equatorial Current. There are twenty-two records from the surface (Sta- tions 4590, 4590, 4600, 4604, 4607, 4615, 4017, 4019, 4024, 4035, 4040, 4044, 4650, 4001 [Salpa], 4000, 4070, 4078, 4080, 4092, 4709 [Salpa], 4741, 4743); at eighteen of these stations the species was taken in surface hauls only; at four stations (4590, 4617, 4650, 4709) in hauls from 300-0 fathoms as well as at the surface. At one station (4737) the species is recorded from 100-0 fathoms and 300-0 SYSTEMATIC ACCOUNT. 145 fathoms; at four stations (4681, 4689, 4701, 4724) from 800-0 fathoms and 300-0 fathoms. All the remaming records refer to hauls from 300-0 fathoms only. The temperature range of these fifty-three stations at the surface was 67°- 85°; the average was 76.2°. At the twenty-two stations in the surface catches of which the species was found, the surface temperature ranged from 67° to 84°; the average was 76.0°. For the surface catches the following frequencies are recorded : — 2% at three stations (4615, 4624, 4650), 1 % at three stations (4600, 4619, 4666), and less than 1 % in the remaining cases. For the catches from 100, 300, or 800 fathoms to the Figure 17. — Occurrence of Phalacroma rapa Stein. Large, solid circles indicate records from verti- cal hauls; squares, records from surface hauls; triangles, records from both vertical and surface hauls; small, solid circles, stations at which this sjiecies was not found; small, open circles, stations from which no plankton catches were examined. surface the records of frequency are as follows: — 5% at one station (4709), 3% at one station (4695), 2% at one station (4697), 1 % at seven stations (4598, 4613, 4617, 4681, 4689, 4701, 4721), and less than 1 % at the remaining stations. The species was first recorded by Stein (1883) "aus dem Atlantischen Meer und der Siidsee." Hensen (1895, 1911) found it at a great number of stations throughout the tropical, subtropical, and warm-temperate regions of the Atlantic ; Cleve (1901c, 1902b, 1903b), at a fairly great number of stations in the Atlantic, between lat. 42° N. and lat. 20° S., in the Caribbean Sea, in the Arabian Sea, and the Indian Ocean and recorded it at lat. 36°-37° N. and long. 10° E.-5° W.; 146 THE DINOPHYSOIDAE. Karsten (1906) in the Atlantic, at lat. 5° N. and long. 13° W.; Stiiwe (1909) off the west coast of Africa, between lat. 4° N. and lat. 9° N.; Jorgensen (1923) in the Bay of Cadiz, off the coast of Portugal, and southwest of Brittany, and at a fairly great number of stations in various parts of the Mediterranean; Pavillard (1916) in the Gulf of Lyons; Forti (1922) in the Ligin-ian Sea; Schroder (1900a) at Naples; Zacharias (1906) at Naples and in the Adriatic ; Entz (1902b, 1905) in the Adriatic Sea. Ostenfeld and Schmidt (1901) found it in the Gulf of Aden; Karsten (1907) in the Indian Ocean; Whitelegge (1891) on the east coast of Australia; and Okamura (1907) in Japanese waters. According to the authors noted, this species occurs in waters of the following temperatures and salinities. Number and Number and Mean of Mean of Temperature Range Oljservations Salinity Range Observations Cleve (1901c) 56.0°-82.0° 39 70.0° 33.44-37.63 28 35.80 Cleve (1902b) 72.6° 12 36.27 Cleve (1903b) 59.2°-83.0° 13 70.0° 36.02-37.29 13 36.59 Ostenfeld and Schmidt (1901) 791)° Stuwe (1909) 80.6°-82.8° Of the writers who have contributed to our knowledge of the distribution of this species, only Stein (1883), Okamura (1907), Pavillard (1916), Forti (1922), and J5rgensen (1923) give descriptions or figures by means of which their de- terminations may be judged. It should be mentioned that Cleve (1901c, p. 273) gives Phalacroma mitra Schiitt as a synonym of P. rapa Stein. Some of the data referred to P. rapa by Cleve therefore may be referable to P. mitra. This is a eupelagic species occurring in tropical, subtropical, and temperate regions of all seas. According to the Expedition records it is almost evenly dis- tributed throughout the area investigated. It probably has its optimum habitat in deeper waters, within the levels of photosynthesis, but it appears to occur more frequently at the surface than most of the other species of Phalacroma. Indeed, of the species of this genus only P. doryphorum (twenty-six surface records) was found more frequently than P. rapa (twenty-two surface records) in the surface* catches. Of P. cuneus and P. f aims, which next to P. rapa were the most frequent in the surface catches, there are only thirteen and sLx records, respectively. Phalacroma favus Kofoid and Michener Plate 2, fig. 7. Figure 14: 4, 5 Phdlacrnmnfarus Kofoid & MicheNeh, 1911, j). 289. P.will.ujd, 1923a, p. 879. Phalacroma hindmarchii Pavill.\rd, 1916, p. 53; of. 1923a, p. 879. ?/'//(;/fjrro«ia /rtrjt-s Jorgensen, 1923, p. 15, 16, 43, fig. 16. Phalacroma simulans Jobgensen ms., 1923, p. 15. SYSTEMATIC ACCOUNT. 147 Diagnosis: — Body subcuneate in lateral view; epitheca verj' broadly rounded; posterior portion of hypotheca constricted, mammilliform; ventral margin of hypotheca broadly rounded or somewhat angular at R3 of left sulcal list; deepest at posterior cingular list; length: depth, 1.14-1.21: 1; longitudinal axis deflected posteroventrally at 5°-10°. In dorsal view cuneate ; hypotheca \'ery narrowly rounded to subacute posteriorly, and its side contours gently undu- lating; length : width, 1.45-1.50: 1. Posterior cingular list 0.21-0.27 the length of body from apex. Left sulcal list 0.50-0.65 the length of body; distance from Ri to R3 is 0.25-0.31 the length of body; unusually decurrent behind R3; R-. is 0.12-0.14, and R3 is 0.14-0.22 the greatest depth of body; margin forms angle of 100°-130° at R3; R3 inclmed posteriorly at 5°-30°; with about 8-15 short riblets. Theca reticulate; 20-25 polygons border girdle posteriorly. Length, 54-83 m- Probably widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, the body of which is subcuneate in lateral view, with very broadly rounded epitheca, with the posterior portion of the hypotheca constricted and mammilliform, with the ventral margin of the hypotheca broadly rounded or somewhat angular at the posterior main rib of the left sulcal list, and with the greatest depth at the posterior cingular list. The ratio between the length and the depth of the body is 1.18 (1.14 1.21) : 1. The longi- tudinal axis is deflected posteroventrally at 5''-10°. The epitheca is about as deep as the hypotheca or slightly less, very l)roadly convex, highest in or near the center, and moderately elevated above the anterior cingular list. The transverse furrow is somewhat concave, and its width is 0.50- 0.67 the greatest height of the epitheca. The posterior cingular list is 0.24 (0.21- 0.27) the length of the body from the apex. The hypotheca is somewhat deflected posteroventrally (see above). The dorsal margin, from the girdle to the antapex, is gently undulating, convex in the middle, and concave anteriorly and posteri- orly; or its anterior half is almost straight and its posterior half gently concave (Jorgensen, 1923, fig. 16). The portion of the ventral margin that is in front of the posterior main rib of the left sulcal list is almost straight or gently convex or concave, and about perpendicular to the girdle. The portion of this margin that is behind the posterior main rib of the left sulcal list is 1.7-2.7 the length of the anterior portion, and moderately to rather strikingly concave. At the mentioned rib this margin is either broadly rounded or somewhat angular. The posterior portion of the hypotheca is constricted and mammilliform, and the antapex is narrowly rounded to subacute. In dorsal view the body is cuneate, with very 148 THE DINOPHYSOIDAE. broadly convex epitheca and with the posterior portion of the hypotheca narrowly rounded to subacute; the side contours of the hypotheca are gently undulating, convex in the middle, and concave anteriorly and posteriorly; the ratio between the length and the width is 1.45-1.50: 1. The cingular lists are subhorizontal, subequal, and about as wide as or slightly narrower than the transverse furrow; each of them has, on each valve, twenty to thirty rather strong, straight, simple, and nearly equidistant ribs. The sulcus is about 0.30-0.40 the length of the hypotheca. The flagellar pore is at the junction of the sulcus and the cingulum. The right sulcal list extends to the posterior main rib of the left sulcal list; in some specimens it is subtriangular, decreasmg gradually in width posteriorly, in others it is of subequal width through- out the greater portion of its length ; anteriorly it is about as wide as or somewhat narrower than the transverse furrow. The left sulcal list is of moderate size. Its length is 0.50-0.65 the length of the body, and the distance between the anterior and posterior main ribs is 0.25-0.31 the length of the body. It extends to the base of the posterior mammilliform projection of the bod}'. The anterior main rib is 0.08-0.11, the fission rib 0.12-0.14, and the posterior main rib 0.14-0.22 the greatest depth of the body. Behind the posterior main rib this Ust is unusually decurrent. Between the anterior and posterior main ribs, the free margin of this list is nearly straight, gently convex, or gently concave between the anterior main rilj and the fission rib as well as between the fission rib and the posterior main rib; at the posterior main rib it forms an angle of 100°-130°; behind the last- mentioned rib it is straight or gently concave. The main ribs of this list generally are of moderate strength and straight or almost so; in exceptional cases, for in- stance, in the type specmien, the posterior rib is club-shaped. The distance from the anterior main rib to the fission rib is 0.33-0.50 the distance between the an- terior and posterior main ribs. The posterior main rib has a posterior mclination of 5°-30°. Besides the main ribs, this list has about eight to fifteen short riblets. At least in some specimens (Jorgensen, 1923, fig. 16) the left sulcal list is con- tinued by a very narrow parasagittal list extending around the posterior portion of the hypotheca. The thecal wall has a reticulum of medium-sized, subequal polygons, each with a small pore in the center. There are twenty to twenty-five of them border- ing the posterior margin of the girdle and two rows in the transverse furrow, each with twenty to twenty-five polygons on each valve. Megacytic stages were seen by Jorgensen (1923, p. 16). The proportions of two of the Expedition specimens and the one represented by Jorgensen (1923) were measured. SYSTEMATIC ACCOUNT. 149 Dimet^sions: — Length of body, 72-76 m (average, 74.3 m; type, 76 m). Great- est depth of body, 62.7-63.6 m (average, 63.2 )x; type, 62.7 m). The specimens measured by Jorgensen (1923, p. 15) formed two size classes, the one 81-83 m long and 68-71 m deep, the other 54-62 /i long and 54 n deep. Variations: — Judging by the material thus far exainined, this species ap- pears to be fairly constant. Most of the specimens examined and the specimen represented by Jorgensen (1923, fig. 16) are strikingly similar. The most variable characters are the size of the body and the shape of the posterior portion of the hypotheca. Comparisons: — The description and figures of Phalacroma fatms are based on the type material. Phalacroma rapa probably is structurally the closest relative of P. Jams. Indeed, these two forms sometimes are so similar that even their specific differ- entiation is difficult; compare Pavillard (1916, fig. 13A) and Figure 14: 5. How- ever, we do not agree with Jorgensen's (1923, p. 16) statement that P. faints is so closely related to P. rapa "that there might be some grounds for regarding it as a variety of that species." The most important distinguishing characteristics are : — (1) P. f aims has a relatively longer and more decurrent left sulcal list, which has a fairly great number of short riblets besides the three main ribs; {2) the posterior portion of the hypotheca in P. famis is somewhat more contracted, i.e., mam- milliform, than in P. rapa. P. favus is most easily distinguished from P. hind- marchi by its lower epitheca, its relatively longer and more decurrent left sulcal list, which has a fairly great number of short riblets besides the three main ribs, an(4 the polygonate reticulation of its theca. It differs from P. mitra, P. doKchop- terygium, and P. acutum in the shape and structure of its left sulcal list and in the mammilUform shapeof the posterior portionof its hypotheca. See P. rapa, p. 143, and Jorgensen, 1923, p. 15, 16. Occurrence: — Phalacroma favus is recorded at twelve of the 127 stations. There are 6, 1,0, 0, 2, and 3 stations on the six lines of the Expedition. Of these twelve stations, six (4587, 4590, 4592, 4594, 4604, 4545) are in the Mexican Cur- rent; one (4617) is in the Panamic .\j-ea; one (4665) is in the Peruvian Current; three (4730, 4737, 4741) are in the South Equatorial Current; one (4542) is in the Equatorial Counter Current. At one of these stations (4617) this species was taken in a surface haul as well as in a haul from 300-0 fathoms; at five stations (4592, 4604, 4741 [Salpa], 4542, 4545) in surface hauls only. All the remain- ing records refer to hauls from 300-0 fathoms only. The temperature range of these twelve stations at the surface was 68°-84°; 150 THE DINOPHYSOIDAE. the average was 80.2°. At the six stations in the surface catches of which this species was found, the surface temperature ranged from 78° to 84°; the average was 80.8°. At two stations (4604, 4542) the frequency is 1%; in the remaining cases it is less. The species was first recorded by Kofoid and Michener (1911) at Station 4737 of the Expedition. Later Jorgensen (1923) found it in the Bay of Cadiz and in the Ionian Sea. Pavillard (1916) reported it from the Gulf of Lyons under the name of Phalacroma hindmarchii. This is a eupelagic, stenothermal, and warm-water species. Presumably it is widely distributed in tropical and subtropical seas, and it occurs only occasion- ally in warm-temperate regions. According to the Expedition records, it is found in waters of very high average temperature (80.2°). Most of the record stations are in the warm Mexican Current, and in the western portion of the South Equatorial Drift, and only one is located in the relatively cooler Peruvian Cur- rent. Another outstanding peculiarity in the occurrence of this species, according to the Expedition data, is the exceptionally high percentage (50%) of surface records. In no other species of this genus has such a high percentage been re- corded. Phalacroma hindmarchi Murray and Whitting Figure 18, 19 Phalacroma hindmarchii Murray & WuiTTiNci, 1899, p. 330, tab. 4, 5, 6, S, 9, i)l. 31, fig. .5. Lemmermann, lS99a, p. 372; igoi.a, p. 372. Cleve, 1901o, p. 271; 1902b, p. 36. .Jorgensen, 1923, p. 1.5, 16. Pavil- L.\RD, 192.3a, 1). 879 (non 1916, p. 53). Phalacroma hindmarchi Stuwe, 1909, p. 251, 288. Diagnosis: — Body of inverted fig-shapo in lateral view; epitheca broadly and more or less strongly convex; posterior portion of hypotheca constricted, mammilliform; ventral margin sigmoid, convex anteriorly, concave posteriorly; deepest at or somewhat behind girdle; length: depth, 1.15-1.31: 1; longitudinal axis usually perpendicular to girdle. Dorsoventral and lateral \icws almost similar. Posterior cingular list 0.27-0.44 the length of body from apex. Cingular lists possibly without structure. Left sulcal list 0.33-0.50 the length of body; distance from Ri to R3 is 0.24-0.33 the length of body; R2 is 0.09-0.16, and R3 is 0.20-0.25 the greatest depth of body; margin forms angle of 70°-100° at R3; R3 inclined posteriorly at 15°-35°; often club-shaped; .sometimes reticulate. Theca finely and closely areolate. Length, 82-98 m- Probably widely distributed in tropical, subtropical, and warm-temperate seas. SYSTEMATIC ACCOUNT. 151 Description: — A medium-sized species, the body of which is of inverted fig- shape in lateral view, with broadly and more or less strongly convex epitheca, with the posterior portion of the hypotheca constricted and mammilliform, with the ventral margin of the hypotheca sigmoid, convex anteriorly and concave posteriorly, and with the greatest depth at or somewhat behind the girdle. The ratio between the length and the depth of the body is 1.25 (1.15-1.31): 1. The longitudinal axis usually is about perpendicular to the girdle, but sometimes it is slightly deflected posterodorsally or posteroventrally. Figure 18. — Plialacroma hindmarchi Murray and Whitting. 1, right, lateral view. 2, 3, left lateral view; surface markings, areolation, and porulation indicated only on small portion of theca in 2, 3. X 430. 1, from Station 47.37 (1.50-0 fathoms). 2, 3, from Station 4730 (300-0 fathoms). The epitheca is about as deep as the hypotheca or somewhat less, broadly and more or less strongly convex, often dome-shaped, highest in or near the center, and moderately elevated or generally \'ery prominent above the anterior cingular list. The transverse furrow is nearly flat or slightly convex, and its width is 0.20-0.40 the greatest height of the epitheca. The posterior cingular list is 0.38 (0.27-0.44) the length of the body from the apex. The hypotheca some- times is almost symmetrical, as in the type specimen and in Figure 18: 1; some- times its dorsal and ventral margins, which are sigmoid, convex anteriorly and concave posteriorly, are more or less different (Figure 18: 3). The posterior por- tion of the hypotheca is constricted and mannnilliform ; in none of the Expedition specimens was this constriction ciuite so pronounced as in the type (Murray and Whitting, 1899, pi. 31, fig. 5). The antapex is narrowly rounded to subacute. In dorsoventral view the body has about the same shape as in lateral view, with the exception that it is somewhat narrower. The cingular lists are subhorizontal, subequal, and about as wide as the transverse furrow; judging bj' the figures of the type and by Figures 18, 19, these lists are hyaline and without structure. The sulcus is about 0.4 the length of the hypotheca. The right sulcal list extends to the posterior main rib of the left 152 THE DINOPHYSOIDAE. siilcal list, is of subequal width throughout the greater part of its length, as wide as or somewhat narrower than the transverse furrow, and rounded posteriorly. The left sulcal list is of moderate size. Its length is 0.33-0.50 the length of the body, and the distance between the anterior and posterior main ribs is 0.24-0.33 the length of the body. It ends somewhat in front of the base of the posterior mammilliform projection of the body. The anterior liiain rib, when present, is 0.07-0.14, the fission rib 0.09-0.16, and the posterior main rib 0.20-0.25 the greatest depth of the body; behind the posterior main rib the list decreases sud- denly in width. Between the anterior and posterior main ribs, the free margin of this list is almost straight, gently convex or concave, sigmoid, i.e., concave an- FiGURE 19. — Occurrence of Phnlncrotiia hhidinarchi Murray and Wliitting. Large, solid circles indi- cate records from vertical hauls; squares, records from surface hauls; small, solid circles, stations at which this species was not found; small, open circles, stations from which no plankton catches were examined. teriorly and convex posteriorly, or it is somewhat irregular; at the posterior main rib it forms an angle of 70°-100°; behind the last-mentioned rib it is either straight or gently concave or convex. The anterior main rib and the fission rib of this list are of moderate strength or rather weak; the posterior main rib usually is quite heavy and club-shaped distally; all of them are straight or almost so, or the pos- terior has a gentle posterior concavity. The distance between the anterior main rib and the fission rib is about 0.33-0.50 the distance from the anterior to the posterior main rib. The posterior main rib has a posterior inclmation of 15°-35°. SYSTEMATIC ACCOUNT. 153 Besides the main ribs, this list sometimes has a well-developed reticulation (Figure 18: 3). There are no accessory lists or sails. The thecal wall has a fairly great number of scattered pores, interspersed with more numerous, small, rounded, and closely set areoles of somewhat varying size (Figure 18: 2, 3). Usually the areoles are of about the same size as the pores, but sometimes they are smaller (see Cleve, 1901c, p. 271). Megacytic stages were found. The proportions of five of the Expedition specimens and of the type speci- men as represented by Murray and Whitting (1899) were measured. Dimensions: — Length of body, 82-98 m (average, 87 n). Greatest depth of body, 65-75 m (average, 69.5 m). The type specimen as represented by Murray and Whitting (1899, pi. 31, fig. 5) was about 92 /x long and 75 n deep. Variations: — The length of the body, the relative height of the epitheca, the degree of symmetry and of posterior constriction of the hypotheca, and the structure of the theca and of the left sulcal list appear to be the most variable characters. Co7nparisons: — Most of the Expedition specimens referred to Phalacroma hindmarchi (Figure 18: 1) agree closely with the type as figured by Murray and Whitting (1899, pi. 31, fig. 5). Others are more or less aberrant (Figiu'e 18: 2, 3), but even in their case the assignment may be regarded as certain. Phalacroma hindmarchi is closely related to P. Jams, P. rapa, P. miira, and P. dolichopterygium, although this relationship appears to be collateral rather than linear. In other words, P. hindmarchi seems to be a highly differentiated member of an evolutionary branch originating from the same ancestral form as the branch represented by the last four species and partly embodying the same tendencies as the latter branch, e.g., the tendency to constrict the posterior por- tion of the hypotheca into a mammilliform projection. Phalacroma hindmarchi is easily distinguished from P. fainis, P. rapa, P. mitra, and P. dolichopterygitim by its higher and more dome-shaped epitheca, and by having its thecal wall finely areolated instead of reticulated. According to Murray and Whitting (1899, p. 330), Phalacroma hindmarchi is "closely allied to P. operculatwn." However, this relationship is not so evident as the ones suggested above. Occurrence: — Phalacroma hindmarchi is recorded at thirteen of the 127 sta- tions. There are 0, 0, 2, 3, 7, and 1 stations on the six lines of the Expedition. Of these thirteen stations, four (4689, 4691, 4697, 4699) are in the Easter Island Eddy; eight (4701, 4730, 4731, 4732, 4734, 4736, 4737, 4739) are in the South ] 54 THE DINOPHYSOIDAE. Equatorial Drift ; one (4742) is in the South Equatorial Current. At one of these stations (4731) the species is recorded from the surface; at one station (4737) from 100-0 fathoms as well as from 300-0 fathoms. The remaining records refer to hauls from 300-0 fathoms only. The temperature range of these thirteen stations at the surface was 72.0°- 81.5°; the average was 77.2°. At Station 4731, the only surface record, the surface temperature was 79.5°. At four stations (4689, 4731 , 4734, 4739) the frequency is 1 % ; m the remain- ing cases it is less. The species was first recorded by Murray and Whitting (1899), who found it at nine stations in the tropical and subtropical regions of the Atlantic, between lat. 14° N. and 31° N., and in the Caribbean Sea. Later Cleve (1901c, 1902b) reported it from the Atlantic, between lat. 9° N. and 34° N., and from the Carib- bean Sea; and Stiiwe (1909) from the Atlantic, at lat. 3° 50' N., long. 26° 15' W. (South Equatorial Current). According to these authors, this species occurs in waters of the following tem- peratures and salinities. Number and Number and Mean of Mean of Temperature Range Observations Salinity Range Observations IMurray and Whitting (1899) 67''-G9° Cleve (1901e) 70.0°-82.0° 16 75.5° 34.88-37.4.3 10 36.27 Cleve (1902b) 76.3° 37.17 Stiiwe (1909) 80.2° Of the authors who have contributed toward a knowledge of the distribution of this species only Murray and Whitting (1899) give any descriptions or figures by means of which their determinations may be checked. Jorgensen (1923, p. 16) writes as follows: "I have not noticed that the species I have noted from the cruise of the Thor as Ph. Hindmarchii ..." However, P. Inndmarchi is not mentioned by this author except in connection with the dis- cussion of P. favus. The statement quoted above therefore is either due to a lapsus pennae, or the account of P. hindmarchi was overlooked. This species is eupelagic and widely distributed, but rare, in tropical, sub- tropical, and warm-temperate seas. Its distribution in the Ea.stern Pacific, according to the Expedition data, is remarkably similar to that of Amphisolenia schauinslandi and A . thrinax (see p. 442). Although there are as many as thirteen record stations, the species was never found in the California Current, Mexican Current, Panamic >Area, and Peruvian Current. With one exception, all the record stations are in or near the Easter Island Eddy and in the western portion of the South Equatorial Drift. The average temperature of its habitat is high, 77.2.° SYSTEMATIC ACCOUNT. 155 6. ExPULSUM Group. Both the species referred to this group, PhaJacroma protuberans and P. expulsuin, were found in the material of the Expedition. Phalacroma protuberans, sp. nov. Figure 20: 6-9 Diagnosis: — Body subovate to subcircular in lateral outline, with dorsal shoulder-like constriction at posterior cingular list, deepest in or somewhat in front of the middle, and 1.08-1.18 times longer than deep; longitudinal axis per- pendicular to girdle or deflected posteroventrally at l°-4°. In dorsal view wedge- shaped, widest just behind girdle, subacute to narrowly rounded posteriorly, and with more or less pronounced rounded protuberances just behind girdle; length: width, 1 .38-1 .74 : 1 . Posterior cingular list 0.23-0.26 the length of body from apex. Cingular lists 1.7-2.0 the width of transverse furrow; their structure unknown. Left sulcal list 0.64-0.65 the length of body; Ri is 0.18-0.20, R2 is 0.14-0.16 the greatest depth of body; R3 absent; margin rounded or rounded angular poste- riorly. Length, 53.0-59.6 //• Eastern tropical Pacific. Description: — A medium-sized species, the body of which is subovate to subcircular in lateral outline, with a dorsal shoulder-like constriction at the pos- terior cingular list, and deepest in or somewhat in front of the middle. The ratio between the length and the depth of the body is 1.13 (1.08-1.18) : 1. The longi- tudinal axis is perpendicular to the girdle, or it has a posteroventral deflection of l°-4°. The epitheca is 0.74 (0.71-0.76) as deep as the hypotheca, highest in the center, of moderate convexity or more or less flat, and moderately to rather slightly elevated above the anterior cingular list. The transverse furrow is some- what concave, and about as wide as or somewhat narrower than the greatest height of the epitheca. The posterior cingular list is 0.25 (0.23-0.26) the length of the body from the apex. The hypotheca sometimes is subsymmetrical (Figm-e 20:6), sometimes it is decidedly flatter ventrally than dorsally (Figure 20:8). The dorsal margin is subuniformly, and gently to moderately convex except just behind the girdle where it is more bulging. The ventral margin, from the girdle to the posterior end of the left sulcal list, is gently convex. The postmargin is moderately to rather strongly convex and confluent with the dorsal and ventral margins. In dorsoventral view the body is wedge-shaped, widest just behind the girdle, subacute to narrowly rounded posteriorly, and with broadly rounded, more or less prominent protuberances just behind the girdle, one on each side of 156 THE DINOPHYSOIDAE. the body; the ratio between the length and the width of the body is 1.56 (1.38- 1.74) :1. The cingular lists are subhorizontal and subequal; their width is about 1.7- 2.3 the width of the transverse furrow and 0.23-0.26 the greatest depth of the body; their structure is unknown. The right sulcal list is unusually short, extend- ing to or slightly beyond the fission rib of the left sulcal list, and subtriangular, decreasing gradually in width posteriorly; anteriorly it is about as wide as the transverse furrow. The left sulcal list is about 0.64-0.65 the length of the body and of subuniform width throughout the greater portion of its length. The an- terior main rib is 0.18-0.20, the fission rib 0.14-0.16 the greatest depth of the body. The posterior main rib is lacking. The anterior two thirds of the free Figure 20. — 1-5, Phahicroma exj)ulsii»i. (Kofoid and Mirhener). 1, in left lateral view; 2, 4, in dorsal view; 3, in right lateral view; 5, in ventral view. 2, from the same specimen as 1 ; 4, from the same specimen as 3. 1-3, X 4-30; 4, of unknown magnification; 5, X 890. 1, 2, from Station 4713 (300-0 fath- oms); 3, 4, from Station 4724 (300-0 fathoms); 5, from Station 4717 (300-0 fathoms). 6-9, Phalacroma proluberans, sp. nov. 6, 8, in right lateral view; 7, 9, in dorsal view. 7, from the same specimen as 6; 8, 9, from type specimen. Porulation of theca indicated only in 8. X 430. Station 4730 (300-0 fathoms). margin of this list is almost straight, or gently sigmoid, concave anteriorly and convex posteriorly. The posterior portion of this margin, which is confluent with the anterior, is gently convex (Figure 20:6) to rounded angular (Figure 20:8). The main ribs are straight or almost so, and not club-shaped or otherwise modified. There are no accessory Usts or sails. The thecal wall is porulate. Megacytic specimens were not recorded. The dimensions of two specimens were measured. Dimensions: — Length of body, 53.0-59.6 n (type, 59.6 m). Greatest depth of body, 44.9-55.2 ^ (type, 55.2 m). Variations: — The two specimens differ strikingly from each other in the depth of the body, in the width and shape of the left sulcal list, in the development SYSTEMATIC ACCOUNT. 157 of the lateral expansions and constrictions of the body, and in the width of the posterior end of the body when seen in dorsoventral view. Figure 20 : 6 may, how- ever, represent a specimen drawn in a somewhat tilted position. Comparisons: — Phalacroma protuberans is established on four outline draw- ings made from the two Expedition specimens. The structure of the cingular and sulcal lists and of the thecal wall is unknown. In spite of several rather striking differences, this species probably is closely related to Phalacrovia expulsum. It differs most strikingly from this species in the less-developed posteroventral inclination of the longitudmal axis of the body, in the greater width and subhorizontal position of the cingular lists, in the greater length of the left sulcal list, and m having a pair of broadly rounded lateral protuberances just behind the girdle. For further discussion on the relationships of these two species, see P. expulsum (p. 159). Occurrence: — Phalacroma protuberans is recorded at onlj^ one (4730, type locahty) of the 127 stations, on the fifth line of the Expedition, in the South Equatorial Drift, from 300-0 fathoms, and at a surface temperature of 79°. The frequency is less than 1 % (two specimens). Phalacroma expulsxjm (Kofoid and Michener) Plate 5, fig. 1. Figure 20: 1-5 Dinophysis exp^ilsa Kofoid & Michener, 1911, p. 268. Phalacroma stenopterygium Jorgensen, 1923, p. 11, 24, 44, fig. 10. Diagnosis: — Body sack-like in lateral outline, truncate anteriorly, with dorsal shoulder-like constriction at girdle, broadly rounded posteriorly, deepest in the middle, and 1.02-1.24 times longer than deep; longitudinal axis deflected posteroventrally at 5°-15°. In dorsal view wedge-shaped, widest at posterior cingular list or in the middle, subacute to narrowly rounded posteriorly, and with broad constriction in front of the middle; length: width, 1.42-1.82: 1. Posterior cingular list 0.11-0.17 the length of body from apex; epitheca barely if at all visible above anterior cmgular list. Cingular lists inclined anteriorly at 30°-45°, with or without ribs; the anterior about as wide as or somewhat narrower than transverse furrow; the posterior narrower than the anterior. Left sulcal list 0.42-0.57 the length of body; Ri is 0.12-0.16, R2 is 0.09-0.17 the greatest depth of body; R3 absent; margin rounded, not angular, posteriorly. Theca centrally faintly reticulate; about 17-20 polygons border girdle posteriorly. Length, 53.7- 67.5 M. Probably widely distributed in tropical, subtropical, and warm-temperate seas. 158 THE DLNOPHYSOIDAE. Description: — A medium-sized species, the body of which is sack-like in lateral outline, truncate anteriorly, with dorsal shoulder-like constriction at girdle, broadly rounded posteriorly, and deepest in or near the middle. The ratio be- tween the length and the depth of the body is 1.02-1.24: 1; in the Expedition specunens this ratio is 1.15 (1.08-1.24) : 1 ; in Jorgensen's (1923) it varied between 1.02: 1 and 1.23: 1. The longitudinal axis is inclined posteroventrally at 5°-15°; in the Expedition specimens this angle is 8° (5°-10°), in that figured by Jorgensen (1923, fig. 10) it is 15°. The epitheca is 0.60 (0.54-0.66) as deep as the hypotheca, gently convex or flat, highest in or ventrally to the center, and barely if at all visible above the anterior cingular list. The transverse furrow is somewhat concave, and about as wide as or somewhat wider than the greatest height of the epitheca. The posterior cingular list is 0.15 (0.11-0.17) the length of the body from the apex. The hy- potheca is more or less inclined posteroventrally (see above). The dorsal margin is subuniformly and gently to moderately convex. The ventral margin, from the girdle to the posterior end of the left sulcal list, is almost straight or gently con- cave or convex. The postmargin is subuniformly and broadly rounded, sub- semicircular, and either confluent with the dorsal and ventral margins, or (Jorgensen, 1923, fig. 10) forming a distinct although well-rounded angle at the posterior end of the left sulcal list. In dorsoventral view the body is wedge- shaped, widest at the posterior cingular list or in the middle, and subacute to narrowly rounded posteriorly; between the middle, where the body is more or less expanded, and the posterior cingular list, there is a broad and more or less pro- nounced constriction; the ratio between the length and the width is 1.60 (1.42- 1.82): 1. The cingular lists, which are characterized by an anterior inclination of 30°-45°, usually are subequal, but sometimes the posterior is more or less strik- ingly narro\\'er than the anterior. The anterior is about as wide as or somewhat narrower than the transverse furrow and about 0.11 (0.09-0.13) the greatest depth of the body. In the specimens examined Ijoth these lists are hyaline and lack distinct ribs. Jorgensen (1923, p. 11), on the other hand, writes about these lists : "both without or with distinct short radial transverse ribs, innermost by the cell." The right sulcal list is unusually short and extends to or slightly beyond the fission rib of the left sulcal list; it is subtriangular, or rounded anteriorly, and decreases gradually in width posteriorly; its maximum width does not exceed the width of the transverse furrow. The left sulcal list is 0.51 (0.42-0.57) the length of the body, and of subuniform width throughout the greater part of its length. SYSTEMATIC ACCOUNT. 159 The anterior main rib is 0.13 (0.12-0.16) and the fission rib 0.13 (0.09-0.17) the greatest depth of the body. The posterior main rib is usually lacking, but some- times a short rudiment may be found (Jorgensen, 1923, p. 11). The anterior half of the free margin of this list is straight or gently concave or convex; the posterior half, which is confluent with the anterior, is gently, moderately, or strongly con- vex, and not angular as in most species of the genus. The main ribs are straight or almost so, and not club-shaped or otherwise modified. With the exception of the main ribs, this list appears always to lack structural differentiation. There are no accessory lists or sails. Except along the dorsal, posterior, and ventral margins, the thecal wall of the hypotheca has a fine reticulum of polygonate meshes; the posterior margin of the girdle is bordered by seventeen to twenty polygons. Sometimes the polygons are subequal in size, sometimes they decrease somewhat m size posteriorly. In the transverse furrow there are two rows of polygons of about the same average size as the hypothecal polygons. On the epitheca no reticulation has been ob- served. The whole theca is furnished with evenly scattered pores. In the trans- verse furrow every polygon has a pore, which usually is located in or near the center. Megacytic stages were not recorded. The dunensions of six of the Expedition specimens and of the specunen figured by Jorgensen (1923, fig. 10) were measured. Dimensions: — Length of body, 53.7-64.5 n (average, 58.3 n; type, 55.8 n). Greatest depth of body, 45.7-51.2 ix (average, 49.1 m; type, 47.8 m)- The speci- mens measured by Jorgensen (1923) were, according to a statement in the text, 54-63 fx long and 53-58 m deep; the one figured (1923, fig. 10) was 67.5 yu long and 55.0 fi deep. Variations: — Phalacroma expulsum is rather variable. The following char- acters are the most variable : — the size of the body, the relative depth and width of the body, the degree of the posteroventral inclination of the longitudmal axis, the relative depth of the epitheca, the shape of the ventral margin of the hypo- theca, the development of the lateral expansions and constrictions of the body, and the width of the posterior end of the body when seen in dorsoventral view. Co?nparisons: — The description and figures of this species are based on the type material. The most aberrant specunen is represented by Figure 20:3,4. It differs from the remaining specunens in its narrower body, in the subuniform convexity of the ventral margm of its body from the girdle to the antapex, and in the shortness of its left sulcal list. Its present assignment is tentative. It has 160 THE DINOPHYSOIDAE. been referred here mainly because of the fact that its body, in dorsoventral view, has an outline of about the same shape as that of the typical specimens. The specimen figured by Jorgensen (1923, fig. 10) as Phalacroma stenoptery- gium differs from the typical representatives mainly in the following respects: its longitudinal axis has a more pronounced posteroventral inclination (15°, as compared with 5°-10°), the ventral margin of its body forms a distinct, although rounded corner at the posterior end of the left sulcal list, and its posterior cingular list is decidedly narrower. Jorgensen (1923) states that his specimens were 54- 63 M long and 53-58 m deep. From this it is evident that at least some of his speci- mens were decidedly deeper relatively than any of the Expedition specimens. The generic assignment of this species is somewhat uncertain. Kofoid and Michener (1911) allocated it to Dinophysis on account of the narrowness of the epitheca, the shape of the hypotheca in lateral view, and the position and anterior inclination of the cingular hst. Jorgensen (1923, p. 11), on the other hand, writes that: "Despite the great resemblance to the Dinophysis species, I have ascribed it to the genus Phalacroma, chiefly on account of the wedge-shaped cell and also because the lower girdle list can apparently have the same short radial ribs as the upper." With regard to the last-mentioned character it should be pointed out, first, that in the specimens examined both the cingular lists lacked ribs; and, second, that even though the ribbing of the posterior cingular list is a character frequently found in the species of Phalacroma, nevertheless, it is not limited to this genus but is found also in typical representatives of Dinophysis; see Dino- physis triacantha,Y ignve 42:2. Furthermore, Dinophysis cuneiformis, which is a typical representative of its genus, is narrowly wedge-shaped in dorsoventral view (Meunier, 1910, pi. 14, fig. 32). However, Jorgensen's (1923) decision is accepted by the close agreement between the dorsoventral outline of the body in this species and in some species of Phalacroma, e.g., in Phalacroma favus (Figure 14 : 2) ; by the regularly ovate, ellipsoidal, or bilaterally flattened dorsoventral outline of almost all the other known species of Dinophysis; and by the fact that in the closely related Phalacroma protuberans the epitheca is rather large and the cingular lists are subhorizontal. Of course, the question is of minor importance, since the genera Dinophysis and Phalacroma are so closely related that their separation is almost arbitrary. The structurally closest-known relative of Phalacroma e.rpulsu7n is P. pro- tuberans. The former species differs most strikingly from the latter in the more pronounced posteroventral inclination of the longitudinal axis of the body, in the anterior inclination of the cingular lists, and in the relative shortness of the left SYSTEMATIC ACCOUNT. IGl sulcal list. These two species occupy structurally a rather isolated position and ought to be made the only representatives of a special group. Jorgensen (1923) assigned P. expulsum to the Cuneus group. This allocation undoubtedly was made on account of the wedge-like shape of the body in dorsoventral view and because of the fact that the free margin of the left sulcal list is rounded postero- ventrally, instead of angular as in most of the species of Phalacroma. However, this allocation greatly decreases the structural uniformity of the Cuneus group, and for that reason should not be maintamed. Note, for instance, the relati\-e narrowness of the epitheca and the sack-like, instead of wedge-like, shape of the hypotheca of P. expulsum in lateral view. On the other hand, these two species show distinct affiliation to the Cuneus group and should thus be placed near to it. Jorgensen (1923, p. 11) also points out that P. expulsum "in several respects, especially in the left longitudinal furrow list," is "remarkably like" Dinophysis sphaerica (= similis). However, the relationship between these two species must be regarded as uncertain; the similarities in the shape of the hypotheca in lateral view and in the shape of the left sulcal list are rather superficial, while the differ- ence in the shape of the body in dorsoventral view is profound. It also may be worth mentioning that Dinophysis okamurai (Figure 31:5) shows a certain re- semblance to Phalacroma expulsum in the shape of the body in lateral view. Occurrence: — Phalacroma expulsum is recorded at four of the 127 stations. There are 0, 0, 0, 1, 3, and stations on the six lines of the Expedition. Of these four stations, one (4713) is in the Galapagos Eddy, and three (4717, 4720, 4724) are in the South Equatorial Drift. There is one record from a surface haul (4720, from Salpa stomach). The remaining records refer to hauls from 300-0 fathoms. The temperature range of these four stations at the surface was 73°-81°, and the average was 76.8°. At Station 4720, where the species was taken at the sur- face, the surface temperature was 76°. The frequency is in every case less than 1 %. The species was first recorded byKofoid and Michener (1911) from Station 4717 of the Expedition, the type locality. Later Jorgensen (1923) reported it to be "scattered throughout the whole of the Mediterranean to the Bay of Corinth, often in deep water samples." It is probably widely distributed in tropical, sub- tropical, and warm-temperate seas. 7. LiMBATUM Group. Three species, viz., Phalacroma Ivmhalum, P. biparti- tum, and P. pulchrum, belong to this group, and all of them occurred in the col- lections of the Expedition. 162 THE DINOPHYSOIDAE. Phalacroma limbatum Kofoid and Michener Plate 3, fig. 3-5. Figure 21: 1 Phalacroma limbiila Kofoid & Michener, 1911, p. 290. Diagnosis: — -Body subcircular in lateral outline, deepest near the middle; length: depth, 1.08-1.10: 1. In dorsal view lens-shaped, 2.27 times longer than wide, with narrowly rounded apices. Posterior cingular list 0.38-0.50 the length of body from apex. Cingular lists appear to be without ribs. Left sulcal list: distance between Ri and Ra is 0.25-0.28 the length of body; R2 is 0.12-0.14 and Rs is 0.19-0.24 the greatest depth of body; margin forms angle of 70°-90° at R3; Ra inclined posteriorly at 20°-35°. Two parasagittal lists encircle body; the left of subuniform width throughout, and its maximum width is subequal to or some- what less than width of transverse furrow ; the right resembles the left but forms on antapex an acute, wedge-shaped, posterior sail directed posteriorly. Sail 0.15-0.27 the greatest depth of body in length, with central rib, whose proximal half might form more or less complex reticulum; angle at its tip, 35°-50°. Right parasagittal list forms du'ect continuation of left sulcal list. Central portion of each thecal valve with reticulum of moderate-sized mesh. Length, G8.9-7G.5 ju. Eastern tropical Pacific. Description: — A medium-sized species, the body of which is subcii'cular in lateral outline, slightly longer than deep, and deepest near the middle. The ratio between the length and the greatest depth of the body is 1.09 (1.08-1.10) : 1. The longitudinal axis is perpendicular to the girdle. The epitheca is about 0.87 as deep as the hypotheca, strongly and evenly convex, dome-shaped, highest in the center, and very prominent above the an- terior cingular list. The transverse furrow is flat, or slightly convex or concave, and its width is 0.24-0.32 the greatest height of the epitheca. The posterior cingular list is 0.38-0.50 the length of the body from the apex. The hypotheca is symmetrical; its dorsal, posterior, and ventral margins are well and evenly con- vex, and confluent. Its posterior portion is of about the same depth as the an- terior portion of the body. In dorsoventral view the body is lens-shaped, about 2.27 times wider than long, widest at the girdle, and with narrowly rounded apices; the side contours are nearly evenly convex. The cingular lists are subhorizontal and subequal; their width about equals or somewhat exceeds the width of the transverse furrow; and they are without ribs, according to available drawings (see p. 164). The sulcus is about half as long as the hypotheca. The flagellar pore is just behind the junction of the SYSTEMATIC ACCOUNT. 163 cingulum and the sulcus. On the ventral side of the left valve a small pore is found near the sagittal suture, just in front of the anterior cingular list. The right sulcal list extends to the posterior main rib of the left sulcal list; it is subtriangu- lar, decreasing gradually in width posteriorly, and anteriorly it is about as wide as the transverse furrow. The left sulcal list is of moderate width and rather short. The distance between the anterior and posterior mam ribs is 0.25-0.28 the length of the body. The anterior main rib is 0.13-0.14, the fission rib 0.12- 0.14, and the posterior main rib 0.19-0.24 the greatest depth of the body; behind the posterior main rib the hst decreases suddenly in width. The free margin of this list is gently sigmoid or nearly straight between the anterior and posterior mam ribs; at the posterior main rib it forms an angle of 70°-90°; behind the pos- terior main rib it is gently concave. The main ribs of this list are of moderate strength and almost straight; or the posterior one is rather strong and gently concave posteriorly; none of them is club-shaped or otherwise modified. The distance between the anterior main rib and the fission rib is 0.33-0.50 the distance between the anterior and posterior main ribs. The posterior main rib has a posterior inclination of 20°-35°. Besides the three main ribs, this list sometimes has a faint reticulation; and just behind the posterior main rib it has a fine rib with a posterior inclination of about 50°-60°. Two parasagittal Usts encircle the entire body; the one on the right valve of the hypotheca forms a direct contin- uation of the left sulcal list. The left parasagittal list is of subuniform width throughout its entire length, has a maximum width subequal to or somewhat less than the width of the transverse furrow, and is furnished with a moderate num- ber of sunple, free or anastomosing, incomplete riblets. The right parasagittal list resembles the left, but it forms on the antapex an acute, wedge-shaped posterior sail, directed posteriorly. WTien fully developed, the sail is 0.15-0.27 the greatest depth of the body m length and has a central rib, whose proximal half might form a more or less complex reticulum; the angle at its tip is 35°-50°. The central portion of each thecal valve, with the exception of the transverse furrow, is characterized by a reticuliun of closely set, rather heavily niai'gined polj'gons of moderate size. The polygons are subequal, and on each valve about thirty of them border the posterior margm of the transverse furrow. The entne theca is furnished with scattered pores. There is a central pore in most of the polygons; and in the transverse furrow there are three rows of pores, each row with thirty to forty pores on each valve. Megacytic stages were not found. The proportions of two specimens were measured. 164 THE DINOPHYSOIDAE. Dimensions: — Length of body, 68.9-76.5 m (average, 72.7 m; type, 76.5 a<). Greatest depth of body, 62.4-70.6 m (average, 66.5 n; type, 70.6 fi). Variations: — This species is fairly constant; the relative height of the epitheca, the width of the parasagittal lists, and the size and structure of the posterior sail of the right parasagittal list are the most variable characters. Comparisons: — The description and figures are based on the type material. Figure 21. — 1, Phalacroma limbatum Kofoid and Michener, right lateral view. X 430. Station 4722 (300-0 fathoms). 2, Phalacroma hipartitum, sp. nov., right lat- eral view of type specimen; porulation indicated only on portion of transverse furrow. X 430. Station 4736 (300-0 fathoms). 3, Phalacroma pulchrum Kofoid and Michener, right lateral view of type specimen. X 430. Station 4G99 (300-0 fathoms). We refer the specimen, Plate 3, fig. 4, tentatively to this species; the similari- ties between it and those described above are as follows: — the body is subcircu- lar in lateral outline; the girdle is subequatorial in position; only the central portions of the thecal valves are reticulated; there is an accessory rib in the left sulcal list just behind the posterior main rib. On the other hand, the differences exhibited by the first specimen also are conspicuous; for instance, it lacks para- sagittal lists except on the antapical portion of the hypotheca ; at the antapex its right parasagittal list is rather wide, but no acute, wedge-shaped projection sup- ported by a central rib is developed. This specimen has been referred to this species, since these differences probably are due to regulatory adjustments fol- lowing binary fission. However, since the regulatory structural changes that take place at binary fission are unknown, this assignment must be regarded as tenta- tive. The specimen is not included in the description given above, and its locality is omitted from the account of the occurrences. Its length is 84 ix, its greatest depth, 78 p.; its cingular lists are ribbed. It was taken at Station 4687 of the Expedition, in a haul from 300-0 fathoms; surface temperature, 73°. Phalacroma limbalum is structurally closely related to P. hipartitum. These species resemble each other in the following respects: — (1) the body is sub- cu'cular in lateral view; (2) the longitudinal axis of the body is perpendicular to the girdle; (3) the epitheca is high; (4) the cingular lists are subhorizontal, sub- SYSTEMATIC ACCOUNT. 165 equal, and about as wide as the transverse furrow; (5) the left sulcal list is angular at the posterior main rib and is contmued posteriorly by a parasagittal list that has one or two acute, wedge-shaped posterior sails with a more or less complex reticulum of irregular ribs; (6) the central portion of each valve, with the excep- tion of the transverse furrow, has a reticulum of closely placed, rather heavily margined polygons; the polygons are subequal, of moderate size, and most of them have a central pore ; in the transverse furrow and near the sagittal margins, the valves are porulate but not reticulate; (7) the size of the body is the same. It should be remembered, however, that several of these similarities are due to the fact that these two species in some respects are fairly low in the scale of the evolutionary development of the genus. The subcircular shape of the body in lateral view, the longitudinal axis of the body being perpendicular to the girdle, the relatively great height of the epitheca, the cingular lists being subhorizontal, subequal, and about as wide as the transverse furrow, and the angularity of the left sulcal list at the posterior main rib are more or less primitive characters and, therefore, must be considered to have relatively little importance in an attempt to determine the degree of relationship between these and other more or less primi- tive species of this genus. Phalacroma limhalum is more primitive than P. biparti- tum in having a relatively higher epitheca, and in the right parasagittal list having one, instead of two, acute triangular posterior sails. On the other hand, it is more advanced than the last species m having the two parasagittal lists encircle the entire body. Phalacroma limhatum is probably also rather closely related to P. pulchrum. This relationship is indicated by the following similarities: — (1) the body of these two species is subcircular in lateral view and lens-shaped m dorsoventral view; (2) on the hypotheca both have two parasagittal lists; the left parasagittal hst is narrow and of subuniform width throughout; the right forms a direct con- tinuation of the left sulcal list and has a large, acute, wedge-shaped posterior sail, which is furnished with a central rib ; (S) at least in some specimens of P. pulchrum (Jorgensen, 1923, fig. 18), the left sulcal list has behind the posterior main rib an accessory rib of the same kind as that found in P. limhalum. Phalacroma limha- tum is more primitive than P. pulchrum in having a relatively higher epitheca and subhorizontal cingular lists. It is more advanced in size of body, and in having parasagittal lists on the epitheca. With regard to the relationship between the species mentioned above and Dinophysis collaris (p. 295), see the section on comparisons. Occurrence: — Phalacroma limbalum is recorded at six of the 127 stations. 166 THE DINOPHYSOIDAE. There are 0, 1, 2, 2, 1, and stations on the six hnes of the Expedition. Of these six stations, two (4667, 4676) are in the Peruvian Current; one (4699) is in the Easter Island Eddy; and three (4681, 4705, 4722) are in the South Equatorial Drift. At one station (4681) the species is recorded from 300-0 fathoms and 800-0 fathoms. All the other records refer to hauls from 300-0 fathoms only. The temperature range of these six stations at the surface was 68°-75° ; the average was 71.2°. At two stations (4676, 4705) the frequency is 1%; at the remaining stations it is less. The species has been found only in the material of the Expedition. It was first recorded by Kofoid and Michener (1911) at Station 4667 of the Expedition, which thus is the type locality. Phalacroma bipartitum, sp. nov. Figure 21:2 Diagnosis: — Body subcircular in lateral outline, deepest in the middle; length : depth, 1 .04 : 1 . Posterior cingular list 0.30 the length of body from apex. Left sulcal list: distance between Ri and R3 is 0.41 the length of body; R2 is 0.13 and R3 is 0.25 the greatest depth of body; margin acuminate at R3 at angle of 40°; R3 incUned posteriorly at 20°. Around posterior portion of hypotheca there is on right ^'alve a parasagittal list forming direct continuation of left sulcal list ; para- sagittal list forms two subequal, acute, wedge-shaped posterior sails, one on each side of midline, both with irregularly anastomosing ribs; length of sails equals length of R3; angles at their tips, 30°-40°; width of Hst between sails and between ventral sail and R3 is 0.20 the length of R3. Central portion of each valve reticu- lated with heavily margined polygons of moderate size. Length, 68 ti. Eastern tropical Pacific. Description: — A medium-sized species, the body of which is subcircular in lateral outline, about as long as deep and deepest Hear the middle. The ratio between the length and the greatest depth of the body is 1 .04 : 1 . The longitudinal axis of the body is perpendicular to the girdle. The epitheca is 0.87 as deep as the hypotheca, strongly and evenly convex, dome-shaped, highest in the center, and very prominent above the anterior cingular list. The transverse furrow is slightly convex; and its width is 0.37 the greatest height of the epitheca. The posterior cingular list is 0.30 the length of the body from the apex. The hypotheca is symmetrical; its dorsal, posterior. SYSTEMATIC ACCOUNT. 167 and ventral margins are well and evenly convex, and confluent. In the type specimen the posterior end of the body is slightly narrower than the anterior. The cingiilar lists are subhorizontal and subequal; their width about equals the width of the transverse furrow; their structure is unknown. The right sulcal list extends to a point about halfway between the fission rib and the posterior mam rib of the left sulcal list ; it is of subuniform width throughout the greater part of its length, and its greatest width is somewhat less than the length of the fission rib of the left sulcal list; its free margin is sigmoid, being slightly concave anteriorly and rather strongly convex posteriorly. The left sulcal list is of moderate length and width. The distance between the anterior and posterior main ribs is 0.41 the length of the body. The anterior main rib and the fission rib are subequal and 0.13 the greatest depth of the body; the posterior main rib is 0.25 the greatest depth of the body; behind the posterior main rib the list de- creases suddenly in width. The free margin of this list is gentlj' concave between the anterior main rib and the fission rib as well as between the fission rib and the posterior main rib ; at the posterior main rib it is acuminate and forms an angle of about 40°; behind the posterior main rib it is gently concave. The main ribs of this list are of moderate strength and almost straight, and none of them is club- shaped or otherwise modified. The distance between the anterior main rib and the fission rib is about 0.50 the distance from the anterior to the posterior main rib. The posterior main rib has a posterior inclination of about 20°. There are no ribs except the three main ribs, but, judging by the short projections from the an- terior side of the posterior main rib in the drawing of the type specimen (Figure 21:2), this list probably has a faint reticulation. On the right valve there is a parasagittal list, which forms a direct continuation of the left sulcal list, runs around the posterior portion- of the hypotheca and extends to the posterior end of the dorsal margin of the hypotheca. The parasagittal list is characterized by two subequal, acute, wedge-shaped posterior sails, one on either side of the mid- line, and both furnished with irregularly anastomosing ribs. The length of these sails about equals the length of the posterior main rilj of the left sulcal list; and the angles at their tips are about 30°-40°. The width of the parasagittal list, between the left sulcal list and the ventral sail and between the two sails, is about 0.20 the length of the posterior main rib of the left sulcal list. It is not known whether there is any parasagittal list on the left ^•alve of the hypotheca; nor whether the parasagittal list of the right valve ever extends farther on the dorsal side than in Figure 21:2 (as in the closely related Phalacroma limbaimn). The epitheca had no parasagittal lists in the type spechnen. 168 THE DINOPHYSOIDAE. The structure of the theca is about the same as in Phalacroma limhatum; i.e., the central portion of each valve, with the exception of the transverse furrow, has a reticulum of closely placed, rather heavily margined polygons. The poly- gons are subequal and of moderate size, and most of them have a central pore; on each valve about thii'ty polygons border the posterior side of the transverse furrow. In the transverse furrow and near the sagittal margins the valves are porulate, but not reticulate. In the transverse furrow there are two transverse rows of fine pores, on each valve about forty to fifty pores in each row. JNIegacytic stages were not found. The proportions of the type specimen were measured. Dimensions: — Length of body, 68.0 n. Greatest depth of body, 65.5 m- Comparisons: — The description of the type is incomplete in some respects; e.g., the shape of the body in dorsoventral view and the structure of the cingular lists are unknown ; and the number and the extension of the parasagittal lists are uncertain. The structurally closest-known relative of Phalacroma bipartitum is P. lim- hatum (see p. 164). The former is more advanced than the latter in ha^'ing a relatively lower epitheca and in having a parasagittal list with two, instead of one, acute, triangular posterior sails. It is more prmiitive in having the para- sagittal list of the hypotheca relatively shorter and in lacking parasagittal lists on the epitheca. It should be noted, however, that the extension of the parasagit- tal list of the hypotheca presumably is variable (see Dinophysis collaris, p. 295). Phalacroma bipartitum resembles Dinophysis collaris in having the parasagit- tal list of the right valve furnished with two subequal and triangular posterior sails. Whether or not this similarity is an indication of a close relationship cannot be decided. Dinophy.sis collaris is more advanced than Phalacroma bipartitum in the rather irregular shape of its body in lateral \-iew, in the reduced height of its epitheca, and in its larger and more differentiated cingular and sulcal lists. Occurrence: — This species is recorded at only one (4736, the type locality) of the 127 stations, on the fifth line of the Expedition, in the South Equatorial Drift, from 300-0 fathoms, and at a surface temperature of 81°. The frequency is less than 1 % (one specimen). Phalacroma pulchrum Kofoid and jNIichener Plate 3, fig. 1, 6. Figure 21:3 Phnlacroma pxdchra Kofoid & Michener, parlim, 1911, p. 290, 291. Phalacroma cireumxuiiim Jorgensen, ■parlim, 192.3, p. 17, 4.3, fig. 18. Phalacroyna ptdchrtun Jorgensen, 1923, p. 18. SYSTEMATIC ACCOUNT. 169 Diagnosis: — Body subcircular in lateral outline, subtruncate anteriorly, deepest near the middle; length: depth, 0.99-1.03:1. In dorsal view narrowly obovate, 1.80 times longer than wide. Posterior cingular list 0.19-0.24 the length of body from apex; epitheca sometimes hardly visible above anterior cingular list. Cingular lists somewhat inclined anteriorly, without ribs. Left sulcal list: distance between Ri and R, is 0.41-0.43 the length of body ; R2 is 0.14-0.16, and R3 is 0.33-0.38 the greatest depth of body; margin forms angle of 50°-60° at R3; R3 inclined posteriorly at 35°-40°. Two parasagittal lists on hypotheca; the left very narrow, sometimes possibly absent. The right continues left sulcal list; dorsally its maximum width is subequal to or less than half the width of trans- verse furrow; on antapex it forms an acute, wedge-shaped posterior sail directed posteriorly. Sail, when fully developed, 0.33-0.43 the greatest depth of body in length, with central rib whose base might be divided; angle at tip, 30°-40°. Ventrally to sail, width of list is 0.50-1.75 the width of transverse furrow; with about 8-11 short riblets. Theca with fine reticulation. Length, 51.2-52.5 p. Tropical, subtropical, and warm-temperate seas. Description: — A rather small species, the body of which is subcircular in lateral outline, subtruncate anteriorly, and deepest near the middle. The ratio between the length and the greatest depth of the body is 0.99-1.03: 1. The longi- tudinal axfs is perpendicular to the girdle. The epitheca is 0.77-0.80 as deep as the hypotheca, highest in the center, of moderate convexity to rather flat, and but slightly elevated above the anterior cingular list. The transverse furrow is flat, or slightly convex to concave, and its width is 0.8-2.0 the greatest height of the epitheca. The posterior cingular list is 0.19-0.24 the length of the body from the apex. The hypotheca is almost sym- metrical; sometimes, as in the type specimen, it is subcircular, with confluent dorsal, posterior, and ventral margins; sometimes, as in the specimen figured by Jorgensen (1923, fig. 18), its ventral margin is flattened, and its postmargin forms a broadly rounded, subrectangular corner. In dorsoventral view the body is narrowly obovate, about 1.80 times longer than wide, widest somewhat in front of the middle, somewhat more broadly rounded anteriorly than posteriorly, narrowly rounded posteriorly, and with evenly convex side contours. The cingular lists have an anterior inclination of 20°-40°; the anterior is about as wide as the transverse furrow, the posterior often is slightly narrower. The sulcus is about half as long as the hypotheca. The flagellar pore is located at a distance about eciualing its own diameter behind the junction of the cingulum and the sulcus. On the ventral side of the left valve a small pore is found near the 170 THE DINOPHYSOIDAE. sagittal suture, just in front of the anterior cingular list. The right sulcal Ust sometimes ends at or somewhat behmd a point midway between the fission rib and the posterior main rib of the left sulcal list ; sometimes it extends even to the last-mentioned rib; its anterior half is about as wide as the transverse furrow; posteriorly it decreases gradually in width. The left sulcal list is rather large ; the distance between its anterior and posterior main ribs is 0.41-0.43 the length of the body. The anterior main rib is 0.14-0.15, the fission rib 0.14-0.16, and the posterior main rib 0.33-0.38 the greatest depth of the body. Behind the posterior main rib this list decreases suddenly in width. Between the anterior and posterior main ribs the free margin of this Ust either is nearly straight or slightly sigmoid ; in the latter case it is slightly concave anteriorly and convex posteriorly, or vice versa; at the posterior main rib it is somewhat acuminate and forms an angle of 50°-60°; behind the last-mentioned rib it is gently concave. The main ribs of this list are of moderate strength and straight or almost so; none of them is club- shaped or otherwise modified. The distance between the anterior main rib and the fission rib is 0.33-0.37 the distance between the anterior and posterior main ribs. The posterior main rib has a posterior inclination of 35°-40°. Somewhat behind the posterior main rib there is in some specimens (Jorgensen, 1923, fig. 18) a fine rib with a posterior inclination of about 75°. Except the ribs mentioned above, the left sulcal list lacks structural differentiations. There are two para- sagittal lists on the hypotheca, but none on the epitheca. The left one of these two lists extends, on the dorsal side of the body, from the posterior cingular list to the antapex; it is very narrow, of subuniform width throughout its entire length, and furnished with a few cross-ribs; its maximum width is less than half the width of the transverse furrow; in some specimens (Jorgensen, 1923, fig. 18) it may be absent. The right parasagittal list forms a direct continuation of the left sulcal list; sometimes, as in the type specimen, it extends to the posterior cingular list; sometimes, as in the specimen figured by Jorgensen (1923, fig. 18), it is not developed on the dorsal side of the hypotheca. On the dorsal side this list is narrow, about as wide as or slightly wider than, the left list, of subuniform width throughout, and furnished with a few cross-ribs; posteriorly it forms an acute, wedge-shaped posterior sail directed posteriorly. The sail, when fully developed, is 0.33-0.43 the greatest depth of the body in length, and has a central rib which arises from the antapex, and whose base might be divided; the angle at its tip is 30°-40°. Between this rib and the posterior main rib of the left sulcal list, the right parasagittal list has a minimum width equaling 0.50-1. 75 the width of the transverse furrow, and its margin is evenly concave, or slightly undulating SYSTEMATIC ACCOUNT. 171 as in the type specimen ; along the base of this portion of the hst there are 8-1 1 short, nearly equidistant, simple or bifurcate riblets; see also the accessory rib of the left sulcal list. The thecal wall is finely reticulate (Jorgensen, 1923, fig. 18) and furnished with scattered pores. Sometimes the reticulation is so faint as to make it difficult to detect. Megacytic stages were not recorded. The dimensions of the type and of the specimen figured by Jorgensen (1923, fig. 18) were measured. Dimensions: — Length of body, 51.2 yu. Greatest depth of body, 51.6 ai. Specimen figured by Jorgensen (1923, fig. 18) : Length of body, 52.5 tx. Greatest depth of body, 51.0 m- Variations: — Very little is known about the variability of this species. The specimen figured by Jorgensen (1923) is somewhat more pointed posteriorly than the type specimen, and its right sulcal list is somewhat smaller. The struc- ture of the thecal wall is sometimes fairly well developed, sometimes almost in- visible. Comparisons: — The description and figures are based on the type material. The structurally close.st-known relative of Phalacroma inilchrum is P. lim- batum. The former can easily be distinguished by its low epitheca and by the absence of parasagittal lists from the epitheca (see P. limhatum, p. 164). Sijnonymy: — Some of the specimens on which Kofoid and Michener (1911) based their description, have in the present paper been referred to P. cimcolus, sp. nov. Phalacrovm circumsutuvi Jorgensen (1923) includes P. circumsuium Karsten and P. pulchrmn Kofoid and Michener. Occurrence: — Phalacroma pulchrum is recorded at six of the 127 stations. There are 0, 0, 0, 4, 1, and 1 stations on the six lines of the Expedition. Of these six stations, one (4699) is in the Easter Island Eddy; one (4713) is in tlie Gala- pagos Eddy; four (4701, 4705, 4730, 4740) are in the South Equatorial Drift. All the records refer to hauls from 300-0 fathoms. The temperature range of these sLx stations at the surface was 72°-81°; the average was 75.9°. The frequency is less than 1 % in all the cases recorded. The species was first recorded by Kofoid and Michener (1911) at Station 4699, the type locality. Later Jorgensen (1923) found it in the Mediterranean, the Thor Expedition, and possibly also in the Guinea Current, the German South Pole Expedition. 172 THE DINOPHYSOIDAE. This is a eupelagic species widely distributed in tropical, subtropical, and warm-temperate seas. The most outstanding peculiarities of its distribution in the Eastern Pacific are its absence from surface catches, as well as from the California Current, Mexican Current, Panamic Area, and Peruvian Current. Its optimum habitat probably is in deeper waters within the levels of photosynthesis, and in the most distinctively tropical regions. 8. DoRYPHORUM Group. Of the five species of this group only Phalacroma pugiunculus was not found by the Expedition. Phalacroma mucronatum, sp. no v. Figure 22:4, 6, 8 Diagnosis: — Body subcircular in lateral outline, sometimes slightly deeper anteriorly than posteriorly; length: depth, 1.07-1.11:1. Posterior cingular list 0.33-0.41 the length of body from apex. Left sulcal list 0.50-0.54 the length of body; distance from Ri to Rs is 0.33-0.37 the length of body; Ro is about 0.17, and R3 about 0.30 the greatest depth of body; margin forms angle of 80°-90° at Rs; R3 inclined posteriorly at 30°-40°. With triangular posterior sail, placed on antapex and directed posteriorly; when fully developed, its length is 0.28-0.40 the greatest depth of body, and it is somewhat narrower than long; without or with central rib ; well separated from left sulcal list. Theca porulate (and finely areolate?). Length, 35.0-45.4 fx. Eastern tropical Pacific. Description: — A small species, the body of which is subcircular in lateral outline, deepest near the middle, and sometimes slightly deeper anteriorly than posteriorly. The ratio between the length and the depth is 1.07-1.11:1. The longitudinal axis of the body is perpendicular to the girdle. The epitheca is 0.89-0.94 as deep as the hypotheca, evenly and moderately convex, highest in the center, and moderately elevated or rather prominent above the anterior cingular list. The transverse furrow is flat or slightly convex, and its width is 0.5-1.0 the greatest height of the epitheca. The posterior cingular list is 0.33-0.41 the length of the body from the apex. The hypotheca is symmetrical, with well or moderately rounded dorsal and ventral margins; the posterior margin is rather strongly convex and confluent with the dorsal and ventral margins. The posterior portion of the hypotheca is of about the same width as, or slightly nar- ower than, the epitheca. The shape of the body in dorsoventral view is not known with certainty, as all the specimens drawn in this aspect were megacytic. It SYSTEMATIC ACCOUNT. 173 appears to be rather narrowly obovate, widest somewhat m front of the middle, with rounded apices, and with the antapical end somewhat narrower than the epitheca. The cingular lists are subhorizontal, subequal, and about as wide as the transverse furrow; their structure is unknown. The right sulcal list is unknown. The left sulcal list is of moderate length and width. Its length is 0.50-0.54 the length of the body, and the distance between the anterior and posterior main ribs is 0.33-0.37 the length of the body. The anterior main rib is 0.15-0.20, the fission rib about 0.17, and the posterior main rib about 0.30 the greatest depth of the body. Behind the posterior main rib this list decreases suddenly in width. Between the anterior and posterior main ribs the free margin of this list is almost straight or slightly concave ; at the posterior main rib it forms an angle of 80°-90° ; behind the last-mentioned rib it is almost straight or slightly concave or convex. The main ribs of this list are of moderate strength, straight or almost so, and not club-shaped or otherwise modified. The distance between the anterior main rib and the fission rib is about 0.50 the distance between the anterior and posterior main ribs. The posterior rib has a posterior inclination of 30°-40°. Except for the three main ribs, this list appears to lack structural differentiations. On the right valve there is an acute, triangular posterior sail, which is located on the ant- apex and is directed posteriorly. When fully developed, its length is 0.28-0.40 the greatest depth of the body, and it is somewhat narrower at its base than it is long; sometimes its length is about twice the basal width. Its margins are almost straight or gently concave, convex or sigmoid, and the angle at its tip is 15°-40°. In some specimens this sail lacks structural differentiations, in others it has a central rib which may be divided at the base. The sail is well separated from the left sulcal list. The distance between these two structures is variable ; in the speci- mens examined it equals at least half the basal width of the sail. There are no parasagittal lists. The thecal wall has scattered pores. Ai'eolation was not seen, but might have been overlooked. Megacytic stages have been seen (Figure 22: 6). The proportions of three specimens were measured. Dimensions: — Length of body, 35.0-45.4 yu (average, 40.7 //; type, 38.8 m). Greatest depth of body, 32.6-41.2 m (average, 36.2 m; type, 34.9 n). Variations: — The five specimens examined are very similar. They exhibit variations mainly in the size of the body, the relative height of the epitheca, and the shape and structure of the posterior sail. 174 THE DINOPHYSOIDAE. Comparisons: — The species is established on outline drawings of five Ex- pedition specimens. It probably has about the same habitus as the ancestral form from which Phalacroma doryphorum, P. circumsutum, P. cuneolus, and P. pugiunculus origi- nated. The following of its characters are more or less prmiitive : its small size, its subcii'cular shape in lateral view, the relatively great height of its epitheca, the fact that its left sulcal list is relatively long and not unusually wide posteriorly, and that the posterior main rib of this list is not club-shaped. Phalaa'oma mucro- FiGUBE 22. — 1, 2, 3, 5, 7, Phalacroma cuneolus, sp. nov. 1, 2, left lateral view; 3, right lateral view; 5, 7, dorsal view (megacytio). Surface markings, areolation, indicated only on small portion of theca in 1. 1, 5, from type specimen. X 430. Station 4711 (300-0 fathoms). 4, 6, 8, Phalacroma mucronalum, sp. nov. 4, 8, left lateral view; 6, dorsal view (megacytic). X 430. 4, 6, typo specimen, from Station 4730 (300-0 fathoms); 8, from Station 4638 (300-0 fathoms). nalwm differs from the four species mentioned in its smaller size and in the sub- circular shape of its bod}'. Phalacroyna doryphorum appears to be its closest relative. Occurrence: — Phalacroma mucronalum is recorded at four of the 127 stations. There are 0, 1, 1, 1, 1, and stations on the six lines of the Expedition. Of these four stations, one (46.38) is in the Panamic Area, and three (4681, 4711, 4730) are in the South Equatorial Drift. All records refer to hauls from 300-0 fathoms only. Station 4730 is the type locality. The temperature range of these four stations at the surface was 68°-79°; the average was 74.5°. At one station (4638) the frequency is 2 % ; in the remaining cases it is less than 1 %. SYSTEMATIC ACCOUNT. 175 Phalacroma doryphorum Stein Figure 23: 1-5; 24 Phalacroma doryphorum Stein, 1883, p. 23, pi. 19, fig. 1-1. Butschli, 1885, p. 942. Schutt, 1895, p. 50, 89, pi. 4, fig. 19; 1899, p. 42, pi. 6, fig. 17. Murr.w & Whittinq, 1899, p. 330, tab. 1-9. Lemmer- MAKN, 1899a, p. 319, 320, 372; 1901a, p. 372; 1905a, p. 35. Schroder, 1900a, p. 19; 1906a, p. 325, 327, 330; 1911, p. 25, 37. Cleve, 1900b, p. 1031; 1901a, p. 17; 1901c, p. 270; 1902b, p. 36; 1903b, p. 347. Schmidt, 1901, p, 137. Ostenfeld & Schmidt, 1901, p. 176. Entz, 1902b, p. 94; 1905, p. HI. LoHMANN, 1902, p. 53; 1908a, p. 161; 1920, p. 484, 492, 508. P.will.^rd, 1905, p. 58, 81, 102; 1909, p. 283; 1915a, p. 2, fig. B; 1916, p. 47, 49, 50, 52, 60, fig. 12, pi. 3, fig. 8. K.^jisten, 1906, p. 185, 187, 189, 191; 1907, p. 228, 238, 240, 247, 257, 285, 295, 304, 318, 321, 334, 337, 340, 341, 343, 347, 348, 349, 352, 354, 355, 421, 438, 464, 471. Nathansohn, 1908, p. 604; 1909, p. 47; 1910a, p. 14, 17, 20; 1910b, p. 61. Graf, 1909, p. 136. Stuwe, 1909, p. 252, 287. Hensen, 1911, p. 166, tab. 15. Okamitra, 1912, p. 18, pi. 5, fig. 77. Schiller, 1912, p. 27. Forti, 1922, p. 104, 190, 208, fig. 107. Johqensen, 1923, p. 16, 17, 37, 44, fig. 17. Forti & Issel, 1923, p. 3. Diagnosis: — Body obovate or subovate in lateral outline, deepest at or gener- ally somewhat behind girdle ; length : depth, 1 .05-1 .17:1. In dorsal view narrowly obovate or subcuneate; narrowly rounded or subacute posteriorly. Posterior cingular list 0.17-0.37 the length of body from apex. Cingular lists without ribs. Left sulcal list rather short, often high posteriorly; length, 0.41-0.55 the length of body; distance between Ri and Rs is 0.26-0.38 the length of body; R2 is 0.11- 0.17, R3 is 0.24-0.45 the greatest depth of body; margin forms angle of 50°-90° at R3; R3 inclined posteriorly at 15°-40°, often club-shaped. With triangular pos- terior sail, either on or usually somewhat ventrally to antapex, and inclined ventrally at 0°-35°; when fully developed, its length is 0.20-0.37 the greatest depth of body, and it is about as wide as long or slightly narrower; with or without central rib or reticulation; usually well separated from left sulcal list. Theca finely and closely areolate. Length, 54-86 m- Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, the body of which is obovate or sub- obovate in lateral outline, deepest at or m most specmiens somewhat behind the girdle and 1.11 (1.05-1.17) times longer than deep. The longitudinal axis of the body is perpendicular to the girdle. The epitheca is evenly and moderately convex to rather flat, highest in the center, and moderately or but slightly elevated above the anterior cingular list. In the Expedition specimens it is about 0.90 (0.85-0.92) as deep as the hypotheca; in the specimen represented by Stein (1883, pi. 19, fig. 2), on the other hand, the epitheca and the hypotheca are of about equal depth. The transverse furrow is flat or slightly convex, and its width is about 0.33-0.50 the greatest height of the epitheca. The posterior cingular list is 0.31 (0.17-0.37) the length of the body 176 THE DINOPHYSOIDAE. from the apex. The hypotheca is symmetrical; sometimes it is, as Jorgensen (1923, p. 16) expresses it, of an "oval wedge-shape," with rather flat dorsal and ventral margins; sometimes it is regularly' oval, with well or moderately rounded dorsal and ventral margins; the posterior margin is strongly convex and confluent with the dorsal and ventral margins. The posterior portion of the body is strik- ingly narrower than the anterior. In dorsoventral view (Stein, 1883, pi. 19, fig. 4; Okamura, 1912, pi. 5, fig. 77b) the body is narrowly obovate or subcuneate, widest somewhat in front of the middle, and narrowly rounded or subacute pos- teriorly. The cingular lists are subequal and subhorizontal, or slightly inclined an- teriorly; their width about equals the width of the transverse furrow, and they are hyaline, and without ribs or other structural differentiations. The right sulcal list ends at a point about halfway between the fission rib and the posterior main rib of the left sulcal list, or it extends to or even slightly beyond the posterior main rib of the last-mentioned list ; in some specimens it is subtriangular, decreas- ing gradually in width posteriorly ; in other specimens it is of almost equal width throughout its anterior half or even throughout the greater portion of its length; anteriorly it is about as wide as the transverse furrow. The left sulcal list is rather short, and often comparatively high posteriorly. Its length is 0.46 (0.41-0.55) the length of the body, and the distance between the anterior and posterior main ribs is 0.29 (0.26-0.38) the length of the body. The anterior main rib is 0.1 1 (0.08- 0.14), the fission rib 0.13 (0.11-0.17), and the posterior main rib 0.31 (0.24-0.45) the greatest depth of the body. Behind the posterior main rib this list decreases suddenly in width. Between the anterior and posterior main ribs the free margin of this list often is almost straight ; sometimes it is gently concave or convex, or it is slightly sigmoid, concave anteriorly and convex posteriorly; at the posterior mam rib it forms an angle of 70° (50°-90°) ; behind the last-mentioned rib it is al- most straight, or gently concave or convex. The main ribs of this list are of moderate strength and straight or nearly so ; in most of the specimens examined the posterior main rib is club-shaped (see also Schiitt, 1895, pi. 4, fig. 19: 2, and Jorgensen, 1923, fig. 17); in the specimens drawn by Stein (1883), on the other hand, this rib is not club-shaped. The distance between the anterior main rib and the fission rib is 0.35-0.50 the distance between the anterior and posterior main ribs. The posterior main rib has a posterior inclination of 25° (15°-40°). Except for the three main ribs, this list seems to be without structure in most specimens; sometimes it may have a very faint reticulation. On the right valve there is an acute, triangular, posterior sail, which is situated either on or usually SYSTEMATIC ACCOUNT. 177 somewhat ventrally to the antapex, and is mcHned ventrally at 0°-35°. The size of this sail is somewhat variable, probably due to the fact that m each binary fission one of the daughter schizonts has to form this structure anew. When fully developed, its length is 0.20-0.37 the greatest depth of the body, and it is about as wide at the base as it is long or slightly narrower. Its margins are almost straight, or gently concave, convex, or sigmoid, and the angle at its tip is 40°-90°. In some specimens the sail has a central rib, in others it is more or less reticulated, especially in its central portion ; sometimes both the central rib and the reticula- tion are developed, sometimes no structure can be distinguished. In most speci- mens the sail is well separated from the left sulcal list; the distance between these two structures is variable, but usually it equals at least half the basal width of the posterior sail. Only in one specimen (Figure 23 : 5) were these structures con- nected, and this specimen appeared still to be in a condition of reorganization fol- lowing binary fission. There are no parasagittal lists. The thecal wall is finely and closely areolate and has scattered pores; the areoles are subequal or somewhat unequal in size. In the transverse furrow there are two rows of pores. Megacytic stages have been recorded (see Pavillard, 1916, fig. 12, and J5r- gensen, 1923, p. 17). The proportions of seven Expedition specimens and of the specimens drawn by Stein (1883), Schutt (1895), Okamura (1912), and Jorgensen (1923) were measured. Dimensions: — Length of body, 62.7-73.8 m (average, 67.2//). Greatest depth of body, 56.7-02.8 m- Though the size of the type specimen figured by Stein (1883, pi. 19, fig. 1) is not known it probably was somewhere between 69 fx and 104 fi. long; and the specimen represented by Stein (1883, p. 31, pi. 19, fig. 2) was somewhere between 86 ju and 128 m long. The specimen figured by Schutt (1895, pi. 4, fig. 19: 2) was about 70.5 ^ long and 61.6 ix deep; Okamura's (1912, pi. 5, fig. 77) about 54 yu long and 48.7 ^ deep; and Jorgensen's (1923) about 68 m long and 62 fi deep. According to Lohmann (1902, p. 53), this species is 86 M long. Variations: — In spite of the fact that Phalacroma doryphorum is "a very characteristic and easily recognizable species " (Jorgensen, 1923, p. 16), it exhibits a considerable variability in several respects. The following characters are more or less strikingly variable : — the size and shape of the body, the rela- tive height of the epitheca, the shape of the left sulcal list, the length and shape of the posterior main rib of this list, the position, direction, and struc- 178 THE DINOPHYSOID.\E. ture of the posterior sail, and the distance between this structure and the left sulcal list. Comparisons: — Under the name of Phalacroma doryphorum, Stein (1883, pi. 19, fig. 1, 2, 3) figures three specimens of fairly different habitus. One, the type specimen (pi. 19, fig. 1), has a regularly obovoidal body, deepest somewhat behind the girdle, and with comparatively high epitheca. The others (pi. 19, fig. Figure 23. — 1-S, Phalacroma danjiiJiorum .Stein, right lateral view. Surface markings, areolation, and jjorulation indicated only on .small portion of theca in 1 and 5. X 430. 1, from Station 4737 (300-0 fathoms); 2, from Station 4590 (300-0 fathoms); 3, 4, from Station 4664 (300-0 fathom.s); .5, from Station 4681 (300-0 fathoms). 6, Phalacroma cir- cumautuia Karsten, right lateral view. X 430. Station 46.38 (300-0 fathoms). 2, 3) are deepest at the girdle, and have the epitheca rather flat and the hypotheca of an oval wedge-shape. The question as to whether or not these differences are specific cannot be settled. Most of the specimens in the material of the Expedi- tion assigned to P. doryphorum agree fairly closely with the type specimen as far as the shape of the body is concerned, but differ in the shape and relative length of the left sulcal list and of its posterior main rilj, and in the position and direction of the posterior sail. In spite of these differences our assignments may be re- garded as fairly certain. The specimens figured by Schiitt (1895), Okamura (1912), and Jorgensen (1923) fall within the range of variations established for the Expedition specimens. The structurally closest-known relative of Phalacroma doryphorum is P. circumsutum. The first species differs from the last mainly in ha\'ing the left SYSTEMATIC ACCOUNT. 179 sulcal list and the posterior sail well separated; furthermore, the posterior main rib of its left sulcal list generally is club-shaped. Next to Phalacroma circumsutum, P. mucronatum appears to be the nearest- known relative of P. doryphormn. Phalacroma mucronatum probably agrees fairly closely with the ancestral form from which P. doryphormn evolved, as indicated by the following characteristics : — it is a small species, 35.0-45.4 m long, sub- circular in lateral view, with rather high epitheca, with the left sulcal list rela- tively long and not exceptionally wide posteriorly, and with the posterior main rib of this list not club-shaped. Phalacroma cuneolus and P. pugiunculus may possibly also belong to the same evolutionary series as P. doryphormn; the last is readily distinguished from these two species by its regularly obovoidal body and wider posterior sail. With regard to the possible relationship between Phalacroma doryphormn and P. ovum, see the section on comparisons (p. 120). Synonymy: — With regard to Jorgensen's (1923, pi. 17) assumption that figure G: 2, of Dinophysis galea Pouchet (1883), represents a specimen of Phala- croma doryphorum, see P. circumsutum, p. 184. Occurrence: — Phalacroma doryphorum is recorded at seventy-five of the 127 stations. There are 16, 21, 8, 9, 12, and 9 stations on the six lines of the Expedi- tion. Of these seventy-five stations, one (4583) is in the California Current; twelve (4587, 4588, 4590, 4592, 4594, 4596, 4598, 4600, 4604, 4605, 4545, 4546) are in the Mexican Current; nine (4609, 4611, 4613, 4617, 4619, 4631, 4634, 4637, 4644) are in the Panamic Area; twenty (4646, 4647, 4648, 4650, 4651, 4652, 4655, 4659, 4660, 4661, 4662, 4663, 4664, 4665, 4667, 4669, 4671, 4675, 4676, 4678) are in the Peruvian Current; five (4689, 4091, 4695, 4697, 4699) are in the Easter Island Eddy; two (4713, 4715) are in the Galapagos Eddy; twenty (4679,4681, 4683, 4701, 4707, 4709, 4711, 4717, 4719, 4720, 4721, 4722, 4724, 4728, 4730, 4732, 4734, 4737, 4739, 4740) are in the South Equatorial Drift; three (4742, 4743, 4540) are in the South Equatorial Current; two (4541, 4542) are in the Equatorial Counter Current; and one (4543) is in the North Equatorial Current. There are twenty-six records from the surface (Stations 4583, 4588, 4592, 4596, 4600, 4604, 4611, 4617, 4619 [Salpa], 4631, 4644, 4648, 4660 [Salpa], 4664 [Salpa], 4669, 4675, 4676, 4678, 4720 [Salpa], 4743, 4540, 4541, 4542, 4543, 4545, 4546) ; at four of these stations (4648, 4664, 4675, 4676) the species was taken in hauls from 300-0 fathoms as well as at the surface; at the other twenty-two stations in sur- face hauls only. At one station (4652) the species is recorded from 100-0 fathoms; at one station (4737) from 100-0 fathoms and 300-0 fathoms; at one station 180 THE DIXOPHYSOIDAE. (4655) from 400-0 fathoms; at two stations (4701, 4724) from 300-€ fathoms and 800-0 fathoms; at three stations (4647, 4751, 4662) from 800-0 fathoms only. All the remaining records refer to hauls from 300-0 fathoms only. The species is also recorded from surface waters in Acapulco Harbor, off the Mexican Current. This station is not included in the 127 stations mentioned above. The temperature range of these seventy-five stations at the surface was 65°- 85°; the average was 75.3°. At the twenty-six stations in the surface catches of Figure 24. — Occurrence of PhaUicroma dorijphorwn Stein. Large, .solid circles indicate records from vertical hauls; squares, records from surface hauls; triangles, records from both vertical and surface hauls; small, sohd circles, stations at which this species was not found; small, open circles, stations from which no plankton catches were examined. which this species was found, the surface temperature ranged from 07° to 84°; the average was 76.9°. At Acapulco it was 83°. For the surface catches the following frequencies are recorded: — 7% at one station (4546), 5% at one station (4619), 3% at one station (4604), 2% at two stations (4669, 4675), 1% at eight stations (4600, 4617, 4720, 4743, 4540, 4541, 4543, 4545), and less than 1% at the remaining stations. For the catches from 100, 300, 400, or 800 fathoms to the surface the records of frequency are as fol- lows:— 5% at one station (4663), 4% at one station (4590), 3% at five stations (4598, 4664, 4667, 4713, 4715), 2% at three stations (4675, 4689, 4699), 1% at SYSTEMATIC ACCOUNT. 181 nineteen stations (4605, 4613, 4634, 4637, 4647, 4648, 4651, 4671, 4676, 4679, 4691, 4695, 4697, 4701, 4719, 4722, 4730, 4737, 4739), and less than 1% at the remaining stations. For the catch made in Acapulco Harbor the frequency of 1 % is recorded. The species was first recorded by Stein (1883) "aus dem Atlantischen Meer und der Stidsee." Murray and Whitting (1899), who recorded it from the At- lantic, between lat. 43°4' N. and lat. 0°16' S., and from the Caribbean Sea, found it to occur "pretty constantly over the whole region examined." According to Cleve (1901c, 1902b, 1903b) it occurs in the Atlantic, between lat. 57° N. and lat. 39° S., and in the Caribbean Sea; only one of Cleve 's several stations is located north of lat. 48° N., and this station, lat. 57° N., long. 14° W., is in the Gulf Stream. Hensen (1911) found it at a fairly great number of stations in various parts of the tropical and subtropical regions of the Atlantic. Lemmermann (1899a), Karsten (1906), and Stiiwe (1909) recorded it from the Gumea Current; Lohmann (1920) from the Brazil Current, lat. 15° S., long. 34° W.; Jorgensen (1923) from the Bay of Cadiz and off the southwest coast of Portugal. From the Mediterranean there are the followmg records. Jorgensen (1923) found it at a very great number of stations "throughout the whole of the Mediterranean." Cleve (1903b) recorded it at lat. 37° N., long. 2° W.-8° E.; Pavillard (1905, 1909, 1915a, 1916) in the Gulf of Lyons; Nathansohn (1908, 1909, 1910a) off Monaco; Forti (1922) in the Ligurian Sea; Schroder (1900a) at Naples; Entz (1902b, 1905), Schroder (1911), and Schiller (1912), in the Adriatic Sea. Cleve (1900b, 1903b) and Ostenfeld and Schmidt (1901) found it in the Red Sea; Ostenfeld and Schmidt (1901) and Schroder (l-906a) in the Gulf of Aden; Cleve (1901a, 1903b) and Schroder (1906a) in the Arabian Sea; Cleve (1901a) and Karsten (1907) in the Indian Ocean; Schroder (1906a) near Singapore; Schmidt (1901) in the Gulf of Siam; Okamura (1912) in Japanese waters; and Lemmermann (1899a) in the Pacific Ocean at lat. 6° N., long. 111° W. and lat. 12° N., long. 117° W. Most of the records referred to in the last paragraph were from surface hauls. The only records of closing-net hauls published as yet are the following by Karsten (1907) :— Station 227, lat. 2°56' S., long. 67°59' E., 1000-800 m.; Station 228, lat. 2°38' S., long. 65°59' E., 420-350 m.; Station 229, lat. 2°38' S., long. 63°37' E., 1600-1400 m.; Station 2.39, lat. 5°42' S., long. 43°36' E., 120-105 m.; Station 268, lat. 9°6' N., long. 53°41' E., 105-88 m. and 63-46 m. All the specunens recorded were reported as "living." 182 THE DINOPHYSOIDAE. According to these authors, this species occurs in waters of the following temperatures and salinities. Number and Number and Mean of Mean of Temperature Range Observations Salinity Range Observations Murray and AMiitting (1899) OO'-SS" Cleve (1901a) 79.r-86.7° 34.77-34.69 Cleve (1901c) 57.9°-82.8'' 55 71.6° 33.88-38.48 41 35.96 Cleve (1902b) 68.1° 11 36.12 Cleve (1903b) 60.3°-84.5° 14 75.9° 35.97-40.70 14 37.08 Ostenfeld & Schmidt (1901) 72.1''-S0.r Stuwe (1909) 6S.5''-75.2° Of the authors who have contributed toward our knowledge of the distribu- tion of this species only Stein (1883): Pavillard (1916), Okamura (1912), Forti (1922), and Jorgensen (1923) give descriptions or drawings by means of which their determinations of this species may be judged. This species appears to be one of the most common representatives of Dinophysoidae (Jorgensen, 1923, p. 17). It is eupelagic and widely distributed in tropical, subtropical, and warm-temperate seas. Occasionally it is carried by warm currents into cooler regions (Cleve, 1901c). According to the Expedition records it is the most common species of this tribe and is almost evenly distributed throughout the area investigated. Although it probably has its optimum habitat in deeper waters, within the levels of photosynthesis, it is rather frequent at the surface. Phalacroma doryphorum, P. rapa, P. cuneus, and P. favus occur more frequently in the surface catches than any other species of Phalacroma; the num- bers of surface records are 26, 22, 13, and 6, respectively; there are more surface records of P. doryphorum than of any other species of Phalacroma. Phalacroma circumsutum Karsten Figure 23:6 Phalacroma rirrumfiuttim Karsten, 1907, p. 421, pi. 53, fig. 8. Steuer, 1910, p. 476, 478, fig. 246a; 1911, p. 252, fig. 214a. Jorgensen, 1923, pnrlim., p. 17, 43. ?Dinoph)jsis galea Pouchet, 1883, parlim, p. 426, fig. (1 : 2. Diagnosis: — Body obovate in lateral outline, deepest somewhat in front of middle; length: depth, 1.20-1.23: 1. Posterior cingular list 0.24-0.20 the length of body from apex. Cingular lists without ribs, sometimes inclined anteriorly at 10°-30°. Left sulcal list: distance between Ri and R3 is 0.33-0.38 the length of body; R2 is 0.20-0.22, R3 is 0.42-0.55 the greatest depth of body; margin acumi- nate at R3 at angle of 35°-7()°; R3 inclined posteriorly at 25°. With acute, almost equilaterally triangular posterior sail supported by strong central rib, which is 0.43 the greatest depth of body, placed somewhat ventrally to antapex and in- SYSTEMATIC ACCOUNT. 183 clined ventrally at 15°-20°; angle at tip of sail, 50°. Left sulcal list and posterior sail connected by list with minimum width 0.3-0.5 the width of transverse furrow, with or without parasagittal list along dorsal side of hypotheca. Theca finely and closely areolate. Length, 75.7-80.0 /i. Widely distributed in tropical, subtropical, and warm-temperate seas. Description: — A medium-sized species, with the body obovate in lateral outline, deepest somewhat in front of the middle and 1.20-L23 times longer than deep. The longitudinal axis of the body is perpendicular to the girdle. The epitheca is 0.87-0.90 as deep as the hypotheca, highest in the center, of moderate convexity or rather flat, and moderately or but slightly elevated above the anterior cingular list. The transverse furrow is flat or but slightly convex; and its width is 0.50-0.60 the greatest height of the epitheca. The posterior cingular list is 0.24-0.26 the length of the body from the apex. The hypotheca is symmetrical; its ventral, posterior, and dorsal margins are confluent; the ventral and dorsal margins are of moderate convexity; the posterior margin is strongly convex. The posterior part of the body is strikingly narrower than the anterior. The cingular lists are subequal, and either subhorizontal or inclined ante- riorly at about 10°-30°; their width about equals or somewhat exceeds the width of the transverse furrow ; and they appear to lack ribs and other structural differ- entiation. The right sulcal list extends almost to the posterior main rib of the left sulcal list; its anterior half is about as wide as the cingular lists, i.e., it is decidedly narrower than the left sulcal list; posteriorly the list decreases gradually in width. The left sulcal list is of moderate length and rather wide posteriorly. The dis- tance between the anterior and the posterior main ribs is 0.33-0.38 the length of the body. The anterior main rib is 0.18-0.19, the fission rib 0.20-0.22, and the posterior main rib 0.42-0.55 the greatest depth of the body; behind the posterior main rib the list decreases suddenly in width. The free margin of this list is gently concave or almost straight between the anterior main rib and the fission rib, as well as between the fission rib and the posterior main rib ; at the posterior main rib it is more or less acuminate and forms an angle of 35°-70°; behind the pos- terior main rib it is gently concave. The main ribs of this list are of moderate strength and none of them is club-shaped or otherwise modified; the anterior main rib and the fission rib are straight or almost so, the posterior main rib is gently concave posteriorly. The distance between the anterior main rib and the fission rib is 0.30-0.45 the distance from the anterior to the posterior main rib. The pos- terior main rib has a posterior inclination of about 25°. Disregarding the three main ribs, this list appears to lack structural differentiation. On the right valve 184 THE DINOPHYSOIDAE. there is an acute, almost equilaterally triangular posterior sail supported by a strong rib which arises somewhat ventrally to the antapex and ends at the tip of the sail. This rib has a ventral inclination of 15°-20°, and its length is about 0.43 the greatest depth of the body; i.e., it is about as long as or somewhat shorter than the main rib of the left sulcal list. The margins of this sail are almost straight or slightly curved, and the angle at its tip is about 50°. The posterior sail and the left sulcal list are connected by a short, but well-developed list, which at its nar- rowest place is about 0.3-0.5 as wide as the transverse furrow. The connecting list and the posterior sail, disregarding the main rib of the latter, appear to lack structural differentiation. The type specimen (Karsten, 1907, pi. 53, fig. 8) had an apparently structureless parasagittal list extending, on the dorsal side of the hypotheca, from the posterior cingular list to the posterior sail but not forming a direct continuation of the latter; this list was widest posteriorly and decreased gradually in width anteriorly; its greatest width about equaled that of the trans- verse furrow. The structure of the theca is about the same as in Phalacroma dorypharum; i.e., the wall is finely and closely areolate and furnished with scattered pores. Megacytic stages have not been seen. Dimensions: — Length of body, 75.7 ii. Greatest depth of body, 61.5 m. Type specimen (Karsten, 1907, pi. 53, fig. 8) : Length of body, 80.0 fi. Greatest depth of body, 66.7 n. Variations: — Very little is known about the variability of this species. The Expedition specimen differs from the type mainly in being slight Ij' smaller (75.7 M as compared with 80.0 m), in having a slightly higher epitheca and a some- what longer posterior main rib in the left sulcal list, and in lacking a parasagittal list along the dorsal side of thehj^potheca. The specimen represented by Pouchet's (1883) figure G:2, of Dinophysis galea has been disregarded because of the im- possibility of bemg certain that his figure represents P. circumsutum. Comparisons: — In spite of the several differences mentioned in the last section between the type of Phalacroma circumsutum and the Expedition speci- men, the determination of the last seems justifiable. The differences in the size of the body, in the height of the epitheca and in the length of the posterior main rib of the left sulcal Ust appear of httle systematic importance, since they are within the range of variation established for the closely-related species, P. dory- pliorum. The "parasagittal list" along the dorsal side of the hypotheca in the type of P. circumsutum may be the intercalary zone not yet resorbed following binary fission. It should be noted that this Ust does not form a direct continua- SYSTEMATIC ACCOUNT. 185 tion of the posterior sail as it does in P. limhatum, P. pulchruni, and in other species of this genus. Furthermore, in the closely related P. doryphorum, Pavil- lard (1916, p. 53) frequently found specimens "en voie de reconstitution portant encore des fragments irreguliers de la zone iptercalaire le long de la ligne de suture." Phalacroma circumsutum is structurally very similar to P. doryphorum (see Karsten, 1907, p. 426; and Jorgensen, 1923, p. 17), differing mainly in having the left sulcal list and the posterior sail connected by a rather wide sail; in addition, the posterior main rib of its left sulcal list is not club-shaped. See also P. dory- phorum, p. 178. Synonymy: — Phalacroma circum^ulum Jorgensen (1923) evidently includes two systematic units. Jorgensen (192.3, p. 17) writes as follows: "Besides a larger form, answering to Karsten's figure, with pro- tracted lower end of left longitudinal fin (at the supporting spine) and large, somewhat ventrally directed terminal spine, there occurred in the 'Thor' material also a smaller and divergent form, with downward trending terminal spine, and slightly prominent corner of left longitudinal fin, shape of cell in profile broader in proportion, and epitheca higlier." Of these two "forms" the larger probably should be as- signed to P. circumtsutum Karsten; the smaller, which is figured (Jorgensen, 1923, fig. 18), belongs to P. pulchnim Kofoid and Michener. Of the four specimens represented by Pouchet (1883) under the name of Dinophysis galea, one (Pouchet, 1883, fig. G: 2) resembles P. circumsutum in the .shape of its body and in having its large, tri- angular posterior sail connected with the left sulcal list by a rather wide sail. It differs from this species in having the left sulcal list relatively narrow posteriorly, in having two instead of one posterior main rib in this list, in lacking a central rib in its posterior sail, and in having its posterior sail directed posteriorly instead of posteroventrally. Jorgensen (1923, p. 37) assigns this specimen to P. doryphorum. This iden- tification is contradicted by the fact mentioned above that, according to Pouchet's (1883) drawing, this specimen had the posterior sail connected with the left sulcal fist by a fairly wide sail and by the shape of the left sulcal list. It may be noted in this connection that Pavillard (1916) foimd P. doryphorum to be common in the Gulf of Lyons, which is the type locality of Dinophysis galea; on the other hand, he never recorded Phalacroma circumsutum from these waters in spite of very intensive investigations. This fact, of course, seems to .support Jorgensen's (1923) identification above mentioned. Pouchet's figure must be considered as insufficient for certainty of specific assignment until the question as to the occasional occur- rence in P. doryphorum of a connection between the left sulcal list and the posterior sail is settled and until the variability of the left sulcal list and of the posterior sail in P. circumsutum has been further investi- gated. The four specimens figured by Pouchet (1883) under the name of Dinophysis galea belong to four different species, two of which (fig. G: 1, 4) are referable to Ornithocercus, one (fig. G:2) to Phalacroma, and one (fig. G: 3) to Ceratocorys. Since of the.se four figures, figure G: 2 appears to be the most accurate, it is suggested that it represent D. galea. This name antedates both doryphorum and circumsutum. Occurrence: — This species is recorded at only one of the 127 stations. This station (4638) is on the second line of the Expedition and in the Panamic Area. The depth is 300-0 fathoms, the surface temperature 75°, and the frequency 1% (one specimen). Karsten (1907), who found this species in the Indian Ocean, did not give any information as to the type locality. Jorgensen (1923) recorded it from a few sta- tions in the Mediterranean (the Thor Expedition) and from the Guinea Current (the German South Pole Expedition). With regard to Jorgensen's (1923) data, see above. 186 THE DINOPHYSOIDAE. This species, which is eupelagic, appears to be very rare and limited to tropi- cal, subtropical, and warm-temperate waters. Phalacroma cuneolus, sp. nov. Figure 22:1, 2, 3,5, 7 Diagnosis: — Body subobovate in lateral outline; epitheca moderately con- vex to rather flat; ventral margin of hypotheca may form broadly rounded corner at R3 of left sulcal list; deepest somewhat behind girdle; length: depth, 1.10-1.28:1. In dorsal view cuneate; hypotheca acute to subacute posteriorly, its side contours gently concave or gently undulating; length : width, 1.44: 1. Pos- terior cingular list 0.22-0.33 the length of body from apex. Cingular lists may be somewhat inclined anteriorly. Left sulcal list of moderate length and width; distance between Ri and R2 0.45-0.52 the length of body; R2 is 0.13-0.20, and R3 is 0.26-0.31 the greatest depth of body; margin forms angle of 70°-100° at R3; R3 incHned posteriorly at 40°-55°. With rather narrow, triangular posterior sail, located on antapex and directed posteriorly; 0.18-0.31 the greatest depth of body in length, and 0.40-0.80 as wide as long; often connected with left sulcal list by narrow list. Theca finely and closely areolate. Length, 59.0-74.0 ix. Eastern tropical Pacific. Description: — A medium-sized species, the body of which is subobovate in lateral outline, with moderately convex to almost flat epitheca, with the posterior portion of the hypotheca more or less narrowly rounded, with the ventral margin of the hypotheca sometimes broadly rounded-angular at the posterior main rib of the left sulcal list, and with the greatest depth somewhat behind the girdle. The ratio between the length and the depth of the body is I.IG (1.10-1.28): 1. The longitudinal axis is perpendicular to the girdle, or it has a slight postero- ventral inclination. The epitheca is 0.88 (0.86-0.90) as deep as the hypotheca, evenly and moder- ately convex to rather flat, highest in the center, and moderately to rather slightly elevated above the anterior cingular list. The transverse furrow is flat, or slightly concave or convex, and its width is 0.60-1.10 the greatest height of the epitheca. The posterior cingular list is 0.26 (0.22-0.33) the length of the liody from the apex. Some specimens (Figure 22:3) have the hypotheca subsymmetrical. In these specimens the dorsal and ventral margins of the hypotheca are of moderate to gentle convexity, sometunes with almost even curvature, sometimes more or less flattened posteriorly; the postmargin is confluent with the dorsal and ventral margins, subrectangular, gently convex or almost straight dorsally and ventrally, SYSTEMATIC ACCOUNT. 187 and strongly rounded at the antapex. Other specimens, the type (Figure 22: 1), which are somewhat asymmetrical, have the dorsal margin of the hypotheca of about the same shapes as the subsymmetrical specimens, but the ventral margin is more or less irregular, being broadly rounded-angular at the posterior main rib of the left sulcal list; the postmargin is subrectangular, rather narrowly rounded at the antapex, and its ventral portion is gently convex to straight, or even slightly concave. Between these two types of hypotheca, transitional forms are to be found (Figure 22: 2). In dorsoventral view the body is cuneate, widest at the girdle, and about 1.44 times longer than wide. The epitheca is broadly rounded to rather flat; the hypotheca is acute to subacute posteriorly, and its side contours are gently undulating, as in the type specimen (Figiu-e 22: 5), or gently concave or convex. The cingular lists are subhorizontal or somewhat (10°-25°) mclined anteri- orly, subequal, and about as wide as or slightly wider than the transverse furrow; their structure is unknown. The right sulcal list (observed in only one of the specimens; Figure 22:3) extends to a point about halfway between the fission rib and the posterior main rib of the left sulcal list; it is subtriangular in shape, decreasing gradually in width posteriorly, and anteriorly about half as wide as the transverse furrow. The left sulcal list is of moderate length and width. The distance between the anterior and posterior main ribs is 0.47 (0.45-0.52) the length of the body. The anterior main rib is 0.16 (0.13-€.18), the fission rib 0.16 (0.13-0.20), and the posterior main rib 0.29 (0.26-0.31) the greatest depth of the body. Between the anterior and posterior main ribs the free margin of this list is straight, gently convex or concave, or shghtly irregular (Figure 22: 1); at the posterior main rib it forms an angle of about 90° (70°-100°). When this list is not connected with the posterior sail, its margin behind the posterior main rib is straight, or slightly concave or convex. The main ribs of this list are of moderate strength, straight or almost so, and not club-shaped or otherwise modified. The distance between the anterior main rib and the fission rib is 0.33 (0.29-0.40) the distance between the anterior and posterior main ribs. The posterior main rib has a posterior mclination of 40°-55°. It is not known whether this list has any structure besides the three main ribs. On the right valve there is an acute, rather narrow, triangular posterior sail, which is located on the antapex and directed posteriorly. When fully developed its length is 0.18-0.31 the greatest depth of the body, and it is, at the base, 0.40-0.80 as wide as long. Its margins are almost straight, or gently convex, concave, or sigmoid, and the angle at its tip is 20°-40°. Its structure is unknown. In some specimens (Figure 22: 3) the posterior sail is 188 THE DINOPm'SOIDAE. separated from the left sulcal list by a distance that about equals or even exceeds its basal width. In other specimens (Figure 22: 1, 2) these two structures are connected by a rather narrow Ust. The thecal wall is finely and closely areolate. Porulation was not observed. Megacytic stages were seen. The dimensions of five specimens were measured. Dimensions: — Length of body, 59.0-74.0 ix (average, 64.2 n; type, 60.3 m). Greatest depth of body, 51.3-58.0 m (average, 54.3 /x; type, 51.3 n). Variations: — This species is rather strikingly variable in the following characters : the shape and relative height of the epitheca, the shape of the ventral margin of the hypotheca, the shape of the side contours of the hypotheca in dorso- ventral view, the development of the list connecting the left sulcal list with the posterior sail, and the inchnation of the cingular list. The structurally closest-known relative of Phalacroma cuneolus is P. pugiun- culus. These two species agree rather closely in the shape of the body in lateral view, in the shape and relative size of the left sulcal list, and in the shape, direc- tion, and relative size of the posterior sail. The outline of P. pugiunculus in dorso- ventral view is unknown. The latter species can be distinguished from the former by its smaller size (49-53 n as compared with 59-74 fj.). The position of these two species is not readily established because of their smiphcity. We have placed them preliminarily with P. mucronatum, P. doryphorum, and P. circumsutum on account of the general resemblance in the shape of the body in lateral view and because of the presence of a posterior sail. • The outline of the body of Phalacroma cuneolus in dorsoventral \'iew is sug- gestive of P. cuneus and Dinophysis expulsa and their near relatives. However, this similarity probably is due to convergence and can hardlj' be considered as an indication of close relationships. Occurrence: — Phalacroma cuneolus is recorded at onlj^ one (4711, type locality) of the 127 stations, on the fourth line of the Expedition, in the South Equatorial Drift, from 300-0 fathoms, and at a surface temperature of 75°. The frequency is less than 1 % (six specimens), 9. Praetextum Group. The single member of this group, viz., Phalacroma praetextum, differs so strikingly from the remaining species of Phalacroma in having a ventral cribriform plate on the hypotheca that it is made the type of a new subgenus, Ethmophalacroma, subgen. nov. SYSTEMATIC ACCOUNT. 189 Phalacroma praetextum Kofoid and Michener Plate 4, fig. 6, 7. Figure 25: 4, 5 Phalacroma praetexla Kofoid & Michener, 1911, p. 291. Diagnosis: — Body rounded subbiconical in lateral outline, slightly broader posteriorly than anteriorly; deepest at girdle, 1.12 times longer than deep. In dorsal view subbiconical, with broadly roxinded apices, and 1.17 times longer than wide. Posterior cingular list 0.51-0.53 the length of body from apex. Cingular lists about half as wide as transverse furrow, reticulated. Left sulcal Ust 0.34 the length of body, subtriangular, gradually decreasing in width posteriorly; anteriorly about as wide as transverse furrow; Ri and Ro weak, straight, and simple, Rs absent. On ventral side of hypotheca a dumbbell-shaped, cribriform plate extending from girdle to antapex. Theca with heavy and rather wide- meshed reticulation ; about fifteen polygons border the girdle posteriorly. Length, 61-62 M. Eastern tropical Pacific. Description: — A rather small species, the body of which is rounded subbi- conical in lateral outlme, shghtly broader posteriorly than anteriorly, and deepest at the girdle. The ratio between the length and the depth of the body is 1.12: 1. The longitudinal axis is about perpendicular to the girdle. The epitheca is about as deep as or slightly deeper than the hypotheca, highest in the center, subcorneal, gently convex dorsally and ventrally, evenly and fairly broadly convex anteriorly, with the dorsal, anterior, and ventral margins confluent, and very prominent above the anterior cingular list. The transverse furrow is somewhat concave and its width is about 0.22-0.27 the great- est height of the epitheca. The posterior cingular Ust is 0.51-0.53 the length of the body from the apex. The hypotheca has almost the same shape as the epi- theca but is somewhat more rounded; its posterior portion, therefore, is somewhat broader than the anterior portion of the epitheca; see the description of the struc- ture of the theca. In dorsoventral view the body is subbiconical, with fairly broadly rounded apices, and with the side contours of the epitheca and of the hypotheca almost straight or shghtly concave ; it is widest at the girdle, and about 1.17 times longer than wide; see below, the description of the structure of the theca. The cingular lists are subhorizontal, subequal, and about half as wide as the transverse furrow. Along the base of the anterior of these lists there is a series of ribs anastomosing into a row of polygons in the same way as for Phalacroma cuneus 190 THE DINOPHYSOIDAE. Schiitt (1895, pi. 3, fig. 14:2); the number of these polygons and the structure of the posterior cingular list are unknown. The sulcus is about half as long as the hypotheca. The flagellar pore is at the junction of the cingulum and the sulcus. On the ventral side of the left valve a fairly small pore is found near the sagittal suture, just behind the anterior cingular list. The right sulcal list is about half as long as the left sulcal list; posteriorly it gradually decreases in width, or its ventral margin is gently sigmoid, convex anteriorly and concave posteriorly; its greatest width somewhat exceeds half the width of the transverse fiu"row. The left sulcal list is 0.34 the length of the body, subtriangular, gradually decreasing in width posteriorly ; anteriorly it is about as wide as the transverse furrow; it has two fairly weak, straight, and simple ribs, both of which are located in the an- terior half of the list; the posterior main rib is absent (Plate 4, fig. 7). There are no accessory lists or sails. On the ventral side of the hypotheca, just to the left of the sulcus, there is a dumbbell-shaped area, extending on both sides of the sagittal suture from the posterior cingular list to the antapex. Due to the fact that it is bordered by the posterior cingular list and by the sulcus, its anterior half is truncate and some- what asymmetrical. The constriction in the middle is rather slight. This area, which has a maximum width of about 0.33 the dorsoventral diameter of the transverse furrow, is characterized by a structure quite different from that of the remaining portion of the theca. It has a faint reticulum of very small polygons, and in the center of each or at any rate of most of these polygons there is an ex- ceedingly fine pore. In other words, this area has the structure of a cribriform plate. It is not known whether this area is permanent, or whether it is temporary and formed just before fission. The first alternative, which appears the more plausible, is suggested by the relative position of this area to the girdle, by the absence of an intercalary zone from the dorsal side of the body and from the ventral side of the epitheca, by the peculiar shape and structure of this area, and by the fact that an area of this kind was found in both the specimens. If this area is of an intercalary nature, then the non-megacytic specimens probably have the ventral margin of the hypotheca resembling that of Phalacroma reiiculatum, and the posterior portion of their hypotheca is somewhat narrower than in the speci- mens described above. The thecal wall has a heavy reticulum of rather large polygons, except in the cribriform plate described in the last paragraph. Most of the polygons are sub- uniform in size, and on each valve about fifteen of them border the po.sterior margin of the girdle. Each valve of the epitheca has about fifty-eight and each SYSTEMATIC ACCOUNT. 191 valve of the hypotheca about seventy-six polygons. In the transverse furrow there are two rows of polygons, each row with fourteen to sixteen polygons on each valve ; near the junction of the cingulum and the sulcus these two rows may merge into a single row. Except in the cribriform plate, pores have not been seen. With regard to megacytic stages, see p. 190. The dimensions of one specimen, the type, were measured. Figure 25. — 1, Phalacroiim Jiinbriatum Kofoid and Michener, right lateral view of type specimen. X 430. Station 4613 (300-0 fathom.s). 2, Phalacroma reticulatum Kofoid, right lateral view of type specimen. X 430. Station 4740 (300-0 fathoms). 3, Phalacroma turhineum Kofoid and Michener, right lateral view of type specimen. X 430. Station 4681 (300-0 fathoms). 4, 5, Phalacroma praetextum Kofoid and Michener; 4, oblique ventral view of detached left valve; 5, right lateral view of type specimen. X 430. Station 4742 (300-0 fathoms). Dimensions: — Length of body, 61-62 ^ (type, 61 m). Greatest depth of body, 53.3 M (type). Comparisons: — The small size, the subcircular shape of the body in lateral view, the subequatorial position of the girdle, the relatively slight development of the cingular and sulcal lists, and the absence of accessory lists and sails are funda- mental primitive features, which place this species among the most primitive Uving representatives of Phalacroma. On the other hand, the surface structure of the theca is better developed than in most species of the genus, and the cribriform plate of the hypotheca is unique and places the species in a rather isolated posi- tion. The species therefore appears to be a representative of a short evolutionary branch which split off at an early stage in the phylogenetic differentiation of the genus. ,, Phalacroma praetextum approaches P. fimbriatum, P. reticulatum, and P. turbineum in the tendency of its epitheca and hypotheca to taper toward the 192 THE DINOPHYSOIDAE. apices, and in the heavy and coarse reticulation of its thecal wall. However, in most respects it differs more or less strikingly from these three species, and it must be regarded as an open question whether or not the three characters men- tioned above are indicative of a close relationship. PJialacroma praetexlum re- sembles P. a-picatum in the subbiconical shape of the bodj' in dorsoventral view, in the reticulated structure of the anterior cingular list, and in the absence of posterior angularity in the free margin of the left sulcal list. Phalacroma -prae- texlum is easily distinguished from all the known species by the large cribriform plate of its hypotheca. Occurrence: — Phalacroma praetexlum has thus far been recorded at only one (4742, the type locality) of the 127 stations, on the sixth line of the Expedition, in the South Equatorial Current, from 300-0 fathoms, and at a surface tempera- ture of 77°. The frequency is less than 1% (two specimens). 10. Reticulatum Group. On account of the striking difference between the left sulcal list of the three members of this group, viz., Phalacroma fimbriatum, P. reliculatum, and P. lurbineum, and that of the typical members of Phalacroma, it appears advisable to give this group the rank of a subgenus : Retephalacroma, subgen. nov., with P. lurbineum the type. Phalacroma fimbriatum Kofoid and Michener Plate 2, fig. 1. Plate 4, fig. 4. Figure 25: 1 Phalacroma fimhriata Kofoid & Michener, 1911, p. 289. Diagnosis: — Body subbiconical in lateral view, with well-rounded apices, deepest at girdle, 1.35-1.40 tunes longer than deep. In dorsal view biconical, subacute anteriorly, narrowly rounded posteriorly; but slightly narrower than in lateral view. Posterior cingular list 0.43 the length of body from apex. Each cingular list with twelve branched ribs on each ^■alve. Margin of right sulcal list widely angular in the middle. Two parasagittal lists encircle body ; the right one, which is much wider than the left, merges so completely into left sulcal list that the boundary between these two lists cannot be estabUshed. Right parasagittal list widest and of nearly uniform width on ventral and posterior sides of hypo- theca, where it is 0.14-0.20 the greatest depth of body ; on dorsal side of hypotheca and on epitheca it is about half this width. Parasagittal lists with numerous ribs, some of which are irregular and branched. Theca with heavy reticulation, form- ing large polygons; about ten polygons border girdle posteriorly. Length, 118 m- Eastern tropical Pacific. SYSTEMATIC ACCOUNT. 193 Description: — A large species, the body of which is subbiconical in lateral outUne, with well-rounded apices, and deepest at the girdle. The ratio between the length and the depth of the body is 1.35-1.40: 1. The longitudinal axis has a very shght postero ventral inclination. The epitheca is about as deep as the hypotheca, highest in the center, sub- conical, gently concave or almost straight dorsally and ventrally, evenly and well rounded anteriorly, with the dorsal, anterior, and ventral margins confluent, and very promment above the anterior cingular list. The transverse furrow is some- what concave, and its width is about 0.19 the greatest height of the epitheca. The posterior cingular list is about 0.43 the length of the body from the apex. The hypotheca has a very slight posteroventral inclination; its dorsal margin is gently concave or almost straight; its ventral margin is sigmoid, rather strikingly con- cave anteriorly, and gently and evenly convex posteriorly; its postmargin is evenly and fairly broadly convex, and confluent with the dorsal and ventral margins. In dorsoventral view the body is biconical, subacute anteriorly and narrowly rounded posteriorly; the side contours of the epitheca and hypotheca are gently concave; the ratio between the length and the width is about 1.45- 1.50:1. The cingular lists are subhorizontal, subequal, and about as wide as or some- what wider than the transverse furrow; each of them has on each valve about twelve rather strong, branched, and nearly equidistant ribs. The sulcus is about 0.40 the length of the hypotheca. The flagellar pore is slightly more than a girdle- width behind the junction of the cingulum and the sulcus. On the ventral side of the left valve a rather small pore is found on the sagittal suture just in front of the anterior cmgular list. The right sulcal list is about 0.22 the length of the body ; the anterior half of this list is about 0.14 as wide as the body, and its free margin is gently concave or almost straight; the posterior half decreases gradually in width posteriorly, and its free margin is gently concave or nearly straight and forms a very wide but distmct angle with the free margin of the anterior half of this list. Two parasagittal lists encircle the body. The right one, which is much wider than the left, merges so completely into the left sulcal list that the boundary between these two lists cannot be established with certainty. For the sake of convenience in describing these structures, it is assumed that the first rib of this compound list behind the fission rib (easily recognized in the type specimen as it is split lengthwise) corresponds to the posterior main rib of the left sulcal list, and that it marks the posterior boundary of the last-mentioned list. Defined in this way, the left sulcal list is about as long as the right sulcal list, and has four 194 THE DINOPHYSOIDAE. simple, and almost straight and equidistant ribs. Three of these ribs would cor- respond to the three main ribs; the fourth, which is placed between the anterior main rib and the fission rib, would be an accessory structure. The width of the left sulcal list is almost uniform throughout the entire length and about equals 0.14-0.15 the greatest depth of the body. From the posterior main rib of the left sulcal list to the antapex, the right parasagittal list is of nearly uniform \\idth, about 0.14-0.20 the greatest depth of the body; anterodorsally to the antapex this list gradually becomes narrower, and its average width on the dorsal side of the hypotheca is only about 0.07 the greatest depth of the body. The right para- sagittal list of the hypotheca has about twentj'-sbc fairly strong and almost equi- distant ribs, most of which are simple and almost straight, a few irregular, or irregular and branched. The left parasagittal list of the hypotheca extends from the fission rib of the left sulcal list to the posterior cingular list on the dorsal side of the body ; it is very narrow, at most about half as wide as the transverse fur- row; its rilibing is unknown. The two parasagittal lists of the epitheca are of about the same width and structure; from the apex, where their width about equals 0.09 the greatest depth of the body, they slightly decrease in width tow ard the girdle; each of them has about twenty almost equidistant ribs, a few of which are branched. The thecal wall has a heavy reticulum of rather large i)olygons, mainly sub- uniform, ten of which on each valve border the posterior margin of the gii-dle. Each valve of the epitheca has about forty and each vaWe of the hypotheca about sixty-seven polygons. The transverse furrow is divided by cross-ridges into rectangular fields, of which there are about twelve or thirteen on each valve. The whole theca has numerous scattered pores, about ten to twenty in each polygon. On the left xaWe of the hypotheca there is the unique feature of a large postcingular plate, bordered by a heavy ridge (Plate 2, fig. 1). The type specmien is megacytic. The dimensions of the type specimen were measured. Dimeiisions: — Length of body, 118 m (140 /i, with the parasagittal lists in- cluded). Greatest depth of body, 83 ii. Comparisons: — The systematic position of Phalacroma fimbriatum is some- what uncertain. In the size of the body, the shape of the body in dorsoventral view, and in the structural differentiation of the thecal wall, both in the reduction in number of polygons, and in the increase in their size and in the weight of the reticulations, this species is one of the most ad\anced members of the genus, and with regard to the development of the parasagittal lists it may be considered as SYSTEMATIC ACCOUNT. 195 the most advanced in the genus. On the other hand, m the position of the girdle it is very primitive. Its closest structural relatives possiblj^ may be P. reticulatum and P. turbineum; see these two species, the sections on comparisons (p. 197, 200). These three species differ strikingly from one another in the shape of the body in lateral view and in the parasagittal Usts. With regard to the possible relationship between Phalacroma fimbriatum and P. ■praetextuni, see p. 191. Occurrence: — Phalacroma fimbriatum has been recorded at only one (4613, the type locality) of the 127 stations, on the first line of the Expedition, in the Panamic Area, from 300-0 fathoms, at a surface temperature of 80°. The fre- quency is less than 1 % (one specimen). Phalacroma reticulatum Kofoid Plate 4, fig. 3, 5. Figiu-e 25: 2; 26 Phalacroma relicuiata Kofoid, 1907a, p. 195, pi. 12, fig. 72. Kofoid & Michener, 1911, p. 291. Pavil- LARD, 1923a, p. 879. Diagnosis: — Body biconical in lateral view, narrowly rounded anteriorly, narrowly rounded to subacute posteriorly, deepest at girdle, 1.25-1.30 times deeper than long. In dorsal view biconical, subacute anteriorly, acute posteriorly, and 1.65 times longer than wide. Posterior cingular list 0.40-0.45 the length of body from apex. Cingular list somewhat narrower than transverse furrow and apparently without ribs. Left sulcal list about 0.33 the length of the body; fau-ly narrow; its maximum width is 0.08 the greatest depth of body; with one rib near posterior end; free edge gently sigmoid, concave anteriorly and convex posteriorly. With a narrow parasagittal list on the hypotheca; this list forms a direct continua- tion of left sulcal list and extends to posterior cingular list. Theca with heavy and wide-meshed reticulation; about seven or eight polygons border girdle posteriorly. Length, 100-115 ti. Eastern tropical Pacific. Description: — A rather large species, the body of which is biconical, top- shaped in lateral outline, narrowly rounded anteriorlj^ subacute to acute posteri- orly, and deepest at the girdle. The ratio between the length and the depth of the bod}' is 1.25-1.30: 1. The longitudinal axis is about perpendicular to the gu-dle or but slightly deflected posteroventrally. The epitheca is about as deep as or but slightly deeper than the hypotheca, highest in the center, and very prominent above the anterior cingular list; its dorsal and ventral margins are almost straight or gently convex, and about per- 196 THE DINOPHYSOIDAE. pendicular to each other; anteriorly the epitheca is narrowly rounded. The trans- verse furrow is flat or somewhat convex or concave, and its width is 0.15-0.20 the greatest height of the epitheca. The posterior cingular list is 0.40-0.45 the length of the body from the apex. The hypotheca is conical, narrowly rounded or even subacute (Figure 25: 2) posteriorly ; its dorsal margin (from the girdle to the antapex) is sUghtly and evenly convex or almost straight; its ventral margin (from the girdle to the antapex) is either gently and almost evenly convex, or it is gently undulating, concave anteriorly and posteriorly, and convex in the middle (Figiu-e 25: 2). In dorso ventral view the body is biconical, top-shaped, widest at the girdle, and 1.65 times wider than long; anteriorly it is nan-owly rounded, posteriorly it is acute; the side contours of the epitheca are almost straight and nearly perpendicular to each other; those of the hypotheca are gently sigmoid, concave anteriorly and convex posteriorly. The cingular lists are subhorizontal, subecjual, somewhat narrower than the transverse furrow, and apparently without ribs. The sulcus is about half as long as the hypotheca. The right sulcal list is low, extends to the posterior rib of the left sulcal Ust, and is reticulated posteriorly. The left sulcal list is about 0.33 the length of the body, and fairly narrow, its maximum width being about 0.08 the greatest depth of the body; its free edge is gently sigmoid, concave anteriorly and convex posteriorly. Near its posterior end this list has a short, straight, and simple rib of moderate strength; with the exception of this rib, this list appears to lack structural differentiation. On the right valve of the hypotheca there is a narrow parasagittal list, which forms a direct continuation of the left sulcal list and extends to the posterior cingular list; this parasagittal list is of almost uni- form width thi'oughout, somewhat narrower than the cingular lists, and is fur- nished with a moderate number (15-20) of sunple ribs. There are no accessory lists or sails on the left valve of the hypotheca and on the epitheca. The thecal wall has a heavy reticulum of relatively large polygons. Gener- ally speakmg, the polygons increase in size from the two apices toward the girdle, and on each valve about seven or eight of them border the posterior margin of the girdle. Each valve of the epitheca has a total of about twenty-four and each valve of the hypotheca about thirty-five to forty polj'gons. The trans\'erse fur- row is divided by cross-ridges into a number of rectangular fields, about ten fields on each valve. Pores were not seen. Megacytic stages were not recorded. The dimensions of two specimens were measured. Dimensions: — Length of body, 100-115 m (type, 100 /x). Greatest depth of body, 77-84 ^ (type, 77 n). SYSTEMATIC ACCOUNT. 197 Variations: — The shape of the hypotheca is rather variable. In some speci- mens the hypotheca is subacute posteriorly, and its ventral margin (from the girdle to the antapex) is gently undulating, concave anteriorly and posteriorly, and convex in the middle. In other specimens the hypotheca is narrowly rounded posteriorly, and its ventral margin is gently and almost evenly convex. Comparisons: — The structurally closest-known relative of Phalacroina reticulatum is P. turbineum. This relationship is especially indicated by the biconical, top-like shape of the body, by the heavy and coarse reticulation of the Figure 26. — Occurrence of Phalacroma reticulatum Kofoid. Large, solid circles indicate records from vertical hauLs; small, solid circles, stations at which this species was not found; small, open circles, stations from which no plankton catches were examined. thecal wall, and by the presence of parasagittal lists. Phalacroma reticulatum is more advanced than P. turbineum in size, but in most other characters it appears to be more primitive; for instance, its body is relatively deeper, its hypotheca is relatively shorter, the reticulation of its thecal wall is less coarse, and it has only one parasagittal list on the hypotheca, while P. turbineum has two such lists on the epitheca as well as on the hypotheca. Phalacroma jimbriatum may be fairly closely related to P. reticulatum. This relationship, which is less evident than that mentioned in the last paragraph, is indicated by the biconical, top-like shape of the body in dorsoventral view, by the heavy reticulation of the thecal wall, and by the presence of parasagittal lists. 198 THE DINOPHYSOIDAE. When compared with P. fimbriatum, P. reticulatum is less advanced with regard to the size of the body, and in the number, size, and structural differentiation of the parasagittal hsts, and it is more advanced in the top-like shape of its body in lateral view, in the position of its girdle, and in the coarser reticulation of its thecal wall. With regard to the possible relationship between Phalacroma rcliculatum and P. -praelextuvi, see the last species, the section on comparisons. Occurrence: — Phalacroma reticulatum is recorded at thirteen of the 127 stations. There are 0, 1, 2, 5, 4, and 1 stations on the six lines of the Expedition. Of these thirteen stations, one (4655) is in the Peru\ian (lUTent; three (4()95, 4697, 4699) in the Easter Island Eddy; nine (4679, 4681, 4701, 4709, 4724, 4730, 4732, 4739, 4740) in the South Equatorial Drift. At one station (4655) the species is recorded from 400-0 fathoms; at one (4681) from 800-0 fathoms and 300-0 fathoms. All the remaining records refer to hauls from 300-0 fathoms only. The temperature range of these thirteen stations at the surface was 68°-81°; the average was 74.4°. At one station (4699) the frequency is 1 % ; in the remaining cases it is less. The species was first recorded by Kofoid (1907a) from Station 4740 of the Expedition; it was found in the Mediterranean by Pavillard (1923a). The most outstanding peculiarities of the distributioii of this species in the Eastern Pacific are the absence of surface records and the fact that all the record stations except one are located either in the South Equatorial Drift or in the Easter Island Eddy. Phalacroma turbineum Kofoid and Michener Plate 2, fig. 3. Plate 4, fig. 1, 2. Figure 25: 3 Phalacroma iwbinea Kofoid & Michener, 1911, p. 291. Diagnosis: — Body biconical in lateral outline, rather broadly rounded an- teriorly, narrowly rounded posteriorly; deepest at girdle, 1.84 times deeper than long. In dorsal view of similar shape but somewhat wider. Posterior cingular list about 0.23 the length of body from apex. Cingular lists about half as wide as transverse furrow, with few ribs. Right sulcal list with T-shaped rib. Left sulcal list small, 0.38-0.39 the length of body, and with maximum width 0.12-0.13 the greatest depth of body; free margin gently and evenly convex; with cross-rib somewhat in front of its middle and submarginal rib along its entire length. Two parasagittal lists encircle body; the one on right valve of hj'potheca continues left sulcal list; maximum width about equaling that of cingular lists; with moder- SYSTEMATIC ACCOUNT. 199 ate number of short ribs. Theca with heavy and very wide-meshed reticulum; five polygons border girdle posteriorly. Length, 69.5 m. Eastern tropical Pacific. Description: — A medium-sized species, the body of which is biconical, top- shaped in lateral outline, rather broadly rounded anteriorly, narrowly rounded posteriorly, and deepest at the girdle. The ratio between the length and the depth of the body is about 1 .84 : 1 . The longitudinal axis is about perpendicular to the girdle. The epitheca is about as deep as the hypotheca, highest in the center, and very prominent above the anterior cingular Ust; its dorsal and ventral margins are almost straight, or gently concave or convex; anteriorly it is fairly broadly rounded. The transverse furrow is somewhat conca^'e, and its width is about 0.40 the greatest height of the epitheca. The posterior cingular list is about 0.23 the length of the body from the apex. The hypotheca is elongated and conical; posteriorly it is narrowly rounded; its dorsal margin (from the girdle to the antapex) is gently undulating, convex anteriorly and posteriorly, and concave in the middle; its ventral margin (from the girdle to the antapex) also is gently undulating, but it is concave anteriorly and posteriorly and convex in the middle. In dorsoventral view the Ijody has about the same shape as in lateral view, but it is somewhat wider; the ratio between the length and the width is about 1.50: 1 ; the side contours of the hypotheca are evenly and moderately concave. The cingular lists are subhorizontal, subequal, about half as wide as the transverse furrow, and have a few (about seven or eight on each valve) simple, straight cross-ribs. The sulcus is relatively short, about 0.26 the length of the hypotheca. The flagellar pore is at the junction of the cingulum and the sulcus. A large pore is to be found in the transverse furrow, just in front of the flagellar pore. The right sulcal list is about 0.20 the length of the body, subtriangular, and decreases gradually in width posteriorly; its maximum width about equals half the width of the transverse furrow ; along its entire free edge runs a marginal rib, from the middle of which arises a cross-rib to the base of the list. The left sulcal Ust is small; its length is 0.38-0.39 the length of the hypotheca, and its maximum width is 0.12-0.13 the greatest depth of the body; its free margin is gently and evenly convex; it has a weak cross-rib somewhat in front of its middle and a submarginal rib along its entire length ; with the exception of these two ribs, this list appears to lack structvu-al diff'erentiation. Two parasagittal lists encircle the body; the one on the right valve of the hypotheca forms a direct continuation of the left sulcal list. On the average the parasagittal lists are about twice as wide 200 THE DINOPHYSOIDAE. on the posterior half of the shell as on the anterior half, and their maximum width about equals that of the cingular lists; each of them has a moderate number of short, simple ribs, approximately six on the epitheca and eighteen on the hy- potheca. On the ventral side of the body the distance between the two para- sagittal lists about equals the width of the transverse furrow ; on the dorsal side of the body it is about 2.5 times as wide at the girdle, and from the girdle it decreases gradually toward the apices. The cingular and the parasagittal lists arise from narrow but well-marked ridges, which are connected by similar cross-ridges. These cross-ridges divide the transverse furrow and the zone between the parasagittal lists into rectangular fields. The number of rectangular fields in the transverse furrow is about seven or eight on each valve ; most of these fields have a fine, central pore. The number of rectangular fields in the zone between the parasagittal lists is about five or six on the epitheca, and seventeen or eighteen on the hypotheca; in these fields no pores were found. The rest of the thecal wall has a heavy reticulum of very large polygons. Generally speaking, the polygons inci'ease in size from the two apices toward the girdle, and on each \'alve five of them border the posterior margin of the girdle. Each valve of the epitheca has about ten, and each valve of the hypo- theca about twenty-nine polygons. Pores were not seen in the polygons. The nucleus is large and rounded; its diameter is about 0.5 the greatest depth of the body. It Ues at the level of the girdle, is filled with beaded chromatin, and contains some spheroidal structures. With regard to megacytic stages, see the section on comparisons, below. The dimensions of the type specimen were measured. Dimensions: — Length of body, 69.5 ti. Greatest depth of bodj', 37.8 m. Variations: — The two specimens were very similar. Comparisons: — In the specimens of this species examined the two para- sagittal lists are separated from the sagittal suture by a broad zone. In premega- cytic specimens of other species of this genus with two parasagittal lists, these Usts are located near the sagittal suture (f/. P. Umhatum, Plate 3, fig. 3) ; in mega- cytic specimens of these species on the other hand, they are separated from this suture by the broad intercalary zone {cf. P.fimbriatum, Plate 2, fig. 1). The zone between the parasagittal lists in P. iurhincum has the same position, relative size, and shape (being wider on the dorsal side of the body than on the ventral) as the intercalary zone. On the other hand, it has not the juvenile structural appearance that usually characterizes the intercalary zone but is furnished with cross-ridges which are as well developed as the ridges on the remaining portion of the thecal SYSTEMATIC ACCOUNT. 201 wall. For this reason we consider the question open as to whether or not the Expedition specimens are megacytic. This beautiful and characteristic species is structurally most closely related to Phalacroma reticulatum (see p. 197). It may also be fairly closely related to P. fimbriatum, but this relationship is less evident. The last two species resemble each other in the biconical, top-like shape of the body in dorsoventral view, in the development of two parasagittal lists extending around the body, and in the heavy reticulation of the thecal wall. Phalacroma fimhriatxmi is much more ad- vanced than P. turhineuvi in the size of the body and in the size and sti-uctural differentiation of the parasagittal lists. On the other hand, P. turbineum is more advanced than P. fimhriatum in the elongated, conical shape of the hypotheca seen in lateral view, in the position of the gii'dle, and in the coarser reticulation of the thecal wall. Indeed, the polygons of the thecal reticulation are relatively larger than in any other known species of this genus. With regard to the possible rel