=CM 1^- -O Ico UNIV. OF FoRr UPRARY I MEMO! Its KKAI> BKI-OKK TUK BOSTON SOCIETY OK \ ATI HAL IIISTolM: BEING A NEW SKKIKS OF THE BOSTON JOURNAL OF NATURAL HISTORY. VOU'MK VII. BOSTON: PUBLISHED BY THE SOHKTY. 1912. PUBLISHING COMMITTEE. REGINALD A. DALY CHARLES S. MINOT WILLIAM G. FARLOW WILLIAM M. WHEELER GLOVER M. ALLEN CONTENTS. PHYLOGENY OF THE ECHINI, WITH A REVISION OF PALAEOZOIC SPECIES. 491 pages, text-figures, 76 plates. By Robert Tracy Jackson. January, 1912. flDemoirs of tbe Boston Society of natural trtatorp. VOLUME 7. PHYLOGENY OF THE ECHINI, WITH A REVISION OF PALAEOZOIC SPECIES. BY ROBERT TRACY JACKSON. WITH SEVENTY-SIX PLATES. BOSTON: PRINTED FOR THE SOCIETY WITH AID FROM THE GURDON SALTONSTALL FIND. JANUARY, 1912. TO THE MEMORY OF THE LATE ALEXANDER AGASSIZ, TO WHOM THE SOCIETY MADE ITS FIRST AWARD OF THE WALKER GRAND PRIZE IN RECOGNITION OF HIS 'REVISION OF THE ECHINI.1 AND OF ALPHEUS HYATT, LATE CURATOR OF THE SOCIETY. MY BELOVED MASTER AND FRIEND. WHOSE PRINCIPLES OF RESEARCH ARE THE KEYNOTE OF THIS MEMOIR. TABLE OF CONTENTS. PREFACE '°g INTRODUCTION ,5 TERMINOLOGY PART I. COMPARATIVE MORPHOLOGY OF ECHINI 31 FORM OF THE TEST 31 ORIENTATION 32 THE PENTAMEBOUS SYSTEM AND VARIATION 35 STRUCTURE OF THE SKELETON AND GROWTH 51 THE AMBULACRUM OF THE CORONA 53 THE INTERAMBULACRUM 62 CHARACTERS OF BASICORONAL PLATES 69 IMBRICATION OF CORONAL PLATES 73 SPINES 77 THE PERISTOME 79 OCULAR AND GENITAL PLATES 86 SPECIAL CHARACTERS OF GENITAL PLATES 185 THE PERIPROCT THE ARISTOTLE'S LANTERN AND PERIGNATHIC GIRDLE 177 PART II. SYSTEMATIC CLASSIFICATION OF ECHINI . PART III. PALAEOZOIC ECHINI GEOLOGICAL DISTRIBUTION SYSTEMATIC DESCRIPTIONS (5) 6 CONTENTS. Order BOTHRIOCIDAROIDA Jackson . . 238 Family BOTHRIOCIDARIDAE Klem . . . 238 Bothriocidaris Eichwald .... 238 B. archaica sp. nov. . . . 239 B. pahleni Schmidt 242 B. globulu* Eichwald. Genotype . . 243 Order CIDAROIDA Duncan .... 244 Family CIDARIDAE Gray .... 245 Miocidaris Doderlein .... 245 M. kei/Ktrlingi (Gcinitz) .... 245 M. cannoni sp. nov. .... 247 Order ECHINOCYSTOIDA nom. nov. . . 250 Family PALAEODISCIDAE Gregory . . . 250 Palaeodiscus Salter 250 P. ferox Salter. Genotype . . .250 Family ECHINOCYSTIDAE Gregory . . . 252 Echinocystites Wyville Thomson . . 252 E. pomum Wyville Thomson. Genotype 252 Order PERISCHOECHINOIDA M 'Coy . . 253 Family ARCHAEOCIDARIDAE M 'Coy . . 254 Eocidaris Desor 254 E. laevispina (Sandberger). Genotype . 255 Archaeocidaris M'Coy . . . .256 A. wortheni Ha\\ 259 A. legrandensis Miller and Gurley . . 260 A. longispina Newberry . . . .261 A. glabrispina (Phillips) .... 261 A. nerei (Mtinster) 262 A. rossica (Buch) 263 A. agassizi Hall ..'... 266 A. illinoisensis Worthen and Miller . . 266 A. coloradensis nom. nov. . . . 267 A.keokukHfdl 267 A. gracilis Newberry .... 267 A. aculeaia Shumard and Swallow . . 268 A. shumardana Hall .... 268 A. edgarensis Worthen and Miller . . 269 A. newberryi Hambach .... 269 A. trudifer White 269 A. norwoodi Hall 270 A. paradoxa (Eichwald) .... 270 A. mucronala Meek and Worthen . . 271 A. dininnii White 271 A.crofwWhite 272 A . acanthifera Trautschold . . . 272 A. pizzulana Gortani .... 272 A. megastyla Shumard and Swallow . . 273 A. biangidala Shumard and Swallow . 273 A. ornate (Eichwald) .... 274 A. ourayensis Girty .... 274 A. triplex White 274 A.trisenalis (M'Coy) .... 275 .4. triserrala Meek 275 A. rankini Young ..... 276 A. prisca (Minister) 276 A. wervekvi Tornquist .... 276 .1. urii : (Fleming). Genotype . . 276 A. haUiana (Geinitz) . . . . 279 A. muensteriana (Koninck) . . . 280 A. forbesiana (Koninck) .... 280 A. spinoclavala Worthrn and Miller . 281 A. sp. b. Girty 281 .4. clamla (Eichwald) .... 282 Lepidocidaris Meek and Worthen . . 282 L. squamosa Meek and Worthen. Geno- type 282 Family LEPIDOCENTRIDAE Lovcn . . . 284 Koninckocidaris Dollo and Buisscrct . 284 A', cotteaui Dollo and Buisseret. Geno- type 285 K. silurica sp. nov 285 Lepidocentrus Miiller .... 286 L. rhenanus (Beyrich) .... 288 L. drydenensis (Vanuxem) . . . 288 L. mMleri Schultze 289 L. whitfieldi sp. nov. .... 290 L. eifelianus Mtiller. Genotype . . 291 Tornquistellus Berg . . . 291 T. gracilis (Tornquist). Genotype . 291 Hyattechinus gen. nov 291 E. rarispinus (Hall) .... 292 H. penlagonm sp. nov 295 H. beecheri sp. nov. Genotype . . 297 Pholidechinus gen. nov 299 P. brauni sp. nov. Genotype . . 299 Family PALAEECHINIDAE M'Coy . . . 302 Palaeechinus M 'Coy . . . .304 P. quadriserialis Wright .... 305 P. ellipticus M 'Coy. Genotype . . 307 P. elegans M "Coy 308 P. (?) minor sp. nov. Maccoya Pomol 311 M. burlingtonensis (Meek and Worth™) . 312 M. intermedia (Keeping) .... 314 M. phillipsiae (Forbes) .... 316 M.sphaerica (M'Coy) . . . .317 M. gigas (M'Coy). Genotype . - 321 M. gracilis (Meek and Worthen) . . 323 Lovenechinus gen. nov 324 L. lacazei (Julien) 326 CONTENTS. L. mutatws (Keyes) . . . .•{;<;•, L. nobilis (Meek and Wort linn . . ;;:{.-, L. mixgouricHsis (Jackson). Genotype 337 L. anglicus sp. nov. . . . 34(5 L. septies sp. nov. . . . ;j4x Oligoporus Meek and Worthen . . :j.-,n O. blairi Miller and Gurley , ;{<•, | 0. coreyi Meek and Worthen . . . :;;,:; O. sulcatus Miller and Gurley . . . 354 O. halli sp. nov. .... :jf>.r> O. danae (Meek and Worthen) . Genotype 3 /if, Melonechinus Meek and Won hen . , 359 M. dispar (Fischer von Waldheim) . . 365 M. parvus (Hambach) .... 365 M . springeri sp. nov. .... 366 M. crassus (Hambach) .... 367 M. indianensis (Miller and Gurley) . . 369 M. stewartii (Safford) . . . .371 M. septenarius (Jackson) .... 373 M. obovatus sp. nov. .... 373 M. liratus sp. nov 374 M. multiporus (Norwood and Owen). Genotype 375 .Vf . keepingi sp. nov. .... 384 M. elheridgii (Keeping) .... 385 M. vanderbilti sp. nov 388 M. giganteus (Jackson) .... 389 Family LEPIDESTHIDAE Jackson . . . 393 Lepidechinus Hall 394 L. irregularis (Keeping) .... 396 L. iowerttii gp. nm .... 397 L. trittrllnlux up. n,,v . . . 397 /.. imi>rir,,t,,i Hall Genotype . . 399 Periachodomus MI . . 4<>l I'. Inner, Genotype . . mi /'. lY/l'/l<» .. /' .-M \\.irlhrll all'l MllIlT . . 4O6 Perischocidaris Nciunayr . . . in? /'. harteiana [Uaily). Genotype . . 4UM Proterocidarii Konim-k . ... 4m i' .'iMinrk Genotype . . 4lo Lepideathei M<*-k :iii.lWnrt>H-ii . uj L. i .'-k.iKii 410 L. laei'i* Tratifm-liiild . . . J|s L.formosa Miller ||* L. devonicans Whii Tornqui.st .... 450 Oligoporus (f) minulux Hm!<* . . . 4."><) PalatcUlttM (/) konigii M'Cuj . -(."><) Paburrhhiiix rcgnyi nom. nov. . . . -I.">1 Palaechinn.i robineti Julien . . . 452 Palechinus tp. Tornquist .... Palatocidaris erilis Eichwald . . . 453 Palaeodiscus gothicuf Wyville Thonixm . 453 Pataeospaiangvs skiptnm Harlr . . 453 Periachodomus magnus Tornquint . . 453 Protoechinus T Austin .... 453 P. anceps T Austin. Genotype. 454 Rhoechiniu sp. Duncan .... 454 Khotchinu* (t) »p. Tornquirt ... 454 8 CONTENTS. INCKRTAE SEDIS (continual . Xenocidaris Schultze 454 X. conifera Schluter . A', clarigera Schultze. Genotype . . 455 X. cylindrica Schultzo . 456 NoMlNA NUDA 456 Archaeocidaris tirolensis Stache . . 456 Lepidocentrus desori Dollo and Buissorot . 457 Echinocrinus cidariformis (?) T. and T. Lepidocentrus duponti Dollo and Buisseret . t.">7 Austin 456 Lepidocentrus gaudryi Dollo and Buisseret . 457 Echinocrinus immuin T. and T. Austin . 456 Melonites youngi Young .... 457 Heterocidaris Hall 456 Palaechinus agassizi Dollo and Buissorot . 457 Heterocidaris keokuk Hall . . . 450 Palaechinus carpenleri Dollo and Buisseret 458 Heterocidaris laerisirina Hall . . . 450 Palaechinus loveni Dollo and Buisseret 45S PALAEOZOIC FORMS INCOKKECTLY REFERRED TO ECHINI Discocystis Gregory 458 Myriastiches Hollas ... 458 D. kaskaskiensis (Hall) .... 458 M. gigas Sollas D. opUitus (Worthen and Miller) . . 458 Palaechinus sp. Mitchell 458 D. sampsoni (Miller) .... 485 Spatangopsis Torell . S. coslata Torell 458 BIBLIOGRAPHY .459 INDEX 47S ERRATA AND ADDENDA . 491 PREFACE. IN 1896, I published with Dr. (now Professor) T. A. Jaggar, Jr., a detail,-.! >tudy of .17 echinus multiporm and at the same time, independently, a general study of Palaco/oic Kchini. These papers, which were published together in the Bullet in of 1 he ( illogical Society of America, were the first attempt to make a comprehensive study of tins intere-ting jrroup of fo-.-il animals. During a year recently spent in Europe, opportunity offered to study most of tin- European species of Palaeozoic Echini and in many cases the types. In this country similar opi*>rt uni- ties have been enjoyed with American species. The great liberality and kindness of all to whom I applied for permission to study material is later acknowledged in detail, but I cannot refrain from saying here that the freedom and liberality with which the choicest and rarest material was placed in my hands and every facility offered for study at home and abroad, was one of the pleasantest experiences of my life. The present memoir is naturally divided into three parts: first, a study of the development and comparative morphology of Echini, based on the young, adult, fossil, and living ty|«-: second, a proposed systematic classification of Echini based on the preceding -tudie-; third, a revision of Palaeozoic Echini comprising the systematic description of all known form-. The late Professor Alpheus Hyatt originated most important and novel method- of study in Palaeontology. It is both an obligation and a privilege to say that during many jn when closely associated with him as student and assistant, he impressed upon me the important principles of stages in development, senescence, acceleration, and parallelism. During my first sea-urchin studies I had the privilege of his ever ready sympathy and personal help. I have tried to carry out this work on his lines and as he would have done it, so far as in me lay. The Hyatt principles are the pith and center of the work, and I take pleasure in feeling that his views worked out largely on the Mollusca are supported and strengthened by their applica- tion to another group of animals. In revising a group, it is most important to see the types or original specimens on which species have been based. Omitting Incertue Sedis, the types have been studied of t>\> «( the 1 lit species of Palaeozoic Echini described in this memoir. Specimens of 96 of the specie- have boon studied. These include almost all of the important forms. The genera and species of Palaeozoic Echini have for the most part been described in the publications of geological surveys as parts of the fauna of a horizon or locali' 'rip- tions of a limited number of species in the proceedings of learned societies. (9) 10 ROBERT TRACY JACKSON ON ECHINI. Of those who have published on Palaeozoic Echini, the most important are as follows. M 'Coy did pioneer work; in 1844 he published several species of Palaeechinus, the first known, also species of Archaeocidaris, and later, Perischodomus. James Hall described several new species of Archaeocidaris, also Lepidechinus. Meek and Worthen, or Meek independently in a few cases, did most accurate and painstaking work, describing many genera and species with a care and faithfulness that have rarely been equalled by investigators of these ancient and difficult fossils. Sir Wyville Thomson described the remarkable Echinocystites. Baily published observations on Palaeechinus and described Perischocidaris harteiana. Schmidt made important studies of Bothriocidaris, describing a new species. Keeping described new species and published good figures of old species. Duncan made studies of the ambulacrum in species of the Palaeechinidae. C. A. White described a number of new species of Archaeo- cidaris and a Lepidesthes. Keyes described a new species of Oligoporus, published a number of new figures, and gave a revision of the American species. Jaekel published a careful study of a species of Bothriocidaris. Jackson and Jaggar published a detailed study of Melonechinus multiporus, and Jackson a general study of Palaeozoic Echini, described a few new species, and made an attempt at a natural classification. Julien described new species and figured others from the Carboniferous of France; his material was evidently not very good as shown by the photographic illustrations. Tornquist made a careful study of German species with most excellent figures; he described a number of new species and genera and gave a classification. Miss Klem published a revision of Palaeozoic Echini with a synopsis of known species. Her bibliography and synonymies are very full and most helpful, but unfortunately there are many errors in the text, so that statements need verification. Fraipont published an interesting series of species from the Carboniferous of Belgium. Besides the above, new species or genera of Palaeozoic Echini or observations on specimens have been published by many authors. Aldrovandus, in 1618, published the first Palaeozoic echinoid that has been discovered in the literature. He figured at this early date a specimen of Bothriocidaris globulus under the caption, "Echinus lapis spoliatus a spinis." It is extraordinary that this especially rare type should have been so early discovered. De Koninck, Miinster, L. Agassiz, Norwood and Owen, Fischer von Waldheim, Forbes, Geinitz, King, Roemer, J. Miiller, and Sandberger published species and genera with more or less full descriptions of the same. Desor published some new forms and gave a revision of the then known Palaeozoic species. Young, Wright, Shumard, Schultze, and Safford published a few types, some of much importance. Loven in his "Etudes" gave a revision of the then known species, but apparently without observations on specimens. A. Agassiz in the "Revision" (1872-74, p. 644-650) gives a general discussion of Palaeozoic Echini and in several other monographs has published observations on the group and some discussions of the observations of others. Stache, Miller, and Schliiter published new species. Zittel in his text-book introduced new PREFACE. 1 1 generic names and higher divisions of the group. Pomel gave a revision of the genera and published a number of new ones. This part of his work was apparently based wholly on the observations of others, to whom he gives neither credit nor reference. Waagen, and Miller and Gurley published new species. Duncan revised the genera in his revi.-ion of the genera of the class. Sollas, Gregory, Whidborne, Dollo and Buisseret, Girty, Bather, and Spencer published new species or observations on older species. In numerous text-books, figures and more or less full descriptions are of course given, wholly or mainly from the observations of others. The important monographs of A. Agassiz, Loven, and Mortensen have been constantly in hand for comparative studies of recent types. The late lamented Alexander Agassiz stands unique in the history of echinology, for his work on the group extended over a period of nearly fifty years, during which time he published numerous extensive monographs besides many smaller papers. The attempt has been made to give full credit to the above authors for their observation-. While I have not always been able to agree with the observations or conclusions of others, it i- to be remembered that these fossils have a complex structure and are often very imperfectly preserved, so that they are exceptionally difficult to study. Also, I have had the privilege of a fuller opportunity than probably any one before to study a large range of Palaeozoic sp« Those who are most familiar with the group can best appreciate the difficulty of avoiding errors, as I hope may be remembered in my own case. Barring possible oversights, the systematic part of this paper includes every published species, practically all of which are figured. A figure is given of all recognized species excepting Archaeocidaris rankini, A. prisca, and Konincko- cidaris cotteaui of which no specimen was available and no figure has been published. \\-« excepting Pholidocidaris gaudryi of which the published photographic figures are too indistinct to be safely copied. The location in museums of types and rare species is given as an aid to investigators. For their kindness and liberality in allowing me freest access to material in collections and for every facility in the use of the same, as well as other kindnesses, I would return grateful thanks to the following curators and private collectors. My friend, Dr. F. A. Bather, of the British Museum, to whom I am under special obligations, most kindly helped me by corre- spondence and the loan of rare specimens, as well as by access to the rich material in the British Museum. He also had the great kindness to borrow, study, and send me drawings and i on the specimen of Lovenechinus lacazei described from the York Museum. During a visit at the British Museum I enjoyed the privileges of the rich library facilities there available. Dr. F. L. Kitchin and Mr. H. A. Allen, of the Geological Museum in Jermyn Street, London, helped in a similar way, and most kindly had photographs taken of some of their important specimens as here reproduced. Professor Henry Woods, of Cambridge, England, and Pro- fessor John Joly, of Trinity College, Dublin, gave access to their choice material. Dr. 1 12 ROBERT TRACY JACKSON ON ECHINI. Scharff, of the Science and Arts Museum, Dublin, gave me access to invaluable material, had casts and photographs of M'Coy's types made, and most generously brought over to this country for study one of their most valuable specimens. Dr. Otto Jaekel, recently of Berlin, kindly gave me the opportunity to study his most precious specimen of Bothriocidaris, which I feel is the backbone of this work. Professor A. Rothpletz and Dr. F. Broili gave me every oppor- tunity to study the rich collections of the Munich Museum. At Geneva, Dr. Bedot, Director of the Mus6e d'Histoire Naturelle, and Dr. Jules Favre, of the same institution, kindly gave me access to their rich' collection of Recent and Mesozoic Echini, including the very valuable material of the late M. de Loriol. Professor G. Steinmann and Professor G. Boehm, of Freiburg i. Br., and Professor A. Tornquist, of Strassburg, placed much fine material at my disposal. In this country, for opportunities to study fossil Echini, I am under deep obligations to many curators of museums and to private collectors. Mr. Samuel Henshaw, Curator of the Museum of Comparative Zoology, kindly gave me free access to the rich collections in that institution. From Professor Charles Schuchert, of Yale University Museum, besides other specimens, was borrowed the superb material of Hyattechinus beecheri and rarispinus collected in Warren, Pennsylvania, mostly by the late Professor C. E. Beecher. I am under similar obligations to the late Professor R. P. Whitfield, of the American Museum of Natural History; Dr. C. D. Walcott and Dr. R. S. Bassler, of the United States National Museum; Dr. George H. Girty, of the United States Geological Survey; Professor Stuart Weller, of the University of Chicago; Professor John M. Clarke, of the New York State Museum; Professor William B. Clark, of Johns Hopkins University; Professor J. W. Beede, of Indiana University, who sent me the remarkable new type, Meekechinus elegans and other material ; Dr. A. G. Ruthven and Professor E. C. Case, of the University of Michigan; Professor R. S. Breed, of Alleghany Col- lege, Meadville, Pennsylvania; Professor L. C. Glenn, of Vanderbilt University; Professor A. W. Grabau, of Columbia University; and Mr. C. W. Johnson, Curator of the Boston Society of Natural History. Of private collectors, Mr. Frank Springer generously loaned me his whole collection of about 125 Palaeozoic Echini, including types and other material recently purchased from Pro- fessor G. Hambach, of St. Louis. Mr. Frederick Braun, of Brooklyn, lent very choice material from his private collection; and Mr. E. Kirk, now of the United States Geological Survey, lent several specimens. Mr. J. E. Hyde, of Columbia University, loaned the remarkable new Lepi- desthes extremis. To all these gentlemen I would render warmest appreciation for their gen- erosity. The actual specimens loaned or used will be referred to as from the institution or collection to which they belong under consideration of the species. For the opportunity to study the great collection of Recent Echini in the Museum of Comparative Zoology, I am indebted to the Curator, Mr. Samuel Henshaw, and to Dr. Hubert Lyman Clark, who is in charge of that department. For similar opportunities in the United I'I!KF\( !•:. ,;{ States National Museum I am indebted to Mr. Austin H. Clark and Mim Mary J. Hathhun. Professor Verrill kindly gave me the opportunity to study the Recent KHuni ,„ Yale Unfa Museum. The authorities at Ward's Natural Science Establishment at |{,,,.|,,M,.r literally allowed me to study their large trade collection. For opportunities to stiifh material in their charge, I am indebted also to Mr. Roy Miner, of the Ameriean Ma-mi, d History; Dr. F. A. Lucas, lately of the Brooklyn Institute of Arts and Science*; Dr. A .- Pearse, of the University of Michigan; and Professor E. S. Morse, of (in- IVabody Museum at Salem. Professor Morse also kindly gave me opportunity to study many .la], him that he collected in that country. Several gentlemen have most kindly supplied me with (in,- - of specimens; they are: Mr. A. P. Romine, of Bellingham, Washington; Dr. \V. K. 1 i-l, Stanford University; Professor W. E. Ritter, of the University of California; Professor 1 Mark, of Harvard University; Dr. H. C. Chadwick, of the Port Erin Biological Station: Dr. F. D. Lambert, of Tufts College; Dr. Thomas Barbour, of Cambridge, Massachu-ett-; Mr. Dwight Blaney and Mr. Owen Bryant, of Boston. Dr. Theodor Mortensen kindly loaned „„. valuable material and helped me by correspondence. In addition to material studied in various institutions, my work has been based on my own collection of some 40,000 Recent and Mesozoic Echini. These I recently nave to the Museum of Comparative Zoology. My Palaeozoic Echini, accumulated during many \ and including 100 specimens, are now also in the collection of the same .Mu.-eum. I would express my warm obligations to my friend, Mr. Samuel Henshaw, Curator of the Museum of Comparative Zoology, for the use of a room and for the use of the great library- facilities there afforded. I would express my deep appreciation of the laborious painstaking care and skill with which Mr. J. Henry Blake made the larger part of the drawings for the plates and text-fij:' It is very difficult to get an artist who can draw a sea-urchin correctly, and without Mr. Blake'- skill and patience I should have been badly handicapped. Any sea-urchin is difficult to draw accurately, but in the Palaeozoic, one has to contend with the difficulties of imperfect often the fusion or indistinctness of sutures; the fossils are frequently external or internal molds or siliceous replacements, and these conditions add much to the difficulties of critical study and correct interpretation. The drawings were all made under my eye, and are as faith- ful to the originals as it was possible to make them. No restorations were permitted. e\ as indicated by dotted lines. Of the text-figures, Mr. Blake drew figures 1 to 230 and '_'! 253, while figure 244 is the work of Mr. J. H. Emerton; figures 2-10 to 2-13 were done by Mr. A. H. Searle, and figures 254 to 256 by Mr. William M. Barrows. I would also expn» obliga- tions to Mr. F. A. Saunderson, of Boston, for the remarkable set of photograph- «>f Kchini which are reproduced as heliotypes. Some of the drawings and photographs were made by other artists in Europe or this country, as mentioned in the description of plates. The illu 14 ROBERT TRACY JACKSON ON ECHINI. tions in the plates are arranged as nearly as practicable in systematic sequence following the classification here presented. I am under great obligations to my friend, Dr. Hubert Lyman Clark, for his help in veri- fying references, and help with my manuscript and other matters during my absence from home. Miss H. I. Cowdery rendered valuable service as a typewriter by her careful painstaking copy- ing of the manuscript for the printer. The requisite research work and the preparation of this memoir have taken my close attention in available time for some seven years. That it has taken so long has been a source of regret for more than one reason, but careful work cannot be done in a hurry. I adopt the title "Phylogeny of the Echini" for this memior, because the phylogenetic rela- tions expressed by stages in development and by variation are considered throughout the work. As I have shown previously in my "Phylogeny of the Pelecypoda" (1890), and also in studies of Echini (1896), and of Plants (1899), I believe that by following the Hyatt methods of a comparative study of young, adult, fossil, and living forms we can arrive at a series of facts which justify us in accepting them as expressing an approximation to the real genetic relationships of the forms under consideration. The genealogical relations of the Echini, as understood from the results of my studies, are shown in tabular form on p. 209. INTRODUCTION. The principles made use of and the methods of work employed in studying Echini are here treated before starting into the detailed considerations. The one essential principle that ban been applied consistently throughout is the principle of stages in development and (he constant comparison of these stages with the characters of more or less closely associated types. This principle applied conjointly to fossil and living forms was urged by Professor I .mi is Agasaiz, and was the center of a large part of Professor Hyatt's work. An attempt has been made to bear in mind the characters of the young, adult, and old age, and to compare these with t he- young or with the adult of simpler or more specialized types, both living and fossil. As far as material permitted, the entirety of the organism has been taken into account. If Echini have taught me anything, they have impressed upon me that classification should be based on thr sum of the characters and not on single characters. Herbert Spencer pointed out the distinction that growth is mere increase in size without the addition of differential characters; development is the addition of differential characters. Development proceeds rapidly during the early growth of an organism, but in later life we may get extensive growth without any development. In Palaeozoic Echini, development, that is, the addition of new characters, is often long continued, so that new characters, especially additional columns of interambulacral plates, may be taken on up to or even dorsal to the mid-zone. Then in the dorsal region we come into the zones of localized stages in development . where the young, last added plates are progressively taking on their full characters as they are pushed ventrally by the intercalation of still younger plates on their dorsal border, lx-t them and the apical disc. Dorsally, we also often find senescent stages or characters of regres- sive development, especially marked by the dropping out of columns of interambulacral plates, as in Melonechinus indianensis (Plate 53, fig. 1). In the Palaeozoic Echini, as elsewhere, specimens of a species vary in ~ize, and doubtless this usually means age, but really young specimens are almost unknown. The only very young one seen is Lovenechinus missouriensis (Plate 39, fig. 1; compare with adult, Plate 39, fig. 5). In the absence of the young, youthful stages are gathered from the characters of the plates at the ventral area of the corona, which, as shown in my earlier paper, is an area that preserves the early stages of development in a remarkable degree. Except when destroyed by rosorption, this area in a perfect specimen represents the first interambulacral plates built in any corona, and the first ambulacral as well, unless they have passed on to the buccal membrane. While these ventral plates have increased in size since early youth, their presence, number, angles, (15) 16 ROBERT TRACY JACKSON ON ECHINI. and mutual relations show developmental stages which it is felt, from numerous and careful comparisons, can be trusted as stages in development. Stages in development are not limited to the ventral border, but are seen in many types appearing progressively up to or even dorsal to the mid-zone. This is especially seen in the development of the interambulacrum, where • new columns come in often very late in the growth of the individual, as shown in numerous cases, for example, Melonechinus multiporus (Plate 57, fig. 1). Localized stages in development is the principle that throughout the life of the individual, stages may be found in definite parts that are comparable to the condition in the young and to the adults of simpler types of the group. This principle was discovered in and applied to the young plates at the dorsal portion of the interambulacrum in Palaeozoic Echini in my paper, " Studies of Palaeechinoidea," published in 1896, p. 228. It was applied t'o Palaeozoic and Recent Echini in my paper (1899) on this principle as a new law in evolution published in the Memoirs of the Boston Society of Natural History, under the title, "Localized Stages in Development in Plants and Animals." In this memoir the principle of localized stages in development is applied to the interambulacrum, but especially to the ambulacrum, where it is found that primitive characters, seen in the nascent plates at the dorsal border of the area, are striking and most valuable for a comparison with the condition in the young and with simpler types in the group. This principle is shown well in the development of young ambulacral plates dorsally in Centrechinus (text-figs. 92, 94, pp. 106, 107) and is seen especially in the family Palaeechinidae (text-fig. 237, p. 231). This principle was found to have a broad applica- tion in various groups of organisms, as ophiurans, crinoids, corals, cephalopods, also plants; and it has been taken up by the late lamented Professors Hyatt and Beecher, by Grabau, Cushman, Ruedemann, Buckman, Hubert Lyman Clark, and Jeffrey, who found it a valuable aid in studying many different groups of animals and plants. Senescence, which was made so much of by Professor Hyatt in his studies of cephalopods, is best shown in Palaeozoic Echini by the dropping out of columns of interambulacral plates at the dorsal or last built portion of the test. In the old individual of Lovenechinus missouriensis (Plate 42, fig. 6) columns 1 and 2 have in part dropped out dorsally, whereas in a younger specimen (Plate 41, fig. 2) they continue directly to the apical disc. Melonechinus giganteus (Plate 59, fig. 14) shows the dropping out of the eleventh or last added column at the dorsal border of the area. Dropping out of columns is shown graphically in the old-age Melonechinus indianensis (Plate 53, fig. 1) where columns 1 and 2 or even more drop out before reaching the apical disc. Hyattechinus beecheri (Plate 26) shows the dropping out of columns 1 and 2 toward the dorsal portion of the areas. Progressive types are those which show in their development to maturity the addition of differential characters only, without the dropping out or disappearing of such characters, unless in senescence. A good case of a purely progressive type is Palaeechinus quadriserialis (Plate 30, INTRODUCTION. 17 fig. 3), which progressively adds characters, but as fur ;is known doc- not ]„<<• any of the«e additions. It may be said that in general must Palaeo/oie Kchini arc pn.grc--i\r i •, Regressive types are those which, after attaining a degree of speciali/ed characi, •, later development, and before old age, lose some of these characters. BO that what we call the adult, as gathered especially from the characters of the mid-xone, i* -im ,,!,.,- t|,;m ;,. ,,wh yitin,v An excellent case of this is Lepidesthes wortheni (Plate (17, fig. 8) which in the young ha.- lour columns of interambulacral plates, but the fourth column drops out early, and in later life it has three columns only. The sixth column represented by only a few plates in an area -e.-m- to mark Lovenechinus missouriensis (Plate 41, fig. 1) as a regressive type, at least in thi- char- acter. To go outside of Palaeozoic Echini, Hemieidaris has compound ambulacral pi: in the lower or youthful half of the test, and above this point has only simple plate-. -Inming a complete reversion to Cidaris, a more primitive type of Kchini. Such an extreme ca-e may be compared to Lituites in cephalopods (Zittel, Handlmeh der Palaeontologie, vol. 2. text- fig. 519), which, after an early coiled stage, takes on a straight stage directly comparable \>, the early straight forms of nautiloid cephalopods. Cases could be multiplied and some will be mentioned later, but here it is the object simply to point out examples that, illustrate the principles made use of. Acceleration of development, one of Professor Hyatt's most important principle-, i- abun- dantly shown in Palaeozoic Echini. Usually columns of interambulacral plates, after t In- first four columns, are added at considerable intervals, as in Melonechimu ninlti/>i>rux (Plate 57, fig. 1), but M. giganteus (Plate 59, fig. 14), which is a higher species in the serie-. adds tin- fifth, sixth, seventh, and eighth columns earlier than does M. muUiporus, as shown in a detailed study in my earlier paper (1896, p. 179). Hyattechinus beecheri (Plate 26), a mo-t -peciali/ed type, has a very accelerated development, and new columns of interambulacral plates are added so rapidly that the fourth to the tenth are added in succeeding rows, or even two column- may be added in a single row. The same character of acceleration is shown well in Ili/nlli-cliinitx rnri- spinus (Plate 23, fig. 1) and H. pentagonus (Plate 25, fig. 1). Acceleration is shown well in the ambulacrum in Melonechinus (text-fig. 237, p. 231), in which at the ventral border we find four plates in each ambulacrum, while the lower genera of its family have only two plat. Parallelism is an important feature which was much studied by Professor Hyatt, and is of great value in studying Echini. Parallelism is the taking on of a similar character by inde- pendent lines, and is sometimes difficult to distinguish from real genetic connection. A case of parallelism is seen in the imbrication of plates of Echini. It has been thought that imbri- cation was a sufficiently important character to group together those forms that po-e-ed it. but it is assumed independently in several distinct groups in the Palaeozoic, a- well as in the post-Palaeozoic Echinothuriidae. In the family of the Palaeechinidae (Melonechimis. . ambulacral plates on the adradial suture are beveled over the adambulacrals i. Plate 45, fig. 5). 18 HOHKHT TRACY JACKSON ON ECHINI. A similar beveling is seen in the petaloid area in some clypeastroids, Clypeaster, surely a parallelism only. Accessory pores in genital plates in modern Echini exist as an individual variation occasionally (Arbacia, text-figs. 197, 198, p. 171; Echinus and others). This appar- ently represents a parallelism rather than a genetic connection with the several pores charac- teristic of these plates in most Palaeozoic genera (Plate 56, fig. 6). Increase in the number of columns of mterambulacral plates is taken on independently in many genera. The absence of resorption of the base of the corona, which permits of the retention of the single pri- mordial interambulacral plate in each area, appears as a parallelism in many independent groups, as represented by Hyattechinus (Plate 26), Perischodomus (Plate 64, fig. 2), Pholi- docidaris (Plate 73, fig. 6), Phormosoma, clypeastroids (text-figs. 43, 52, p. 80), and spatan- goids (Plate 3, fig. 15). Resorption is an important process to bear in mind; it occurs continuously in the growth of each individual plate, where there is a constant resorption within the plate concurrently with increase in external dimensions. Resorption of the base of the corona by the encroach- ment of the actinostome is a very important factor, as shown by Lov4n (1892). In Palaeozoic types, as I showed in my earlier paper (1898), there is either no resorption (Hyattechinus, Plate 26), resorption of apparently one plate only (Palaeechinus, Plate 30, fig. 3), or resorption of several rows of plates (Archaeocidaris, Plate 9, figs. 6-8). Resorption may cut holes directly through the test, as shown by Mr. Agassiz (1872) in the development of the lunules in the recent Mellita sexiesperforatus (Leske). See text-figs. 22-31, p. 70. Variation is an extremely important subject and is graphically shown in sea-urchins. Here we find the striking character of radial variation well developed, as seen especially in the corona and ocular and genital plates. One radius may be more or less accelerated, or may reach a greater or lesser degree of differential development than other radii in the same individual. This is especially marked in the variation of rate of development and number of columns of interambu- lacral plates attained in Palaeozoic Echini, and in the number of ocular plates reaching the peri- proct in Recent Echini. The range of radial variation in one individual may equal the range of variation of different individuals within the limits of the species. In Melonechinus typically there are four plates at the ventral border of the ambulacrum, but in one specimen of Melon- echinus multiporus (Plate 57, fig. 3) it is seen that in area B there are two plates only. This is the normal character of the ventral border of Oligoporus (Plate 50, fig. 8) and Lovenechinus (Plate 42, fig. 1), the next lower genera of the family. In order to appreciate variation it is of fundamental importance to be familiar with the characters of the associated species and genera of a case in hand, and also the developmental characters of the same. Variation may be fairly classified under five more or less distinct heads : 1. Arrested variation, in which the variant retains characters seen in its own young and INTRODUCTION. 1<» typical of the adults of more primitive allies, but character- whirl, are n-ually eliminated in development. Arrested variants are shown abundantly in tin- consideration of ocular plates, when fewer plates may become insert than is characteristic of the -perie- ' Triplicate-, text- figs. 123-125, p. 124). 2. Progressive variation, in. which the variant has characters not typical of tl,, but which are further evolved on the direct line of differential development, and are -een typi- cally in more evolved nearly allied species or genera. Such progressive variants are al-o -linwii abundantly in the consideration of ocular plates, where more plates become in-ert than i- typical in the species (Centrechinus, text-figs. 93-95, p. 107 and 176, p. 153,). 3. Regressive variation, in which the variant takes on characters of the adult of .-ome >imple and more primitive type of the group. Such characters are not necessarily a repetition of youth- ful characters but may go back to a remote ancestry. An arrested variant in a sense is one form of regressive variation, but a regressive variant includes much more than arrested variation. To distinguish them, an arrested variant is one that has developed to a certain point as usual, and then failed to take on the later added characters typical of the >pe<-ie-. >o that, although an adult, it has immature characters. A regressive variant is one that has attained full char- acters and then in later life has reverted to youthful or primitive characters as an individual variation, or it is a variant that from youth has primitive characters not normally seen in the development of the species. A modern horse with extra digits as in Tertiary times could be considered a regressive variant, but could not be considered an arrested variant. In Echini, cases of regressive variation are shown in the simple ambulacrum in Meloiiechinus i Plate 57, fig. 3), and in the single column of interambulacral plates in Arbacia (Plate 4, fig. 11) and Trip- neustes (Plate 6, fig. 4). 4. Parallel variation is where a character is taken on exceptionally which may be com- pared with characters normally occurring in some type of the group not closely connei -led. -.. that it cannot be genetically compared. A case apparently is the extra genital pores fre- quently developed in Recent Echini (Echinus, text-fig. 115, p. 117). 5. Aberrant variation is where a character is taken on which is (mite abnormal, not to be correlated with the typical condition in associated forms. Cases of aberrant variation are sea-urchins which have four or six areas developed (Plate 6, figs. 1-4). All the e\i.l goes to show that aberrant variation is rare, and most variants can be considered a> am progressive, regressive, or parallel variants, and as such can be correlated with >perie> more or less nearly allied which typically possess the character which is a variant of the <-a>e in hand. This holds true as far as known in both animals and plants, as seen in the present paper, and as I showed in detailed studies of plants (1899). Next to stages in development, variation is the most suggestive line of study in attempt- ing to work out the genetic relations of plants and animals. When a specimen of one species 20 ROBERT TRACY JACKSON ON ECHINI. has characters approaching those of another, hybridity is often assumed as a cause. I have found numerous cases of variation to the character of another species where hybridity cannot be considered on account of geographical separation, and it is felt that we should be extremely cautious in assuming hybridity when the same results might be attained by variation. From my studies on Echini, all the evidence goes to show that variation is in perfectly definite lines, mostly arrested or progressive in character. When variation is aberrant, it still follows defi- nite lines of aberration, and sporadic variation is very rare. This opinion is based largely on a detailed study of genital and ocular plates which were carefully examined in over 50,000 specimens of Echini (text-fig. 176, p. 153; p. 164). To the late Professor Sven Loven all students of the Echini owe a great debt for the keen eyesight and insight with which he studied these fascinating animals. His method was largely a critical detailed study of plate structure and relations, and this method I have attempted to follow in the study of Palaeozoic forms. Frequently sutures are so difficult to see and speci- mens are so contorted or badly preserved in these ancient forms, that I can hardly hope to have escaped mistakes; but this method has been followed out consistently and with every effort faithfully to describe and figure the specimens. Loven worked with Recent or post-Palaeozoic Echini, in which the axes are known from the presence of the madreporite as well as in many types by the bilateral symmetry. With known axes he devised a nomenclature of areas which is of very great value and convenience in brevity and clearness of description. He numbered the ambulacral areas from I to V, Roman, and the interambulacra from 1 to 5, Arabic. The enumeration passed from left to right, re- volving like the hands of a watch, with the specimen viewed from below and the odd anterior ambulacrum being III. This nomenclature is considered more fully under Morphology. It is readily seen in its application to Goniocidaris (Plate 2, figs. 1-3). In dealing with Palaeo- zoic types, there was usually no means of ascertaining the axes, for the madreporite was seen in only four species. Since, in the absence of known axes, Lov6n's system could not be used, a system of nomenclature like that given in my earlier paper is followed. Taking any inter- ambulacrum as A, the several areas are lettered from A to J inclusive, revolving like the hands of a watch, with the specimen viewed from the dorsal side. When a specimen is viewed from below, the letters naturally revolve in the reverse order. This is shown in its application to Lovenechinus (Plate 39, figs. 4, 5). It may be well to call attention to the application of this nomenclature of areas to speci- mens viewed from different points so that it may be clearly in mind. External views, or in- ternal molds, viewed dorsally: the axes revolve clockwise, from left to right (Maccoya, Plate 34, fig. 4; Lovenechinus, Plate 39, fig. 5). External views, or internal molds, viewed ventrally: the axes revolve anticlockwise, or from right to left (Melonechinus, Plate 55, fig. 1; Lovene- chinus, Plate 39, fig. 4). In molds of the exterior, if dorsal: the axes revolve anticlockwise, from I.NTUODC* TION. 21 right to left, as Hyattechinus rarispinus (Plate 23, fig. 3) ami //. i>entagonus (Hat,- •_•:,, fig. 3). In molds of the exterior, if ventral: the axes revolve clockwise, from left to right, 11* in ////«//- echinus rarispinus (Plate 23, fig. 1) and //. /*-,//«,/»////« ( I'lute •_>:>, fin. 1 1. Orientation. ,,,,i only for the sake of the axes, but also for the correct position and introduction of columns .if plate* and direction of imbrication, must be borne in mind in a rever-ed -prcim.-n; for naturally confusion results unless this is taken into consideration. It *M a -trong temptation to n the drawings, so that external molds scon from the interior might appear as if -em from tin- exterior. It would have simplified matters as regards orientation, hut then tin- drawing- would not have corresponded with photographic figures of the same -peciim-H: also the (•.mi- plication is so great that I feared to make errors by reversing drawings. The terms molds and casts are often used indifferently, but it is nece— ary to distingui-h them. A mold, either internal or external, is an impression of a fossil and represents the ol.ject in reverse. A cast, either natural or artificial, is a mechanical filling of the mold and n-pre-ent- therefore a replica of the original. A pseudomorph differs from a ca>t simply in that it is a molecular chemical replacement of the original, as in silicification. in-tead of a mechanical filling of a mold, as in the case of mud, sand, or plaster. Most fossils, when they are not tin- original skeleton, are either pseudomorphs or molds; natural casts, strictly speaking, arc com- paratively infrequent. In the figure of Hyattechinus rarispinus (Plate 23, fig. 1) the te>t i- wanting, ami the view- represents an external sandstone mold of the ventral side, together with an internal mold of the dorsal side, seen from above. The mold of the ventral side, being external, -hows the tuberde- and peripodia of the ambulacral pores, but the mold of the dorsal side, being an imprr>.-ion of the interior, has no tubercles, and the ambulacral pores are represented by vertical plug*. This shows that the point of view must be constantly borne in mind and orientation carefully considered. As an aid in orientation, a rubber ball was marked with ambulacral and inter- ambulacral areas, then cut down on these lines, and marked within. Also dorsal and ventral plaster molds of a Cidaris were made and lettered as models, for it was found difficult to keep orientation clearly in mind in reversed views, as are external molds. An interesting matter is the condition of preservation of Palaeozoic or other fn>.-il Kchini. I have never seen a fossil sea-urchin in which the test was preserved in its original condition, but rather some chemical change seems always to have taken place even in late Tertiary s|M-ci- mens. In other groups of animals, as fossil molluscs, corals, etc., the original skeleton is often preserved without any change except the leaching out of organic matter. The sea-urchin skeleton is composed of such loose network-like structure, that it seems to be peculiarly ..|*-n to chemical readjustment and change. When the skeleton is calcified, the original microscopic structure is, at least usually, quite destroyed. The skeleton is often replaced by silica, when we may get very beautiful pseudomorphs preserving the finest details; an example of this Melonechinus giganteus (Plate 60, fig. 3). 22 ROBERT TRACY JACKSON ON ECHINI. One of the most interesting and instructive methods of preservation is when the surround- ing matrix, both internal and external, is completely silicified and the original skeleton is entirely gone, but is represented in finest details by molds in silica. Such an -example is shown in Loven- echinus missouriensis (Plate 39, figs. 4, 5). Here it is seen that everything that was not, is represented by the silica. This is rather a paradoxical statement, but fairly represents the facts. The plates are not preserved, but the sutures between the plates are represented by vertical siliceous ridges; the pores, both ambulacral and genital, are represented by vertical tubes, which can be actually seen (Plate 43, fig. 5) passing from the proximal to the distal side through the space which the plates originally occupied, but now simply a hollow. When the external as well as the internal matrix is in hand (Plate 44, figs. 3, 4), we find on one side, the internal matrix, a mold of the proximal side of the plates; on the other or external matrix we get the distal mold of the plates showing spine tubercles and other external features. Sili- ceous molds of the interior or exterior may be found in which there are no ridges representing spaces between the plates, but the difference of conditions between these two types is not understood. Molds, either internal or external, in fine sand or calcareous clay, are often ex- tremely clear and may be accompanied by more or less of the shell of the test, or this may be wanting. In a specimen of Palaeechinus quadriserialis in the British Museum, the test is crystalline calcite, but only part of the plates are preserved; most of the rest are, however, represented by impressions of their proximal faces on the matrix, as shown in Plate 29, fig. 1 , and Plate 30, figs. 1, 3. Sandstone molds may be so fine in details of preservation as to show the outline of plates, tubercles, pores, and even peripodia. Internal sandstone molds show only impressions of the proximal sides of plates with pores in relief as slight plugs. An excellent example is Hyatt- echinus beecheri, a unique specimen (Plate 24, figs. 5-8), which shows the details of outline of the proximal faces of the plates so clearly that I am enabled in Plate 26 to represent the sea- urchin spread out, in which every plate was measured and the angles counted. External sandstone molds are even better, for, on the exterior, details of structure are more strongly marked; tubercles and peripodia exist as depressions (the impression being in reverse), and ambulacral pores as slight elevated plugs. Examples are shown in Hyattechinus rarispinus (Plate 23, fig. 1) and H. pentagonus (Plate 25, figs. 1-4). A curiously complex case is the Hyattechinus rarispinus previously mentioned (Plate 23, fig. 1), in which is seen an external mold of the ventral side, showing tubercles and peripodia, and in the same view an internal mold of the dorsal side. The counterpart of this remarkable specimen (Plate 22, figs. 1, 2) shows just the reverse condition; that is, an internal mold of the ventral side and an external mold of the dorsal side. The test, which was extremely thin, is mostly wanting, but is existent on the margins. The dorsal and ventral sides are brought almost in contact, yet the sandstone did not close up, but retained as a thin interspace the vertical space originally occupied by INTRODUCTION. the thickness of the test with some sand which filled the interior of tin- tot, thu- making an internal mold possible. Loven devised the incomparable method of representing tin1 structure of a nca-un-hiii by a figure drawn from the ventral view and with the several ambulacra! and intcrambiilacral areas spread out flat in one plane in a star-like fashion. Of cour-e in tin- Palaeo/oic it i- only rarely that one finds a fossil sufficiently perfect to admit of such treatment ; but I give figure- drawn by this method of Bothriocidaris (Plate 1), Hyattechinus i Plate •_'»',), Archaeoci.lari- (Plate 10, fig. 10), Palaeechinus (Plate 30, fig. 3), Lovenechinus missouriensi* I'late- lo. 41), Lovenechinus septies (Plate 45), and Melonechinus (Plate 57). The-e genera are fairly repre- sentative of the several groups of Palaeozoic Echini, and the figures show tin- characters of the plates and the method of introduction of columns better than by any other method. While perfect specimens are desirable and most highly prized, yet a great deal can l>e made out of fragments when studied carefully. A left or right half of an ambulacrum repre- sents the character of the whole. A piece out of the mid-zone, that is, halfway between tin- mouth and middle of the periproct, represents the area where full specific characters are devel- oped in both the ambulacrum and interambulacrum, and many species are repn-ented by a figure taken from the mid-zone (Plate 47). Such a figure doe- not show the development as seen ventrally, or the apical disc, but these features are often wanting, or shown in related species, so that a figure of an ambulacrum and interambulacrum from the mid-zone gives for these areas the essential specific criteria. The skeletons of Recent sea-urchins are often very fragile, and even if not so. the periMomal and periproctal plates are easily injured and lost. It has been found a great help to dip tin- specimens in, or brush them over with, a dilute solution of shellac in alcohol, or gelatmc dissolved in water. Specimens so treated are firm and solid and will stand even rough treat- ment. A specimen with the spines all in place may be soaked in this manner by .lipping, and on account of the porosity of the skeleton, there will be no external evidence at ment; the spines will be firmly fixed in place, and the specimen is in much safer .-..u.li storage or study. Where sutures are difficult to see, as in minute recent material, or ami, lacral details, it has been found a great help to wet them with Ix-n/.ole. sutures stand out clearly that are nearly or quite unrecogni/able in the dry state. ing fresh material of Echini, I have found that a satisfactory method is to soak over night in a considerable volume of fresh water to remove the salt, then immer, minutes in boiling water containing a liberal amount of corrosive sublimate m treatment coagulates the albumen, poisons the specimens, and does no, affect will dry out without odor, and in excellent condition as museum specimens, the advantage of cheapness and quickness. When specimens are to be pr« the treatment with fresh water is also desirable, as it kills the animal nicely relaxed. .„ removing much of the salt. 24 ROBERT TRACY JACKSON ON ECHINI. The theoretical views expressed in this paper are supported by a sufficient basis in facts, so that they appear reasonable to me ; but I have endeavored to keep the descriptions of struc- tural detail and the conclusions drawn from them distinct, so that the facts will stand for them- selves, whether the deductions are accepted or not. TERMING LO( IV Some new terms are made use of and old terms are not used uniformly by all investigators, so that the principal terms employed are given here in brief. Test: the whole skeleton including the spines; or without spine.-, denuded lest. quently test alone is applied to the skeleton in which spines arc more or less wanting, the .-.„„- mon condition in fossils. • Corona: the portion of the test, including the ambulacral and interambulacral plates, extending from the periphery of the peristome to the ventral margin of the apical .li-c. In describing an ambulacrum or interambulacrum, the terms rii/lil or left are frequently u>c,|. They mean the right or left side as seen facirig the given area, viewed from the exterior and with the dorsal portion uppermost. Ambitus: the zone of greatest circumference as viewed from above. The ambitus may coincide with the mid-zone, Maccoya sphaerica (Plate 32, fig. 5), or it may lie ventral to the mid- zone, Hyattechinus beecheri (Plate 24, fig. 7), or Clypeaster; or rarely dorsal to the median zone, Lepidesthes coreyi (Plate 66, figs. 8-10). A sea-urchin is divisible into a series of zones which theoretically are as many as then- are horizontal rows of plates, and each zone, at least in earlier life, differs or may differ in char- acter from the preceding or succeeding zone. This is shown graphically in Hi/altrcli/nu.- beecheri (Plate 26); here in the first zone of interambulacral plates there is one plate in area, in the second zone two plates, in the third three plates, and so on up to the introduction of the full number of columns of plates, above which we reach zones of senescence, where plates begin to drop out. In practice, radial variation interferes somewhat with the perfect zonal expression, as all the areas do not develop with exactly the same degree of rapidity. For example, in Lovenechinus missouriensis (Plate 41, fig. 1), the fifth column originates in the fifth row above the initial plate of the fourth column in area A, whereas in the other areas it origi- nates in the third or fourth row. Similar variations in rate of development are frequent in later added columns, as shown (Jackson and Jaggar, 1896) in detailed studios of Meloncchinus multiporus, and as shown here in many figures. A column of plates may be quite wanting in one area, though developed in other areas of the same specimen. In Hyattechinus rarispnmx (Plate 23, fig. 3) there are only eleven columns of plates in areas A and (1, while there are twelve in area I and thirteen in C and E. In Lovenechinus missouriensis (Plate 41. fig. 1) the sixth column is represented by one or two plates in areas E, G, and I, but is wanting in A and C. A single zone is of course greatly modified in certain areas in bilateral types, as in ambu- (25) 26 ROBERT TRACY JACKSON ON ECHINI. lacrum III in many spatangoids. Such extreme zonal modification does not occur in normal regular Echini. The term zones has been sometimes applied as "ambulacral zones," but this seems an unfortunate use of the word, for such areas do not surround the test, as a zone should, and moreover are not parallel to the equator, which also the term commonly implies. Three main zones may be recognized in any sea-urchin, which I would designate as the basicoronal zone, mid-zone, and placogenous zone. In the basicoronal zone occur the basicoronal plates, the first row of ambulacral and interambulacral plates of the corona bordering on the peristome or buccal membrane. Love"n called these plates peristomal plates, but it seems an undesirable use of the word, which is usually applied to the buccal membrane and plates on the same. I therefore introduce the term basicoronal as meaning exactly what is intended, and not to be confused with terms applied to other parts. The basicoronal plates are of special interest as being the oldest or first formed plates occurring in any given corona, and also they are the plates giving support directly or through the perignathic girdle to important muscles of the lantern (text-figs. 22-31, p. 70; and 221-230, p. 193). The median zone, or mid-zone for brevity, is that horizontal zone measured halfway between the poles; it may coincide with the ambitus or lie dorsal to it, or rarely ventral to it. The mid- zone is important in Palaeozoic and most other Echini, as the area in which in the ambulacra and interambulacra the differential specific characters are typically most fully developed. Ventral to it the full features may not have been attained, and dorsal to it we soon get into the area of localized development, where the young plates have not attained the full characters of the species. In clypeastroids and spatangoids that have petaloid areas, these lie dorsal to the mid-zone, so that in such types special consideration of the dorsal area is necessary, but it does not invalidate- the mid-zone as an area of importance in the consideration of structure. The placogenous zone (wXaf = plate, + yeved = birth) is that portion of the corona next to the apical disc in which the newly added coronal plates occur both in the ambulacrum and the interambulacrum. This zone is of importance as the plates in it quite generally present youthful characters, which, as localized stages in development, can be compared with the characters seen in the young, or in the adults of simpler types in the group (text-fig. 237, p. 231). Row, as applied to ambulacral and interambulacral plates, refers to plates lying in one horizontal plane or zone, in contradistinction to columns. Column, as applied to ambulacral and interambulacral plates, refers to plates lying super- posed in a vertical series. The column is of course made up of nothing other than plates of a succession of rows, but is a convenient distinction to maintain in Palaeozoic types, where we find in various forms from two to twenty columns of ambulacral or one to fourteen columns of interambulacral plates. The column, especially in the interambulacrum, usually consists of a very definite succession of plates forced into a continuous series by the mechanical impact TKKMINOIAHJY. 27 of adjacent plates in the several succeeding rows. In the figure>. tin- columns of interambula- cral plates are numbered from one upward (Plate 57, fig. 1 ; text-fig. 246). Adradial suture, a term introduced by Bather (1909a), is the suture twtwmn the intcram- bulacrum and the ambulacrum. As a corollary, in Palaeozoic Echini, \vln-n ihere are more than two columns of interambulacral plates, those lying next the umlnilacra are i-alled the adradial plates. The term adambulacral plates or columns has been used, but the term mlrndial has the advantage of brevity. Median suture is the suture in the median line of the ambulacrum. When there are only two vertical columns of plates, it is perfectly obvious, but when more, it is dislinnui-hiiMe by the size of the two medial columns, as in Melonechinus (Plate 56, fig. 4); or if the plates do not differ in size, it is distinguished by the fact that the pores in the plates are set on t In- side toward the next adjacent interambulacrum and therefore are set on opposite -ides of (he- plates on either side of the median suture, Lepidesthcs wortheni (Plate 67, fig. H). The term median suture in Recent Echini is ordinarily applied also to the interambulaerum, and in Heccnt forms it is applicable, as there are two columns of plates; but, taking sea-urchins as a whole, it is not applicable to the interambulacrum; for it is only a coincidence of ordinal or specific character, if there is an even number of columns, and when there is, as in Palaeechinus quadri- serialis (Plate 30, fig. 3), the suture in the median line is riot distinguishable from any other interambulacral suture except the adradial. In considering ambulacral plates, a certain degree of nomenclature is convenient. Pri- mary plates extend from the middle of the ambulacrum to the interambulacral suture (Palae- echinus, text-fig. 9). Demi-plates extend from the interambulacrum inward, but do not r the middle of the ambulacrum. Occluded plates extend outward from the middle of the am- bulacrum, but do not reach the interambulacrum. Demi- and occluded plates are typically shown in Lovenechinus (text-fig. 11). Isolated plates do not reach either the interambulacral suture or the middle of the ambulacrum; such plates are extensively developed in Melonechinus and Lepidesthes (text-figs. 13, 14, p. 54). This nomenclature was based on the elemen compound plates in the Centrechinoida,1 but it seems that it may equally be applied to the complex arrangement of simple plates in Palaeozoic Echini. 1 The name Diadema, given by Schynvoet in 1711, cannot stand for a genus of eeliinodenns. The firsi |K«l-l.mnaean use of the generic name Diadema is in the "Museum Colonnianum," a dealer's eat:d<>giie published in Ixmdon, in \', of this work, the author's name does not appear on the title page, but in the Hritisli Museum ropy it is stated on two author- ities that the author was G. Humphreys. There are 12 species listed under I)i:id<-m:i, but of the-e only one is recognisable, :i« it is stated to be the same as Echinus esculentus Linne. On this evidence, if this work should be aeeepted. which is very doubtful, the genus Diadema would become a synonym of Echinus, as esculent™ is the ty|x- of that Reims. Linnaean use of the name Diadema was by Schumacher, 1817, who gave this as a generic name for a eirri|x>d, basin. Lepasdiadema Linn6, which Schumacher (1817, p. 90-91) changed to l)in-i,-m-i rufy.iri*. This name is a synonym of ( ,,ronvla diadema Oken (Lehrb. Naturg., 1815, part I, section 1, p. 360). Ranzani. in IS'.'O, also used the generic name Diadema a cirriped, adopting, as did Schumacher, Lepas diadema Linne, as the type and giving it the new name Diadema eandi 28 ROBERT TRACY JACKSON ON ECHINI. A simple plate is one which has held its original character of one undivided and independent piece. All plates in Palaeozoic Echini are of this character. A compound plate is one made up by the coalescence of adjacent plates, seen in the ambula- crum in certain groups, in which area alone is it known to exist. It is a character of the ambu- lacral plates in the Centrechinoida and some Holectypina, but is unknown in the Palaeozoic. The statement that compound ambulacral plates occur in Palaeozoic types has been made (Duncan, 1889a, p. 13), but it is an error; no such plates occur in any known type. Occasion- ally in regular Echini two genital plates, or a genital and an ocular, may fuse when the resultant may in a sense be considered a compound plate (text-figs. 186, 195, 196, pp. 168, 169). Divided plates are those derived by the splitting on lines of solution of a previously continuous plate. This has been shown by Mr. Agassiz (1904) in the genital plates of Phor- mosoma. According to him (1904, p. 96), splitting occurs in interambulacral and ambulacral plates in Phormosoma. Mr. Agassiz (1874, p. 642) attributed the formation of compound ambulacral plates in the Centrechinoida, etc., to the splitting up of original plates. He also says (1883, p. 17) that anal plates in Palaeozoic Echini are formed by splitting. I have had this possible origin of plates in mind, but in my studies have seen no evidence of the origin of plates by splitting in Palaeozoic or other Echini excepting genital plates in echinothuriids, and rarely the same or ocular plates as variants (text-figs. 190-194, p. 169). When the antero-posterior axis is known, Loven's nomenclature of areas is adopted, num- bering the ambulacra I-V and the interambulacra 1-5. In Palaeozoic species the axes are rarely known on account of the usual absence of madreporic pores. The axes are known from the presence of madreporic pores in Lovenechinus- lacazei (text-fig. 240), Lepidesthes formosa (Plate 68, fig. 5), L. colletti (Plate 71, fig. 1), and Meekechinus elegans (Plate 76, fig. 1). Axes are, assumed from bilateral symmetry in Hyattechinus beecheri (Plate 24, figs. 5, 8), from the orientation of primordial ambulacral plates, Bothriocidaris archaica (Plate 1, fig. 1), and from the apparently eccentric anal area, Echinocystites (Plate 20, fig. 1). In other Palaeozoic types the axes are oriented arbitrarily by letters A to J, as discussed in the Introduction. Dr. Bather called my attention to a paper by M'Clelland (1840) in which he recognized that the name Diadema is not available for a sea-urchin, but he did not propose a new name. To quote his words, p. 170, "We luckily get rid of the genus Diadema [for Echini], from the term having been previously applied to a genus of Cirrhopoda by Ranzani." High authorities reject Muerchen's (1774) names, therefore his Anadema is unavailable. The name Calmarius annellala is given by A. Agassiz (1872, p. 104) as a manuscript name of Gray's, and is treated by Agassiz as a synonym of Diadema setosum. As there is a closely related species, Echinothrixcalamaris (Diadema calamaris Gray), it seems probable that Gray's generic name was Calamarius, taken from that species. Calmarius is evidently the same name as Calamarius with the letter a omitted by error; on this basis it is preoccupied by Calamaria Boie, 1827 (reptiles). As a new name is thus necessary for this c;enus, I propose Centrechinus (Kt'vrpov, a sting, and t'xivos, sea-urchin) with C. setosus (Leske), from Key West, Florida, as the type. The Florida and West Indian Diademas are considered as Diadema anlillarum Philippi by A. Agassiz and Clark (1908), but here anlillarum is considered a synonym of setosum. As the name Diadema cannot stand for an echinoderm, being preoccupied for a crustacean, the family and ordinal names derived from that genus cannot by the rules of nomenclature be retained. They can be replaced by names from the typical genus and may be called Centrechinidae and Centrechinoida. TKIIMINOIXXJY. 2!) The term peristome is not used in LoveVs sense, but in the more usual sense of the buccal membrane with its plates extending from the mouth to the basicoronal plates. The peri-stome may be more or less plated with ambulacral plates only, with ambulacra! and non -ambulacral plates, with non-ambulacral plates only, or may be a naked membrane (text-figs. 40-54, p Primordial ambulacral plates: these are the first formed ambulacral plates, ten in number, primarily situated around the mouth in the buccal membrane (Plate 3, fig. 11), or secondarily a« basicoronal plates of the corona, as is usual in clypeastroids and spatangoids (Plate 3, fig. 15). Primordial interambulacral plates: these are the first formed interambulacral plates, five in number, one in each area, which may be retained at the base of the corona in the adult, or may disappear by resorption (text-figs. 22-31, p. 70). Ocular and genital plates are used in preference to radial and basal, as not implying an homology with those plates in crinoids. The sum of these plates may conveniently be termed the oculo-genital ring. Gills are external and interradial in position, situated on the border of the peristome, where they may well be called peristomal gills (text-figs. 55, 56, p. 83) ; or they are internal and radial in position, as Stewart's organs, Cidaris; or they may be external as modified tube- feet, when they may be called ambulacral gills to distinguish them from the interradial peristomal gills. The terminology applied to spines is necessarily rather arbitrary, as such great difference in size exists, but it is convenient to have some basis for description. Primary spines are the large spines occurring in such types as Cidaris or Arbacia. Secondary spines an- Ix-st represented by the smaller spines clasping about the base of the large ones in ( 'idaris. Mili.-mi- are minute spines seen between the smaller ones in Cidaris, or all the spines of Eohinarachniiis could be classed under this head. These are spines so small that it requires a microscope to see their structure. In the Palaeozoic we find primary spines and secondary spines in .Vrchaeo- cidaris (Plate 9, fig. 13) and Lepidocidaris (Plate 17, figs. 10-14). In some typos secondary spines only are known, as in Melonechinus (Plate 52, figs. 10, 11) and allies. Miliary -pines are so far known in Archaeocidaris only (Plate 11, fig. 4). The points of attachment of the spines are the tubercles which may be primary, secondary, etc., according to their size. The consideration of nomenclature of the parts of spines, plates, etc., of Echini is very clearly and definitely set forth by Bather (1909a). The Aristotle's lantern is described as inclined, when in side view it subtends an angle of about 90°, the character of the Echinocystoida and Perischoechinoida (Plate 27, fig. 6); erect, when the faces of opposite sides are approximately parallel, the usual character of Recent regular Echini (Plate 5, fig. 2); and procumbent, when the flaring lantern rests almost on the base of the test, as in the Clypeastrina. Terms applied to the parts of the lantern are as foil. IWB. There are five teeth which are grooved or keekd (text-figs. 210, 212, p. 184). Kach tooth is 30 ROBERT TRACY JACKSON ON ECHINI. embraced and held tightly in place by one of the pyramids, and proximally the soft growing end is enveloped by the dental capsule (Plate 5, figs. 1, 6). The pyramid dorsally includes a triangular space, the foramen magnum, which is shallow, or deep, and dorsally open, or closed by the lateral extension of the epiphyses (text-figs. 207-216, p. 184). The two half -pyramids, forming one pyramid and joined by suture, are interradial in position (text-fig. 211, p. 184); or the two half-pyramids joined by an interpyramidal muscle are radial in position (text-fig. 220, p. 191). These radial half-pyramids are a feature connected with the view of considering a sea-urchin as composed of five radial parts (pp. 62, 190, text-figs. 217-220). Each half-pyramid bears on its inner face an elevated ridge, the dental slide, which supports the tooth (Plate 2, fig. 10); and has a lateral wing that extends to the oesophageal cavity; on the outer face of the wing in regular Echini are ridges for the attachment of interpyramidal muscles (Plate 5, figs. 3, 5, 9). The dorsal face of a half-pyramid, seen when the epiphysis is removed, is described as smooth when no pits exist, Perischoechinoida, Cidaroida, or is described as having pits when such structures exist, Centrechinoida (text-figs. 208-213). Each half-pyramid is surmounted by an epiphysis, which is narrow, when it extends only slightly beyond the half-pyramid, or wide, when it extends across the foramen magnum uniting in median suture with its fellow of the opposite side (text-figs. 207-216, p. 184). Each epiphysis presents a glenoid cavity and tubercles for articulation with the brace, and in the Camarodonta crests for support of the tooth (Plate 2, fig. 14; Plate 5, figs. 2, 5, 9). The brace is a block-shaped plate and presents condyles and foramina which interlock with the glenoid cavities and tubercles of the epiphyses (Plate 2, figs. 9, 13, 15). In all regular Echini there are five compasses, each composed of twro pieces joined by a transverse suture (Plate 2, fig. 12). The lantern muscles are termed protractors, retractors, interpyramidal, brace muscles, circular compass and radial compass muscles (Plate 5, figs. 1, 2, 4, 12; Plate 4, fig. 4; text-figs. 218-236, pp. 191, 193, 197). The perignathic girdle, when existent, consists of processes arising from the basicoronal plates. Apophyses are upward growths, of basicoronal interambulacral plates; auricles are here limited to separate pieces arising from the basicoronal ambulacral plates, to wrhich they are joined by close suture, not being continuations of these plates as apophyses are of inter- ambulacral plates (text-figs. 218-230, pp. 191, 193). The auricles in Phormosoma give rise to radial somatic and radial peristomal muscles, which are known only in the Echinothuriidae (text-fig. 226). The diameter of the test in regular circular Echini, where the axes are known, is measured on the plane of the ambitus and passing through ambulacrum III and interambulacrum 5. In regular Echini, which are elliptical in horizontal outline (Echinometridae) , or elongate irregular Echini, the length is taken in the longer axis and includes the over-all measurement of the corona. PART I COMPARATIVE MORPHOLOCY OF K( HIM Having enjoyed the opportunity of studying most of the genera and >pecie- nf I'nlaeo/.oic Echini, it is of importance to sum up the comparative structure :md morphology of tln-«e t\ ]»•- and to show their relations to living forms. Palaeozoology is only one aspect of zoology, distinguished from the study of living animals about as embryology, a study of the young, is in so far separated from a study of adult organ- isms. As Huxley said, the only difference between a collection of fos-iN and a collection of recent animals is that one has been dead longer than the other. For an intelligent -tudy of fossils their living representatives must be constantly borne in mind, as their details of -truc- ture throw a flood of light on fossil forms. Conversely a study of fn-.il> in relation to the living gives a knowledge of the earlier and often primitive representatives of a group, throws light on the structure of the adult, and especially of the young of living types, and gives a rounding out of the knowledge of a group that cannot be attained by a study of the living forms alone. This is my excuse, if such is necessary, for including in this discussion representatives of living and other post-Palaeozoic Echini in the summing up of the relations and structure of the Pal- aeozoic types, with which this memoir is primarily concerned. Under the consideration of Morphology are taken in order the form of the test, orienta- tion, the pentamerous system and variation, the structure of the skeleton, and growth. In the sea-urchin there are many anatomical parts for consideration, and they are taken up in the following order: the ambulacrum and interambulacrum of the corona, l.asieoronal plates. imbrication, spines, peristome, ocular and genital plates, peripn.ct. Arutotie'fl perignathic girdle. FORM OF THE TEST. The general shape of the test of a sea-urchin varies greatly, but is more constant in zoic than in post-Palaeozoic types. The test may be elliptical with the vertical : longer than the horizontal through the mid-zone, Bothriocidaris. ftbaecfl 29, fig. 2), Lepidesthes cottetti (Plate 69, figs. 2-6). In Recent Echini the test elliptical as in Amblypneustes formosus Valentin, a species in which the height may the diameter, though not always (A. Agassiz, 1873, p. 479). The test (31) 32 ROBERT TRACY JACKSON ON ECHINI. quite spherical, Maccoya sphaerica (Plate 32, fig. 5), most species of Lovenechinus and Melon- echinus (Plate 55) ; or depressed spheroidal, as in Archaeocidaris and Cidaris. In all the above types the ambitus coincides very nearly with the mid-zone. The hori- zontal section in any zone may be nearly or quite circular, or modified by more or less pro- nounced melon-like ribs or elevations of both the ambulacra and the interambulacra, as in Melonechinus (Plate 60, fig. 3). The test may be depressed spheroidal with ambitus below the mid-zone, as in Lepidocentrotus whitfieldi (Plate 19, figs. 6, 7), or recent Strongylocentrotus. Rarely the ambitus is above the mid-zone, as in the high obovoid Lepidesthes corcyi (Plate 66, figs. 8-10) and Melonechinus obovatus (Plate 54, fig. 2). As far as I am aware, this character of ambitus above the mid-zone is known otherwise typically only in the recent depressed Echino- strephus molare (Blainville), in which Mr. Agassiz (1873, p. 457, Plate 5a, fig. 11) showed that the greatest diameter is near the abactinal surface. It may occur occasionally as a variation, as I found in three specimens of Strongylocentrotus purpuratus out of 120, and in one specimen of Strongylocentrotus drobachiensis in 33,000. It is undoubtedly an exceptional character for the ambitus to be above the mid-zone in fossil or Recent Echini. The test may be depressed with strongly pentagonal outline, as in Hyattechinus pentagonus (Plate 24, figs. 1-4). It may.be circular but greatly flattened dorso-ventrally, as in Hyattechinus rarispinus (Plate 22), which apparently closely approached Echinarachnius in form. Or finally, in Palaeozoic types, the test may be flat on the base with rounded dorsal side, of moderate bilaterality, almost Cly- peaster-like in form, as in Hyattechinus beecheri (Plate 24, figs. 5-8). This includes all the forms of tests known in the Palaeozoic species. The test may be radially equal with central periproct, as are most Palaeozoic Echini and most post-Palaeozoic regular Echini except Echinometra and allies. Or it may be bilateral with central periproct, Hyattechinus beecheri (Plate 24, figs. 5-8; Plate 25, fig. 5), a character not known to me in any other Echini. Or it may be more or less regular in form but with the periproct eccentric in an interambulacrum, which is probably the odd posterior interambu- lacrum, Echinocystites. ORIENTATION. The matter of orientation of a sea-urchin in relation to its true axis is important, and has been briefly touched upon in the Introduction. Love"n (1874) urged that the proper orienta- tion of an echinoid is to take as the antero-posterior axis a line drawn through an ambulacrum and opposite interambulacrum, in such a plane that the madreporite lies in the right anterior interambulacrum. It seems rather arbitrary in the regular modern Echini at first sight, but there are good reasons for the acceptance of this orientation here. The most obvious reason, as pointed out by Lovdn, is that it is morphologically the same line on which bilaterality is ORIENTATION. developed in all the irregular Echini. The ambulacra fall into a po-terior pair, the bivium of Lov<5n, and an anterior set of three, consisting of the right and left anterior ambulacra and the odd anterior ambulacrum, the trivium of Loven.1 It has been claimed that in regular Echini the madrcporite is tin- only structure .MI which orientation could be based (A. Agassiz, 1881, p. 7). While this is apparently true in many Echini, I have attempted to show under the discussion of ocular plates that in many regular modern Echini a bilateral symmetry is expressed and orientation obtained by the order in which ocular plates reach the periproct. To state the case in brief: in the young of apparently all modern regular Echini, the ocular plates are exsert." The same condition exists in the adult of many species. On the other hand, many species have in the adult one or more plate - i; or reaching the periproct, either as a typical character or as a variation. On the bttH of ob- servations on 50,000 specimens, the evidence is that the first oculars to become insert are tin- plates of the bivium, next the plates of the posterior pair of the trivium. and la-t. if at all, t he- anterior odd plate of the trivium. The order of reaching the periproct i- I. V. or V. I. then IV, II, III. This order is very closely adhered to, as shown later in tabulated form. The ocular plates therefore in many regular Echini express a bilateral symmetry in this group, and an orientation passing through ambulacrum III and interambulacrum 5, the plane of symmetry adopted by Loven. As studied from the ventral view, Love"n (1874) showed graphically that the si/.c and character of the primordial ambulacral plates give excellent data by which to ori< i urchin, at least in the Irregulares and often in the Regulares as well. He -howed that of the ten basicoronal ambulacral plates in (typical) clypeastroids and .spatangoids, the In, II<;. III/.. IVa, V6 are larger, and in spatangoids possess two separate pairs of pores, or two separate single pores, indicating two tube-feet. On the contrary, the 16, 116, Ilia, ]\'l>. \'n are -mailer, and in the spatangoids bear only a single tube-foot, Collyrites (Plate ',',. tig. l.~>). Tin- -\-i.-m of alternation has but this one combination, a sort of key, by which the axes can be • tained with entire certainty, as shown in numerous genera and species 1 1. oven. Is? I . Mr. A. Agassiz shows the same characters in his splendid work on Panamic Echini in numerous spatangoids as well as in many regular Echini. Loven (1892) showed that in the primordial ambulacral plates on the peri-tome in young Goniocidaris (Plate 2, fig. 1) the same system of alternation of large and small plate- prevails. He (1874) also showed that it exists in the primordial plates surrounding the mouth in adult 1 Mr. Agassiz (1881, p. 7) objected to Loven's orientation as it does not take account of the madreporitr in relation to the spiral system of development of plates. The spiral system was first suggested l>y I'n.iY-^.r I.. \ci>-i; I vil) and considered by A. Agassiz in several publications (1864, p. 12; 1874, pp. 640, 722, T'.'l; ISM. p. 7; i t hat I have not succeeded in recognizing the spiral arrangement of plates in Echini. 2 It is possible that in Aspidodiadema and close allies the oculars are insert from thrir cai : 34 ROBERT TRACY JACKSON ON ECHINI. Cidaris. Mr. A. Agassiz (1904) in the Panamic Echini shows the same system in young Poro- cidaris cobosi A. Ag. (his Plate 12, fig. 2), young Saknocidaris miliaris A. Ag. (his Plate 16, fig. 1), young Phormosoma placenta A. Ag. (my Plate 3, fig. 10). He also shows the interesting fact that the same order of ambulacral plates exists around the mouth in the adults of Cidaris (Dorocidaris) panamensis (A. Ag.) (his Plate 3, fig. 4), Porocidaris milleri A. Ag. (his Plate 7, fig. 6), Echinosoma hispidum (A. Ag.) (his Plate 41), Phormosoma zeylandiae A. Ag. (his Plate 50, fig. 1), and Kamptosoma indistinclum A. Ag. (his Plate 50, fig. 1). It is true that in the adult of most of the regular Echini, where the primordial ambulacral plates surround the mouth, usually more or less isolated, they have not retained the relative proportion of the Love"n system seen in the young, and from them one could not orient a sea- urchin. This has been dwelt upon at some length because in my studies of Bothriocidaris archaica (Plate 1, fig. 1) it was found that the ambulacral plates around the mouth are arranged according to the Lov6n law, which shows that it already was at work in the oldest known sea- urchin. It is worth mentioning that I was ignorant of the law at the time the drawing was made so that no prejudice came in to influence the making of the drawing. Love'n maintained that the sea-urchin could also be oriented by the relative size and posi- tion of the ten interambulacral plates found at the base of the corona in regular Echini, the la, 2a, 36, 4a, 56 plates being smaller, the 16, 26, 3a, 46, 5a larger. This is often true, but often not true, and it seems that the law has no general application. Loven's laws of orientation were carefully studied to see if correct orientation could thus be obtained in the Palaeozoic types, but with the exception of Bothriocidaris without success. In Palaeozoic genera, as far as known, ambulacral plates always extend on to the actinostome as far as the mouth, as shown in Bothriocidaris, Hyattechinus, Pholidechinus, Melonechinus, and Lepidesthes, and if suffi- ciently well preserved, the orientation by primordial ambulacral plates might be applied, as in Bothriocidaris. This, however, must await future study. In the cases of Lepidesthes formosa (Plate 68, fig. 5), L. colktti (Plate 71, fig. 1), Meek- echinus elegans (Plate 76, figs. 1, 6), and Lovenechinus lacazei (text-fig. 240), the specimens are correctly oriented by the presence of a madreporite. Bothriocidaris archaica (Plate 1, fig. 1) is oriented by the relation of the primordial ambulacral plates; Bothriocidaris pahleni and B. globulus (Plate 1, figs. 6, 9) by the large ocular plate which, as shown in B. archaica, overlies ambulacrum III. Hyattechinus beecheri (Plate 24, figs. 5-8) is oriented by the plane of bilateral symmetry through an ambulacrum and posterior interambulacrum. Echinocystites pomum (Plate 20, fig. 1) is oriented by the eccentric anal area situated in an interambu- lacrum, presumably the odd posterior. The other species of Palaeozoic Echini figured cannot strictly be said to be oriented, as the letters designating areas are selected arbitrarily in each specimen without regard to a definite axis, which is an unknown quantity. The letters are used simply as a convenience in description for reference to specific areas. THE PENTAMEROUS SYSTEM AND V.Mil ATION. THE PENTAMEROUS SYSTEM AND VARIATION. In echinoderms as a whole the pentamerous system is remarkably constant an a character. In cystoids, however, we may have less than five ambulacra, as in Kcliinospl.a.Tit,-. uhirh has three ambulacra, or more than five, as in Caryocrinus, which has many aniliul.-icral p.v In starfishes many genera, as Heliaster and Solaster, have typically more than liv.- areas, and in some that have five, variation is common. In brittlestars more than five areas occur rarely as a specific, and in one instance as a sexual character. In all other groups of echinoderms the pentamerous system is very constant in all genera, and is departed from only as an indi- vidual variation. This variation is quite common in blastoids and crinoids. In Echini amongst Palaeozoic species, no case is known of departure from the pentamermis system, and it is apparently rare in living Echini. Bateson (1894) gives thirteen cases of complete or partial reduction to four-rayed sea-urchins in several genera of post-Palaeozoic fossil or Recent Echini. He also gives two cases of six-rayed urchins, a Galerites and an Amblypneustes, and three cases in which there is a sixth ambulacrum only. Chadwick (1898) described a four- rayed Echinus esculentus Linne", in which, however, there were five teeth. Ritchie and Mclntosh (1908) describe, very carefully, an Echinus esculentus with a partial reduction to four areas. Tower (1901) records an Echinarachnius parma from Woods Hole with one of the ambulacra imperfectly developed, and Hawkins (1909a) an Amblypneustes with two ambu- lacra incomplete dorsally. Osborn (1898) described a four-rayed Arbacia punclulata, de Loriol (1883) a partially six-rayed specimen of Stomopneustes, and Ribaucourt (1908) a completely hexamerous Strongylocentrotus lividus. I have been fortunate enough to study 71 specimens of Echini with a complete or partial departure from the pentamerous system. Besides being curiosities, these show very interest- ing morphological characters. Sixty were discovered in an examination of about 50,000 specimens for the characters of the apical disc, so that the variants from the pentamerous system averaged a little more than one to a thousand. The variants are partially or completely trimerous, tetramerous, and hexamerous. They are numerically as follows: one Eucidaris tribuloides in 849 specimens, six Arbacia punctulala in 2,329 specimens, two Echinus nuigel- lanicus in 200 specimens, 38 Strongylocentrotus drobachiensis in 33,000 specimens, one Stmngy- locentrotus eurythrogrammus in 56 specimens, two Toxopneustes variegatus in 1,043 specimen-, five Toxopneustes atlanticus in 2,643 specimens, three Tripneustes esculentus in 703 specimen-, one Echinometra lucunter in 754 specimens, and one Colobocentrotus atratus in 82 specimens. As later discussed, the ocular plates seem to exert a controlling influence in the building up of the corona, as below and in immediate contact with the oculars originate the coronal plates, both ambulacral and interambulacral. In connection with each ocular is developed a whole ambulacrum, and, in addition, a half-interambulacrum on either side. That is. while 36 ROBERT TRACY JACKSON ON ECHINI. an ambulacrum originates on the ventral border of an ocular, each interambulacrum may be considered as composed of two halves, the plates of which originated on the left or right of the area in contact with the adjacent oculars (text-figs. 217, 218, p. 191). If this is true, then the loss of an ocular would cause a failure to develop of the plates that normally went with it, also an abnormal position of an ocular (Plate 7, fig. 2) should cause an abnormal distribution of the associated coronal plates. The cases of departure from the pentamerous system are taken up in the order of their structural characters. They are described in at least one case of each class and other cases are noted. The cases fall under twenty more or less distinct combinations of characters, and to facilitate the distinctions, they are numbered under so many distinct heads. Trimerous. 1. Three ambulacra, inter ambulacra, oculars, and genitals, four teeth. — A specimen of Strongylocentrotus drobachiensis collected at Dumpling Islands, North Haven, Maine, measur- ing 5.5 mm. in diameter (R. T. J. Coll., 812), is the nearest approach to a completely trimerous sea-urchin known. There are three ambulacra and interambulacra throughout the corona. There are also three oculars and genitals. The oculars all reach the periproct, an extraordinary character in the species, but no rules can be expected to apply in such a freak. There are four teeth and eight primordial ambulacral plates in the peristome. 2. Pentamerous ventrally, three ambulacra and five interambulacra dorsally, five oculars and genitals. — It is quite a frequent occurrence for one ambulacrum to fail to reach the apical disc, but rarer for two ambulacral areas to drop out. In a specimen of Strongylocentrotus drobach- iensis from Dumpling Islands, 43 mm. in diameter (R. T. J. Coll., 813), the test is quite normal ventrally, but dorsally ambulacra III and IV drop out (similarly, but later than in Plate 7, fig. 4), so that interambulacra 2, 3, 4 come in contact dorsally and make a continuous series of plates. All five interambulacra continue to the apical disc. There are apparently five oculars, but III and IV are imperforate and merged in a series of split genitals. There are five genitals, but genital 3 is imperforate and much split up by secondary sutures. A Strongy- locentrotus drobachiensis from Frenchman's Bay, Maine (R. T. J. Coll., 907), which measures 53 mm. in diameter, is pentamerous ventrally but ambulacra I and V drop out below the mid- zone. All oculars are in place but I and V are imperforate. As a result of this structure interambulacra 1, 5, 4 are confluent dorsally and the six columns of plates of these three areas extend to oculars II, I, V, IV as usual. A specimen of Toxopneustes atlanticus from Bermuda (R. T. J. Coll., 814) is quite similar. It is 52 mm. in diameter and ventrally normally pentamerous. Ambulacra III and IV fail to reach the apical disc by a distance of 10 mm., so that interambulacra 2, 3, 4 are in contact THE PENTAMEROUS SYSTEM AND \ Aid ATlo.V '.M dorsally. There are five oculars and genitals, but oculars III and IV are imperforate. An imperforate ocular is usual when an ambulacrum drops out i Plate 7, fig. 4) and evident!;, correlated structure. The same structure is shown also in a specimen of Arbacia punctnlntn from Woods Hole, Massachusetts (R. T. J. Coll., 815). It i> a -mall individual. 22 mm. in diameter, and distorted. Pentamerous ventrally, the ambulacra I and IV drop out dor-ally so that interambulacra 5, 1, and 3, 4 are in contact dorsally. Five oculars and genital- are in place dorsally but somewhat distorted. There are as an independent variation eight plates in the periproct of this specimen. 3. Pentamerous ventrally, three ambulacra and interambulacra dorsally, three oculars and Jin- genitals in place, two oculars out of place. — An ocular or a genital may be wanting, but when present, they are almost universally in place in the apical disc. No case of a disjunct genital TEXT-FIO. 1.- Strongylocentrotus drobachiensis (O. F. Muller). Sullivan, M:,in.-. I)i:un. « mm. II. T. J. < 710. X 3.5. Oculars I and IV with associated coronal plates displaced. 38 ROBERT TRACY JACKSON ON ECHINI. has been seen, but in two cases oculars are separated more or less widely from the apical disc (text^fig. 1, and Plate 7, fig. 2). In a Strongylocentrotus drobachiensis (text-fig. 1) a curiously abnormal and instructive condition occurs. The test is pentamerous ventrally, but dorsally the terminations of two ambulacra and four half-interambulacra are disjunct from the apical disc. There are five genitals and three oculars in the apical disc, but two oculars, I and IV, have become separated from the oculo-genital ring. The system is the same as that described in Toxopneustes (p. 42; Plate 7, fig. 2), only, as the separation occurred later in life, the distance of the oculars from the apical disc is not so great as in the Toxopneustes. Ocular IV (text-fig. 1), is furthest removed. Ambulacrum IV is twisted dorsally, but extends ventrally as usual. The right half of interambulacrum 3 abuts against ocular IV, and the left half of interambulacrum 4 curls around dorsally so as to come in contact with the opposite side of ocular IV. The left half of interambulacrum 3 and right half of 4 extend to oculars III and V respectively as usual. A similar condition exists in the relation of the ambulacrum and half interambulacra to the misplaced ocular I. If the abnormality had occurred earlier in growth, this would have made a very striking specimen, but yet it elucidates the principles involved quite clearly. In this specimen it is clear that ambulacra I and IV, with the associated half interambulacra follow the oculars I, IV in their displaced position. Tetramerous. 4. Four ambulacra, interambulacra, oculars, genitals, and teeth. — More or less completely four-rayed specimens are the commonest departure from the pentamerous system, yet com- pletely four-rayed specimens were seen in only nine cases, all in three species. In a specimen of Strongylocentrotus drobachiensis (Plate 6, fig. 9) there are four ambulacra, interambulacra, oculars, genitals, and teeth, and eight primordial ambulacral plates in the peristome. It is oriented by the madreporite and character of the bivium reaching the periproct, or insert, as it is here called, which is a strongly dominant feature of the species. Accepting this orienta- tion, the absent parts are ocular IV and its associated parts, which are ambulacrum IV, the right half of interambulacrum 3 and the left half of interambulacrum 4. The missing genital may be either 3 or 4, which, it is perhaps impossible to say. Four other specimens of Strongylo- centrotus drobachiensis show the same structure. In all, the bivium is insert and the missing parts are the same as in the specimen just described. One of these specimens is from Dumpling Islands, Maine (R. T. J. Coll., 816), and measures 18 mm. in diameter. Two are from French- man's Bay, Maine (R. T. J. Coll., 908, 909), and measure 42 and 52 mm. in diameter respectively. The fourth specimen is from Truro, Massachusetts (R. T. J. Coll., 817), and measures 26 mm. in diameter. In this specimen the lantern is wanting, but there are eight auricles which indicate a four-parted lantern. Four specimens of Microcyphus maculatus, THK I'ENTAMKKOCS SVSTK.M AND VAItlATIO.V 39 from Mauritius, with complete or partially tetramerous tests, were found in :{|:{ -periiiu-ii- examined in the Museum of Comparative Zoology by Dr. H. L. Clark. Three of them fall under the present head, with four teeth, eight primordial ambulacral plates, four ambulacra! and interambulacral areas in the corona, four oculars and genitals. In one of the specimen- two of the genitals are fused, and in one of them a genital is split into three part - An Echinometra lucunter from Jamaica, in the Museum of Comparative Zoology, i.- cnm- pletely four-rayed, with four teeth, eight primordial ambulacral plates, four ambulacra ami interambulacra in the corona, four oculars and genitals. The absent parts are ocular and ambulacrum I and genital 1, the left half of interambulacrum 1 and the right half of interambulacrum 5. 5. Four ambulacra, interambulacra, and oculars, five genilals, four teeth. — This structure differs from the last described only in that there are five instead of four genital plates. An example is seen in Arbacia punctulala (Plate 8, fig. 2; Plate 6, fig. 1). The specimen is small, 2G mm. in diameter, but is higher than usual proportionately, 19 mm. It is perfectly shaped, not abnormal in appearance. There are five genitals, the only pentamerous part of the animal observed, but there are only four genital pores, one being absent in the madreporite. The specimen is oriented by the madreporite and planes of arrangement of the periproctal plates. Only four oculars are present. The absent parts are ocular and ambulacrum II completely, also the right half of interambulacrum 1 and the left half of interambulacrum 2. The corona consists, therefore, of four ambulacra with three interambulacra and two half-interambulacra. There are four teeth, four pairs of auricles, and eight primordial ambulacral plates. A second almost completely four-rayed Arbacia punciulala, from Woods Hole, Massachu- setts, is in the American Museum of Natural History. This like the above is small, |>erfeetly formed/ not at all distorted. It measures 25 mm. in diameter through the ambitus and 18 mm. in height. There are five genital plates, but the madreporite has no genital pore, and lies in close contact with genital 3 just as the madreporite lies in contact with genital 1 in Plate G, fig. 1. There are four oculars, ambulacra, interambulacra, and teeth throughout. The absent parts are ocular and ambulacrum III, the right half of interambulacrum 2, and the left of interambula- crum 3 (compare Plate 6, fig. 1). A third specimen of Arbacia punciulala, from Woods Hole, in the Museum of Comparative Zoology, has a similar structure. It has four ambulacra, interambulacra, and oculars, but five genitals, one depauperate and imperf orate. The wanting parts are ocular and ambulacrum I, the right half of interambulacrum 5, and the left half of interambulacrum 1. The terth are wanting. The Arbacia punciulala described by Osborn (1898) is similar to the above three, the five genitals being the only pentamerous portion. In his specimen as gathered from tin- description and figure, the absent parts are ocular and ambulacrum I, the right half of inter- ambulacrum 5, and the left half of interambulacrum 1. 40 ROBERT TRACY JACKSON ON ECHINI. In Yale University Museum a specimen of Arbacia lixula from the Mediterranean has four areas. It is one of a lot of four specimens (cat. no. 199). There are five genital plates, but only four oculars and four ambulacra and interambulacra which extend from the basi- coronal row to the apical disc. The lantern is wanting. The absent parts are ocular and ambulacrum I, the right half of interambulacrum 5, and the left half of interambulacrum 1; therefore the left half of interambulacrum 5 and the right half of interambulacrum 1 are in contact and form a single area (compare Plate 6, fig. 1). This area is wider than usual for an interambulacrum, and the plates bear more primary tubercles than usual, but the tubercles are spaced about as in other areas, and in normal specimens. This indicates, as shown in the reverse condition in Tripneustes (p. 47), that tubercles and spines are distributed at a given distance apart, rather than a given number to a plate, as a species character. Genital 1 is somewhat distorted. Professor Verrill (1909) has given an excellent photographic figure of this specimen. A small specimen of Strongylocentrotus drobachiensis (Plate 7, fig. 3) has much the same character as the above described Arbacias. The specimen is normally shaped except that it is unusually high, dome-shaped. It is 35 mm. in diameter and 24 mm. high. There are four ordinary genitals and a small plate between the madreporite and ocular I may be considered a depauperate and imperforate fifth genital. There are four oculars. The specimen is oriented by the madreporite and the two insert ocular plates which in this species mark the bivium. The absent ocular on the basis of this orientation is evidently that one which should lie between the madreporite and the depauperate genital next to it. The absent part of the corona is ambulacrum II, also the right half of interambulacrum 1 and the left half of interambulacrum 2. The lantern is wanting, but there are four pairs of auricles indicating a four-parted lan- tern. A similar structure occurs in a specimen of the same species from Dumpling Islands (R. T. J. Coll., 818). It is small, 15 mm. in diameter, not distorted, and completely four-rayed except for the five genitals. The madreporite has no genital pore. The missing parts are ocular and ambulacrum II, the right half of interambulacrum 1 , and the left half of interambula- crum 2. 6. Four ambulacra (but ten primordial ambulacral plates) , four interambulacra and oculars, but five genitals and teeth. — This combination was found in a specimen of Strongylocentrotus drobachiensis from Dumpling Islands, 5.5 mm. diameter (R. T. J. Coll., 819). Being very young, all the genitals are imperforate except for the madreporic pores. Ocular I only is insert. The missing parts are ambulacrum and ocular II, the right half of interambulacrum 1, and the left half of interambulacrum 2. Surrounding the five teeth are ten primordial ambulacral plates. This indicates that it began life as a pentamerous individual, but no trace of a fifth ambulacrum is seen in the corona. A second specimen with these characters occurs in an Echinus magellanicus, from Port THE PKNTAMKKOrS SVSTKM AM) VARIATION 41 Gallant, Patagonia, in the Museum of Comparative Zoology. It ha- live teeth and ten pri- mordial ambulacral plates, four ambulacra and interainbula'Ta in tin- corona, four ocular-, but five genitals. The wanting parts are ocular and ambulacrum V, the right half of inter- ambulacrum 4 and the left half of interambulacrum 5. 7. Four ambulacra, but five interambulacra, oculars, genitals, and teeth.— In Arbacia punctulata (Plate 7, fig. 1) an ambulacrum is entirely absent, but otherwise tin- -pecimen is pentamerous. It is a small specimen, 22 mm. in diameter. Dm-sally there are five genitals and oculars, ventrally five teeth and ten primordial ambulacral plates. Then' i- no trace i.f ambulacrum IV in the corona. Interambulacra 3 and 4 have each two column- of plates which extend dorsally to oculars III, IV, V, as usual in columns of these two areas. In addition to the four columns, there are ventrally several plates representing a fifth column and one plate a sixth column. These extra columns cannot be referred with assurance to either areas 3 or 4, but were in all probability developed below ocular IV and serve as space filler- in the corona to occupy the place that would have been filled by ambulacrum IV if it had develo(>cd. This specimen superficially is suggestively like Palaeozoic Echini where four or more columns exist in an interambulacrum, the median columns being made up of plates which in general are hexagonal, and the adambulacrals pentagonal. Here, however, the many columns are tin- result of the union of two areas, not one area as in the Palaeozoic. 8. Five ambulacra, four interambulacra, four oculars (one with two pores), four ome\vliat irregularly r-hapod plate (compare oculars in text-fig. 1, p. 37). Below this ocular extends aml.ulacrum II, which finds its dorsal limit in this plate. Also extending vent rally from ocular II then- arc two half-interambulacra, the right half of interambulacrum 1 ami tin- l.-ft half of interaml.ula- crum 2. Proceeding dorsally from ocular II, the coronal plat.- that an- typically awoeiated with this plate cease, but the left half of interambulacrum 1 ami the right half of interaml.ula- crum 2 fill the space and extend respectively to ocular I and ocular III, their normal i>omt of origin. There are five teeth. This specimen owes its peculiarities to relatively late influence-, not congenital. It is similar in principle to text-fig. 1, p. 37, but is more striking :is the ocular is farther removed from its normal position in the apical disc. It lends weight to the view held that ocular plates are a controlling influence in the development of the corona, and that from each ocular originates an ambulacrum and two half-intcrambulacra (compare text- fig. 218, p. 191). 13. Pentamerous ventrally, four ambulacra and inlerambulacra dorsally, J genitals.— A Strongylocentrotus drobachiensis from York, Maine (R. T. J. Coll., 823), 40 mm. in diameter, is pentamerous ventrally, but ambulacrum II consists of only a pair of |.l basicoronal row. The associated two half-interambulacra of areas 1 and highly reduced. Above this extreme ventral area there are only four ambulacra an. ambulacra. The ocular associated with ambulacrum II has quite disaPI>eare«l. pmbabl resorption. Four oculars and five genitals are in place in the apical disc depauperate and lies against the madreporite. There are five pairs of auricles. structure is shown in an Echinus mageUanicus from the Straits of Magellan in the . of the United States National Museum. There are five teeth and ten prunor lacral plates. In the corona there are five ambulacra and interambulacr ambulacrum I and the associated interambulacral plates exist for only a short du which there are only four areas. There are four oculars and five gcnit; 1 and 5 are depauperate and imperforate. 14 Pentamerous ventrally, four ambulacra and inlerambulacra dorsntl,, genitals.- A Strongyhcentrotus drobachitnsis from Dumpling Islands. M, 824) 18 mm. in diameter, is completely pentamerous ventrally. ventral border ambulacrum V drops out and also the two associated half- Ocular V has quite disappeared. There are four oculars and genitals in p h differs from the last considered only in that there are four instead of 15 Pentamerous ventrally, four ambulacra and five interambulacra dorsal!,. J, s-TKs is the commonest type of departure from the complete ,x-nta aena- Id, 17 cases having been seen. A small specimen of Stron^loc.^,, (Plate 7 fig 4) shows interesting features. The specimen is 17 mm. m dmmeU 44 ROBERT TRACT JACKSON ON ECHINI. and misshapen on the abnormal side. Ventrally there are five ambulacra, interambulacra, and teeth, but ambulacrum II is developed for a short distance only. Dorsally there are five genitals and oculars, but ocular II is imperforate. The dorsal border of the ambulacrum is widely separated from its ocular. Ocular II lies dorsally and produces its share of interam- bulacral plates, although ambulacral plates ceased to be built. Columns 1 and 2 of interam- bulacrum 1 extend dorsally and abut against oculars I and II as usual. In interambulacrum 2, columns 1 and 2 extend dorsally, but only 2 reaches the apical disc, column 1 dropping out, so that in the last three rows or zones of growth there is only a single column of plates in this area, a condition somewhat comparable to that seen in area 4 of Arbacia (Plate 4, fig. 11) where also a single column of plates exists dorsally. Just above ambulacrum II in this speci- men (Plate 7, fig. 4) there are extra interambulacral plates that cannot be definitely referred to either areas 1 or 2. They are virtually space fillers, which, in my opinion, is what the interambulacral plates are. This specimen is structurally almost identical with the interesting Echinus esculentus described by Ritchie and Mclntosh (1908). In both, the ocular remained in place dorsally but imperforate, the ambulacrum existed ventrally only, and the adjacent interambulacra developed in a comparable manner, though with certain differences. In the Echinus only the four columns of the two interambulacra exist above the imperfect ambulacrum, and extend dorsally to their respective three ocular plates. A Strongylocentrotus drobachiensis (Plate 6, fig. 6) has five oculars and genitals as usual; there are five interambulacra continuous to the apical disc, but one of the five ambulacra, IV, dies out dorsally, so that interambulacra 3 and 4 come in contact and alone touch ocular IV. The distance of separation of the ambulacrum from its ocular is only slight, but it repre- sents a zone in which there are only four ambulacra. In this specimen ocular III is split, a rare variation, and genital 5 is divided. A few pores in the dorsal part of interambulacrum 3 are apparently supernumerary genital pores that lie below genital 3. An Arbacia punctulata, from Woods Hole, Massachusetts, in the American Museum of Natural History, is peculiar in that ambulacrum III fails to reach the apical disc so that there are only four ambulacra in that region. The structure is almost the same as in Plate 6, fig. 6, except that a different ambulacrum is involved. Six specimens of Strongylocentrotus col- lected at Dumpling Islands, Maine, (R. T. J. Coll., 825-830), one from Calderwood Island, Maine (R. T. J. Coll., 845), one from Frenchman's Bay, Maine (R. T. J. Coll., 846), and two from Friday Harbor, Puget Sound (R. T. J. Coll., 903, 904), & Strongylocentrotus eurythrogrammus from New South Wales (R. T. J. Coll., 905), also a Tripneustes esculentus fromHayti (R. T. J. Coll., 831), and two specimens of Toxopneustes atlanticus from Bermuda (R. T. J. Coll., 894, 897), all show a similar structure to Plate 7, fig. 4, with five genitals and oculars in place and an ambulacrum dropping out at a greater or less distance from the apical disc. In all but one of these cases the ocular lying above the imperfect ambulacrum is imperforate. In the THE PENTAMEROUS SYSTKM AND VARIATION. 45 several cases, each of the five ambulacra is involved, but IV appears to be more frequently imperfect than any other area. 16. Pentamerous ventrally, four ambulacra and five inter ambulacra dorsally, four oculars, five genitals. — This type is similar to that of 13 in that the ocular a— oeiat. ••! with an area ha* disappeared, but differs in that there are five inter:imlml:irr:i. A Simrigylneeiitrotu- from Calderwood Island, Maine (R. T. J. Coll. ,832), 4(1 nun. in diameter, is completely |>eni:imenui* ventrally, but ocular II is wanting, and ambulacrum II falls short of the apical disc by 10 mm. The two bordering interambu-acra, 1 and 2, are in contact dorsally. The dorsal plates of column 1, in interambulacrum 2 and of column 2, in intcrainbulacrum 1 are large, not small as is usual in dorsal plates, indicating that no new ones have been recently added, which i- in accord with the absence of ocular II, from which the plates of these two columns take origin. Three other specimens of the same species from Calderwood Island (R. T. J. Coll., 833-835) and a Colobocenlrotus atratus from the Hawaiian Islands, in the State Museum at Albany, New York, have a similar structure. In all, an ocular is absent, and the corresponding ambulacrum falls short of the apical disc, but the associated interambulacra extend to the apical disc simi- larly to the specimen just described. In the Colobocentrotus noted, ocular I is absent, and ambulacrum I falls short of the apical disc. 17. Pentamerous ventrally and throughout the corona, five oculars, but four genitals.— This line of departure from the pentamerous system is where only one genital is absent. It is a typical condition in spatangoids where genital 5 is always absent, but occurs only as an aber- rant variation in regular Echini. In Eutidaris tribuloides (text-fig. 185, p. 167) there are only four genital plates, 1 being absent. Oculars I and II are in contact, and as a result interambulacrum 1 comes in contact with two oculars as it does in Bothriocidaris archaica and in the posterior interambulacrum in spatangoids. This interambulacrum is also much narrowed dorsally and at one point a single plate fills the area laterally. A more striking case is the Arbacia punctulata shown in Plate 4, fig. 11. In this remarkable specimen there are five oculars but only four genitals. Genital 4 is absent so that oculars IV and V are in contact. The interambulacrum 4 dorsally drops out to a single column of plates; the single column and the ocular contact of the dorsal plate of the same as a regressive variation is an exact repetition of the character seen in Bothriocidaris archaica (Plate 1, fig. 2). A quite comparable case is seen in Strongylocentrotus drobachiensis (Plate 6, figs. 7, 8 this specimen there are five oculars, of which I and II reach the periproct and V, IV, III are exsert. There are only four genitals, number 4 being absent, so that oculars IV and V are in contact. These plates are peculiar in that they are produced ventrally in an elongate fashion. Interambulacrum 4 ventrally consists of two columns of plates as usual; above the mid-zone it narrows, and the two columns give place to a single column of plates for three rows, that is. ROBERT TRACY JACKSON ON ECHINI. three plates (Plate 6, fig. 8). Above this point two columns are built again for a short distance being at this point three plates in column 1, and two in column 2. Proceeding dorsally' a change again occurs, and two single plates are built; the last is very high and narrow unlike anythmg seen in any other echinoid. This structure is very difficult to see on the exterior the test, but on the interior (Plate 6, fig. 8) it is perfectly plain. The dropping out to a column is comparable to the typical character of Bothriocidaris and to the peculiar Arbacm (Plate 4, fig. 11). Dorsally, interambulacrum 4 doe, not reach the ocular plates but separated for a short distance in which ambulacra IV and V come in contact and alone reach oculars IV and V. Another case was found in an Arbacia punctulata from Florida (R. T. J. Coll 889 Plate 4 The specimen is 33 mm. in diameter. It is pentamerous throughout except for the absence of genital 4, which is wanting, as in Plate 4, fig. 11. It differs from that specimen however, m that interambulacrum 4 is completely developed, its two columns extending as al, to the aplcal disc, but abutting against oculars IV and V without any contact with a gemtal as that plate is absent. Again, a similar structure is shown in a specimen of Toxo- pneustes atlanticus from Bermuda (R. T. J. Coll., 898). This specimen measures 53 mm in s quite pentamerous throughout except that genital 4 is wanting. Oculars IV and V are therefore in contact and cover completely ambulacra IV and V and interambula- crum 4 as in the Arbacia, Plate 4, fig. 12. In this Toxopneustes there are two columns of m contact with the two oculars, but the plates are small. These several cases demon- strate that the absence of a genital does not cause a loss of the corresponding interambulacral fl.rpfl area. Hexamerous. 18. Sv ambulacra, inter ambulacra, oculars, genitals, and teeth.- In a fine large Tripneustes escukntus from Pernambuco, Brazil (Plate 6, figs. 2, 3) there are six areas throughout L cond,tion hitherto definitely known only in Strongylocenlrotus lividus. The specimen measures 110 mm. in all diameters as it is perfectly circular in outline. It is 58 mm in height this species, when two oculars are insert, they are the bivium (see tabulation of 703 speci- 1), so that the specimen is oriented on the basis of the insert bivium and position the madreporite. Obviously the additional ambulacrum, ocular, and interambulacrum lie .tween mterambulacrum 3 and ambulacrum IV. There are four normal genitals, but two 3 and 6, are fused into a single plate, a somewhat rare condition, but similar cases are en m Strongylocentrotus and Tripneustes (text-figs. 195, 196, p. 169). There are six oculars lying between the tips of genitals 3, 6. The ambulacra are all normal in appear- 3 and at the mid-zone measure 28 mm. in width, except V, which is 29 mm. The width the same that is found in the ambulacra of a normal five-rayed specimen measuring THE PENTAMKHors SYSTEM AND VAUIATION. 47 • the same diameter of 110 mm. The interambulacra are normal in appearance RtJMffiekdljr, but at the mid-zone they all measure 27 mm. in width, that is, they are narrower than tin- ambulacra. In a normal specimen of the same size the five iiiti-nunbulacra measure each 38 mm. in width when the ambulacra measure 29 mm. In the six-rayed specimen, therefore, evi- dently the space gained to add the extra ambulacrum and interambulacrum is attained by building ambulacra of practically the usual width, but narrowing all the intenmbolttM equally to much less than the usual width. This emphasizes the conclusion gathered from normal Echini that the interambulacrum is essentially a space filler and adapts itself to fill what space is available between the ambulacra which are the more essential structures. There are twelve cuts in the test ventrally for the peristomal gills, and the lantern has six teeth and all its other parts in sixes or multiples of the same. In the narrowed interambulacral areas the tubercles (Plate 6, fig. 3) occupy the same distance apart as in ordinary pentamerous speci- mens, but owing to the narrowness of the areas there are fewer tubercles on each plate. case with the Arbatia lixula previously considered (p. 40) demonstrates that the distance apart and size of tubercles is the species feature and not .the actual number of tubercles on a given plate. The same hexamerous structure as just described occurs in a Strongylocentrolus drobachien- sis from Dumpling Islands, North Haven, Maine (R. T. J. Coll., 838, Plate 8, fig. 3). This choice specimen measures 53 mm. in diameter, and 25 mm. in height. There are six ambulacra and interambulacra complete, six oculars and six genitals, but genitals J ocular VI between them exactly as in Plate 6, fig. 2. The ambulacra at the mid-zone mea< 11 mm. in width and the interambulacra 12 mm. In a normal pentamerous specimen of same size the ambulacra measure 12 mm. and interambulacra 19 mm. in width, therefore, that as in the Tripneustes, the space for the sixth areas is attained mainly narrowing the interambulacra and retaining ambulacra of practically the usual wi. areas. Ventrally there are twelve cuts for the peristomal gills. Unfortunately the j absent but they were doubtless hexamerous as all other parts of the sea-urchin hav« arrangement. I was startled by finding this same structure for a third Strongylocentrotus drdbachiensis, also collected at Dumpling Islands (Plate 7, ffes. , specimen is 14 mm. in diameter and 6 mm. in height; it is perfectly shaped w.thout tortion There are six ambulacra and interambulacra throughout the corona, i genitals, but as in the two other cases, genitals 3, 6 are fused, with ocular \ I as seen in Plate 7, fig. 7. It is certainly most extraordinary that this par should exist in three specimens, and indicates what I have elsewhere pointo definite even extremely rare variation may be. Ventrally there are six tee, mordial ambulacral plates around the mouth and twelve cuts for the penstomal fig 8) The three similar specimens of hexamerous Tripneustes and Strongylocenn ROBERT TRACY JACKSON ON ECHINI. described were evidently cases of congenital variation, whereas the next type considered is a variation to six parts taken on at a comparatively late stage in development. The specimen of Strongylocentrotus lividus described by Ribaucourt (1908) would belong in this series, as he says that it is completely hexamerous, having six teeth, six ambulacral and interambulacral areas, six oculars and genitals. It would be interesting to know in which area the modification takes place and if there is a fusion of genitals as in the specimens above described. 19. Pentamerous ventrally, six ambulacra and interambulacra dorsally, six oculars, five genitals.- A most interesting condition occurs in a specimen of Tripneustes esculentus found in material kindly collected for me in Jamaica by Dr. Thomas Barbour. This choice speci- men (Plate 6, fig. 4) measures 76 mm. through III, 5 and is 45 mm. in height; it presents a slight hump in the aberrant area. There are six oculars, but only five genitals. The addi- tional sixth ocular lies between ocular II and the madreporite. Ventrally the specimen is pentamerous and quite normal, but above the mid-zone a sixth ambulacrum appears interca- lated between ambulacrum II and interambulacrum 2. It extends dorsally, the two columns of plates reaching ocular VI in the usual fashion. About halfway, up the sixth ambulacrum a sixth interambulacrum appears. It consists of a single column of narrow plates which extend to oculars II and VI. The single column and ocular contact are comparable to the character seen in Bothriocidaris archaica (Plate 1, fig. 2). I believe it and the next described case are the only known instances since Ordovician times of an interambulacrum consisting of a single column of plates throughout its length. At two points the single column of interambulacral plates is separated dorso-ventrally, and at these breaks ambulacra II and VI are in contact for a brief space. Genital 3 is split horizontally, as in text-fig. 190. A like partially hexamerous condition exists in a Strongylocentrotus drobachwnsis from Truro, Massachusetts (R. T. J. Coll, 836), 35 mm. in diameter. It is quite normal ventrally, but dorsally there are, as in the above case, five genitals and six oculars. Ocular VI lies between ocular V and genital 5 and is fused with the latter. A sixth ambulacrum for a length of 10 mm. lies between ambulacrum V and interambulacrum 5, the condition being as in Plate 6, fig. 4. A sixth interambulacrum, consisting of two plates in a linear series, lies between ambulacra V and VI as in the same figure. A small and distorted specimen of Arbacia punctulata (R. T. J. Coll., 882) kindly sent me from Johns Hopkins University through Dr. G. T. Hargitt, again shows a similar structure. The specimen measures 36 mm. in diameter through 4, I and 19 mm. in height. Pentamerous ventrally, dorsally a sixth ambulacrum exists for a distance of 6 mm. The additional area lies between interambulacrum 1 and ambulacrum II (compare Plate 6, fig. 4). A sixth inter- ambulacrum consisting of two plates in a vertical series lies between ambulacrum VI and ambulacrum II, as in Plate 6, fig. 4. There are six oculars and five genitals, but the latter are THE PENTAMEROUS SYSTEM AND VARIATION. 49 confused by secondary sutures. There are six periproctal plates, probably u coincidence in number only as six plates in that area may occur in a perfectly penlamen.u- specimen text-fig. 204, p. 175). An Echinarachnius parma, from Chelsea Beach, Massachusetts, in the collection of tin- Boston Society of Natural History, no. 348, is another case of a similar structure. Tlii- -peci- men (Plate 8, fig. 4; Plate 7, fig. 9) is 59 mm. in diameter. It is not unusual in appearance except for the added areas. There are five ambulacra and interambulacra ventrally and nearly to the ambitus where the extra ambulacrum originates. The specimen is readily oriented by the position of the periproct in 5 (Plate 8, fig. 4) and also by the proportionate si/e of tin- primordial ambulacral plates (Plate 7, fig. 9), the la, Ha, III6, IVa, Vb, being the larger plates as usual, according to LoveVs law. The sixth areas as seen are late in development and occur between interambulacrum 1 and ambulacrum II. In the fused oculo-genital mass there are six ocular pores, one to each area as usual. There are, however, only four genital pores. One is wanting in 5 as usual, and also in 1, which is not usual. There is, however, a pore in the aberrant interradial area 6. Ambulacrum VI originates just below the ambitus, has two columns of plates and a petal as usual, and differs only in that plates below the petal are smaller, and the petal is slightly narrower than in the other areas. Interambulacrum 6 original. - slightly later than ambulacrum VI and differs from the other interambulacra only in that the plates are smaller. In this specimen the hexamerous variation was evidently not congenital, for as shown, a pentamerous condition was maintained for a time, expressed in terms of growth by the introduction of six horizontal rows or zones of ambulacral plates, as seen in area 1 1 (Plate 7, fig. 9). Above this zone the added sixth ambulacrum is introduced, and it, with the extra interambulacrum, is continued throughout succeeding growth to the apical disc. 20. Pentamerous ventrally, six ambulacra, five interambulacra darsally, six oculars, five genitals. — This structure is shown in a specimen of Strongylocentrotus drobachiensis from York Harbor, Maine (R. T. J. Coll., 847). The specimen is somewhat flattened, 27 mm. in diameter and 13 mm. in height. There are five ambulacra and interambulacra ventrally, but within 5 mm. of the peristomal border a sixth ambulacrum appears and is extended to the apical disc. The sixth ocular and ambulacrum lie between ocular and ambulacrum I and genital and inter- ambulacrum 1. The relation is comparable to that shown in Plate 6, fig. 4, except that tin- two ambulacral areas are in contact, as in Plate 7, fig. 5, since there is no intervening inter- ambulacrum. The genital plates in this specimen are considerably split by secondary sutures and somewhat distorted. De Loriol (1883, Plate 4, fig. 3a) describes a partially hexamerous Sl<»n»i>ncustes variolari* that is referable to this type of variation. I studied the specimen in Geneva. Ventrally there are five teeth, ten primordial ambulacral plates, five ambulacra, and five interambulacra. Dorsally there are six oculars and a sixth ambulacrum, but there are only five interambulacra and five genitals. 50 ROBERT TRACY JACKSON ON ECHINI. Bateson (1894) reports two cases of "total" hexamerous Echini. One is a Galerites, in which there are six ambulacra and interambulacra as seen from below; the dorsal portion and jaws are not shown. I have not seen Meyer's original paper where this was described. The other is a six-rayed Amblypneustes, but there is no description of the specimen. Bateson also records three specimens in which there is an accessory ambulacrum. These, with de Loriol's and Ribaucourt's cases above mentioned and the eight more or less completely hexamerous specimens here described, include all cases I know of in which there is an increase in parts over the typical pentamerous system in Echini. It is evidently a very rare variation. Other variations from the normal have a certain interest. Four plates in the periproct is typical of Arbacia punctulata, but as later shown, variations of fewer or more than this number are common (text-figs. 200-205, p. 175). Variations in the number of genital pores are common, also as regards the distribution of madreporic pores. The variants of genital plates, or genitals and oculars, are all discussed later. The above variations from the pentamerous symmetry can all be considered as monstrosi- ties. Variation of another kind is more common, and interesting from another point of view; that is, variation in which the whole animal, or a part, is more or less fully developed in the direct line of the differential development or evolution of the species. This in Palaeozoic Echini is marked as radial variation, which was discussed in my earlier paper (1896, p. 151), and is shown in many cases here. An example is seen in Lovenechinus missouriensis, which has five columns of interambulacral plates with often a sixth column represented by one or two plates near the mid-zone. In Plate 41, fig. 1, the sixth column is represented in areas E, G, I, but in areas A, C, there are only five columns. In the young specimen (Plate 40, fig. 1) there are five columns in four areas, but in area E the fifth column is represented by only a single plate, a great departure from the typical and a close approach to the character seen in lower species of the genus, as L. lacazei (Plate 36, figs. 1-6), which has only four columns of interambulacral plates in an area as a specific character. As shown in my earlier paper in detailed studies of Melonechinus multiporus, a given column of interambulacral plates, especially the columns from 5 upward, may come in at vary- ing zones in different areas of the same specimen, showing considerable variation in the rate of radial development. This is shown well in the zone of introduction of the seventh column in Lovenechinus septies (Plate 45, fig. 1). The actual number of columns, or differential char- acter, may vary in different areas of the same specimen, as in Hyattechinus rarispinus (Plate 23, fig. 3). In Melonechinus multiporus (Plate 54, fig. 5) there are nine columns in area A, but only eight in the four other areas; in Plate 60 the specimen figure 2 has nine columns in all areas, but figure 1 has eight in all areas; Plate 55, fig. 3, has nine columns in areas C, E, and G, but the other areas are not known definitely; the specimen, Plate 55, figs. 1, 2, and Plate 57, has only eight columns in all five areas. A specimen may have but seven columns of inter- STRUCTURE OF THE SKKLKTON AND GROWTH. 51 ambulacral plates in an area, a rather rare variation in this species. This same variation of greater or less degree of radial differential development is shown in many Hjx>ries in this paper. The radial variation in a specimen may be as great as the variation of dinVr.-nt specimens within the limits of a single species. Variation is marked as regards the number of ocular plates that meet the periproct in Recent and some Palaeozoic Echini, as fully discussed later. Variation occurs all through Echini in all parts of the organism, and numerous cases are considered in the following pages. All the evidence goes to show that aberrant variation is relatively rare, and in :tlnn^t all cases variation in Echini is either arrested, progressive, or regressive on the direct line of differential development of the given character in the ontogeny of the individual and the adults of asso- ciated species and genera. A variant in a species can, therefore, usually be compared eitli.-r as a direct connection, or, if not that, as a parallelism with the typical condition in some other species of the group. It seems that Echini are a particularly good group in which to study questions of variation because here variations can usually be expressed in very definite terms of numerical or other equally positive characters. STRUCTURE OF THE SKELETON AND GROWTH. The skeleton of a sea-urchin is made up of plates, spines, jaws, and other parts which are situated more or less deeply, and the skeleton is covered by living ciliated epithelial tissue. The plates and spines, while apparently external, are in reality included within living tissue. An exception to this covering of living tissue occurs in the primary spines of Cidaris, where, as Lang shows (1896, p. 389), a cortical layer is formed, and the integument dies away from the area covered by that tissue and persists only around the base of the spine. This may l>o com- pared with the velvet on deer's antlers, which, after the completion of growth, dies away, leav- ing the antler bare. The secondary spines of Cidaris, however, have no cortical layer, and are always covered by a ciliated integument, like a permanent velvet in antlers, and which is seen in the horns of the giraffe and okapi. This condition of the skeleton of Echini, of being cnvi-rctl by living tissue, is of fundamental importance to a proper understanding of the structure. As the parts are internal, they are capable of being added to or resorbed at any part through- out the life of the individual. This is true of all parts except the distal points of the teeth, which are truly external. The individual plate of the test grows by a constant addit i»n to the exterior and resorption of the interior, which latter is composed of open lattice-like or trabecu- lar tissue. The growth of a sea-urchin plate may be aptly compared to the growth of the head of a femur or similar bone with its hard dense exterior and open trabecular internal structure. Sectioning a sea-urchin plate, we find no trace of its earlier shape or character within, any more than we find the traces of a young femur within in sectioning the femur of an adult dog. 52 ROBERT TRACY JACKSON ON ECHINI. The mineralogical structure of the sea-urchin plate, as seen in a section of a plate of Recent Strongylocentrotus drobachiensis, is crystalline calcite, with the axis of the crystal perpendicular to the surface of the plate, as shown by extinguishment under the polariscope. The plate is made up of a crystal which is optically continuous. Whether one, or more than one crystal enters into the composition of a single plate is doubtful, but it may perhaps be compared to ice on a pond, in which also the crystalline structure is optically continuous and the crystalline axis is perpendicular to the surface. It may be noted that the same crystalline structure, with axis perpendicular to the surface, was observed in the plates of Synapta, Asterias, and the calyx plates of a young Antedon rosaceus. In the stem of Antedon, however, the crystalline structure is parallel to the longer axis of the stem, not perpendicular to the surface. While in the sea-urchin the corona grows by increase in size of the plates, often to a relatively great size, as in Cidaris, or the two plates in the second row of the posterior interambulacrum of Micraster, it also grows by the addition of new plates. In the corona, the new plates, both in the ambulacral and interambulacral areas, are always added dorsally, in immediate contact with an ocular plate. This holds good for Palaeozoic as well as later types; the only excep- tion appears to be the aberrant Pourtalesia jeffreysi Wyville Thomson, in which, according to Love"n (1883), in adults, at least, oculars are apparently wanting. In Bothriocidaris archaica (Plate 1, fig. 2) it is seen that the ocular plates cover both the ambulacrum and interambu- lacrum entirely, and in all other Echini, as already stated, the oculars overhang the ambulacrum entirely and the interambulacra in part on either side, as in Melonechinus (Plate 56, fig. 6), and Lovenechinus (Plate 41, fig. 3). It is true that in many, perhaps most Echini, the interam- bulacral plates originate in contact with both the ocular and the genital plates in the angle between them, but they apparently never fail to come in contact with the oculars and they may not touch the genitals, as seen in Bothriocidaris archaica (Plate 1 , fig. 2) . In the posterior interambulacrum of Ananchytes (text-fig. 175) and in adult Phormosoma placenta (text-fig. 170) interambulacral plates originate against the oculars without touching a genital, and the same may often be seen in abnormal specimens as in area 4 of Arbacia (Plate 4, figs. 11, 12), and in the extraordinarily modified specimen of Strongylocentrotus lividus (Plate 6, fig. 5). It is strik- ing in the Palaeozoic genera with many columns of plates that the new interambulacral plates originate against the oculars, Lovenechinus, Plate 41, figs. 2, 3, as discussed more fully later. What part, if any, the ocular plays in the origination of new plates is unknown, but at this area they originate. Mr. A. Agassiz (1904, p. 80) notes that in specimens of Lovenechinus (Oligoporus) missouriensis and Lepidechinus imbricatus the young interambulacral plates originate against the ocular. The specimen of Lovenechinus to which he refers is that figured in my Plate 42, fig. 6, and the Lepidechinus in my Plate 63, fig. 7, as L. tessellatus sp. nov. The periproct grows by increase in the size of plates and the addition of new plates quite independently of the corona. The peristome grows in area by increase in the size of basicoronal TIIK AMI!I'I,A( KIM OK TIIK .\\ plates of the corona and in cases by resorption of the base of the corona. The platen of tho peristome are various in origin. The primordial aml,,ilm-nil plates of regular Kchini an- appar- ently in this area from their inception (Plate 3, fig. 7). Additional aml.ula.-r.-.l plafs arc derived by flowing down from the corona (text-figs. 41-48, p. 80). All other peristomal plate*, it is believed, are formed on that area and are not derived from the corona (text-fin. 57, p. 84). These matters will be considered in detail in their appropriate plan THE AMBULACRUM OF THE CORONA. The ambulacrum is the most essential feature of a sea-urchin, and has a first import ance in classification and morphology, on account of the varied structure that it presents. We can conceive of a sea-urchin without an interambulacrum, although such is not known, or wanting in almost any other skeletal parts, but it seems that an ambulacrum is an essential character of the class. The detailed structure of the ambulacrum in post-Palaeozoic type- is for tin- most part fairly well known, but the Palaeozoic types have not been closely studied, and throw a great deal of light on the structure of this area in the group as a whole. The ambulacrum is essentially an area for bearing tube-feet, which are important as a means of locomotion in most Echini, or are modified more or less fully as organs of respiration in other Echini (clypeastroids and others). The ambulacrum is never composed of less than two vertical columns of plates, and when more than two, it always has an equal number on each side; therefore there is a distinct median suture with an equal area on each side of it. From this it follows that half an ambulacrum, barring exceptional variation, is as good as a whole one for study, which is important in fossils where one half is often all that is available. A partial exception to the rule of never less than two columns of ambulacral plates occurs in Palaeotropus josephinae Loven, as figured by Loven (1874, Plates 13, 32). In this exception. dorsally in all five areas the two columns drop out to a single column for a distance of three to seven plates from the oculars. This indicates that a sea-urchin might have a single column of ambulacral plates throughout at least the greater part of an area, but such is unknown. The width of the ambulacrum varies greatly. It is narrow usually, in types with low unisonal plates, Eucidaris (text-fig. 4), Palaeechinus (text-fig. 9); but it may be wide, a.s in the ]x»taloid area of Clypeaster. The ambulacrum is wider usually when the plates are compound, Strongy- locentrotus (text-fig. 5a), or when four columns, Lovenechinus (Plate 45), or more columns, Melonechinus (Plate 57), are developed. It may be much wider than the interambulacrum, Lepidesthes colletti (Plate 70, fig. 1), Meekechinus (Plate 76, fig. 1), and about twice the width of the interambulacrum in Bothriocidaris (Plate 1, fig. 1). In the primitive type, Bothriocidaris archaica (Plate 1, fig. 1), the ambulacral plates are high, hexagonal, and there are therefore few tube-feet, about sixteen, to ea,ch area excluding 54 ROBERT TRACY JACKSON ON ECHINI. the two peristomal rows. In young Goniocidaris (Plate 2, figs. 1-3) the ambulacral plates are also high, hexagonal, and there are few tube-feet, about ten to each area. From this condi- tion, which I would call primitive, increase of tube-feet or increase of locomotive power, is attained on three independent lines of development. First and simplest, by producing low plates with pore-pairs uniserial, so that many plates are contained in the vertical extent of the area, as in Archaeocidaris (Plate 9, fig. 6), Eucidaris (text-fig. 4), and Palaeechinus (Plate 30, fig. 3). A second method of getting tube-feet is by increasing the number of columns of ambu- lacral plates from two to a greater number, but always by even numbers and always by simple, never compound plates (text-figs. 10-21). The increase is from two to four, six, eight, ten, twelve, sixteen, or twenty columns of plates in an area, which is the most at present known. This method is known in the Palaeozoic Echini only, and is especially developed in the Palae- echinidae and Lepidesthidae. It is, however, taken up as a method in other types, as Echinocy- 'stites. The third method of attaining increase of tube-feet is by building compound plates, 4 formed by the coalescence of originally simple plates, Centrechinus (text-figs. 92, 94). The I 9 10 TEXT-FIGS. 2-14. — Character of the ambulacrum in representative Echini; left half represented. The horizontal dotted line is on the plane of the mid-zone. 2. Bothriocidaris archaica sp. nov. Ordovician. From Plate 1, fig. 1. 3. Goniocidaris canaliculate A. Agassiz. Young. From Plate 2, fig. 2. 4. Eucidaris tribuloides (Lamarck). Bahamas. 5. Strongylocenlrolus drobachiensis (O. F. Muller). Young. From Plate 3, fig. 11. 5a. The same. Adult. York Harbor, Maine. 6. Micrasler cor-anguineum (Lamarck). Cretaceous, England. 7. Echinarachnius parma (Lamarck). Eastport, Maine. 8. Metalia pectoralis (Lamarck). Bahamas. Showing plates of two areas. 9. Palaeechinus elegans M'Coy. Lower Carboniferous. From Plate 31, fig. 1. 10. Maccoya burlingtonensis (Meek and Worthen). Lower Carboniferous. From Plate 33, fig. 2. 11. Lovenechinus missouriensis (Jackson). Lower Carboniferous. From Plate 43, fig. 3. 12. Oligoporus danae Meek and Worthen. Lower Carboniferous. From Plate 50, fig. 7. 13. Melonechinus multiporus (Norwood and Owen). Lower Carboniferous. From Plate 56, fig. 4. 14. Lepidesthes colletti White. Lower Carboniferous, From Plate 70, fig. 3. THE AMBULACRUM OK Till: c <)IU)NA. .V. component elements of a compound plate are frequently low, but the plate a» a whole \s UHually high. This method occurs in the Centrechinoida and is seen in some of the Holeetypina, but is unknown in the Palaeozoic. A good example is Hlrongylocenlrotus drdbaehiensut (text-fix. 5a), which at the mid-zone is characterized by compound plates composed of five or six component parts, each of which bears a pair of pores. As a very rare aberrant variant. |>ore« may In- wanting in such plates. In three specimens of Rtrongylocenlrolus drobachiensis, collected in Maine, the plates are compound, as usual, but in one area of each specimen the platen dor-ally are somewhat distorted and have no ambulacral pores. It must be strongly urged that the full character of the ambulacrum in a given type is to be based on the plates at the mid-zone. Below this point, or ventrally. they may not have attained the full differential characters, and dorsal to the mid-zone, one gets into the area of localized stages in development, where the young plates again have not taken on the full char- acter; or again, one may also dorsally reach an area of senescent stages win-re the full character- are dying out. To illustrate this important principle, in Maccoya burlinglvncnxin (Plat' figs. 1, 2) the plates at the ventral border are all primaries and pore-pairs uniserial; at tin- mid- zone the plates are alternately primaries and occluded, and the pore-pairs biserial; dorsally, the young plates are again all primaries and pore-pairs uniserial. In Lovenechinus miasourien- sis (Plate 42, figs. 1-4) the plates ventrally are all primaries, at the mid-zone demi- and occluded, and dorsally again primaries. In Melonechinus multiporus (Plate 56, figs. 2-7 ; Plate.")"; text- fig. 245) ventrally, plates are demi- and occluded; at the mid-zone demi-, occluded, and many isolated; close to the ocular, primaries only. In all of these series, and many others as well, the same system exists of simpler conditions ventrally in the plates built when the animal \\a- young, and also in the nascent plates dorsally; and from there passing to the plates of the mid- zone, it is easily seen how the complex conditions there existent are built up. From these plates also one can arrive at genealogical relations, it is believed, of a very definite character (text-fig. 237, p. 231), as discussed later. Of the Centrechinoida, in the young Strongylocentrotus, Lovdn (1892) showed that tin- plates are simple with a single pore-pair (Plate 3, fig. 11). These plates in the adult at moved by resorption, but still the plates at the ventral border are unlike those of the mid-zone. At the dorsal border in Strongylocentrotus, as Love'n (1874) showed, and as Duncan 1885) showed in a number of types, the plates are simple, not compound. Dun. 'an -ays (1885, p. 421), "It is an interesting and highly suggestive truth that all the regular Echinoidea should have their most radially situated plates in the form of the simple primaries of the Cidaridae ' Loven showed in Strongylocentrotus drobachiensis that these simple plates are shoved down- ward and become fused to form the compound plates, characteristic of the species. At this region of young plates we find, therefore, as a localized stage, a simplicity like that d cialized forms of Echini, as Cidaris. This character of dorsal simple plates is shown very well 56 ROBERT TRACY JACKSON ON ECHINI. in Centrechinus (text-fig. 94, p. 107), Astropyga (text-fig. 99), Echinus (text-fig. 115), and Phor- mosoma (text-fig. 170). Alexander Agassiz (1874, p. 642) said that the compound ambulacral plates are formed by the splitting of the original plates, but he was clearly mistaken. Passing dorsally, we may pass from compound plates into an area of simple plates which have dropped all attempt at fusion, as seen in Hemicidaris of the Jurassic (p. 17). Or, as A. Agassiz (1904, Plate 20, figs. 1-4) shows in Salenocidaris miliaris A. Ag., there is a single primary plate ven- trally succeeded by one compound plate, which is again succeeded by simple plates throughout the area, a case of extreme reversion, in which simplicity is the dominant character, and com- poundness or specialization is shown by only a single plate. This may be aptly compared to Baculites amongst the ammonoid cephalopods, in which its coiled (ammonite) character is reduced to a minute, almost microscopical basal portion, which is rarely preserved. What- ever the complexity of the ambulacrum in Palaeozoic or later types, it is striking that a simple condition obtains in the nascent plates of the placogenous zone. This all shows the fact of stages in development as evinced by the ambulacrum passing dorsally or ventrally toward the mid-zone, and the importance of differentiating zonal areas in the description of the ambulacrum. While the regular Echini maintain a pair of pores in each ambulacral plate, or plate ele- ment in the case of compound plates, the case is different in the irregular post-Palaeozoic Echini. In the clypeastroids below the petaloid area, the ambulacral pores soon drop out, as in Echi- narachnius parma (Plate 8, fig. 4) , and the ambulacral plates for the most part at least are non- poriferous. It is true that there are very fine pores on the ventral side, as described by A. Agassiz (1874, p. 703), but these are so peculiar that they can fairly be distinguished from the usual pores of the ambulacral system. In spatangoids ventrally the pores may be want- ing, or reduced to a single pore, instead of a pair of pores to a plate, in numerous cases. As stated, ambulacral plates typically bear a pair of pores representing a single tube- foot, or the pair may be reduced to a single pore, as in some spatangoids. In spatangoids, however, we find a remarkable exception to the rule of a single tube-foot to a plate. In Colly- rites (Plate 3, fig. 15) and other types, as shown by Loven (1874), A. Agassiz (1904), and others, in the basicoronal row, the la, Ha, III6, IVa, Vb have two pairs of pores, and this is the only case of two pore-pairs, indicating two feet to a simple plate, known in Echini. Loven thought it indicated a compound plate because of the two pairs of pores, or in cases two separate single pores, but always representing two tube-feet. The fact that no suture has been seen in these plates in any of this group of Echini militates against this view, and it seems best to consider this as a peculiar case of two feet to a simple plate rather than a compound plate, the suture of which has not been observed. As discussed under consideration of these plates (pp. 69, 71), the ambulacral plates in the basicoronal row of spatangoids and clypeastroids may reason- ably be homologized with the first row of ambulacral plates found around the mouth in regular Echini and transferred to the basal row of the corona in the process of evolution of these spe- THE AMUITI,A< IUM OF TIIK CORONA. :,7 cialized forms. In spatangoids, tube-feet as locomotive organs are largely abandon..,!. and t hey have only or mainly a respiratory function; here no compound plat,- an known. With a loss of the locomotive importance the plates below the petaloid areas, as in Mir,,,-!,., (text- fig. 6), are relatively high, even hexagonal, as in the embryo and the ancient H.,thri.,rid.-tri«. This primitive character of plates may exist in only one area. In Melalia pectoral,* t,-xl -fig. 8), for example, the plates at the mid-zone of the bivium and posterior pair of the trivium an- low and wide, with pore-pairs horizontal. In the odd anterior ambulacrum, however, the plat- are as high as wide, pore-pairs are superposed and in the middle of the plate, a- in Bothri.H cidaris. In such plates we have often in the shape and height, also the snperjx.se, 1 p,.>ition of the pores in each pair, a condition which is a closer approach to the embryonic character and also to the character of Bothriocidaris than is seen at the mid-zone in the adults of any regular Echini excepting the ancient Bothriocidaris. The position and mutual relation of the ambulacral pores is of considerable interest. It appears to be typical of the primitive and great majority of adult Echini to have two pores for each tube-foot, and the pair of pores to be surrounded by a more or less strongly marked peri- podium. In many spatangoids the peripodium is absent. In all Palaeozoic genera there are two pores to every ambulacral plate and a peripodium is present apparently without exception (Plate 23, fig. 1). Of course it is such a slight eminence that it is very commonly worn off, but it has been found so widely that its frequent absence is attributed to conditions of erosion. In all Palaeozoic types and most modern Echini, the pores lie either in the middle of the ambu- lacral plate, which is rare, or nearer the next adjacent interambulacrum than the middle of the plate, which is the usual position. In no Palaeozoic type do they lie nearer the media; suture of the ambulacrum than the middle of the ambulacral plate. In the demi-plat< Echinosoma hispidum (A. Agassiz, 1904, Plate 48) the pores lie nearer to the mid-suture than to the middle of the plates in which they occur. The same is true of occasional spatangoiiU. but is exceptional. In Bothriocidaris (Plate 1, fig. 1) the ambulacral pores of each pair lie in the middle of the plate, superposed dorso-ventrally, and surrounded by an oval peripodium, the axis of which coincides with the vertical axis of the area. In young Goniocidari-s (Plate •_'. fig. 2) the pores of each pair also lie superposed as in Bothriocidaris. From the superposed position, which may be called primitive, the position of the pores in all Palaeozoic types except Bothriocidaris and in most other regular Echini takes on a change in which there is a revolu- tion through more or less of an angle of 90 degrees from the perpendicular, the revolution lx>ing in such a plane that the upper pore of the two is revolved toward the next adjacent interam- bulacrum. The revolution is therefore to the left of the perpendicular in the left half ambu- lacrum and to the right of the perpendicular in the right half-ambulacrum. Only rarely in regular Echini does the revolution exceed 90 degrees from the vertical, and in no case that I have found does the revolution take place toward the middle of the ambulacrum, but in the 58 ROBERT TRACY JACKSON ON ECHINI. opposite direction. From this it occurs that the pores of each pair occupy usually an inclined position, and the outermost pore of a pair is a little higher than the inner pore, Hyattechinus (Plate 23, fig. 1). It may be on a line with the inner pore, as in Melonechinus (Plate 61, fig. 8), but it is rarely lower than the inner pore in regular Echini. At the ventral border of the test the pores of each pair lie much more nearly vertical than at the mid-zone in Strongylocentrotus and Arbacia. In the latter the pores of the two pore-pairs adjacent to the median spheridium are actually superposed, as in Bothriocidaris. It is to be noted also that the pores on the peristomal ambulacral plates, as in Eucidaris (Plate 2, fig. 6), Phyllacanthus (Plate 2, fig. 18), Phormosoma (text-fig. 43, p. 80), and Strongylocentrotus (text-fig. 50), are nearly or quite vertically superposed as in the young and in the primitive Bothriocidaris. Also it may be shown that in very young, newly formed plates next the ocular, of Goniocidaris (Plate 2, fig. 4), the plates are high, not low, and the pores are nearly or quite superposed. This is in a measure like the young of Goniocidaris (Plate 2, fig. 2) or adult of Bothriocidaris. I have seen the same character in very young plates of Eucidaris tribuloides close to the ocular. In many clypeastroids, as Echinarachnius parma (Plate 8, fig. 4), the pores revolve through an angle of more than 90 degrees from the vertical, so that the outer pore of each pair lies lower than the inner pore. In many spatangoids the pores ventrally, and in most of the other ambula- cral plates, are superposed as in the embryo and Bothriocidaris, but in the petaloid areas they are nearly or quite horizontal. In Metalia pectoralis (text-fig. 8) the plates in ambulacrum III are high, without petaloid expansion, and the pores are superposed in the middle of the plate; in the four other areas the plates are relatively lower, petaloid dorsally, and in these areas at least the pores are horizontal, not superposed, and not in the middle of the plates. From this it seems that the relative position of the pores represents a greater or less departure from the primitive, and that a more primitive or more specialized relative position of pores occurs at definite parts of the test in the same specimen. In adult Bothriocidaris, Palaeechinus (text-fig. 15), and in the young, as seen in Gonio- cidaris, Strongylocentrotus (Lov6n, 1892) ; also in the young, as shown at the ventral border of the test, in Maccoya (text-fig. 16; Plate 33, fig. 1) and Lovenechinus (Plate 42, fig. 1), we find that the pore-pairs in succeeding plates lie over one another in a continuous or uniserial system. This arrangement is certainly primitive. It is to be observed that in this condition all tube-feet extend to the ground from one continuous line, and when the plates are low, that they are proximally closely crowded as in Cidaris. FVom this condition of uniserial pores and tube-feet, we pass in many independent series to types in which the pore-pairs are biserial, triserial, or polyserial in each half-ambulacrum. This is accomplished by alternate plates failing to reach the interambulacrum in whole or in part, thus producing a biserial arrangement, Maccoya (text-fig. 16; Plate 33, fig. 1) and Lovenechinus (text-fig. 18; Plate 42, fig. 2). In addition isolated plates may be introduced to make a triserial arrangement of pores, Melon- THE AMBULACRUM OF THE CORONA. 59 echinus springeri (text-fig. 19; Plate 52, fig. 2), Perischocidaris (Plate 67, fig. 1); or still more additional isolated plates may be introduced to make many series of pores in each half-ambula- crum, Melonechinus multiporus (text-fig. 20; Plate 56, fig. 4), Ijepidesthes colletti (trxt-fiK. 21; Plate 70, fig. 1), and Meekechinus (Plate 76, fig. 1). In the Centrechinoida the pores of the 21 TEXT-FIGS. 15-21. — Ambulacra of Palaeozoic Echini showing development of pore series by a drawing-out process of plate movement. 15. Palaeechinus elegans M'Coy. Lower Carboniferous. Adapted from Plate 31, fig. 1. All plates reach the interambulacrum . 16. Maccoya burlingtonensis (Meek and Worthen). Lower Carboniferous. Adapted from Plate 33, fig. 1. Ventrally all plates reach the interambulacrum; further up, only alternate plates. 17. Lovenechinus septies sp. nov. Lower Carboniferous. Adapted from Plate 45, fig. 2. Ventrally all plates reach the interambulacrum; further up, every alternate plate. At the mid-zone the plates are as in text-fig. 18. 18. Lovenechinus missouriensis (Jackson). Lower Carboniferous. Adapted from Plate 42, fig. 2. Every second plate reaches the interambulacrum. 19. Melonechinus springeri sp. nov. Lower Carboniferous. Adapted from Plate 52, fig. 2 Every third plate reaches the interambulaorum. 20. Melonechinus multiporus (Norwood and Owen). Lower Carboniferous. Adapted from Plate 56, fig. 4. Every fifth plate reaches the interambulacrum. 21. Lepidesthes collelli White. Lower Carboniferous. Adapted from Plate 70, fig. 3. Every eighth plate reach™ the interambulacrum. 60 ROBERT TRACY JACKSON ON ECHINI. compound plates tend strongly to fall into arcs in such fashion that succeeding pore-pairs fall in different vertical series, as seen well in Strongylocentrolus franciscanus. In Diplocidaris and Tetracidaris the pore-pairs, though in primary plates, are alternately pulled out of line, so that succeeding tube-feet would not lie quite over one another. This passage from the primitive condition of monoserial pore-pairs to the biserial or poly- serial, which is attained by the three methods of more than two columns of simple plates (Palaeozoic), compound plates with pores tending to arcs (Centrechinoida) , or primaries with pore-pairs biserial (certain Cidaridae), is all in accordance with the mechanical principle of each tube-foot attaining fullest play by being out of line with its fellows in so far as is possible. The arrangement reminds one of the phyllotactic arrangement of leaves in plants, where each leaf is not succeeded by another in a vertical line until one or more have been added which are off that vertical line, but in a succession of lines of their own series. In types, as spatangoids, in which below the petals the plates are relatively high and tube- feet therefore not crowded, the pore-pairs fall nearly in vertical uniserial lines, as in the young and primitive forms. This is aided probably by the fact that the ambulacral feet are for the most part modified as respiratory rather than locomotive organs. Ambulacral plates on their proximal side differ from the same plates on their distal side, and this difference, as far as observed, is usually in the line of greater simplicity and relative primitiveness of structure. In Melonechinus multiporus (Plate 56, figs. 4, 5) and 'M. gigan- teus (Plate 61, figs. 5-9), the ambulacral pore-pairs distally are eccentric and lie nearest to the interambulacral suture, but proximally, as shown, the pore-pairs of isolated plates lie in the middle of each plate, a primitive character. In general the pores proximally are nearer the middle of the plate than on the distal side. In Maccoya intermedia (Plate 34, fig. 2) the plates alternately reach and are cut off from the interambulacral suture and pore-pairs are biserial. All this is as seen from the outer or distal side. When seen from the inner or proximal side (Plate 34, fig. 3), all the plates at the mid-zone cross the half-area instead of alternate plates being cut off from the interambulacral suture. Also the pore-pairs are uni- serial instead of biserial, as they are on the outer side of the very same plates, so that in all these characters they are primitive like the young and the next lower genus Palaeechinus (Plate 31, fig. 1). A similar condition is seen in distal and proximal sides of the plates in Maccoya burlingtonensis (Plate 33, figs. 4, 5). In Lovenechinus missouriensis the outer demi-plates, as seen distally (Plate 43, fig. 3) are very narrow, the inner occluded plates are relatively wide and the pore-pairs of both lie very near the interambulacral suture. In a proximal view of the same plates (Plate 43, fig. 4) the demi- and occluded plates are of about the same width, and the pore-pairs of both lie near the middle line of the half-ambulacrum. Also proximally the plate that lies opposite the horizontal suture lines of the adradial plates is spread out? in a fan-shaped manner, whereas on the distal side the fan-shape is nearly or quite wanting. TIIK AMi»n.A< KIM oi TIIK r.\\ til A similar condition of fan-shaped plates proximally, which an- m.t -« -h.-ip«-il di-tally. i- Men in Melonechinus mulliporus (Plate 50, figs. 4, 5) and M. i/ii/milm* (Plate HI, CIRH. 5-9). Comparable differences between the interior and exterior side- of tin- -ame plates are BW-II in interambulacral, ocular, and genital plates, us docribed in tin- consideration of these purl- pp. 75, 96, 172). All this shows that in the study of specimens and the description uf -peeie-, ,,i,,- must bear in mind whether the specimen represents the internal or external characters of I lie te-t. Another feature noticed on the inside of ambulacra! plate- i- elevated nodo-e or -pino-e projections that occur in some Echini. These were first seen in the fo-.-il Il\atterhinu> 'Plate 24, fig. 6), where low, knob-like or spinose elevations exi.-l between the inner [tore and tin- middle of the area. Alexander Agassiz (1904, p. HI) has described spine- extending into tin- body from the inner face of the peristornal ambulacral plates of I'ororiiltiris mlinsi, but I In-lieve they have not been noticed before in coronal ambulacral plates. In Phyllacanthu- Plate :{. fig. 12) near to the ventral border of the test, there are small spines between the inner pore.- and the middle of the area; these seem to be the equivalent of those occurring in the Palaeo/nie Hyattechinus. Close to the peristornal border these spine< increase in height, arch over and then fuse in a continuous ridge (text-fig. 224, p. 193). Passing dorsally, in Phyllaeanthii- a second series of spines occurs, one over each inner pore, and above the ventral area the-e alone exist. In Eucidaris tribuloides I find a similar condition to that of Phyllacanthu-. except that there are commonly three spinules over the inner pore (Plate 3, fig. 13). Such >pino-«- growths are most delicate and are destroyed by a touch so that they can only be -een in a te-t cleaned without any brushing. They have not been noticed in any of the (Yntrechinoida. Closely associated with the ambulacrum are the spheridia described by I .oven (1874), which, as he showed, are characteristic of all modern Echini except the C'idaridae. If they had existed in pits, as is so often the case, we might expect to find them in the Palaeozoic. The fact of their absence in the primitive Cidaridae is an argument for the a»umption that they were also probably absent in Palaeozoic genera. Certainly they are not known. Pedicellariae have recently come into prominence through the critical -tudie.- of Morten-en and others. It is of interest to note that tridentate pedicellariae occurred in the Palaeozoic, as shown in Meekechinus elegans gen. et sp. nov. (Plate 76, figs. 8, 9). Except a- >lmwn in the Jurassic Pelanechinus by Groom (1887) I believe these are the first found fossil, and they will probably always remain rarities. Special respiratory organs are also closely associated with the ambulacra. ( 'harle- Stewart (1879) first described internal branchiae in Eucidaris tribuloidr* which lie dorsal to the lantern and extend over the ambulacral areas radially from beneath the compa-e- and between the-e and the braces. The same structures were described by Ludwig (1880) and by Pn.uho 1 1887) in Cidaris papillata. Prouho gave them the name of Stewart's organs, a convenient distinction from the quite different external gills. I have seen them in dissections of Culnrin ajfnw, 62 ROBERT TRACY JACKSON ON ECHINI. Eucidaris tribuloides and thouarsii. Stewart's organs are described in Asthenosoma by P. and F. Sarasin (1888), and in several echinothuriids by A. Agassiz and Clark (1909). External gills are developed as five pairs of branched appendages which are outgrowths of the oral integu- ment (text-fig. 55, p. 83). They are characteristic of the Centrechinoida and by inference the fos- sil Holectypina. Their presence is marked by the indenting of the interambulacral basicoronal plates so that they are recognizable in fossils. These peristomal gills, as I would call them for distinctiveness, are interambulacral in position in contradistinction to Stewart's organs, which are ambulacral or radial in position. In clypeastroids and spatangoids, as well as par- tially in some of the Centrechinoida (Arbacia), the function of respiration is maintained by the dorsal ambulacral tentacles, which have lost their function as locomotive organs. These I would call in distinction ambulacral gills. We do not and probably cannot know definitely what respiratory organs existed in Palaeozoic Echini. Branchial slits for peristomal gills I have found no evidence of, though carefully looked for. There is no evidence of specialization of tube-feet as ambulacral gills, though they may have performed that function in part. As the primitive Cidaridae have the Stewart's organs so well developed, it is not unlikely that these organs were the respiratory organs of all Echini in Palaeozoic times. THE INTERAMBULACRUM. The interambulacrum in Echini functions chiefly as a space filler and a bearer of spines and pedicellariae. The spines serve for protection and more or less in locomotion, and pedi- cellariae as grasping, cleansing, and protective organs. In spite of this secondary physiological importance, the interambulacrum forms a large part of the test of the sea-urchin in most types, and is of very great interest, especially in Palaeozoic genera. The interambulacral plates originate in direct contact with the ocular plates and quite independently of the genitals. The young last added plates may always be found in direct contact with the oculars in Palaeozoic and later Echini, and their independence of the genitals is proved in cases where no genital reaches the interambulacrum, as in Bothriocidaris archaica (Plate 1, fig. 2), the posterior area in spatangoids (text-figs. 174, 175, p. 149), the aberrant Arbacias (Plate 4, figs. 11, 12), and Tripneustes (Plate 6, fig. 4). As any given interambulacrum comes in contact with two oculars, one on either side, and as at the base of these two oculars new interambulacral plates originate (Melonechinus, Plate 56, fig. 6, and numerous other figures), it seems that an interambulacrum may theoretically be considered as composed of two halves, one half-interambulacrum being associated with the ocular and ambulacrum on one side, and the other half being associated with the ocular and ambulacrum on the other side. In other words, the corona may be conceived as made up of five areas, each surmounted by an ocular plate, an ambulacrum and adjacent half-interambulacrum on either side making up each THK INTERAMBUIACBUM. li.'i of these five parts. Such an ideal area composed of plates associated with a single ocular is shown in Palaeechinus and Eucidaris (text-figs. 217, 218, p. 191). Support for this view is found in the fact that the perignathic muscles of the lantern, which are nearly <>r quite nml>ul;i< -r.il in position, are inserted wholly on the base of the associated two lialf-mtenu.il.ulacra, EH in Eucidaris (text-fig. 218); or if not, they are inserted on two half-interambularra and auricles of the ambulacrum itself, as in Centrechinus (text-fig. 219, p. 191). In the Echinothuriidae where oculars and genitals are separated hy an inter-pare. Mr. Agassiz (1883, p. 32; 1904, p. 96), says that the interambulacral plat.- an- derived from the periproct, as the two areas are there in contact. Dr. Mortensen (1903, p. 175) opposes this view. Evidently this contact is a mere coincidence of structure and has no bearing on the origin of plates. In the echinothuriids which I have seen, the young intcrambularral plate- are in contact with the oculars as usual (text-fig. 170, p. 149). While in regular Krhini outside the Echinothuriidae the oculars and genitals typically form a closed ring, yet occasionally in variants the ring may be open so that the periproct reaches the interamlmlarrum. a- in Strongylocentrotus (Plate 5, fig. 15; Plate 6, fig. 5). The full differential characters of the interambulacrum as of the ambulacrum are expressed at the mid-zone of the adult. Here are usually found the full number of columns of plate- characteristic of the species, also the typical tubercles, spines, imbrication, or other characters which go to make up the specific description. The ventral border in the basicoronal /.one represents the earliest formed plates and the youth of the individual, as far a> it can lx> gathered from the study of an adult specimen, though the actually first formed plates may have I resorbed in development. Passing dorsally, with later added plates, new characters may come in until we get the full differential features developed at or about the mid-zone. Dorsal to the mid-zone we pass into the area of young last formed plates which have not yet acquired the full characters. Or again dorsally, we may find senescent features in the loss of columns of plates. Passing from the basicoronal row dorsally, we find in most Palaeozoic types, and many post-Palaeozoic as well, stages in development strongly marked, which stages can be correlated with the adult condition of simpler genera or simpler species within the genus. The interambulacrum in Echini has from one to fourteen vertical columns of plates in each of the five areas, which represents the least and greatest number known at present. There are intermediate grades representing every step between this lea-t and grcate-t socialization of the area, and it is a matter of great interest to follow the progressive series as represented by stages in development, and by adult types, to see how the progressive differential structure is built up. As the plates of the ventral border are the oldest or first formed of any plates seen in an individual specimen, and as the later added plates succeed one another a.- we pass dorsally, it might be thought that we could read stages in development as expressed by rows and columns of plates with ease and certainty, and such can be done in many type-, as in 64 ROBERT TRACY JACKSON ON ECHINI. Hyattechinus beecheri (Plate 26) and Perischodomus biserialis (Plate 64, fig. 2). Complications may come in, however, especially resorption of the base of the corona by encroachment of the peristome cutting off part of the ventral plates, and also rarely resorption within the corona, as exceptionally in Arachnoides, or differential growth of associated plates, which may separate plates originally in contact (Echinarachnius). There may be few plates in a given interambulacrum, as in Bothriocidaris (Plate 1, fig. 1) or Cidaris, or a very large number, as in Hyattechinus beecheri (Plate 26), and many other species. There is every evidence that these plates all originated as separate plates and never by division of previously formed plates. Mr. Agassiz (1881, p. 95; 1904, p. 104) says that in Phormosoma, interambulacral plates are formed by the splitting of earlier continuous plates. Mortensen (1904, p. 25) suggests that these planes of division may be due to fracture in the handling of the specimens which have excessively thin plates, and my limited observations of Echinothuriidae accord with this view. If these are natural suture lines in Phormosoma, the numerous plates thus formed cannot be homologized with the numerous columns of plates in Palaeozoic types to which Mr. Agassiz compared them, for the latter originate independently, not by the splitting of previously continuous plates. While fusion into compound plates is seen in the ambulacrum of the Centrechinoida, such fusion is unknown in the interambulacrum in all Echini. Loven (1874, p. 51) assumed, it is true, fusion of certain plates around the base of the corona in spatangoids. No sutures exist, and it seems that single plates at this area in these and other types are not cases of fusion, but of failure to develop more than one plate in the row to which they belong. In the important ancient type Bothriocidaris, as best shown in B. archaica (Plate 1, fig. 1), there is a single column of interambulacral plates in each area extending from just above the second row of ambulacral plates of the peristome to the apical disc, where in this species they are completely covered by the large ocular plates and do not reach the genitals. The full details of this and other cases given are considered under the description of the species. This is the simplest and, I think, the most primitive condition known in any adult echinoid. In my paper on Echini (1896, p. 233) I considered Bothriocidaris as representing the archaic radical as regards interambulacral structure from which the interambulacra in all other Echini could be derived. Further evidence and study confirm this view. Mr. A. Agassiz (1904, p. 80) says, "The existence of an interambulacral zone composed of a single row of plates [in Bothriocidaris] does not give us any clue to the mode of formation of the Palaechinid type of interambulacra with its manifold rows of plates." I cannot agree with this view, as it seems that the single primordial plate found so universally in young Echini, or in adults when resorption has not removed it, may fairly be considered as representing in development a stage consisting of a single column which in all but Bothriocidaris is succeeded by additional columns during development, as shown in my first paper and in numerous cases THE INTERAMBULACRUM. (i.-, in this paper. Dr. Mortensen (1903) describes a very young Hypsiechinus (my Plate 3, fig. 0), in which the interambulacrum consists of but a single plate in each of the five areas.1 In young Echinus (Plate 3, fig. 5) Bury (1895) figures a similar single plate, and lyove'n (1874, Plate 17, fig. 49) figures a young echinoid in which there is only a single intenmbulMnl plate in each area. This single plate, it seems, represents a single-column stage consist ing of thi.- one pl.-itr. and may fairly be homologized with the plate at the ventral border of the interainbiilacnim of Bothriocidaris. Lov6n (1892) showed that in young Goniocidaris (my Plate 2, fig. 1), also in Strongylo- centrotus (Plate 3, fig. 11), and Echinus, at the ventral border of the interamlMilacnim then- is a single plate which lies dorsal to the continuous row of primordial ambulacra! plate-. T!ii> plate is evidently the single first formed plate, and is homologized with the ventral plate of the interambulacrum in Bothriocidaris. In the young of the Recent Echini mentioned, the first plate is succeeded in the second row by two plates introducing the character of a second column, which is the next stage in differential development of the interambulacrum. A >imilar single first plate succeeded by two plates in the second row is shown by A. Agassiz (1904) in young Salenia (his Plate 21, fig. 1), young Phormosoma (my Plate 3, fig. 10), and in young Arbacia (his Plate 54, fig. 2). In later life, in regular Echini, as shown by Levin , this single initial plate is usually resorbed by the encroachment of the actinostome, so that in the adult there are two plates on the peristomal border, as in Cidaris and most regular Recent Echini. Arbacia (text-fig. 227, p. 193) and Phormosoma (text-fig. 43, p. 80) are exceptions, for, as Mr. Agassiz showed (1904, p. 54, Plate 41), the single plate is retained at the ventral border of the adult in these genera. As Loven (1874) showed in the clypeastroids and spatangoids. the plate is retained at the ventral border of the corona in most cases, as the corona is not resorbed by the encroachment of the peristome. There are certain exceptions to this, as later discussed. Turning to Palaeozoic types, we find in Perischodomus (text-fig. 30, p. 70; Plate 64, fig. 2) that there is a single plate ventrally succeeded by two plates in the second row, as in young Cidaris, etc., but in the third row there are three plates, which introduces another stage in differential development, structurally an advance on that seen in Cidaris and all modern Echini. In the next row of Perischodomus there are four plates, and later a fifth column i: introduced. In this type we see that a form with five columns of plates in the adult is buill up by a series of stages starting with a single column represented by a single plate ventrall: and the succeeding stages are represented by additional rows or zones of growth pmgr.- introducing new columns or new characters in differential development. In Hyattechinus beecheri (Plate 26) we find ventrally a single plate representing a s • In his text Dr. Mortensen (1903, p. 89) calls this plate a genital, but he wn,.,- .,„• that .his wa. an e second part of his Ingolf Echinoida (1907, p. 172), corrects the error, saying that t and the genitals are discernible on the abactinal side. 66 ROBERT TRACY JACKSON ON ECHINI. column of plates in each of the five areas. In the second row there are two plates, in the third three, in the fourth four, in the fifth five, and so on. There is not always a new column added in each new row or zone of growth in this species, but this is very nearly the case up to the maximum number of columns added, which is eleven. Dorsally the adradial columns 1 and 2 drop out, so that columns 3 and 4 come against the ambulacrals in further dorsal growth. The same series of stages of progressive development marked by adding columns, and regressive senescent stages marked by the dropping out of columns of interambulacral plates are shown in Hyattechinus rarispinus (Plate 23, figs. 1, 3) and H. pentagonus (Plate 25, figs. 1, 3). In this last species in senescence, several columns are dropped, so that close to the apical region there are ten columns instead of the fourteen characteristic of its full development near the mid-zone. H . pentagonus is also especially interesting, as it attains fourteen columns of plates in the adult in each area, the maximum specialization in this line of differential development of all known Echini. Yet as resorption has not removed any plates, we can trace the development from the simple ventral or young condition, represented by a single plate on the peristomal border, to the complex adult and senescent old age without a single gap in the series of stages in develop- ment. In other Palaeozoic genera a similar progressive individual development may be traced in which the single ventral plate is retained in the adult, as in Pholidechinus (Plate 28, fig. 1), Pholidocidaris (Plate 73, fig. 6), Lepidocentrus (Plate 20, fig. 7), and Lepidesthes (Plate 68, fig. 3). The above represent Palaeozoic genera in which there is no ventral resorption of the corona, and therefore all the interambulacral plates, built during the life of the individual, are retained and can be seen in a well preserved adult individual. Such successive stages in the development of an interambulacrum can be fairly compared to studying the development of a cephalopod or other mollusc, as has been done so successfully by Hyatt and others, by tracing the characters from the umbo or original apex of the shell by a series of steps or stages to the completed adult or old-age individual, all worked out in a single specimen. There is the great difference, however, that in the mollusc the shell is external, in the sea-urchin internal, so that in the latter the plates have grown since first formed and may have suffered changes, but from their presence stages can be read. Resorption, however, comes in in Palaeozoic as well as in post-Palaeozoic types. Studying genera representing the Palaeechinidae, we find that there are two plates at the ventral border of the interambulacra in all cases where the ventral part of the corona is complete, as seen in Palaeechinus (Plate 30, fig. 3), Maccoya (Plate 33, fig. 1), Lovenechinus (Plate 43, fig. 1), Melonechinus (text-fig. 25; Plate 56, fig. 2; Plate 57, fig. 1), and others. This character is explained by the fact that the single initial ventral plate, found so universally in young modern Echini, and retained ventrally in numerous fossil and living genera, has been resorbed in the advancement of the peristome, as in Cidaris and most modern regular Echini. Miss Klem THE INTEHAMBULACRl M 67 (1904, p. 3) criticizes this view and claims that there are more than two plat.- wln-n the v.-ntral area is complete. I can only say that Miss Klem is mistaken. I have never seen an ,-x,-«.,,t ion. Two of the specimens here figured, showing this character of two plates ventrally, an- from tin- Hambach Collection which Miss Klem studied and herself figured, but it is fair to >tat<- that they have been freed somewhat from matrix since she studied them. Tin- .-IM-HIIII-IIS n-ferred to are Lovenechinus septies (Plate 45, fig. 1 = Miss Klem's Plate 2, figs. 5a-5d) and .17. limechimu multiporus (Plate 57, fig. 1 = Miss Klem's Plate 3, figs. 6a-6d). In Palaeechinus quadriteriali* (Plate 30, fig. 3) there are two plates in the first row or zone, three in the second, four in the third (excepting in one area, C), and above the introduction of the fourth column no more columns are added, but all are continued to the apical disc. Love"n (1874, p. 39) made the acute observation that in Palaeozoic genera with multiple columns of plates, the adambulacral plates alone are continued from the peristome to the apical disc. This observation holds true of most of the family of the Palaeechinidae, as in Palaeechinus (Plate 30, fig. 3) and I^ovem-chimis (Plate 41, fig. 1). The statement, however, needs modification. In those types where there- is a single plate at the ventral border, Perischodomus (Plate 64, fig. 2), obviously two columns do not reach the peristome. Also in senescence (Melonechinus indianensis, Plate 53, fig. 1), usually the two adambulacral columns drop out before reaching the apical disc; or in special- ized types they may drop out very early, as in Hyallechinus beecheri (Plate 26) or H. pen- tagonus (Plate 25, fig. 3). In the family of the Palaeechinidae the species have as a range from three to eleven columns of interambulacral plates. In the several species the early development is as in Palaeechinus quadriserialis, but in later growth additional differential characters are usually taken on. In a young Lovenechinus missouriensis (Plate 40) a fifth column comes in soon after the fourth, and in this specimen, which is very young and the only really young Palaeozoic echinoid yet known, the fifth column originates near the mid-zone. In an older individual (Plate 41, fip. 1 where many more rows of plates have been added dorsally, we find that the introduction of the fifth column has been relatively shoved ventrally by the later added plates. In addition, a sixth column is represented by one or two plates in three areas, E, G, I, but in two areas, A, C, no sixth occurs. This occurrence of a column represented by only one or two plates is very exceptional in Echini and suggests a disappearing part. In many specimens of tht- >pcrir> it is entirely absent. In Lovenechinus septies the method of introduction of columns is well shown (Plate 45, fig. 1), as it is one of the best preserved specimens I have seen. In three areas the two plates are present in the basicoronal row, restored in the other two; from this point up or dorsally in the several areas the new columns come in quite regularly. In th<> very choice specimen of Melonechinus multiporus (Plate 57, fig. 1 ; text-figs. 245, 246) there are two plates ventrally in areas G, I, one of the two in areas A and C, and they are restored in areas where wanting, as indicated by dotted lines. Above this zone the introduction of columns is shown without the absence of a single plate in all five interambulacral areas. 68 ROBERT TRACY JACKSON ON ECHINI. In Melonechinus multiporus there are eight or nine, rarely seven, columns of plates in each area. In M. vanderbilti there are nine columns of plates, and in M . giganteus (Plate 59, fig. 14) there are eleven. The columns are all added in a perfectly definite method and are in this feature further developments of the system seen in Palaeechinus quadriserialis. The progressive addition of columns as we pass dorsally from the single column ventrally to the two to fourteen columns dorsally, I believe, represents distinctly stages in development through which the animal passes in its growth, the progressive stages being comparable to the conditions seen in the adult of simpler genera or simpler species allied to the type under con- sideration. The method of introduction of interambulacral columns was shown in detail by Jackson and Jaggar (1896) and Jackson (1896), but will be briefly stated here. In the Palaeechinidae and most Palaeozoic Echini, excepting those that have strongly imbricate plates, the plates of the interambulacrum are typically hexagonal excepting the adambulacral columns which are nearly pentagonal but crenulate or rounded on the adradial suture. While the plates arc typically hexagonal, this symmetry is modified where new columns are introduced. The initial plates of columns above the third are typically pentagonal with an apex of the pentagon pointing ventrally, and an adjacent ventral plate on the left or right is heptagonal, the added side com- pensating for the one side short in the initial pentagon. An exception to this rule of pentagonal initial plates of columns is seen in the initial plate of the third column, which is typically hex- agonal and is immediately succeeded by the initial plate of column 4, which is a pentagon, as seen in Melonechinus multiporus (Plate 57) and many other species. If by rare exception the initial plate of column 3 is not immediately followed by the initial plate of column 4, as in area C of Lovenechinus septies (Plate 45, fig. 1), then the initial plate of column 3 is also pen- tagonal. When odd-numbered columns, as columns 3, 5, 7, 9, 11, etc., are introduced, they are typically introduced in the middle of the area with an equal number of columns on each side of them, and also typically the heptagonal associated plate lies on the right ventral border of the initial pentagon. When even-numbered columns are added, as columns 4, 6, 8, 10, etc., they are typically added to the right of the center with one more column on the left than on the right. While this is the rule in the large majority of cases, there are frequent exceptions in which even-numbered columns are added on the left instead of the right of the center. As a concurrent character, the associated heptagonal plate in even-numbered columns typically lies to the left of the initial pentagon. Why this systematic position of columns and associated heptagonal plates should come in with such regularity is not obvious, but it is a very constant character, as shown by Jackson and Jaggar (1896, p. 163) who worked out the percentages of normal cases and variations. In the dorsal portion of the interambulacrum the plates are nearly or quite rhombic in outline and gradually take on the typical hexagonal outline, as they are pushed ventrally by later intercalated plates and come into mechanical contact with adjacent plates of their several associated columns (Plate 59, fig. 14). CHARACTERS OF BASICORQNAL PLATKS. 69 Dorsally each interambulacrum comes in contact with a genital ami tun adjacent ocular plates, except in Bothriocidaris archaica (Plate 1, fig. 2) and in part in B. pahleiii < I 'I at.- I , I,. and.in the posterior interambulacrum of many spatango ids (Micraster), where the iniiTaiiilnila- crum abuts against two ocular plates only (text-figs. 174, 175, p. 149). The iiitcramliularnim also comes against oculars only in the remarkable variations in Arl.a.-ia -howri in Plate 4, fig». 11, 12. The new interambulacral plates in Echini are formed against the ocular plates on either side of the area, never in the middle against the genital. The relation of the interambulacrum to the ambulacrum in development i> of much interest, and it seems may be expressed in terms of acceleration of development. In BothriocidariH (Plate 1, fig. 1) two continuous rows of ambulacral plates surround the mouth, funning the peristome of that type, before reaching the initial plate of the interambulacrum in the third aboral row or zone. This character in Bothriocidaris is discussed in detail under consideration of that type. In young Goniocidaris (Plate 2, fig. 1) and in young Strongylocentrotu- ' Plate 3, fig. 11), young Salenia (A. Agassiz, 1904, Plate 21, fig. 1), and young Phorniosoma (Plate .3, fig. 9), a single row of continuous ambulacral plates surrounds the mouth forming the peristome at that age, but the initial single plate of the interambulacrum appears in the second row which is the base of the corona, instead of the third row as in Bothriocidaris. In clypea.-troids and spatangoids (Collyrites, Plate 3, fig. 15) the initial single plate of the interambulacrum appears intercalated between the plates of the primordial ambulacral row, which, therefore, are not continuous as in regular Echini, but discontinuous, and, moreover, do not form part of the peristome, but form with the primordial interambulacral plates the basicoronal row of plates of the corona proper. CHARACTERS OF BASICORONAL PLATES. Basicoronal plates are the oldest or first formed plates existent in any given corona, and unless plates have been removed by resorption, or by flowing down on to the poristome. as in the ambulacrals of cidarids, they are the actual plates formed at this area in the young animal. Therefore, as elsewhere discussed, they often present simpler characters than plates dorsal to them, and thus show stages in development. These plates on the proximal side give rise to the attachment of part of the muscles of the Aristotle's lantern, either directly or through the elevated processes of the perignathic girdle, which is later discussed. There are certain types of structure in basicoronal plates which are comparatively constant in large groups, so that they are of more than specific or generic value. The characters of basicoronal interambulacral plates are the more striking and may be stated in brief. Where no plates have been removed by resorption, there is a single plate at the ventral border of the interambulacrum. The primitive type of this character is Bothrio- 70 ROBERT TRACY JACKSON ON ECHINI. cidaris (text-fig. 22), which continues to build a single column. This same character of a single plate ventrally, but succeeded by two plates in the second row, is characteristic of the young of all modern regular Echini, as shown by Lov£n (1892) (Goniocidaris, text-fig. 23). In the adult of most regular Echini the single plate and probably more have been resorbed by the advance of the peristome (Eucidaris, text-fig. 24) . In the Palaeechinidae with many columns of plates, apparently only one plate has been resorbed, when we find two plates in the basicoronal 27 28 29 30 31 TEXT-FIGS. 22-31. — Characters of the base of the interambulacrum in representative Echini. 22. Bothriocidaris archaica sp. nov. Ordovician. From Plate 1, fig. 1. 23. Goniocidaris canaliculata A. Agassiz. Young. From Plate 2, figs. 1, 2. 24. Eucidaris tribuloides (Lamarck). Bahamas. 25. Melonechinus mulliporus (Norwood and Owen). Lower Carboniferous. From Plate 57. 26. Archaeocidaris wortheni Hall. Lower Carboniferous. From Plate 9, fig. 6. 27. PUxechinus cinctus A. Agassiz. Adapted from A. Agassiz, 1904, Plate 58, fig. 1. 28. Echinocyamus pusillus (Muller). Adapted from Lov6n, 1874, Plate 44. 29. Rotula dentata (Lamarck). Adapted from Love"n, 1874, Plate 46. 30. Perischodomus biserialis M'Coy. Lower Carboniferous. From Plate 64, fig. 2. 31. Tiarechinus princeps (Laube). Triassic. Adapted from Loveii, 1883, Plate 13, figs. 152, 154. In figures 22, 23, 27-31 the primordial interambulacral plate is in the basicoronal row; in 24-26, it, with or without additional plates, has been resorbed. row (Melonechinus, text-fig. 25), or in the Archaeocidaridae, several rows of plates may have been resorbed, and we find four plates in the basicoronal row (Archaeocidaris, text-fig. 26). In modern Echini where there has been no resorption, the single primordial plate is retained in the adult. This character, as shown by Lov6n (1874) and others, occurs in most clypeas- CHARACTERS OF BASK OHONAL PI.ATKS. 71 troids and spatangoids (text-figs. 27-29). In Plcxrrhinus (text-fig. 27) the single plate in followed by another single plate, and these by a second column. This is a very ran- ••.v.-ptic,,,, as the typical character is for the initial primordial plate to be immediately succeeded by two plates in all Echini except Bothriocidaris. In Rotula (text-fig. 29) the primordial interam- bulacral plate is separated from the next two of its area by the lateral introvenient ambulacral plates. As shown by Love"n, plates originally in contact in the young may be thu- -••parated during growth. A few modern regular Echini retain the primordial plate in the adult (Phor- mosoma, text-fig. 43, p. 80; Arbacia, text-fig. 227, p. 193). In Palaeozoic Echini with imbricate plates and many interambulacral columns, there is no resorption, and therefore the primordial interambulacral plate is retained in the adult, as in Perischodomus (text-fig. 30), Hyattechinus (Plate 25, fig. 1), Lepidocentrus, Ix-pidesth. ~. and Pholidocidaris. The primordial plate in all these is succeeded by two plates, then three, then four, etc. (text-fig. 30). In the remarkable Tiarechinus from the Trias, Lov6n (1883) showed that the primordial interambulacral plate is succeeded by three plates (text-fig. 31), and then no more plates are built, a unique condition. Considering the general characters of the basicoronal row, with special reference to the ambulacral plates, we find the following types of arrangement. In BothriocidarLs the basi- coronal row consists of two high hexagonal ambulacral plates with pores superposed in each ambulacral area and one interambulacral plate in each interambulacral area (Plate 1, fig. 1). This same character is seen in young cidarids (Plate 2, fig. 2) (Love"n, 1892; A. Agassiz, 1904), young Strongylocentrotus (Plate 3, fig. 11), and Echinus (Love"n, 1892), young Salenia, Arbacia, and Phormosoma (A. Agassiz, 1904). It is, I think, fab- to call this a primitive character, and it represents what I (1896, p. 235) described as the protechinus stage. The protechinus stage is comparable in other groups of animals to the protoconch of cephalous Mollusca, what I (1890) described as the prodissoconch of Pelecypoda, and to Beecher's (1901) protegulum of Brachio- poda and protaspis of Trilobita. All are referable to what I termed (1890, p. 289) the phylembryonic stage in development, a stage in which the differential characters of the class are established in ontogeny. A second type of basicoronal plates, in which there are two ambulacral plates alternating with one interambulacral plate in each area, is seen in types where the ambulacral plates have in part flowed down on to the peristome, so that the plates originally there are gone, and yet the primordial interambulacral plate has retained its original place. Such is seen in the Palaeo- zoic Hyattechinus (Plate 23, fig. 1), Pholidechinus (Plate 28, fig. 1), Lepidesthes (Plate 68, fig. 3), and Recent Phormosoma (text-fig. 43, p. 80). This last type differs markedly from those just considered in that the ambulacral basicoronal plates in the adult are compound instead of simple. No compound ambulacral plates on the peristome are known in any type. A third type of basicoronal plates is seen in clypeastroids (Echinarachnius, text -fig. 52, 72 ROBERT TRACY JACKSON ON ECHINI. p. 80) and spatangoids (Micraster and Collyrites, Plate 3, fig. 15). In both of these the primordial ambulacral plates typically alternate with the primordial interambulacral plates to form the basicoronal row. In all other echinoids the primordial ambulacral plates are on the actinostome and form buccal plates both in the young and in the adult. Some very peculiar special modifications of this plan occur in aberrant cases in clypeastroids and spatan- goids, as follows. In Arachnoides placenta (Linne"), Lov6n (1874, Plate 51) showed that in the young, ambulacral and interambulacral plates alternate as usual. In the adult, the posterior odd interambulacral plate has been pushed dorsally out of the basicoronal ring, and the other primordial interambulacral plates in areas 1, 2, 3, 4, have disappeared by intracoronal resorption, so that as a result, the ten primordial ambulacral plates have come in contact and alone make up the basicoronal ring. They are in contact as they are typically in the buccal membrane around the mouth in regular Echini (Bothriocidaris) , but the contact in Arachnoides placenta is a secondary contact not homologous with, though analogous to the original primitive con- tact. In specimens of Arachnoides that I have examined, both smaller and larger than those figured by Loven, the primordial interambulacral plates are in place in the basicoronal row. It is probable, therefore, that Lov6n's larger specimen as described was an exceptional indi- vidual variant, and not typical of the species. In Lovenia forbesi Woods and Duncan, from the Miocene of Australia, the primordial interambulacral plates of areas 2, 3, 5, are in place in the basicoronal row, but the plates of 1 and 4 have been pushed dorsally so that the primordial ambulacrals Ife, Ila, and IV6, Va have come in contact instead of being separated by an interambulacral plate as usual. In Pourtalesia jeffreysi Wyville Thomson, Loven (1883, p. 13) shows the extraordinary condition that the primordial interambulacral plates 2, 3 join posteriorly the base of primordial interambulacral 5 and shut out the primordial ambulacrals I, V and II, IV from the peristomal row. In this highly aberrant type, therefore, the ventral margin of the corona is made up of the two primordial ambulacrals Ilia, b, and the sum of primordial interambulacrals 2, 3, and 5, as far as known a unique condition. Dr. Mortensen (1907, p. 73, Plate 17, fig. 21) shows in Echinosigra (Pourtalesia) paradoxa Mortensen, a most excessive lengthening and also narrowing of the basicoronal plates in areas I, 5, and V, making them, perhaps, the most peculiar plates of any echinoid, in a type that takes delight in breaking all rules of echinoid structure. All the above are types of basicoronal plates in which there has been no encroachment by resorption of the ventral border of the corona. Where resorption has taken place to a greater or less extent, a different character of basicoronals prevails. In the Palaeechinidae resorption has apparently cut away only the single primordial interambulacral plate and at the same time, as gathered from Melonechinus (Plate 56, fig. 8), some ambulacral plates have been transferred to the peristome. In these types we find two IMBRICATION OF CORONAL PLATKS. 7.'i plates at the ventral border of the interambulacrum and two in the ambulacrum 'Ma.-. Plate 33, fig. 1; Lovenechinus, Plate 43, fig. 1; Oligoporus, Plate 50, fig. 8), or two in the interambulacrum and four in the ambulacrum (Melonechinus, Plate ;,ti. fin. •_',. I;, -.,,-ption may have cut away more than one row, probably three or more rows, when we have the condi- tion in Archaeocidaris (Plate 9, figs. 7, 8; Plate 10, fig. 10), where there arc four plat.- in the interambulacrum and two in the ambulacrum in the basicoronal row. Resorption may cut away an indeterminate number of plates, when \\e find the condition seen in most modern regular Echini, as Cidaris and Strongylocentrotus, with two interambula- cral and two ambulacral plates in each area in the basicoronal row. Thi- include-. I believe, the essential structure of the basicoronal row of all Echini. The proximal modification of these plates by the development of the perignathic girdle are considered under that head (p. I '.MI . The enlargement of the peristomal aperture in Echini is attained by two method-: by the growth of the individual plates, which will enlarge the opening to any extent ; or by cutting away the plates by resorption, which is a more obvious method of enlargement. The growth of the plates is, however, the more important factor. Even when resorption has not cut away any interambulacral plates, as in Echinarachnius, Spatangus, Arbacia (text -fig. 227, p. P.':; and especially Phormosoma (text-fig. 43, p. 80), the size of the peristomal opening i- many times larger than it was in the young individual. IMBRICATION OF CORONAL PLATES. In Echini, in many types, there is no imbrication in the coronal plates, the suture lii the plates being so nearly perpendicular to the surface that the sides of a plate are a- nearly parallel as possible in a curved test. The sides of a plate may be far from parallel when- the plates are very thick, as in Lovenechinus nobilis (Plate 38, fig. 9), but still they are jx-riM-ndicular to the surface and are therefore not imbricate. Certain plates in Echini may present a strong angle on the suture line in a given direction, which Bather suggestively calls beveling. Beveling is applied as a term where the inclination is in a limited number of plates only. An excellent example is in the adradial suture <»f the Palaeechinidae. Here in all species of the family, as shown in Loivnechinus seplics (Plate i:, fig. 5), the ambulacral plates are inclined over the adjacent interambulacral plates. -<> that a strong bevel results in the plates concerned. A similar bevel is seen in the petaloid area in some clypeastroids (Clypeaster), where the ambulacra are strongly inclined over the interam- bulacra on the adradial suture. In Clypeaster rosaceus a curious combination of direction of beveling occurs. A- -tated, in the petaloid areas, the ambulacra bevel over the interambulacra as they do in the Palae- 74 ROBERT TRACY JACKSON ON ECHINI. echinidae. On the other hand, ventrally in Clypeaster, the interambulacra bevel over the ambulacra (text-fig. 234, p. 197) as in Pholidechinus or other types that have imbricate plates. A succession of bevels, in a meridional or transverse series, as Bather (1909a, p. 64) says, produces imbrication properly so called. Imbrication is a character of many quite independent series in Echini, and while of genetic value in a limited series, cannot be used as a basis of close systematic connection in Echini as a whole, as I have shown (1896, p. 237). As imbrication is confusing, especially in fossils where specimens are often viewed from the internal side, diagrammatic figures are given (text-figs. 32-39), illustrating the chief char- acters. Imbrication in Echini is curiously constant in its direction. Interambulacral plates in the corona always imbricate aborally in the vertical plane, so that the dorsal border of one plate is inclined over the ventral border of the next adjacent dorsal plate of its series (text-fig. 32). Interambulacral plates also always imbricate outwardly or adradially from the center, so that each plate from the center of the area laterally imbricates over its neighbor toward the ambulacral area and on the adradial suture imbricates over the ambulacral plates, as seen in Lepideslhes wortheni (Plate 67, fig. 8). In the ambulacrum, on the contrary, the imbrication is always adoral, so that the ventral border of one plate inclines over the dorsal border of the next adjacent ventral plate, in the opposite direction from that of the interambulacral plates (text-fig. 38). Laterally there is little or no imbrication in ambulacral plates (Lepidesthes) except on the adradial suture, where the ambulacral plates dip under the adjacent interambulacrals instead of over them, as they do in the Palaeechinidae and in some clypeastroids, as above noted. The imbrication of ambulacral and interambulacral plates, as described, occurs weakly in Archaeocidaris, Lepidocidaris, Lepidechinus, strongly in Lepidocentrus (Plate 20, fig. 8), Hyattechinus (Plate 22), Pholidechinus (Plate 28, fig. 2), Perischodomus (Plate 64, figs. 2, 3), Lepidesthes (Plates 66, 70), Pholidocidaris (Plate 73, fig. 4), and Meekechinus (Plate 76, fig. 1). Imbrication also occurs in the modern thin-plated Echinothuriidae. This character has been considered a basis of connecting the Echinothuriidae with Palaeozoic types having imbri- cate plates, but so many characters are opposed to it, that this must be considered a case of parallelism. In modern forms, imbrication is not limited to the Echinothuriidae, but occurs also in the Centrechinidae. This character is well developed in Astropyga pulvinata (text-fig. 100, p. 109), where interambulacral plates imbricate dorsally and laterally, and the ambulacral ventrally. The plates are I5o thin that it is difficult to see the sutures of imbrication in cross section, but the imbrication is readily seen on the internal view of the test. The interambula- cral plates imbricate over the ambulacrals, as they do also in echinothuriids, in Centrechinus, and in the Palaeozoic types with imbricate plates (as noted in the Palaeechinidae, the ambula- cral plates are beveled over the interambulacrals, but imbrication proper does not occur in this family). Mr. Agassiz (1881, p. 71) notes the occurrence of imbrication in Astropyga, but IMBRICATION OF CORONAL PLATKS. 7.-, TEXT-FIGS. 32-39. — Method of imbrication of plates in Echini; the figures 32-38 an- NVIII lirtir, l>nwrir:iii<>n n-vrrwd from external view, ambulacral plates with pores in the middle of plates, instead of near the interaiiiluilarnirn an in external view. 35. Cross section of same. 36. Optical section of plates seen from exterior. 37. Optical section of plates seen from interior. 38. Showing in vertical section direction of imbrication of plates in the inlet-ambulacrum and ambulacrum. 39. Eucidaris Iribuloides (Lamarck). Bahamas. R. T. J. Coll., 693. X 4. Base of corona and peristome. On the peristome both ambulacral and non-ambulacral plates imbricate adorally, a condition not known in the corona of any echinoid. 76 ROBERT TRACY JACKSON ON ECHINI. says the plates of both areas imbricate in the same direction dorsally. I have studied imbri- cation in only one specimen, an Aslropyga pulvinala; but in that one the ambulacra imbricate ventrally, interambulacra dorsally as described. I believe the fact has been overlooked, but a weak imbrication occurs in Centrechinus setosus. It is not obvious in external view, but it is readily seen on viewing the interior of a test. The interambulacral plates imbricate dorsally as usual, and the ambulacral slightly ventrally; the interambulacra are inclined over the ambulacra on the adradial suture as usual in imbricate Echini, living or fossil. If a specimen of Centrechinus from alcohol is sectioned horizontally by cutting through the ambitus, it is found that there is much flexibility of the test. The same is seen in a dried specimen if it is first soaked in water. In Chaetodiadema the test is thin and highly flexible. It is very interesting that flexibility and imbrication are so charac- teristic of the Recent Centrechinidae, for many characters connect this family with the Echinothuriidae, as clearly shown by Messrs. A. Agassiz and Clark (1909). The rule of ventral imbrication for ambulacral and dorsal for interambulacral plates in the corona, is apparently without exception in the corona for all Echini where imbrication occurs. Certain exceptions according to the literature are said to exist. Worthen and Miller (1883) supposed that in Lepidesthes ( = Hybochinus) spectabilis the interambulacral plates imbricate ventrally and the ambulacral dorsally. Their specimen was doubtless incorrectly oriented on account of the position of the teeth as discussed under the systematic description of that species, so that if I am correct it is no exception to the rule. In my earlier paper (Jackson, 1896, pp. 223, 224) a serious error was made in regard to Lepidocentrus mulleri where the interambulacra were described as imbricating ventrally; this was wrong, since the specimen was inverted, as discussed under that species in this paper. Again, an error was made in describing Pholidocidaris meeki (1896, p. 211, Plate 9, fig. 54). The interambulacra and ambulacra were described as both imbricating adorally. The speci- men (Plate 73, figs. 6, 7) is imperfectly preserved, and I can only plead guilty of an error of observation. I was also partly misled by the fact that Meek and Worthen's (1873, Plate 15, fig. 9a) figure of Pholidocidaris irregularis, the. only good figure published, was inverted, a fact that was since ascertained. There is no proof at present that imbrication of coronal plates is ever other than dorsal in the interambulacra and ventral in the ambulacra in types of Echini with imbricate plates. On the peristome, imbrication is adoral when it exists in both ambulacral and interambula- cral plates, as in Eucidaris (text-fig. 39, also text-figs. 43, 46, 47, p. 80). When imbricate specimens of fossil Echini are viewed from within (text-fig. 34), the struc- ture appears very different from that as seen from without (text-fig. 32). This is shown well in Perischodomw biserialis (Plate 62, figs. 6, 7; Plate 64, figs. 2, 3). From the interior, the ambulacra appear to imbricate dorsally and laterally overlap the adjacent interambulacra; SPINES. also the ambulacra are wide internally instead of narrow, on account of their lateral The interambulacra appear to imbricate ventrally, as seen from the interior, and dip under tin- adjacent ambulacra. All this is reversed when the specimen is viewed from tin- exterior This complication must be constantly borne in mind in a study of internal and external of fossils or confusion will ensue. SlMNES. Having discussed the corona, a brief consideration may be given to spines as an obvious and salient feature of Echini. The name Echinodermata implies the character «.f -pine-.. It is a misnomer, if the group as a whole is considered, for in the Pelmatozoa, spines are rarely developed, and in the holothurians are absent. Spines are, however, a feature of the Echini, and there is no known species which is without them. In the very young plates at the <1 area of the test, spines are absent, not yet having developed. The nearest approach to (hi condition as a species character is seen in Bothriocidaris pahkni (Plate 1, fig. 3), which it. the interambulacrum apparently has no spines in the adult. It is true that minute granules exist, which possibly bore spines, but such are not known. This species, how.-vrr. ha> >pim- on the ambulacra and all other Echini have them on the interambulacra as well. Spines are classed as primary, secondary, and miliary, and are attached to tuber. corresponding size. In the Palaeozoic, primary spines are especially well .level ....... 1 in Ar.-h:..-, cidaris, where in each interambulacral plate there is a single large central perforate tub. with an associated spine of variable but always relatively large si/e. In the y..unp->t plate at the dorsal area, as shown in Archaeocidaris rossica (Plate 11, fig. 2), neither tubercle primary spines are developed, and when the tubercles develop, they are at fir>t as seen in the younger dorsal plates in the figure cited. In Eucidaris (Plate 3 condition exists : the young tubercle is imperforate and the young spine is a thin h like an inverted saucer, its spine-like character develdping in later growth. of a cidarid is short, broad, and distally rounded, and reminds one of the character „ of Colobocentrotus, except for the absence of marginal angles commonly . spines of that type by mutual pressure. Central primary spines are well developed in Lepidocidaris (Plate 16, of larger size than associated spines and which may be fairly called primane, « larly distributed in Lepidocentrus (Plate 19, figs. 3-5), in Hyn^dnnu, rwuf* fig 6) and on the adambulacral columns in Pholidocidaris (Plate 7». fig. : the tubercles, in part in Perischocidaris (Plate 67, fig. 2). In the ,,,n;, there are also small secondary spines clustered around the primaries and ambulacral plates (Archaeocidaris). Or secondary spines and tubercles may , 78 ROBERT TRACY JACKSON ON ECHINI. maries on adambulacral columns and exist alone on other interambulacral columns and on the ambulacrum (Pholidocidaris, Plate 73, fig. 3; Perischocidaris, Baily, 1874, Plate 4). Secondary spines may exist without any primaries. Such is the condition in all the Palae- echinidae (Plate 52, figs. 10, 11), in Lepidesthes (Plate 70, fig. 4), and, judging from the small and uniform size of the tubercles, in Lepidechinus (Plate 63, fig. 3) such spines and tubercles may be fairly compared in size to those characteristic of Clypeaster and the usual type seen in clypeastroids. Such small spines as occur in Bothriocidaris (Plate 1, fig. 3) may probably be considered as primaries on account of the perforate tubercles and the small size of the whole animal. As far as known, spines are very uniform in character within the species in the Palaeozoic, cases of marked deviation, such as occur in some Cidaridae, being almost unknown in these older types. From this uniformity in the Palaeozoic, spines present very good species characters, which is fortunate, as they so often occur in a dissociated condition among fossils. As discussed (p. 51), spines are typically internal, and the evidence indicates that they were internal, that is, covered by living epithelial tissue, in all Palaeozoic types excepting Miocidaris and possibly Archaeocidaris. Stout, thick, and club-shaped spines are largely characteristic of the Cidaridae and a few other types. A specimen of Strongylocentrotus drobachiensis in the Peabody Museum at Salem is interesting as showing thick club-shaped spines (Plate 6, figs. 11, 12), which are quite cidarid in appearance. These spines are numerous but rather local in distribution, not covering the whole specimen. The specimen is of normal size and appearance otherwise, and it appears to be merely a rare variation. This was the only such case seen in 33,000 specimens of this species examined, nor was such a structure seen in any other species of the family. Tubercles as well as the spines with which they are associated may be divided into primary, secondary, and miliary. Primary tubercles may be perforate or imperforate. They are perforate in all Palaeozoic species where they occur; they are also perforate in the Cidaridae, Centrechinidae, and some of the Saleniidae, also in some spatangoids. Primary tubercles are imperforate in the remaining Centrechinoida, the Holectypina, and many of the Spatangina. Secondary tubercles are imperforate in the Palaeozoic, whether they occur with primaries or alone, as in the Palaeechinidae. They are also imperforate in the Cidaroida and in Acrosalenia, but they are perforate in the Centrechinidae and certain clypeastroids and spatangoids (Clypeaster, Metalia, Meoma). Perforation of tubercles is evidently a character of primitive types and of some specialized types of clypeastroids and spatangoids. Primary tubercles in a species occur with a definite distribution which is characteristic, as seen especially well in the Centrechinoida, a given number typically existing on a plate. It seems that the distance between tubercles which is maintained in a species is the real feature of their distribution. If, by chance, a plate is narrower than usual, as in Tripneustes (Plate 6, fig. 3), the tubercles are their usual distance apart, but there are fewer to a given plate; THE PERISTOME. 79 or, if, by chance, a plate is wider than usual, as in the tetramerous Arbacia lixula figured by Verrill (1909), then again the tubercles are their usual distance apart, but there are more tubercles to a plate than is typical of the species (pp. 40, 47). THE PERISTOME. The peristome is closely associated with the corona, and is next considered. Tin- peri- tome, which is the tissue lying between the mouth opening and the basicoronal plates, present - various characters in different groups of Echini, and these characters fall into six quite distinct types as described below. The peristome in almost all Echini is more or less extensively covered with plates. Tin-H- are in regular Echini ambulacral plates bearing tube-feet, either in one or in many rows. With these there may be in addition what I would call non-ambulaeral plates, which do not boar tube-feet. Such non-ambulacral plates, where they occur in the Perischoechinoida and Cid.-i- roida, occupy an interradial position; or, where they occur in the Centrechinoida, they occupy also a radial position, being a more or less generally distributed series of plates (Toxopneu text-fig. 57). In spatangoids there are no ambulacral plates on the peristome, but non-ambula- crals only. These are generally distributed over the area. I have adopted the term ti»n- ambulacral for such plates because, though they may be interradial only (Cidaridae), they may also have a general distribution, and they have no relation to the interambulacra of the corona. The most ancient type of peristome known is that represented by Bothriocidaris (t<-\t- fig. 40) in which there are two continuous rows of ambulacral plates, a structurally primitive character. The first row around the mouth can fairly be considered the primordial ambulacral plates, and, as shown in B. archaica (Plate 1, fig. 1), this row follows LoveVs law of la, II|>cr begins with a row of five interambulacral and ten ambulacral plates. The line of separation between the peristome and the corona is not so strongly marked as in most typos, but it is comparable to that of young Phormosoma (text-fig. 41), as pointed out by Mr. Agassi/, i 1 of peristomal plates formed before the development of the corona. In Phormosoma at a \vry young stage (Plate 3, fig. 9), as shown by Mortensen (1904, p. 54), there is only one row of p«>ri- stomal plates, whereas a little later (text-fig. 41; Plate 3, fig. 10), as shown by A. Agjissiz. there are. two rows of peristomal plates almost exactly as in Bothriocidaris. a- Mr. Agassiz (I p. 79) pointed out. The peristome of Bothriocidaris makes also very close approach to the character of the young in cidarids (Plate 2, figs. 1, 6) and young Stroimyloecntn.t..- t.-M-fig. 49), also other young Centrechinoida. It differs from these early stages principally in having 80 ROBERT TRACY JACKSON OX ECHINI. IE b n THE PEHISTOMi: gj TEXT-FIQS. 40-54.— Characters of peristome anil ba.H<- of the .-on-.m in rrprem.t alive Ki-hini. 40. Hothriocidarisarchaicasp.iiov. Ordovician, Uutwiu. From Hair 1, fig. 1. On il,,- i*n*tome two row.of.mbu- lacral plates. 41. Phormosoma placenta Wyvillc Thomson. Young. Dium. 0 mm. Adapt.-.! from A. Aganmi, 1904, IMaU- 43, fiK. 3. On the peristome two rows of aiiibulacral plates. 42. The same. Diam. 7 mm. Adapted from A. Agassiz, l«JO-f, Plat,. I.I, fig. I. PoriMtomnl plaint with porai in a central peripodium. 43. The same, adult. Off Cape May to Cape Sable, 95ti fall,. Diam. 5ii mm. It. T. .1 Coll , 707. X 3. On the peristome many rows of ambulacra! plates. 44. The same. Peristomal gills enlarged. 45. Goniocidaris canaliculata A. Agassiz. Young. Diam. 1.45 mm. From Plate 2, fig. 1. On il,.. i- rutomc one row of ambulaeral plates. 46. Eucidaris tribuloitles (Lamarck). Bahamas. Diam. 45 mm. R. T. .1. Coll, 708. X 3. On the periiitome many rows of ambulacra! and in addition interradial non-ambulacra! plates (.•(impure with young. I'lulr 2, fig. 6). 47. Archaeocidaris worlhnri Hall. Lower Carboniferous. From I'late 9, fig. 6. Partially restored. On the peri- stome many rows of ambulacra! and in addition interradial non-ambulacra! plates. 48. Melonechinus multijmrus (Norwood and Owen). Ixiwcr Carboniferous. Restored. From I'lai.- .V>, fig*. 7, g. On the peristome many rows of ambulaeral and in addition two rows of inlerrtulial non-ambulacriil pliiti*; aml.iilarrnU pass from two plates orally to many on the periphery of peristome in each area. 49. Slrongylocentrotus drobachiensis (O. F. Miiller). Young. Diam. 1.2 mm. From Plate 3, fig. 1 1 . On the prri- stome one row of ambulaeral plates. 50. The same. York Harbor, Maine. Adult. Diam. 40 mm. R. T. J. Coll., 709. X 3. On th.- IHTIM.,,,,,. one row of ambulacra! and scattered, small, non-ambulacral plates. 51. Dermatodiadema anlillarum A. Agassiz. West Indies, 955 fath. Diam. 9 mm. R. T. J. Coll. ,670. X 8. On the peristome one row of large ambulacra! plates. 52. Echinarachnius parma (Lamarck). Eastport, Maine. R. T. J. Coll., 747. X 2. On tin- |Nri.it<>rni- no plate*. 53. The same. X 6. Peristome enlarged. 54. Echinocardium flavescens (Miiller). Adapted from Lov6n, 1874, Plate 3, fig. 34. On the |»>ri.-i<>mi- many non- ambulacral plates only. In text-figures 40, 41, 43, 45, 49, 52, and 54 the primordial intcrambulacral plates are in place in the basicoronal row; in other figures they have been resorbed, with or without additional plates. two rows of ambulaeral plates around the mouth instead of one row, a difference which is bridged in some types as shown in the development of Phormosoma. A second type of peristome is that in which the area is plated with several rows of ambulacra! plates. The primordial ambulaeral plates surround the mouth as usual, and succeeding rows are composed of ten plates each, which are continuous, as are the primordial plates. Such a condition is seen in Hyattechinus (Plate 23, fig. 1), Pholidechinus (Plate 28, fig. 1), Lepidothrs (Plate 68, fig. 3), and Palaeodiscus (Plate 18, fig. 2). It is to be observed that in all these types the primordial interambulacral plates were doubtless in place in the basicoronal row of the corona. The same character of only ambulaeral plates on the peristome is seen in Recent Asthenosoma (Loven, 1892) and Phormosoma (text-fig. 43)'. It also occurs exceptionally in cidarids, as shown by Mr. Agassiz (1904, p. 30, Plate 11, fig. 1). In the Cidaridne. however, the primordial interambulacral plates are not retained at the base of the corona, but have l>een 82 ROBERT TRACY JACKSON ON ECHINI. resorbed. In all of these cases the ambulacral plates of the peristome are strongly imbricated adorally, and, as in Bothriocidaris, the pores are nearly or quite superposed dorso-ventrally. A third type of peristome is where there are both ambulacral and non-ambulacral plates on the buccal membrane. The ten primordial ambulacral plates surround the mouth, at least as far as known, and are succeeded by rows of two or more plates in each ambulacral area aborally, separated by more or fewer interradial non-ambulacral plates. Such a structure is seen in Archaeocidaris (text-fig. 47) and Melonechinus (text-fig. 48) in the Palaeozoic. In Archaeocidaris there are two vertical columns of ambulacral plates and many columns of scale-like non-ambulacral plates increasing in number aborally to the margin of the actinostome, where they have a greater number of plates than exist in the basicoronal row of the inter- ambulacrum. Both ambulacral and non-ambulacral plates on the peristome imbricate strongly adorally. This structure has been made out more or less fully in four species of Archaeocidaris, namely, A. wortheni (Plate 9, fig. 6), A. rossica (Plate 11, fig. 1), A. agassizi (Plate 13, fig. 3), and A. urii (Plate 15, fig. 1). In Melonechinus (text-fig. 48; Plate 56, figs. 7, 8) there are two plates in each ambulacral area around the mouth, but passing outward, they increase to m,any plates in each row before reaching the corona. There are but three non-ambulacral plates in each interradial area on the buccal membrane. This is based on a single specimen, but it is probable that a similar structure may exist in other members of the family of the Palaeechi- nidae. Ambulacral and non-ambulacral plates of this type on the peristome are a character of the Cidaridae alone among Recent Echini. The plates imbricate strongly adorally in both areas (text-fig. 39, p. 75), as in Archaeocidaris, emphasizing the primitive character of this struc- ture. In the peristome of Eucidaris (text-fig. 46; Plate 2, fig. 6) there are two plates in each row in each ambulacrum. In the interradial areas there may be one plate in each row, or passing outward, this may increase to two plates in a row; or in Phyllacanthus (Plate 2, fig. 18), as shown by A. Agassiz and Clark (1907a), there may be as many as five plates in a row in each area interradially on the border of the actinostome. While in adult Eucidaris tribuloides there are many rows of very low scale-like ambulacral plates on the peristome (text-fig. 46), in a young specimen of 5 mm. diameter (Plate 2, fig. 6) there are only four rows, and the plates are high, hexagonal in outline, resembling the similar plates in Bothriocidaris. Mr. Agassiz, in the Revision of the Echini (1874, p. 646), compared the actinostome of Cidaris to the whole ambulacral and interambulacral system of Palaeozoic Echini. As he said, "Obliterate the two rows of coronal plates [of Cidaris] and we have a spherical urchin composed of a series of plates corresponding in every respect to the hypothetical Palaechinus. It consists, namely, only of an abactinal system, .... of an ambulacral and interambulacral system, composed of hexagonal and pentagonal plates, perfectly flexible, and of an oral opening through which we find teeth projecting." Mr. Agassiz (1892, p. 72) again said in his mono- graph on Calamocrinus diomedae, "The structure of the test of Bothriocidaris is represented THE PEHISTOMI: B8 by the buccal system of Cidaris. One range of interambulacral plates extending from the apex to the actinostome intercalated between rows of ambulacra with two pair* of pores each." There are several objections to comparing the test of Palaeozoic Kchini with the peri-tome of Cidaris. Representative genera of Palaeozoic types have a peri>tome and ventral border of the corona directly comparable to the same parts in living Kchini. The family of the Palae- echinidae (Palaeechinus, Melonechinus, etc.) which have hexagonal plates, do not have flexible tests. Of course specimens may be crushed and plates displaced in fossili/ation, but they cannot be described as flexible. Those Palaeozoic genera which do have flexible testH have imbricate plates, but the imbrication in the interambulacra of the corona is alway- dor-al (text-fig. 32, p. 75), as in the Echinothuriidae, not ventral as is the imbrication of all the plate- on the peristome of Cidaris (text-fig. 39, p. 75). While cidarids usually have a single column of plates in each interradial area on the actinostome, this is not a constant number, and on the aboral portion there may be two plates in a row, or as many as four or five, as in the Phylla- canthus noted. The above three types of peristomes cover all the known ea.-es in Palaeozoic Kchini, but there are yet three other types in post-Palaeozoic Echini which have interesting relations to the Palaeozoic forms. A fourth type is seen in the Centrechinoida (excluding the Echinothuriidae), in which we have typically (Strongylo- centrotus, text-fig. 50) only ten ambulacral plates around the mouth. These plates have each two pores which are superposed dorso-ventrally, as in Bothriocidaris. In the young (text-fig. 49), as shown by Lov6n, these plates lie close under the corona, as do the similar plates in young cidarids and in adult Bothriocidaris (only in this last type there are two rows of plates). In the adult (text-fig. 50) the primordial ambulacral plates are usually far removed from the base of the corona, and the surrounding mem- brane is usually more or less covered by solid, scaly, isolated, or granular plates which apparently cannot be distinguished as ambulacral or interambulacral, but seem to have developed independently in place. On the mar- gin of the peristome in the Centrechinoida are found ten peristpmal gills. These may be very small, as in Phormo- soma (text-fig. 44), or may be large and frondescent, as in Strongylocentrotus (text-figs. 55, 56). While, as a rule, there are ten primordial ambulacral plates typically in all Kchini, as far TV \T-no8. 55, 56. 55. Stroitfylocentrottu (O. F. Mttller). York Harbor, Maine. X 5. IVristoni.il gill* in plan-, expanded. 56. The same. Profile view of a gill. 84 ROBERT TRACY JACKSON ON ECHINI. as known, Dr. Mortensen (1904, p. 78) gives a remarkable exception, for he says that in Pkurechinus doderleini Mortensen there are only five buccal ambulacral plates, a "unique feature." This may fairly be considered an exceptional departure from the ten-plate system rather than instituting a distinct type. In the Centrechinoida the non-ambulacral buccal plates are usually small, thin, and scale-like, often widely scattered, and may be mere granules, or they may be quite absent, as in Echinus magellanicus and some of the Temnopleuridao. They may, however, be relatively thick and solid and form a pavement-like plating of the whole n TEXT-FIG. 57. — Toxopneustes variegalus (Lamarck). Tampa Bay, Florida, tliam. 70 mm. R. T. J. Coll., 784. X 4. Peristome with ten ambulacral and many non-ambulacral plates. area, as in Toxopneustes variegatus (text-fig. 57). Here the primordial ambulacral plates fall in sets of twos in the radial areas with a rather wide interspace between the sets. The pores of these plates are superposed dorso-ventrally as usual in peristomal plates. In Dermatodiadema (text-fig. 51), as shown by Mr. Agassiz (1883, p. 26, Plate 9, fig. 5; 1904, p. 61, Plate 25), the primordial ambulacral plates are extraordinarily large and fill a considerable part of the buccal membrane, a retention of a primitive character. TIIK I'KKISTOMK. s.-, A fifth type of peristome is seen in clypeastroids (Kchinaraelmin-. \< -\t -li^ I), in which the primordial ambulacral plates no longer exist as part of the buccal system, hut have become transferred to the basicoronal row of the corona, when- they are typically retained throughout life, alternating with the primordial interambiilacral plates. The bueeal membrane proper in Echinarachnius and, as far as I have been able to ascertain, in other genera of this suborder, is leathery without plates. Still a sixth type of peristome is seen in spatangoids (Kchiiiocardinm, text-fig. f>4). In these the primordial ambulacral plates are in the basicoronal row of the corona, as in elypeas- troids. The buccal membrane, however, is covered with numermi- thin, scaly plates which, as in the Centrechinoida, cannot apparently be considered as ambulacral or interambiilaeral, but as plates which developed in place and independently of the corona. In brief the six types of peristomes are: — 1. Two rows of continuous ambulacral plates, — the primordial row and one in addition (Bothriocidaris, text-fig. 40). 2. Many rows of continuous ambulacra! plates (Hyattechinns, Plate '2'.], fig. 1, Phor- mosoma, text-fig. 43). 3. Many rows of ambulacral with intercalated interradial non-ambulacra! plates (Kuci- daris, text-fig. 46; Archaeocidaris, text-fig. 47; Melonechimis, text-fig. 48). 4. One row of continuous primordial ambulacral plates around the mouth, and usually, in addition, solid, scaly, isolated, or granular non-ambulacral plates1 (Dermatodiadema, text- fig. 51; Centrechinus, Salenia, Strongylocentrotus, text-fig. 50; Toxopnenste-. text-fig. 57). 5. No primordial ambulacral plates, as they are in the corona; peristome leathery with no ambulacral or other plates (Echinarachnius, text-fig. 52). 6. No primordial ambulacral plates, as they are in the corona; area of peri-t<>me with scaly plates which are not referable to ambulacra or interambulacra (Kchinoeardiiim. text-fig. 54). The origin of the plates of the peristome is a matter of much interest. Without question the primordial ambulacral plates, when they exist on the peristome (as they apparently do in all Echini excepting the Exocycloida, where they appear typically as basicoronal pl:r originate in that area and entirely independently of the corona. In Bothriocidaris it is possible that the second row of ambulacral plates, like the primordial ambulacra! plates, originated on the peristome and independently of the corona, but more probably they were derived by flowing down from the corona. When ambulacral plates other than primordial ambulacral plates exist on the peristome. ' In some of the Temnopleuridae (A. Agassis, 1872, p. 286; Mortensen, 1904, p. 80) ami KrhinMa.- . IV.!ntrin, 1905, p. 226) the non-ambulacral plates are absent. 86 ROBERT TRACY JACKSON ON ECHINI. it seems, as shown by Love'n (1892, p. 18) and A. Agassiz (1904, pp. 31, 96, 97, et al), that they are derived from the corona. As Love'n describes it, the ambulacrals flow downward between the interambulacrals and pass as if discharged through the outlet of a river on to the buccal membrane. Such is the condition in the Palaeozoic Hyattechinus (Plate 23, fig. 1), Pholi- dechinus (Plate 28, fig. 1), Melonechinus (Plate 56, fig. 8), modern Eucidaris (text-fig. 46) and Phormosoma (text-fig. 43). Love'n (1892, pp. 22, 31) also assumed that the interradial plates on the peristome of Cidaris and the granules and small non-ambulacral plates of " Ectobranchiat.es " are formed by the disintegration and remodeling of coronal into buccal plates. He speaks of coronal plates as disintegrating and the calcareous substance being redeposited as buccal plates. This seems a quite untenable view. If the plates are dissolved, that should be the end of them, and we cannot assume that buccal plates are derived from the resulting lime any more than the thicken- ing of teeth or any part of the test. I believe no one has shown the interambulacral plates separating from the corona in Echini and passing on to the peristome, there to be represented by actually transferred larger or smaller plates. Outside of the transferred ambulacral plates, as seen in Cidaris and similar types, it seems that all plates of the peristome originated in that area and cannot be considered as derived from the corona. In spatangoids the peristome is usually densely plated, yet no resorption of the base of the corona has occurred, and the pri- mordial ambulacral and interambulacral. plates are in place in the basicoronal row, therefore no transfer of coronal plates can have taken place. OCULAR AND GENITAL PLATES. The range of characters presented by the ocular and genital plates is most interesting. Their mutual relations are discussed here, and in the next section certain considerations of the genital plates by themselves are taken up. Cases of marked aberration occur in some spatan- goids as Collyrites, and especially Pourtalesia; these I have not studied, and they are eliminated from the discussion. The characters of oculars and genitals are typical of the several groups of Echini, and the later forms present striking relations to Palaeozoic genera. An ocular plate in Echini overlies an ambulacrum wholly and the two adjacent interambulacra in part on either side. Immediately on the ventral borders of the oculars all coronal plates originate. It seems that at this point the tissues exist which give rise to new plates. As earlier discussed (p. 62), the corona may be considered as made up of five areas, each of which is directly con- nected with one of the ocular plates, the areas being each an ambulacrum and two half- interambulacra (text-figs. 217, 218). The five oculars are always present barring the excepted Pourtalesia. The genitals overlie the interambulacra in part, but not the lateral borders of the same, and never reach the ambulacra. In some cases the genitals may not OCTI.AK AM) (JKMTAI, I'l.ATKS. s? reach the interambulacra. Five genitals are typically present, but the |>osterior genital may be wanting (spatangoids) or one absent as an aberrant variation (Arbacia, Plat* 4, fig.-. 1 1 , 12; or Eucidaris, text-fig. 185, p. 167). The apical disc is large relatively to the diameter of the test in young Kchini i Plate '_'. fig. 3); it is also relatively large in the adult primitive Bothriocidaris. With growth to the adult the apical disc in Echini loses its preponderance but is still relatively large in the ( 'idarid.-n-. in Tiarechinus, in the Aspidodiadematidae and Saleniidae. In the Devonian and Carlxm- iferous Echini and in the Centrechinoida, other than those mentioned, the apical disc i« rela- tively small. In the Echinometridae which in other respects are amongst the most s|>eeiali/.i-d of regular Echini the apical disc is very small as it is also in the Exocycloida. A.- far a> commonly the apical disc in relation to the test as a whole grows with a progressively decrea.-ing ratio, a fact that can be verified from the figures shown here as text-figs. 63, 67, 128, 129a, 135, 137. Very large individuals do not necessarily have larger peripmets than smaller indi- viduals of the same species (text-figs. 94-95, 151-153). In general a proportionately large apical disc is a youthful and primitive character, a small one is a progressive character. In the ancient Bothriocidaris the oculars are exceptionally large, relatively to the -ize of the animal; on the other hand, the genitals are exceptionally small, relatively the smalle.-t of all known Echini. There has been much confusion in regard to the genital plates of this type, but, having enjoyed the privilege of studying perhaps the most perfect specimen known, which is in the Berlin Museum, I have reached the following conclusions. In Bothriocidaris archaica (Plate 1, fig. 2) the oculars are very large; they are in contact with the periproct dorsally, and meet in a continuous ring covering entirely both the ambulacral and interambulacral areas. What I consider the genitals are five small plates lying in t he . I angles of the oculars and extending into the periproct. The relative position of the ocular- and genitals in this most ancient and, I believe, primitive echinoid is closely comparable to that of the same plates in the larval Echinus (Plate 3, fig. 5). In Bothriocidaris pahleni (Plate 1, fig. 6) as shown by Schmidt ilS74) the oculars are also large; two of the genitals extend down between the oculars and come in contact with the dorsal border of the interambulacra (one is absent), but two lie completely dorsal to the oculars as do all the genitals in B. archaica. In this character, therefore, it is intermediate l>et wem that species and the next. In Bothriocidaris globulus (Plate 1, fig. 9), as Schmidt (1874) showed, the oculars are large, as in the two other species, but the genitals all extend down Ix-tv the oculars and reach the dorsal border of the interambulacra in their several areas a> in all later Echini. The position of genitals dorsal to the oculars is, of course, a common condition in living Echini, the main peculiarities in Bothriocidaris being the relatively small size of the genitals, and the fact that they may be excluded from contact with the interambulacra in B. archaica, a unique specific character, 88 ROBERT TRACY JACKSON ON ECHINI. It is interesting to note that in a striking regressive variation in Arbacia punctulata (Plate 4, fig. 11), interambulacrum 4 drops out to a single column of plates in the last four rows built, and dorsally abuts against two oculars, the single column and ocular contact being exactly as in Bothriocidaris archaica. A similar condition is seen in Tripneustes (Plate 6, fig. 4), Strongylocentrotus (Plate 6, figs. 7, 8), and Eucidaris (text-fig. 185, p. 167). In a unique specimen of Strongylocentrotus drobachiensis (Plate 5, fig. 16) genital 1 lies wholly dorsal to the oculars as do all the genitals in Bothrioddaris archaica (p. 42). No pores have been observed in genital plates in Bothriocidaris. It is possible they did not have genital pores, as such are wanting in the young of Recent Echini; more likely they were present, but do not show in external view, and in this they may fairly be compared with Salenia patter soni (Plate 4, fig. 1) where no pores were seen from the exterior, though they are perfectly visible on the interior of the test (Plate 4, fig. 2). Also no pores have been observed in ocular plates of Bothriocidaris, though in ocular III (Plate 1, fig. 2) there is a peculiar arcuate impression that may function as a pore. Neumayr (1881) and Mortensen (1911) consider as genitals in Bothriocidaris the plates lying ventral to the oculars, which I consider as the dorsal plates of the interambulacra. If they are right, then the genitals would be ventral to the oculars, a position opposed to that in all known Echini ; also the interambulacra would be separated from contact with the oculars, whereas they are in contact with the oculars in all known Echini. Bather (1902), speaking of the periproct of Bothriocidaris, says that the area is filled with minute plates, none of which can safely be selected as the homologues of the genitals of later forms. If it depended on Bothriocidaris archaica alone, it might be doubtful, but when we see in B. pahkni in part, and in B. globulus in full, the five plates extending down between the oculars so as to come in contact with and cap the interambulacra as genitals do in all later types, it is reasonable to consider these plates as genitals. Mr. Agassiz (1892, p. 72) says of Bothriocidaris, "... .we find five radials and five inter- radials forming a single ring round the anal system. At the [dorsal] angles of the radial plates five small anal plates are situated." Again Mr. Agassiz (1904, pp. 79, 80) says, "The genital ring of Bothriocidaris as well as of the Palaechinidae is much like that of the recent echinids, only in the former the ocular plates are far larger than the small plates corresponding to the geni- tals. The anal system of Bothriocidaris globulus Eichw. as figured by Jaeckel : shows, as in the very young Cidaridae, five anal plates in the angles of the ocular plates " Mr. Agassiz evi- dently considered as genitals those plates ventral to the oculars as did Neumayr and Mortensen, and those dorsal to the oculars as anals; whereas I consider those ventral to the oculars as the last formed plates of the interambulacra, and the five interradial plates dorsal to the oculars 1 The specimen mentioned is the Bothriocidaris archaica sp. nov., Plate 1, figs. 1, 2, of this memoir. OCfLAIt AND CKMTAI. I'I.\TKS. VI as genitals. By a slip of the pen Mr. Agassi/, j,, d,,. paragraph Dinted compare- the live plate, in the dorsal angles of the oculars of Bothrioeidaris to live an:il plate- in young ri.lnri.l-. Tin- five plates in Bothriocidaris (Plate 1, fig. 2) arc interradial in po.-iti.,n and li.- between the oculars, whereas the five somewhat similar plates in young cidan.l- t.-xi-fig. (il. /'../ //in.- cobosi A. Agassiz, 1904, Plate 13, fig. 5), arc radial in position and lie between the genitals, for the genitals alone reach the periproct, the oculars at tin- Mage in ddarid.- being ev-ert. Genital and ocular plates are rare in Palaeozoic types, yet excepting the Erhiimcy-tnida I am able to show them in all families other than the An-haencidaridae and in most genera. After Bothriocidaris just considered, the leading character in the Palaeozoic i- for all the oculars to reach the periproct, and to cover the ambulacra and in part the interambulacru on either side. Also the genitals reach the periproct, arc larger than the ocular.-, and cover the interambulacra in part, but not wholly, because the lateral borders of the interambulacra abut against the next adjacent ocular on either side. This character is shown in Palaeechinu- (Plate 31, fig. 4), Maccoya (Plate 34, fig. 6), Lovenechinus (Plate -li>, lig. . Melonechinu- (Plate 56, fig. 6), Hyattechinus (Plate 25, fig. 5), Lepidcchinus 1 1'late (i:?. fig. 7). and nth. In one specimen of Lovenechinus missouriensis (Plate 41, fig. 2) in areas D and F, the oculars are exsert, but in six other specimens of the species, with all ocular- in plan-, all tin- oculars reach the periproct. In Lovenechinus lacazei (text-fig. 243, which I owe to the kindness of Dr. Bather), all the oculars are exsert. In Maccoya intermedia (Plate 33, fig. 1 1 1 one ocular is exsert, four insert; and in Plate 33, fig. 12, all the oculars are exsert. In l.< />i>l, chinu* li-xm Un- tus sp. nov. (Plate 63, figs. 7, 8) the oculars arc all exsert as far as preserved, and the same is true of Meekechinus elegans (Plate 76, fig. 5). These are the only cases of e\-crt ocular- observed in Palaeozoic Echini, and may be fairly considered as forerunners of the dominant character seen in Mesozoic and many Recent regular Echini. In the Palaeozoic the oculars of Lepidesthes formosa (Plate 68, fig. 5) have two p<>: Oculars in Lovenechinus missouriensis (Plate 42, fig. 6) show a single pore of small >ixe close to the ventral border of the plates, and the same is seen in Lepiiiu-lihnis t,;™ill[>ccimcn is shown in Plate 29, figs. 3, 6; Plate 31, fig. 4. The specimen does not have any pores in the oculars and Baily's observation was an error, which has proved unfortunate as his figure of the apical disc has been extensively copied. The characters of pores in the genitals and other special features of these plates are considered in the next section. In pn.-t-Palacozoic Echini ocular plates .have one pore not always visible externally (Salenia. Arbacia) and very rarely a second pore may exist as a variant. I have seen only two or three such. 90 ROBERT TRACY JACKSON ON ECHINI. Genital plates may be divided by secondary sutures as later discussed, but oculars are very rarely divided. A case, however, is shown in text-fig. 193, p. 169, in which dividing sutures develop in ocular plates, as also seen in Plate 6, fig. 6. Having seen the characters of ocular and genital plates in their mutual relation in the Palaeozoic, it is of much interest to compare those of later times. Little attention has been directed to these plates, but a close study reveals characters of importance to general mor- phology, to the evolution of the group, to the relation of the species in the genus and related genera, and to geographical distribution. Ocular plates present an excellent systematic char- acter which has been largely overlooked. Osborn (1901) in a brief but very suggestive paper called attention to the variations of ocular plates in Arbacia and compared these variations with the characters of Palaeozoic types. Early in my studies of these plates it was seen that they had an important bearing, and observations were made on all available specimens of regular Echini, Mesozoic and Recent. In the fossils this is not always easy, as for purposes of study, all five oculars and genitals must be observed, and they are frequently lost in fossils. I have succeeded, however, in making observations on something over 50,000 regular Recent and Mesozoic specimens representing 133 species. The results are presented in tabular form and the more interesting cases are described. In the tables in certain species, developing series are given as well as developed series, notably in Slrongylocentrotus drobachiensis; in other species the specimens listed were not all adults, but were all large enough so that they were believed to be fully developed, being for the most part nearly or quite half grown. Of the species tabulated all specimens seen are included excepting young specimens, those without locality, where this was a feature of importance, tetramerous or hexamerous individuals, and a very few distorted specimens that could not properly be included. The reason for making so many observations was that while the character of a species is usually gathered correctly from five or ten specimens, the varia- tions seen in a large number present interesting data for comparative study. One may expect to find the common variants in from 25 to 100 specimens, and 500 to 1,000 may reasonably be expected to yield all the variants at all likely to occur. For an exhaustive study of variation, however, many thousand specimens of a species may be profitably studied. In Mesozoic regular Echini the dominant character is for all the oculars to be exsert, or excluded from the periproct. In the Recent regular Echini the young also have all the oculars exsert.1 In the adult all the oculars may be exsert or one or more may be insert. While the exsert character of the young is like the Mesozoic, the becoming insert in development is the taking on of a character which in this respect is directly comparable to the dominant character of the Palaeozoic. 1 By young is meant specimens of from 2 to 5 or more millimeters in diameter. At an extremely early stage, at least as shown in Echinus, Plate 3, fig. 5, all the oculars reach the periproct. A general conception of the characters of this stage is represented schematically in Plate 3, fig. 7. OCULAR AND GENITAL I'LATKS. 91 Most species have a definite character as to whether all plates are exwrt or how many become insert, but in some species there is much variation, and in mo.-i ipeda when- many observations have been made there is some variation. The relative frequency of typical variation in selected species is shown diagrammatically in text-fig. 170, p. 153. In the tal.l.-. pp. 100, 101, 142, 143, 154-164, are given in detail the relations of the oeiilar plates to the periproct as observed in 50,000 specimens, including the leading genera and species of poet- Palaeozoic regular Echini belonging to the orders Cidaroida and (Vnlreehinoida. As becoming insert is a progressive character with development, specie- in a genus that have the greatest number of ocular plates insert may be considered in this respect more evolve'l than other species which have a less number (Arbacia, Echinometra). Also, as a matter of variation, individuals that have fewer oculars insert than is characteristic of the species may be considered arrested variants, and those that have more plates insert than is typical may be considered progressive variants. Such variants can frequently be compared directly with related species or genera where the fewer or greater number of oculars insert is a typical specific character (Centrechinus). Specimens of a given species from different localities present often quite striking differences as regards the number of plates which are insert, those from one locality having typically fewer oculars insert than those from a different locality. Such varia- tion with locality may well be considered as indicating incipient species, as, where there is a difference, specimens from one locality must be more progressive or less progressive than those from another (Cidaris affinis, p. 100, Tripneustes esculcntus, p. 161, Slrongylocenlrolut drobachiensis, p. 143, and Echinometra lucunler, p. 163). The number of oculars insert has been spoken of by previous writers as if it were a current of age, and the largest specimens had the most oculars insert. My observations are directly opposed to this view. All the evidence goes to show that the full numher of oculars that are to become insert are developed early in the life of the individual, and apparently later no change in this respect takes place. A series of specimens half the mature size or larger may in most species be safely accepted as showing the mature characters as regards oculars. Thi- is on the basis of observations on 11,500 specimens of Strongylocentrotus drobachiensis, all from one locality, Dumpling Islands, the specimens varying from very young to adult, and all meas- ured and tabulated as later described. With few exceptions it was found that the larger individuals in a species are typical as regards ocular plates, and that variations, lx>th urn and progressive, are more frequent in smaller individuals, often half grown as regards In many cases it has been found that my observations of the typical number of oculars insert do not agree with the published descriptions of the species. This is probably due to the fact that variation was not considered, and descriptions were drawn from a specimen or speci- mens that happened to be variants. It is not enough to consider how many ocular | become insert, but which ones is an important matter. In this there is a certain difference 92 ROBERT TRACY JACKSON ON ECHINI. in the two orders of modern regular Echini, and the sequence of incoming in these orders will now be taken up. In the Cidaroida, ocular plates are all exsert in the young, and in adults may be all exsert, or part or all may be insert as a species character (text-figs. 58-74). When oculars become insert, typically V comes in first. It is possible that in some species ocular I may come in before V as both systems occur in the Centrechinoida. After V, ocular I comes in, marking a bilateral symmetry, as these are the plates of the bivium. After the bivium, ocular IV next becomes insert. Up to this point the sequence is as in the Centrechinoida, and V, I, IV insert is a common character in the Cidaroida. Ocular II may come in next (Eucidaris tribuloides) when we have the sequence V, I, IV, II insert, the bivium and posterior pair of the trivium, indicating a bilateral symmetry and being the character that prevails strongly in the Centre- chinoida and Spatangina. Or, on the other hand, ocular III may typically come in after IV (Cidaris affinis), when we have the sequence V, I, IV, III. This is the sequence described by Clark (1907, p. 193) in several genera of the family. It is rare in the Centrechinoida and unknown in the Spatangina. If ocular II comes in first, then III is the last to enter the peri- proct, or if III comes in first, then II is the last to enter the periproct. The sequence as stated in the Cidaroida is adhered to in 99.31% of the 1,459 specimens observed. There were only ten aberrants, or 0.69%. These aberrants all occurred in two species, Cidaris affinis and Eucidaris tribuloides as there described, and all but one of these may be considered cases of incomplete I, V, IV, III (pp. 96, 97, 99.) In the Centrechinoida the ocular plates, barring slight variation, come in or reach the periproct in a perfectly definite order. The sequence of incoming is I, V, or V, I, then IV, II, III (text-figs. 118-127). It is to be noticed that this order is the bivium first, then the posterior plates of the trivium, and finally, if at all, the odd anterior ocular. This emphasizes the orientation of Lov6n in comparison with the bilateral Echini, and points out a bilateral symmetry in the regular Echini not before suspected. The bilateral symmetry is shown by the fact that ocular plates come in, or become insert, in definite sequence on each side of the axis through III, 5, which is the elongate axis of bilateral types, as in spatangoids. Thus the posterior plates (the bivium) in the Centrechinoida are the first two to become insert, as in the spatangoid Cassidulus (text-fig. 172, p. 149), next the left anterior ocular comes in, as in Micraster (text-fig. 174), then the right anterior ocular follows, as in Ananchytes (text-fig. 175, p. 149). There is therefore a direct relation between the order of incoming of oculars in regu- lar Echini and that which obtains in the Exocycloida. The order of sequence in which the bivium comes in emphasizes family characters. The order I, V is characteristic of the Hemicidaridae, Centrechinidae, Saleniidae, Stomopneustidae, Temnopleuridae, Echinidae, and Strongylocentrotidae (text-figs. 128-134). On the other hand, the order V, I is characteristic of the Arbaciidae and the Echinometridae (the latter as here restricted, see tables pp. 158, 163), text-figs. 111-114, 158-161. OCILAH AND GENITAL PLAT! '.»:; To show the regularity of sequence of incoming of oculur plate- in the- ( Vntrechinoida. it may be put briefly as follows. In the total 48,541 specimens of this order examined and tabulated, 6,235 have all the oculars exsert. In 3, 300 spec! men- there i- one ocular in-ert, and of these in 3,279 cases, it is either ocular I or V, that is, 99.36% are correct by rule. Only 21 specimens are aberrant, and these have either ocular IV (text-fin. 140, p. 134) or II in-ert, or in three instances ocular III alone is insert. In 35,184 specimens, two ocular- are in-. -it, and of these it is I and V, the bivium, in 34,881, or 99.14%, are correct by rule. In all of the :{03 exceptions, one of the two plates insert is either I or V. In 97 of the-e. ocular- I. IV are inaert, and in 76% of them genitals 4, 5 are fused, as in text-fig. 144, p. 134, mechanically excluding ocular V from the periproct. These may therefore be properly con-iderrd cases of an incom- plete I, V, IV insert. In 56 of the exceptions, oculars I, II are insert (text-fig. 141, p. i:: I This character was found only in the Echinidae or in the nearly allied Strongylocentrotidae ami is a species character in Gymnechinus pulchellus and robillardi (text-figs. 177-179, p. Ui."». In 82 of the exceptions, oculars V, IV are insert (text-fig. 142, p. 134). This is especially common in the Arbaciidae, and in no case was an ocular excluded by the fusion of genitals. In ii.'{ cases, oculars V, II are insert. This combination was seen in the Saleniidae, Kchinidae, Strongylocen- trotidae, and Echinometridae, and in all of the cases in the families Kchinidac and Strongylo- centrotidae genitals 5, 1 were fused, excluding ocular I (text-fig. 14i..nally the right, posterior plate of the trivium, and this rule is adhered to in 98.87% of the : cases observed. There were only 33 exceptions to the above. In 17 of these, ocular- V. IV. II are insert, but ocular I was always excluded by the fusion of genitals 5, 1 (text-figs. 1 IS. , , and 196, p. 169), so that this combination may reasonably be considered an incomplete I. V. IV, II insert. In one case oculars I, IV, II are insert (text-fig. 147, p. 134), with genitals 4, 5 fused, excluding ocular V, evidently also an incomplete I, V, IV, II insert . In addition, four of the cases are I, V, III insert, a sporadic variant, and eleven are cases of V. IV. Ill iiiM-rt. 94 ROBERT TRACY JACKSON ON ECHINI. This last is the dominant character of Slrongylocentrotus gibbosus (text-fig. 156, p. 145), in which species a commensal crab profoundly modifies the apical disc. In 387 specimens, four oculars reach the periproct, and of these in 340, which is 87.86 % of the cases, the order is I, V, IV, II, the bivium and posterior pair of the trivium (text-fig. 120, p. 124). Of the 47 exceptions, the order in all is I, V, IV, III insert (text-fig. 149), and this order is common as a character in the Cidaroida (text-fig. 69, p. 98). It is interesting to note that 32 of the 47 cases of this aberration occur in Centrechinus, which genus is relatively near the base of its order, and therefore nearer to the Cidaroida. When, therefore, four oculars are insert in the Centrechinoida in all, or 100%, the arrangement is that characteristic of the order, or is reversionary to the character frequent in the Cidaroida. In 518 specimens all the oculars are insert. Of the total 48,541 specimens of Centrechinoida observed and tabulated, when oculars become insert, they come in in the order of sequence I, V, or V, I, IV, II, III in 98.55%, and they are out of order, or aberrant for the Centrechinoida in 704 cases, or 1.45%. Of the above considered aberrants as there stated, certain combinations of ocular plate arrangement can be definitely accounted for, the I, V, II insert (300 specimens) as right-handed individuals (text-fig. 145, p. 134); the I, IV (97 specimens) are incomplete I, V, IV by the usual exclusion of ocular V, due to the fusion of genitals 4, 5 (text-fig. 144, p. 134) ; the V, II (63 specimens) text-fig. 146, as incomplete I, V, II, due to the usual fusion of genitals 5, 1, excluding ocular I; the V, IV, II (17 specimens), text-figs. 148, p. 134 and 196, p. 169, may be considered as incomplete I, V, IV, II, due to the exclusion of ocular I by the fusion of genitals 5, 1; the I, IV, II (1 specimen), text-fig. 147, (p. 134) is similarly accounted for by the exclusion of ocular V. Finally, the I, V, IV, III (47 specimens), text-fig. 149, (p. 134) is accounted for as a reversion to the character typical of some of the Cidaroida. The sum of these definitely accounted for variants, which is 525, subtracted from the total number of aberrant variants, which is 704, leaves only 179, or 0.37 %, which can be considered as distinct departures from the rule of ocular plate arrangement. Of these last, 56 specimens have oculars I, II insert (text-fig. 141, p. 134), which is the species character of Gymnechinus pulchellus and robillardi (text-figs. 177-179, p. 165), and 82 specimens have oculars V, IV insert (text-fig. 142, p. 134), which is a left-handed equivalent of the I, II insert. It is evident that even aberrants follow a quite definite arrangement and sporadic variants are extremely rare, only 41 cases as a whole in the 48,541 specimens of the order examined. Of these last, which are considered sporadic variants, ten specimens have ocular IV alone insert, three have III ^ilone, and eight have ocular II alone insert; one specimen has oculars I, III insert, and four have V, III insert; four specimens have oculars I, V, III insert, and eleven have oculars V, IV, III insert. The detailed distribution of aberrants in families, genera, and species of the Centrechinoida can be seen in the table of aberrant variants, p. 164. OCULAR AND GENITAL I'LATHS. '.»:, In the tables of ocular plate arrangement (pp. 100, 101, 142, 143, 154-163) are shown numeri- cally the typical character of the species listed with the normal arn-ted ami progressive vari- ants, and in the right-hand column the number of aberrant variants, the detail- of which for the Centrechinoida are separately listed in the final table (p. 164). In the numlx-rs given in the tables the denominator, in Arabic numerals, shows the number of >peciin<-n- in which the given character was found and the numerator, in italic numerals, expresses the JMT- centage which this number bears to the total number of specimens examined. In t he last table are shown the characters of all aberrant variants tabulated in the (Vntrechinoida. It is noteworthy that in only a few species are such aberrants common, and it is a curious fact that has no obvious explanation, that most of such species occur off the west coast of South America. They are, namely, Arbacia spatuligera and nigra, and Strongylocenlrotu* aUnu and gibbosiis. In the table of aberrants (p. 164) it is a striking fact as there brought out that certain aberrant variations are a characteristic of definite species or families in the order. In all of the tables of ocular plate arrangement the species within the genus are arranged on the baMH of the number of oculars insert or its frequency as a variant. When no difference \\a< observed they are arranged alphabetically. In the text they are considered in the same sequence. The Cidaroida of the Mesozoic rarely have the oculars and genitals preserved, but they were found in seven specimens, all alike in character. The oculars are all exsert in a choice specimen of Cidaris florigemma from the Coral Rag, near Calne, in the Jermyn St. Museum; and in two specimens of Cidaris sceptifera, from the Chalk, one being in the Jermyn St. and the other in the British Museum. The same structure is shown in Cidaris caronata (text-fig. v TEXT-FIGS. 58-tiO — Ocular plate arrangement in Cidaridae. 58 Diplocidaris desori Quenstedt. White Jura, Sonntheim. Stuttgart Museum Coll., 9,77 59. CidarisaffmisPhilippi. Naples Station. Diam. 30 mm. R. T. J. Coll., 643. character of this species. 60. The same specimen, internal view. All oculars exsert as in the young ami has one large madreporic pore as in the young (Plate 2, fig. 3), not many pores as on th«- .-xirri,* of aamo pU 96 ROBERT TRACY JACKSON ON ECHINI. 164) and Diplocidaris desori (text-fig. 58). In both species the oculars are strongly exsert. The specimen of Cidaris coronata (text-fig. 164, p. 149), which is in the Stuttgart Museum, is exceptionally perfect for plates of the periproct, which are very rarely preserved in the Mesozoic. The character of having all the oculars exsert is seen in the young of Recent cidarids. It also occurs as the adult character of some Recent species and as an arrested variant in species typically having some oculars insert as seen in the table, pp. 100, 101. Cidaris abyssicola (74 specimens) has typically all oculars strongly exsert, but in two specimens all the oculars are narrowly insert. It is remarkable that the only variants in this species should have this extreme character. Cidaris cidaris l is apparently a rare species. Ten specimens were studied, in nine of which all oculars are strongly exsert. Four of these were kindly sent me by Dr. Mortensen. One specimen has oculars I, V, IV insert as a progressive variant. Cidaris affinis is a difficult and interesting species presenting an exceptional amount of variation. In the form from the West Indies and Florida in 161 specimens in the U. S. National Museum, identified by Dr. Mortensen, the typical character by a small majority is for all oculars to be exsert as in the young, and in the adults of Jurassic species. There is, however, great variation, and only 30% have the typical species character of this locality. As all exsert is the character, cases with more or less oculars insert may be considered as pro- gressive variants. In 18 % ocular V only is insert, in 2 % oculars V, I and in 7 % oculars V, I, IV are insert, which is the species character of Euddaris Iribuloides. In 0.6% oculars V, I, IV, II are insert, like typical progressive variants of Euddaris tribuloides; in 20% oculars I, V, IV, III are insert. This, which is a common character in this species, is uncommon in tribuloides and rare in the Centrechinoida, where typically, if four plates are insert, it is the bivium and posterior pair of the trivium. In 20% all the oculars are insert; this, which is the extreme progressive variant for the southern form, is the typical character in the Medi- terranean form of Cidaris affinis. Three specimens are aberrant with oculars V, IV, III insert. These are sporadic variants and are apparently imperfect cases of I, V, IV, III. In the Mediterranean form of Cidaris affinis (frequently and incorrectly referred to Doro- cidaris papillata = Cidaris cidaris) a quite different condition prevails. The ocular plates are all insert (text-fig. 59) as the typical condition in 53 % of the 120 specimens seen. On the proximal side (text-fig. 60), however, the oculars are all exsert as in the young, and in adults of Jurassic species. This is of interest as showing a primitive character internally and a pro- gressive externally in the same plates. It is due to the adoral beveling of periproctal plates over the genitals so that they extend further and present a different relation to the oculars 1 This is the Dorocitlaris papillala of authors. It is gen Tally agreed that this is the Echinus cidaris of Linnaeus, and the type of Cidaris; also the three Recent species commonly attributed to Cidaris s. s. belong rather to Euddaris Punirl (Bather; H. L. Clark, Ann. Mag. Nat. Hist., 1908-'09; Mortensen, 1909).. OCULAR AND CKMTAI. I'l.A'l I 97 on the exterior from what they do on the interior of the test. The madreporite -how- -imilar differential characters. On the exterior there are numerous line pores, hut on the interior only one large madreporic pore as in the young, a primitive character common to tlie whole family. Since typically in the Mediterranean form all oculars are insert, u .-penmen with any le— mu-i be considered an arrested variant. As such variants, 11',', have all ocular- e\-ert like tin- dominant character in the West Indian form, 4% have V only insert, I ' , have V and I. the bivium, 10% have V, I, IV, and 14% have V, I, IV, III insert. Of aberrant- there are five specimens, 4%. Of these, one has V, IV only insert, two have V, I, III, and two have V, IV, III insert. Cidaris affinis is an important species in these studies because it shows strongly the char- acter of V, I, IV, III insert when four plates meet the periproct, instead of V, I, IV, II. The same is probably true of a number of species in this order. Messrs. Agassiz and Clark (1907, p. 40) in their Acanthocidaris hastigera give V, I, IV, III insert as the species character, but do not say how many specimens showed it. It would be inter- esting to know, as it is the only species of echinoid known in which this is the character, as far as I am aware. Eucidaris metularia has typically all oculars exsert, but in 39 specimens, two have V, I, IV insert as a progressive variant. Eucidaris thouarsi has typically V, I, IV insert, but the observations show a wide range of characters from all exsert to all insert. This species is very close to Eucidaris tribuloides of the West Indies. In both species oculars V, I, V IV are typically insert, but in thouarsi, arrested variants are J * J I i \T-KKI. til. —Kiiriilnnxlnhuloidef common, progressive variants less frequent; while in tribuloides, (i.;llll;ink). Florida. I Mam. r, mm. arrested variants are rare and progressive variants common, .... •, • t *!,„ individual. No genii til ami but frw indicating that thouarsi is the more primitive of the two madnponc ixinw, all orulara enert. closely related species. Of Eucidaris tribuloides 849 specimens were studied, and they present most interesting characters. In the young of a few mm. in diameter (text-fig. 61) all the oculars are strongly exsert and there are few madreporic p The full number of oculars travels in very early. In the adult typically (58%), oculars V, I, IV are insert (text-fig. 66). The variations of the adult as seen in the large >• studied are most interesting as the variants cover nearly the whole range of characters occur- ring as species features in all regular Echini known from the Lower Carboniferous to the prc-mt time.1 The arrested variants are relatively rare, but progressive variants are common. Of arrested variants, in 0.6% all oculars are exsert (text-fig. 62), as in the yom.B and the adult ' The only known exceptions are Gymnechinus and Stnm.julwnlr,*!* giU»«i,*, in both of whirl, this arra in peculiarly modified awl typically has an aberrant arran^m,,,. of oriilai* (..•xt-figs. 154-157. ,,. 1 1.',, an.1 177 II HI ROBERT TRACY JACKSON ON ECHINI. I TEXT-FIGS. 62-71. — Ocular plate arrangement in Eucidaris trilmlinilcs (I.amarck). 62. Jamaica. Diam. 38 mm. R. T. J. Coll., 798. All oculars exsert. 63. Jamaica. Diam. 33 mm. R. T. J. Coll., 799. Ocular V insert. 64. Jamaica. Diam. 35 mm. R. T. J. Coll., 800. Ocular I insert, genital 3, plates X' , and genital 4, plates X, are split by secondary sutures. 65. Nassau, Bahamas. Diam. 32 mm. R. T. J. Coll., 646. Oculars V, I insert. Figures 62-65 all arrested variants. Nassau. Diam. 47 mm. R. T. J. Coll., 647. Oculars V, I, IV insert, the typical character. R. T. J. Coll., 648. Oculars V, I, IV, II insert. All oculars insert. 66. 67. 68. 69. 70. Nassau. Nassau. Diam. 52 mm. Diarn. 40 mm. R. T. J. Coll., 649. Jamaica. Diam. 35 mm. R. T. J. Coll. ,801. Oculars V, I, IV, III insert. Figures 67-69 all progressive variants. Nassau. Diam. 47 mm. R. T. J. Coll., 654. Seen from exterior. The genital has many madreporic pores. 71. The same specimen seen from interior. The genital has only one large madreporic pore, and the genital pore is larger than on the exterior. All figures X 3. (XT I .All AND <; i:\ITAI, IM.ATKS. 00 of species that typically have all oculars exsert. In three speeimens (0.4%) ocular V alone is just insert (text-fig. 63) and in one specimen ocular I alone i- insert V insert is a frequent variant in the order, probably it typically comes in first in tl.i- -peei.->. In 3% ocular* V, I are insert (text-fig. 65). These are all arrested variants. As progressive variant- instead of the typical three plates, oculars V, I, IV, II arc insert ins', • irxt-fig. 67). Tlii- i> .if interest as these plates are the bivium and posterior pair of the trivium marking the bilateral -ymmetry of regular Echini. In 4% oculars V, I, IV, III are insert (text-fig. 69). This arrangement of four plates is relatively rare in E, tribuloides while it is a common variant in Citlnri* affmu as there discussed. In 25 % all oculars are insert (text-fig. 68). This is the ext n-me pn>nn— ive variant of tribuloides, and is comparable to the typical character of Phyllacunthu* baculota (text-fig. 169, p. 149), or other species in which typically all oculars are insert. In only two specimens out of the 849 examined was the arrangement aberrant. In these variants one has oculars I, IV, III insert, V, II exsert; the other has oculars V, IV, III insert .1.11 exsert. Both are sporadic variants and evidently cases of incomplete V, I, IV, III insert. In studying the specimens they were tabulated in lots of one hundred each, and it is worth noting that the percentage of the typical arrangement and the variations came out in each lot with hardly any difference, and the same regularity occurred in most species studied. In Goniocidaris nutrix (text-fig. 72), typically (86%) the oculars are all fully exsert and a ring surrounds each ocular pore. This ring is a striking character not existent in Goniocidaris 1 V TEXT-FIGS..72-74. — Ocular plate arrangement in C'ularidae. 72. Goniocidaris nutrix (Wyville Thomson). Kerguelcn Island, Antarctic. Dial... '-'7 ....... X 4. All oculars exsert, elevated ring around ocular pores, genital pores huge. 73. Goniocidaris canalicvlala A. Agassiz. Falkland Island*. Di:u,,. -' t mm. R. T. J. Coll.. 7 1 1 insert (compare with young, Plate 2, fig. 3). 74. The same. Falkland Islands. Dial... 22 mm. H. T. J. Coll., 71-V reaching beyond plates. 100 ROBERT TRACY JACKSON ON ECHINI. Table of Typical Ocular Plate Arrangement and Variation in the Cidaroida. tf E B C S t 1 | B I V • £ V O . a M I-H >-< t— t t—t 1 s M »— i £ -M M i" J ;>" ^ ^ M B ta B § W >— » i— i b .S C! £ * - .A • (— 1 I-H 3 s ^j "•* t; .£ M U o 'C 1 iT tt • ;> >" >' 1 6 5 i S •2 I-H M • _c ° •8 t .s •- **__ ^ ^ ^ £ § 1 Order CIDAROIDA _« "3 o 0 "3 i H- 1 E 3 hH~ 1 3 i— T E t-T n E J 1 S i B a 1 Cidaridae ^ 0 0 o O cS I 1 < ^ 2 Cidaris coronata Goldfuss. 100* Jurassic, Nattheim and Sonntheim. (Text- 2* fig. 164.) 74 Cidaris abyssicola (A. Agassiz). 97 3 Florida, 100-200 fathoms. 72 2 10 Cidaris cidaris (Linn6). 90 /o Off coast of Norway and Sweden. 9 i Cidaris affinis Philippi. SO 18 2 7 o.e 20 20 2 Cuba to Yucatan, 45 fathoms; Florida (161 48 29 3 12 1 32 33 3 specimens). 281 The same. 11 4 ^ 10 14 53 / Mediterranean (120 specimens). (Text-figs. 13 5 5 12 17 63 5 . 59-60.) 39 Eucidaris metularia (Lamarck). 95 5 Mauritius; Samoa; Hawaiian Islands. 37 2 34 Eucidaris Ihouarsi (Valentin). J5 9 18 47 6 6 Gulf of California; Panama. 5 3 IT 16 2 2 849 Eucidaris tribuloides (Lamarck). 0.6 0.1 0.4 3 5S 8 4 25 />..' Jamaica; Bahamas; Florida; Bermuda. (Text- 5 1 3 28 493 72 36 209 •2 figs. 62-69, 176.) 7 Goniocidaris nutrix (Wyville Thomson). S •— T M M — — r 1 j S >' - C 1 = = I CO IM 5 tn j HH 1 i— « — • - ± - ! •s S Order CIDAROIDA (continued). f j § § 1 15 Cidaridae (continued). 3 5 § <5 ; ; 5 17 Phyllacanthus annulifcra (Lamarck). ft. M / ' &* Australia. !• a •2 a 100 Phyllacanthus baculosa (Lamarck). / 1 '•- Mauritius. (Text-figs. 169, 176, Plate 3, figs. i 1 101 3,4.) 1 Diplocidaris desori Quenstedt. 100 Jurassic, Sonntheim. (Text-fig. 58.) 1 1 Kplocidaris giganlea Desor. 100 Jurassic, Besangon. 1 1,459 207 1 43 42 648 91 441 10 * Italic numerals represent percentages, Arabic numerals flic number of spccimrns »|>SITVI .1 canaliculata, and I know it only in Porocidaris milleri A. Agassiz, as figured by Mr. Agassis (1904). The genital pores are relatively huge, break through the confines of tin- n<'nit:il plati- and impinge upon the interambulacra. One specimen in the seven examined has all the oculars insert like the typical character of canaliculata. In Goniocidaris tubaria, 17 specimens, all the oculars are insert in 41%, but there is cmi- siderable variation. In 12% all the oculars are exsert, as in G. nutrix, in G% ocular V. in 35 % oculars V, I, IV, and in 6 % oculars V, I, IV, III are insert. The sequence of coming in is apparently V, I, IV, III, II. The character of the apical disc in Goniocidaris canaliculata is of especial interest a.* t he- very young was studied carefully by Love"n (1892) and is here figured (Plate 2, figs. 1-3). Of seven adults the oculars are all broadly insert in six specimens (text-figs. 73, 74), and in the seventh, oculars V, I, IV, III are insert. There is no elevated ring around the ocular pores and the genital plates and pores are small, not large, in distinction from (i. nulrix. The genital pores, however, extend beyond the limits of the plate as in nutrix. The oculars are broadly 102 ROBERT TRACY JACKSON ON ECHINI. exsert in the very young (Plate 2, fig. 3), as in the Jurassic. In a series of eight young speci- mens from Patagonia in the American Museum of Natural History, varying from 15 to 20 mm. in diameter, the oculars are slightly or more strongly exsert in all but one, the largest, in which ocular V alone is insert. The genitals are high in the young rather than low as in the adult, therefore more like typical cidarids, and all or part of the genital pores are wanting in the smaller specimens. This all indicates that adult characters are taken on late in this species, indeed much later than usual in Echini. In adults the genitals are relatively the lowest, especially those shown in text-fig. 74, of any genitals seen in Echini ; perhaps in some way correlated with the peculiar brooding habit of this species. Mr. Agassiz (1873, p. 396) said of G. canaliculate that the genital plates are in contact. He included (1881, p. 44), however, Goniocidaris nulrix in this species, and it is possible that his observation of exsert oculars was based on nutrix, in which it is characteristic. As I find six out of seven adults with all oculars insert, it is fair to assume that as the specific character. In Goniocidaris biserialis all the oculars are insert in three specimens. In Phyllacanthus there is wide range in species as to the insertness of oculars, as shown in the table; but with one exception only a few specimens were studied. In Phyllacanthus imperialis oculars are typically all exsert. In P. thomasii, in 33%, oculars V, I, IV, or all, are insert, but one specimen has all exsert and one has V only insert, these last two being the largest specimens of the species seen. In P. annulifera oculars are typically all insert, as seen in 53 % of the 17 specimens. Of arrested variants 6 % have ocular V only insert, 18 % have I, V, IV, 12% I, V, IV, II, and 12% I, V, IV, III insert. In these characters the species is dis- tinctly more primitive than the next. In Phyllacanthus baculosa (106 specimens) the oculars are all insert in 98% of the cases (text-fig. 169, p. 149). In one exception oculars V, I, IV are insert (Plate 3, fig. 3), for this species an arrested variant, comparable to the typical character of Euci- daris tribuloides (text-fig. 66). In another specimen oculars V, I, IV, II are insert and III. exsert (Plate 3, fig. 4). This arrested variant is especially interesting as it is like the progressive variant of Eucidaris tribuloides (text-fig. 67), and also as it indicates that III is the last ocular to become insert as in that species and in the Centrechinoida. Phyllacanthus baculosa with all oculars insert is in this feature like the majority of Palaeozoic species, and like progressive variants of those in its own order that typically have fewer oculars insert. It is the only species of Echini with all insert typically in which a considerable number of specimens have been studied, and it is interesting to see that its variants, though so few, accord with the characters of associated types. Considering the ocular arrangement in the Cidaroida as a whole, it is seen that they follow very closely the order of insertness that is characteristic of the group, but yet show a very wide diversity of arrangement within the species. The variants skip about within the limits of variation in a degree that is unknown in the Centrechinoida, yet aberrant variants are (X'ULAK AN!) (JKMTAL I'l.ATKS. 103 relatively rare in the Cidaroida. The character of the apical disc in the I'alaeo/.oic ( ' idaridac (Miocidaris) is unknown and would be most interesting to ascertain. Turning to the Centrechinoida, it is found that in this order the arrangement of the ocular plates as regards insertness is much more definite and constant than in most of the < 'idaroidii. Taking up the first suborder Aulodonta,' we find that in the Meso/oic Memicidaridae the lea-l- ing character is for all the oculars to be exsert, as shown in the first two specie- li-ted in tin- table. In Hemicidaris intermedia (169 specimens) the oculars arc exsert in X'.C , 'text-fig but 13 specimens, 8%, are progressive variants with ocular I insert, and in five specimens, 3%, the bivium is insert. In H. crenularis (58 specimens) 81 % have all oculars cxscrt, but 16% are progressive variants with ocular I insert, and 2% progressive with oculars I, V insert, like the typical character of the next higher species. One specimen is aberrant with ocular III alone insert, a very rare variation seen in only two other sea-urchins (table, p. lf>4). In Hemicidaris luciensis typically, 56%, the bivium is insert (text-fig. 77) like tin- mo-t progressive variants of H. intermedia. Seven specimens in 16, however, are arrested variant-. two with all oculars exsert, the dominant character of the genus, and five with ocular I in-crt (text-fig. 76), like the progressive variants of Hemicidaris crenularis and intermedia. Hemi- cidaris langrunensis likewise has typically the bivium insert, 67%, as a species character. but of 18 specimens, 11% have all the oculars exsert and 22% have ocular I only insert, as arrested variants. In Hemidiadema stramonium (10 specimens) the oculars are typically all exsert, 90%, but 10% are progressive with ocular I insert. In Asterocidarix minor (text-fig. 78), Goniopygus peltatus, and Glypticus hieroglyphicus (text-fig. 79) the oculars are strongly exsert in all of the 134 specimens seen (table, p. 154). m m m TEXT-FIGS. 75-79.- Ocular plate arrangement in the Hemin.l:iri,l:i.-. 75 Hemicidaris intermedia (Fleming). Coral Rag, Cain.-, Wilt*. K.,K!,ind. Duun. .U mm. .digny. Junu-e.B-h.ur Me, Diam. 22 mm. U. T. J. O,,., 7,v , ,lllar , inMrt, an arrested variant. ^ ^^ ^ y ^ fc ^^ ?S. ^e^aris^nor Cotteau. Jura.io, Sollies, France. G. IJoehn, Co..., Fmbun. L ». « - - 79. Glypticus hieroglyphicus Ag^. Coral Rag, St. Pierre, Neuchatel. Eham. 19 mm. all exsert. All figures X 4. • The suborders of the Centrechinoida are now divisions ,Mi,,,-,l and discussed in the aection on cU«fic»Uo«, «d p. 183 104 ROBERT TRACY JACKSON ON ECHINI. R. T. J. Coll. 670. oculars broadly insert. Of the Aspidodiadematidae 123 specimens, including four species, have been examined. In all the oculars are widely insert, as in Dermatodiadema antillarum (text-fig. 80). The oculars are relatively exceptionally broad and large, as pointed out by Mr. Agassiz (1904, p. 59, 75), and, as he notes, are comparable to the Palaeechinidae in that all meet the periproct. They differ, however, in their relatively great size, especially their width, as compared with the genitals. The genitals are peculiar in that the pores are large and nearly or quite in the middle of each plate. The apical disc in the Aspidodiadematidae is relatively very large, being about 30 to 60 % of the diameter of the test. In this it differs radically from the Palaeechinidae in which the apical disc is relatively small, usually being less than 20% of the diameter of the tost. In the Mesozoic Centrechinidae the ocular plates are all TEXT-FIG. 80. — DermaUxiiadema exsert typically, in strong distinction to living species of the antillarum A. Agassiz. West In- . , , T . _ , ,. , ,. „,, .. .. family. Of 18 specimens ot the Jurassic rseudodiadema pseu- dies, 955 fathoms. Diam. 9 mm. x 6. All dodiadema, in 89 % all oculars are exsert (text-fig. 81), but in 11 % ocular I is insert (text-fig. 82), a progressive variant. It is of in- terest to note that this ocular, I, is the first to become insert in the development of the recent Centrechinus (text-fig. 90). In the Jurassic Magnosia (text- fig. 83), Cottaldia, Phymechinus (text-fig. 84), and Pedina, all oculars are exsert as usual in Mesozoic species of the family 1 excepting one specimen of Phymechinus in which the bivium is insert. Of Jurassic Stomechinus several species, including 82 specimens, were studied. Usually all the oculars are exsert as in S. bigranularis (text-fig. 85). In a few cases, six in all, ocular I or V, or I and V, are insert as in text-fig. 86. These are distinctly progressive variants for the species and the geological horizon, and are comparable to the second and third stages in the development of oculars in recent Centrechinus, where one ocular or the bivium is insert as in text-figs. 90, 91 (table, p. 155). In the Mesozoic Polycyphus and Orthopsis (text-fig. 87), oculars were all exsert in the 51 specimens seen, except that in one specimen of P. normannus ocular I is insert. In Centrechinus setosus 2 we have the type species of the family and therefore one of much importance. Mr. Agassiz early recognized several species of the genus; in the Revision he recognized only two. Dr. Mortensen (1904) revived the earlier species and Messrs. A. Agassiz and Clark (1908) followed him in taking up the older divisions of the genus. Having had speci- mens of the several species, I confess I cannot recognize the specific distinctions as diagnostic 1 Text-figs. 78 and 82-84 were drawn from specimens in the personal collection of Professor G. Boehm of Freiburg i. B., who kindly gave the opportunity to study them and other material. 2 For the change of name from Diadema selosum to Centrechinus setosus, see footnote pp. 27, 28. OCULAR AM) (JKMTAI. IM.VIl ,„- and here consider the several forms from the Pacific and A.laM.i, M all n-f-ral,!,. „, r «to, In this species we find most interesting characters in nwin| ,„ (((,1,;irs, fnr „„. ]thtgm ^ M stages m development and variation in the adult cov,r th,- whol. „,„„,. of ehaneton MM in in OK Off O7 o t/ o o o / TEXT-FIGS. 81-87. — Ocular plate arrangement in Mesozoic Ccntrerhinidau. 81. Pseudodiadema pseudodiadema (Lamarck). Coral Rag, Yonne, France. Diam. 20 mm. R. T. J. Coll., 716. X 8. All oculars insert, typical character. 82. The same. Corallien, Trouville. G. Boehm Coll., Freiburg i. B. X 4. O.-ular I insert, aprogremive variant. 83. Magnesia punclvlata (Lamarck). Oxford, Berner Jura. G. Bochm Coll., Freiburg i. B. X about 20. All oculars exsert. 84. Phymechinus mirabilis Agassiz. Oxford, Bcrner Jura. G. Boehm Coll., Freiburg i. B. X 4. All orulweaert, typical character. 85. Stomechinus bigranularis Lamarck. Inferior Oolite, Broad Windsor, Dorset. Diain. 47 mm. U. T. J. Coll., . X 4. All oculars exsert, typical character. 86. The same. Diam. 48 mm. R. T. J. Coll., 715. X 4. Oculars I, V insert, a progmwive variant. 87. Orthopsis miliaris (d'Archiac). Cretaceous, Lcs Tamarins, Algiers. Diam. 20 nun. R. T. J. Coll., 717. X 8. All oculars exsert, typical character. the fossil and recent members of the family. In a very young specimen (text-fig. 88) all the oculars are fully exsert and this early stage may be compared with the adult Jurn-i.- I'-i-udo- diadema (text-fig. 81). In an older specimen (text-fig. 89) the oculars are still all exsert, but 106 ROBERT TRACY JACKSON ON ECHINI. I is nearly in. In text-fig. 90 ocular I is insert, the others all exsert, a developing condition like the progressive variant of Jurassic Pseudodiadema (text-fig. 82). A later stage is shown in text-fig. 91, in which oculars I and V are insert and IV is nearly in. This may be compared with the extreme progressive variant in Jurassic Stomechinus (text-fig. 86), in which also the bivium is insert. A still later stage (text-fig. 92) has oculars I, V, IV insert, II, III exsert, and v 90 TEXT-FIGS. 88-92. — Development of ocular plate arrangement in Ccnlrechinus setosm (Leske). 88. Bahamas. Diam. 8 mm. R. T. J. Coll., 672. X 10. Oculars all strongly exsert, marginal plates of the peri- proct are large, a youthful character, compare text-fig. 98. See p. 174. 89. St. Thomas, West Indies. Diam. 33 mm. R. T. J. Coll., 755. X 5. Oculars still all exsert. 90. The same. Diam. 33 mm. R. T. J. Coll., 756. X 5. Ocular I insert. 91. The same. Diam. 31 mm. R. T. J. Coll., 757. X 5. Oculars I, V insert. 92. The same. Diam. 31 mm. R. T. J. Coll., 758. X 5. Oculars I, V, IV insert. Ambulacra! plates simple dor- sally above the 18th, which is the first compound plate (p. 55). this, though only 31 mm. in diameter, has taken on the full species character in this respect. Interesting features of the corona are shown also in text-fig. 92. The ambulacral plates near the ocular are all simple as in cidarids, the first compound plate being the 18th from the base of the corona, as indicated. In the adult specimen (text-fig. 94) a similar condition of simple plates is seen in the placogenous zone, and the first compound plate is the 24th from the base of the corona. This condition of simple plates in the placogenous zone was pointed out by Lovdn (1874), but is much clearer in Centrechinus than in many genera. The development of the interambulacrum is shown in a similar manner in text-fig. 92; plates 11 and 12 are nearly OCULAR AND GKNITAI. IM.ATKS. 107 smooth and 10 has the primary tubercle. In the adult (text-fig. 94), plates 14 to Hi are -month and 13 has the primary tubercle. This is in accordance with what I -howed '.lack-on. 1899) as localized stages in development in Strongyloccntrotiis and Arl»aeia. that the young hurt, added plates are simple, and that differential characters are progressively added »> the platrx grow older and are pushed ventrally by newly added plates on their dorsal border. It would be extremely interesting to study a large series of young developing Crntrrchinut setosus. I succeeded in getting 110 specimens from 8 to 40 mm. in diameter from the \\V-t Indies, Bermuda, and the Pacific. Of this series, as shown in the table (p. 155), 23% have all oculars exsert, 5 % have I insert, 9 % I and V, and 55 % have the adult typical char: of I, V, IV insert. Progressive variants in this immature series are infrequent, as would In- expected; 5% have I, V, IV, II insert, and 3% have all oculars insert. With later growth unquestionably more oculars would have come in in some of the specimens, so as to give tin- usual adult percentage of progressive variants. There are two aberrant variants, one with oculars V, IV, and one with I, V, IV, III insert. m *• — nr 95 93 1 TEXT-FIGS. 93-95 — Ocular plate arrangement in Centrechinus seloswi (Leske). 93 Bermuda. Diam. 85 mm. R. T. J. Coll., 686. X 2.5. Oculars I, V, IV inw-rt. tl 94. Florida. Diam. 70 mm. 11. T. J. Coll., 687. X 2.5. Oculars I, V, IV, II insert, » progrc cral plates simple dorsally above the 24th, which is the first compound plain (pp. 56, 174) 95. Florida. Diam. 82 mm. R. T. J. Coll., 688. X 2.5. All oculars insert, a progrc The development of ocular plates of Centrechinus being as above descried, the adult shows striking features as a matter of individual variation. All individuals considered under variation were not fully grown, any more than in other species, but all here considered are 108 ROBERT TRACY JACKSON ON ECHINI. 40 mm. or more in diameter, at which size full species characters are attained in development . From several localities 1,168 specimens were studied. Of these, 57 % have oculars I, V, IV insert (text-fig. 93), which is strongly the species character, and little variation from this percentage was seen in specimens from any locality. The variations from the typical cover the whole range of characters seen in development and also adults of all species of the family, fossil and living. Two arrested variants have all oculars exsert, a feature seen in the young (text-fig. 88) and in the adults of Jurassic species (text-fig. 81). Two specimens have ocular I only insert, and all other oculars exsert, though V and IV are barely exsert. This character can be compared with the second stage in development (text-fig. 90) and with progressive variants of Jurassic species where I also is insert (text-fig. 82). These extreme arrested variants of Centrechinus are small individuals (the all exsert 50 mm., the I only insert 51 mm. in diameter). One speci- men has ocular V alone insert, an exceptional character. Eleven specimens, or 1 %, have as arrested variants only oculars I, V insert, being comparable to the young (text-fig. 91) and to an extreme progressive variant in Jurassic species (text-fig. 86). As progressive variants of Centrechinus setosus, 17% have oculars I, V, IV, II insert (text-fig. 94), the bivium and pos- terior pair of the trivium marking the bilateral symmetry as an order of developing parts. ffi I 96 "' 98 TEXT-FIGS. 96-98. — Ocular plate arrangement in the Centrcchinidae. 96. Centrostephanus rodgersi A. Agassiz. Parramalta, N. S. W. Diam. 110mm. R. T. J. Coll., 750. X 2. Oculars I, V, IV insert, madreporite split, young ambulacral plates simple (p. 174). 97. Centrostephanus longispinus (Philippi). Naples Station. Diam. 27 mm. R. T. J. Coll., 751. X 2. All oculars insert, plates of periproct numerous and minute, excepting a few large plates on the periphery of the area (p. 174). 98. Chaetodiadema pallidum A. Agassiz and Clark. Hawaiian Islands. Diam. 65 mm. R. T. J. Coll., 700. X 2. All oculars widely insert, plates of periproct large (p. 174). In 22% all the oculars are insert (text-fig. 95). This character, which is a progressive variant of Centrechinus setosus, is the typical feature of Echinothrix, Centrostephanus longispinus (text- OCULAR AND GENITAL H. \TI.S 111') fig. 97), Astropyga (text-fig. 99), and Chaetodiadema (text-fig. 98). There are M alx-rrapt*, 3%. Thirty-one of these have I, V, IV, III insert. This character i- common in ciduritfo an discussed, but is rare in the Centrechinoida, most of the cases seen occurring in tin One aberrant has oculars I, IV insert, V being excluded by the fusion of genital.- 4, ">, a- in text- fig. 144; and one aberrant has V, IV, III insert, evidently an imperfect I. V, IV, III, ami a very rare variant, which, however, is the species character of Str<»ii/i/l<>n nlrntiu gibbottws (le\t- fig. 156). While three plates insert is strongly the character of C. selosus, in no case \\ ere . n-ulars I, V, II insert, which is so markedly a character of the Echinidae and Strongylocentroti.lae. It is a remarkable fact that the aberrants of this species fall so definitely in one plan-, I, V. IV. Ill insert, there being only three exceptions to this in the whole 1,278 specimen- examined. In Echinothrix calamaris (11 specimens) oculars are all insert in ten, and in one I, V, IV are insert like the typical character of Centrechinus selosus. In Echinothrix diadema (18 specimen- • all oculars are insert. Centrostephanm asteriscus is interesting as the only Recent species of the CentnohinidM in which the oculars are all exsert in the adult, as they are typically in .lura»ic -pecie- of the 99 TEXT-FIGS. 99-1 01 .-Ocular plate arrangement in Centnvliii.i.hi- im.l 99. Astropyga pulvin.,1,, (Lamarck). Gulf of California. Di.,m. '..I mm. O. The same, section of ambulacral plates showing .dor.il i,nt,ri,-:ition,andof m.,™nlmUrnU n. Tokyo, Japan, 55 fath. Db.. 105 mm. R. T. J. Ooi. ,Un, d in- sert, genitals, split up, especially vent rally (p. 108). 110 ROBERT TRACY JACKSON ON ECHINI. family. In this respect it is therefore primitive; only two specimens were seen. Centro- stephanus rodgersi (text-fig. 96) has typically oculars I, V, IV insert, but in twelve specimens, three have I, V, IV, II, and one has all oculars insert as progressive variants. The range of characters is therefore the same as the dominant ones of Centrechinus setosus. The specimen figured shows a secondary splitting of the madreporite and also unplated tissue ventral to the apical disc, both of which features are seen in Echinothuriidae. In Centroslephanus longispinus (text-fig. 97) all the oculars are insert; only four specimens were seen, but if four agree in a character, it is strong evidence that the typical feature is ascertained. The plates of the peri- proct are numerous and minute ; a few large plates lie on the periphery mainly over the oculars. Astropyga is a very interesting type as. an extreme form of the family. All the oculars are broadly insert (text-fig. 99). In this type the plates are imbricate (p. 74) as seen in text-fig. 100, and leathery tissue exists between the oculo-genital plates as in Echinothuriidae, yet the genus is clearly one of the Centrechinidae as shown by the character of the peristome. In Chaetodiadema pallidum the plates are excessively thin and imbricating. The ocular plates are all broadly insert (text-fig. 98), almost exactly as in Melonechinus (Plate 56, fig. 6). No difference was observed in 36 specimens seen. The periproctal plates on the outer border are exceptionally large, but minute in the center, in this feature being like the young of Centr- echinus (text-fig. 88). Of the Echinothuriidae, only a few specimens have been studied. In Asthenosoma ijimai (text-fig. 101) the oculars are all broadly insert. Ocular and genital plates meet in a continu- ous ring, but are deeply covered on their lateral borders, as are also in part the coronal plates, by living tissue. Genital plates are split up ventrally into many minute plates and the madreporite is split so that the pores exist in several dissociated plates. This type makes a rather close approach to the character of Astropyga. In Phormosoma placenta, when 3 mm. in diameter, the genitals are in contact and all oculars exsert (Plate 3, fig. 8), as shown by Dr. Mortensen (1903, p. 174; 1907, text-fig. 1, p. 24). This is much like the condition in Jurassic Phymechinus (text-fig. 84). Later the oculars travel in and meet the periproct, the oculo-genital ring being continuous as in pro- gressive variants of Centrechinus (text-fig. 95), and in the typical condition of Chaetodiadema (text-fig. 98). Mr. Agassiz (1904) shows this early stage in Phormosoma and in a beautiful series of figures its development to the adult condition (text-fig. 170, p. 149), in which the genitals and oculars are separated so that the periproct comes in contact with the interambu- lacra (p. 63). This character of separation of oculars and genitals occurs as a feature in regular Echini only in the Echinothuriidae, but has been seen as a variant in Strongylocentrotus (Plate 6, fig. 5, and Plate 5, fig. 15). In the corona of Phormosoma (text-fig. 170, p. 149), in the placogenous zone, the ambulacral plates are simple and the young interambulacral plates originate against the oculars as usual in Echini. The suborder Aulodonta exhibits a wide OCULAR AND GENITAI, I'l.ATKS. Ill range of characters as regards oculars, from all exsert, the Jurassic and youthful rhararter, to all insert, and finally oculars and genitals separated by an interspace, a condition <><-eurriiiK typically in no other regular Echini. The oculars reach the periproct in tin- >e<|iienee I, V. IV. II, III, whereas in the two other suborders a different sequence occurs in two of the families, the Arbaciidae and Echinometridae, in which the sequence is V, I and not I, V (WH- table-.. Considering the next suborder, the Stirodonta, we find in the Salcniidac the Mesozoic species of Peltastes have all oculars exsert (127 specimens), as in Peltastes wrighli (Plate 4, fig. 7). In Salenia scutigera (16 specimens) also all oculars are exsert, the same character being seen in many other. Cretaceous species of the genus. In the Cretaceous Salenia petalifera (20 speci- mens) the oculars are all exsert in 95%, but in one specimen, 5%, ocular I is insert as a progres- sive variant, in this feature being like the typical character of Recent species of the family. Of many other species of Cretaceous Salenias seen, but not tabulated, all had the oculars exsert excepting one specimen of Salenia clarki (?) Forbes, in the Jermyn St. Museum, in which ocular I was insert. 102 105 TEXT-FIGS. 102-105.— Ocular arrangement in the Saleniidae (pp. 174, 175). 102. Salenocidaris profundi (Duncan). North of Tristan da Cunha, 1,425 fath. Diam. 10 mm. 667. X 4. Ocular I insert, the typical character; the suranal plate is dorsal to genital 3. 103. Acrosalenia sjnnosa^saiz. Cornbrash, Chippenham, England. Diam. 14 mm. I, V insert, the typical character; the suranal plate is dorsal to ocular III. 104. Acrosalenia hemicidarMes Wright. Forest Marble, near Malmsbury, England. 735 X 8 Oculars I, V insert, the typical character; the suranal plate is dorsal to genital :i 105. Acrosalenia mltoni Wright. Bradford Clay, near Cirencester, England. X 8. All oculars insert, a progressive variant; the suranal plate is dorsal to ocular II The Recent species are very interesting in comparison. As Mr. Agassi* >hmv> Plate 21 fig. 2), in the young of Saknocidaris varispina, all the oculars are en«i M in : of Cretaceous species. Of adult Saknia patkrsoni in 16 specimens, 003 and 31% are arrested variants with all oculars exsert, like the character of 112 ROBERT TRACY JACKSON ON ECHINI. species. The typical condition is shown in Plate 4, fig. 1. In this external view a number of fine madreporic pores are seen, but no ocular nor genital pores are visible. The specimen was cut in two and viewed from the interior (Plate 4, fig. 2) ; here ocular and genital pores are plainly visible, but in place of a number of fine madreporic pores as seen on the exterior, there is only one large madreporic pore, a condition similar to that in cidarids (text-figs. 59, 60, p. 95); also similar to the condition characteristic of the exterior of the plate in very young Echini (text-fig. 131, p. 129). In Salenia cincta (two specimens) ocular I is insert. In Sakno- cidaris profundi (ten specimens) typically, 70%, ocular I is insert (text-fig. 102), but in three specimens, all the oculars are exsert as in the young and in adults of Mesozoic species. Saleno- cidaris varispina (26 specimens) in 73% has ocular I insert (Plate 4, fig. 6), and 27% are arrested variants with all oculars exsert. In Salenocidaris miliaris (16 specimens) 81 % have ocular I insert, and 19 % all oculars exsert. All the evidence is that modern representatives of the Saleniidae have ocular I insert as a typical character, and more or less frequently have all oculars exsert as arrested variants, like their own young and the adults of Mesozoic species. In the Jurassic Acrosalenias a much wider range of characters prevails. The oculars may be all exsert like the Cretaceous Salenias, as seen in Acrosalenia aspera (ten specimens). In Acrosaknia decorata (five specimens) the oculars are all exsert in 60 %, but in 40 % oculars I, V are insert, this as a progressive variant being comparable to the typical character of the next species. In Acrosaknia spinosa (101 specimens) typically, 92%, oculars I, V are insert (text-fig. 103). As arrested variants, in 1 % all oculars are exsert, as in the lower species, A. aspera, and in 7% ocular I is insert like progressive variants of Cretaceous Salenias and also like the typical condition in Recent species (text-fig. 102). In Acrosalenia hemicidaroides (58 specimens) oculars I, V are insert in 86% (text-fig. 104). As arrested variants, 2% have all oculars exsert, 5% ocular I insert. Aberrant variants are rather frequent in this species, 7%. Of these, one specimen has oculars V, II insert, one has I, V, III insert, a rare variant in Echini, and two have oculars I, V, II insert. The species Acrosaknia pustulata is more progressive in character. Of 16 specimens, 63 % have oculars I, V insert as a species character. Of arrested variants, only 6 % have ocular I insert; 19% are progressive, with oculars I, V, IV, and 6 % progressive, with I, V, IV, II insert. One specimen is an aberrant variant with oculars I, V, III insert, IV, II exsert, a rare character in Echini. In Acrosalenia pseudodecorata (text- fig. 168, p. 149), according to Cotteau (1875-'80), typically oculars I, V, IV, II are insert. This is interesting, as it is the only regular sea-urchin I know of in which this arrangement is a specific character, although it is a common or rare variant in a good many species; also, it is the same character that is found in the Cretaceous spatangoid Ananchytes ovatus (text-fig. 175). In Acrosaknia wiltoni (12 specimens), oculars I, V are insert as a species character in 58%; five of the specimens showing this character of the bivium insert are in the Jermyn St. Museum, observations on which were kindly sent me by my friend, Dr. Kitchin. Of this OCULAR AND CKNITAI, I'l.ATHS. 113 species, one specimen, 8%, has ocular I only insert as an arrested variant; of progressive variants, one specimen has oculars I, V, IV insert, two, or 17% have I, V, IV, II, and one baa all oculars insert (text-fig. 105). A large series of observations on this species would be most interesting. The wide range of characters of the Saleniidae and the progressive feature of the same, as shown in the table (pp. 150, 157), are striking. Of the fossil Phymosomatidae I have only seen the ocular plates of I'hymogoma delamur, i of the Cretaceous. In ten specimens of this species all the oculars are insert (text-fig. HM, . a very unusual Mesozoic character. In the Recent Glyptocidaris (Phymosoma) crenularf A. Agassiz, Mr. Agassiz (1873, p. 488, Plate 7a, fig. 8) says that two oculars reach the peri- proct. His photographic figure shows only ocular I insert, and the same condition of I insert exists in the only specimen I have seen, therefore apparently one or two oculars may be insert. On the basis of this evidence, ocular I enters the periproct first in the Phymosomatidae as in the Saleniidae, not ocular V as in the Arbaciidae. Additional observations on species of this family would be of much interest. The Stomopneustidae of Mortensen with the one species. Stomopneustes variolaris, was set apart by that author (1903, p. 133) as a distinct family. I include the family here as its lan- tern has keeled teeth and epiphyses not meeting across the foramen magnum, thus referring it to the suborder Stirodonta. Other features of the lantern associate it closely with Glyptocidaris as described under consideration of the lantern. In Stomopneustes variolaris (64 specimens) typically, 70 %, oculars I, V are insert (text-fig. 108). In 2%, ocular I only is insert as an arrested variant (text-fig. 107), and in 22%, oculars I, V, IV are insert as TK.xT-riu. 106. — Pkymotoma de- progressive variants (text-fig. 109). Aberrant variants are 6%, ,„„„„,,, (I)c9or). senonilin> L« of which one specimen has ocular IV only insert, a very rare Tamarins, Algiers. Diam. 29 mm. variant in Echini, and three have oculars I, V, II insert (text-fig. oculnrs insert. 110). The occurrence of I, V, II insert is of special interest, as this and Acrosalenia hemicidaroides are the only known species in which it has been found ex- cepting in the Echinidae and Strongylocentrotidae, where it is a common character. This with other characters suggests a connection between the families (pp. 180, 214). The Arbaciidae present interesting characters as regards ocular plates in their relations to the genitals. Some species are characterized by having all oculars cxst-rt. others by having three plates insert. Those which have most oculars insert are geographically southern species. The order of incoming is V, I, IV, not I, V, IV, and this sequence is characteristic of this family and the Echinometridae (as here restricted) only in the order of the ('entrechinoida. This is a striking distinction, and only two cases of I coming in before V were seen in over 2,900 Arbaciidae examined, as seen in the table, p. 158. 114 ROBERT TRACY JACKSON ON ECHINI. In Arbatia stellata (78 specimens) the oculars are typically all exsert, 95%. In three specimens, 4 %, V is insert as a progressive variant, and in 1 % oculars V, I, IV are insert. This, although southern, on the basis of ocular plates, is the most primitive of the living species. I •**• in ffl 107 108 TEXT-FIGS. 107-110. — Ocular arrangement in Stomopneusles variolaris (Lamarck). Ceylon. 107. Diam. 62 mm. R. T. J. Coll., 858. X 3. Ocular I only insert, an arrested variant. 108. Diam. 88 mm. R. T. J. Coll., 859. X 3. Oculars I, V insert, typical character. 109. Diam. 74 mm. R. T. J. Coll., SCO. X 3. Oculars I, V, IV insert, a progressive variant. 110. Diam. 86 mm. R. T. J. Coll., 861. X 3. Oculars I, V, II insert, an aberrant variant (p. 93). Arbada lixula (141 specimens) has 94% with oculars all exsert, the typical character; 6 % are progressive variants, with V insert, and one specimen is aberrant with ocular IV alone insert, a very rare variant in Echini. Of Arbada punctulata I was fortunate enough, through the kindness of the Woods Hole Biological Laboratory and other sources, to examine 2,100 specimens from Woods Hole, Massa- chusetts. In this species typically, 87%, all oculars are exsert (text-fig. 111). As progressive variants, 11% have ocular V insert (text-fig. 112). Only two specimens, 0.1%, have ocular I alone insert. In 0.3 % V and I are insert (text-fig. 113), and in 0.4 % V, I, IV are insert (text- fig. 114). This range of characters covers essentially the same series as seen in Arbada nigra, the most progressive species of the genus; but the relative frequency of characters is radically different. In 0.6 % of the Woods Hole specimens the arrangement is aberrant. In nine out of the twelve aberrants found, the arrangement is V, IV alone insert, which is a quite common variant in this genus (see table, p. 164), but rare in other genera. One specimen has ocular IV alone insert, a very rare character, one has I, IV and one has I, III insert, the last a unique variant. Arbada punctulata, from Woods Hole, is distinctly more progressive in character than the two previous species. It is worth noting that in this species, as in most studied, the character was gathered from the first few examined and the commoner variants came along with great regularity, so that the percentages in 2,100 specimens vary very slightly from what they were OCULAR AND GKMTAI. H.ATF.S. 115 when only 100 were counted. Of course the rarer variants arc usually found in only large series, and one cannot know whether they are rare or not without having examined large num- bers. A series of 229 specimens of Arbaria punctulata from Florida is interesting for compari- II TEXT-FIGS. 111-114. — Ocular plate arrangement in Arbacia imiiriuliita (Ijimarck). \\. -JiN) 2<).r>, p. 17:. Of the South American Arbacia spatuligera (76 specimens) in only '.»' , an- tin- ocular- all 116 ROBERT TRACY JACKSON ON ECHINI. exsert. In 30% ocular V is insert, 14% V, I, and 33% V, I, IV. This last is the typical feature by a small margin. This is a curious case in which the typical character falls so nearly on two distinct points. It is interesting also that these two points are not structurally contig- uous. A large number of observations would be interesting. There are ten aberrants, 13 %, which is a very high percentage in the order, and these variants are all V, IV insert, a common aberrant in this genus. It quite probably may be considered an imperfect V, I, IV with I left out by failure to become insert. Mr. Agassiz (1873, p. 403) says of this species, "The ocular plates are in contact with the anal system." From his context this is evidently a misprint for two ocular plates. In no case seen in the genus do all the oculars reach the periproct as the quoted sentence implies. The South American species, Arbada nigra, may be considered the most progressive of the genus with typically three oculars insert. In ten young specimens a few millimeters in diameter, all the oculars are exsert as in the typical condition of adult punctulata. Of adults, in 246 specimens only 1 % have all oculars exsert, the typical character for several species, but an extreme arrested variant in nigra. Ocular V only is insert in 22% and V, I in 12%. Both of these are arrested variants for nigra while they would be progressive variants for most other species of the genus. The typical character of V, I, IV insert (text-fig. 167, p. 149) occurs in 57%. Aberrant variants are unusually frequent in this species, 8%, which is high where a considerable number of specimens were examined. Thirteen of the nineteen variants have V, IV insert, a common variant in the genus, as noted under spatuligera. One speci- men has oculars I, IV, and one has I, V, III insert. Four of the variants have V, I, IV, III insert, a sequence also noted by Clark (1907, p. 193). These are the only cases of four oculars insert seen in the family; it is a rare sequence in the order, but quite common in the Cidaroida. Arbada nigra with a high percentage of three plates insert is in this character the most progressive species of the genus, and it is of importance that three other characters bear out the same conclusion. The auricles of the perignathic girdle quite commonly meet in an arch (text-fig. 228, p. 193), a progressive character not usual in other species (text-fig. 227, p. 193) ; also there are more pore-pairs to an ambulacral plate than in other species, and secondary spines are present, all concurrently marking it as the highest species in the genus. In two specimens of Coelopleurus floridanus, all oculars are exsert as in the more primitive Arbacias, and in the young of the more specialized species of the same. The Arbaciidae present quite a limited range of characters in regard to ocular plates. All plates exsert is the most frequent species feature, or three plates may be insert. All other characters found are variants, either arrested, progressive, or aberrant. Of 53 aberrants seen in the family, 40 are cases of oculars V, IV insert; the other thirteen aberrants are scattering (tables, pp. 158, 164). Of the Camarodonta, which is the last suborder of the Centrechinoida, I have had the opportunity to examine many species and large series of several. 0(VI,AK AM) CKNITAI. I'l.ATKS. 117 Of the first family, the Temnopleuridae, 400 specimens inclmlinn !."> -pcrio li studied as listed in the table, p. 159. The Cretaceous (Ih/phocyphuH rmlinlux h;i- vrry low- genitals and oculars, and the latter are all insert in the x-vm -pecimens seen. Tin Temnopleurus reevesii shows a strong tendency for ocular I to be in.-eri. and tlii- with other cases indicates that this is the first plate to become insert in this family an in the Kchinid.-ie. All the other species have all oculars exsert with rare except ion. Mimici/phut macul" specimens) in one case has oculars I, V insert, the only case seen in the family, and two al>errantx were found, one with ocular IV insert and one with II insert, both very rare occurrence- m Echini as a whole. Mr. Agassiz (1873) and Dr. Mortensen (1904, p. (>.'*) note that one or mon- ocular plates may be insert in species of this family, but in Recent species they are apparently exceptional characters, and, as a whole, the family from present evidence is characterized by oculars all exsert. In the family of the Echinidae I have had the opportunity to examine a large number of m i in in Ma TEXT-FIOS. 115-117.— Ocular plate arrangement in species of Echinus. 115 Echinus affinis Mortensen. Off east eoast of rnit.,1 Slat™, 1,022-1,106 full......*. M 851 X 3. All oculars exuert, extra genital pores, ambulacra! plates compose,! »f !».. .-Inn-iitr. primaries next the ocular. Plates of periproct numerous and very small ,-N.T,,I ing t he surana ' 116a. Same species and locality. R. T. J. Coll., 891. X 3. Ambulacra! plaU* of two ek-m-n,, down to the mid-zone, below which all have three elements (p. 216). 115b The same R T. J. Coll., 892. X 3. No ambulacral plnir* with two *M U6.' Echinus esculentusUnut. English Channel. Diam. 103 mm. R. T. J. Coll.. V.':. Plymouth, England. Diam. 94 mm. R. T. J. O-U.. 7,,, X ,. , Vuh, 1 ta«t. . variant. 118 ROBERT TRACY JACKSON ON ECHINI. specimens, and the characters in regard to ocular plates present a wide range. When oculars become insert, they do so in the sequence I, V, IV, II, III. Rarely V alone is insert, and when this occurs, the character in so far is an approach to the Echinometridae (table, pp. 1(50, 161). Echinus as the type genus of the family is of especial interest. Of Echinus affmis Morton- sen, 605 specimens were observed in the National Museum. The material was from the Albatross Station 2,094, off the Carolina coast in about 1,000 fathoms depth, and had been identified by Dr. Mortensen. This species is remarkable as regards oculars in that all were exsert without exception (text-fig. 115). This is the only species of Echini studied in which with a large number of observations no variation in this respect was seen. One marked pe- culiarity of the species, which seems to have been overlooked, is the fact that, while the ambula- cral plates up to the mid-zone or further consist of three elements each, dorsally the plates to a greater or less extent may consist of two elements, as shown in text-fig. 115. The two-element plates may be wanting (text-fig. 115b) or they may occur only near the upper end of the ambula- crum, while in other specimens they may extend nearly or quite to the mid-zone (text-fig. 115a). In Echinus elegans and E. gracilis all oculars are exsert in the specimens seen. In Echinus csculentus (200 specimens) 97% have all oculars exsert (text-fig. 116), but in 3% ocular I is insert (text-fig. 117). This is the ocular that first comes in in this family when one or more oculars are insert. The specimens with I insert, barring one exception, are small or moderate sized, emphasizing the fact elsewhere noted that the incoming of oculars is a matter of relative development, not of age and size of the individual. This species attains a very large size, my largest from Plymouth, England, being 132 mm. in diameter. Echinus miliaris (129 specimens) has 98% with oculars all exsert, but in one specimen ocular V is insert, a character unusual for the family, and in two specimens I, V are insert, a normal progressive variant for the species. Echinus microtuberculalus (299 specimens) has typically, 96%, all oculars exsert; but in 2% ocular I is insert, in 1% ocular V, and in 0.3% oculars I, V are insert as progressive variants. Two specimens are aberrant with oculars I, IV insert. Of the species Echinus melo, only ten specimens were seen. Of these, 90 % have all oculars exsert, but one specimen, 10%, has ocular I insert as a progressive variant. A speci- men of Echinus melo from the Mediterranean, in the Peabody Museum, Salem, Massachusetts, is of exceptional size, the largest sea-urchin I have seen. It measures 168 mm. in diameter and 132 mm. in height, the circumference measuring 532 mm. The largest sea-urchin as far as known is recorded by Messrs. A. Agassiz and Clark (1909), who say that the type of Sperosoma giganteum A. Agassiz and Clark measures nearly 320 mm. in diameter. As this form is highly flattened, its cubic contents is proportionately lessened. Of Echinus aculus (127 specimens), in 82 % all oculars are exsert, but in 18% ocular I is insert, showing that in this character it is much more progressive than the above species. In a superb series sent me by the Plymouth (England) Biological Laboratory, there is great indi- OCl'LAH AM) (IK.MTAI, I'l.ATKS. I III vidual variation .as regards shape, some being depre.-i-d spheroidal, other- alim.-t conical. The largest specimen measures 145 mm. in diameter and '.Hi mm. in height. Echinus angulosus, which is a distinctly southern species, from South Africa (100 .-pecin,. has typically, 54%, all oculars exsert. In 30% ocular I is insert us :i progn-.-.-ivc variant, and in 4% ocular V alone is insert. In 9% oculars I, V and in 2' :;, I, V, IV are in-erl. One -|>eci- men is aberrant with oculars I, IV insert. This species is distinctly more evolved OH ren oculars than any northern species of the genus. Another southern species is Echinus magellanicus, from Patagonia antl that region. A fine series was studied in the collections of the Museum of Comparative Zoology and the National Museum. In the very young, 2.5 to 5 mm. in diameter (3d .-pecimensi. the oculars are all exsert in 97%, but one specimen, the largest of the series, has ocular I reaching the periproct, as in the adult typically. This immature condition of all oculars exsert is directly comparable to the adult character of the northern Echinus esculentus. In the younger specimen- -tudied (Plate 3, fig. 14) the oculars are broadly exsert, but I is furthest in. genitals are iinperforate, and there is a single madreporic opening in the middle of genital 2; also the suranal plate lill- the periproctal area, all as in young Strongylocentrotus (text-fig. 131, p. 129). On the |>cri- stome the primordial ambulacral plates nearly fill the area, and, as in Strongylocentrotus i Plate 3, fig. 11), the primordial plates Ib, lib, Ilia, 1Mb, Va have an ambulacral perforation whereas the other plates are imperf orate. The largest immature specimen, which has ocular I insert, is 5 mm. in diameter and has four madreporic pores and two periproctal plates in addition to the suranal. Adult Echinus magellanicus (104 specimens) has typically, 88 %, ocular I insert (text-fig. 165, p. 149). In 5% all the oculars are exsert as arrested variants, like the young and the typical character of the northern species of the genus; two of these variants were the largest specimens seen of the species. In 4% oculars I, V are insert as progressive variant-, like the typical character of Echinus margaritaceus, and one specimen has oculars I, V, IV. II insert. Two specimens are aberrant variants, one with oculars I, II insert like the typical character in Gymnechinus, and one with V, II insert, ocular I being excluded by the fusion of genitals 5, 1, as in text-fig. 146, p. 134. Echinus magellanicus has the highest percentage of ocular I only insert of any sea-urchin known. In this species there are ten primordial ambulacral plates in the peristome, as usual, but, as shown by Doderlein (1906), the peristome is otherwise without plates, a very unusual character, seen, however, in some of the Temnopleuridae (p. 84). Echinus margaritaceus, from southern South America and the Antarctic, i- a most inter- esting species. Sixteen specimens were studied, twelve being in the Museum of Comparative Zoology, one in de Loriol's collection, and three were kindly loaned me by Dr. Mortenson under the name Echinus (Sterechinus) neumayeri, but they seem referable to this species as a synonym, and therefore are included with it in the tabulation. Out of the sixteen specimens, in nine, 120 ROBERT TRACY JACKSON ON ECHINI. or 56 %, oculars I, V are insert, as the typical species character. As variants, a most extraordi- nary range of characters is presented for such a limited series of specimens. In one specimen each, the following structural characters are shown: oculars all exsert, I insert, and V insert as arrested variants, and I, V, IV insert, I, V, IV, II, and all insert as progressive variants; one specimen is aberrant with I, V, II insert, a feature rather common in this family. The three specimens sent me by Dr. Mortensen as above noted are two with I, V insert and one with I, V, II insert. The range of normal arrested and progressive variants with the typical character covered by the few specimens seen of this species, is greater than has been found in any other species in the family. Koehler (1906) says of this species that in most cases two oculars reach the periproct, and he shows a wide range of characters in his excellent figures. In his figure 30d oculars I, II are insert, the same as I found in an aberrant E. magellanicus. According to de Loriol (1883), in Echinus verruculatus Liitken, from Mauritius, two oculars are insert, the bivium as shown in his figure. Mortensen (1909) shows in Sterechinus anlarcli- cus Koehler and S. diadema (Studer) from the Antarctic that three, four, or five ocular plates may be insert. His table (1909, p. 75) shows some aberrant arrangements of oculars that I have not seen in any Echini. All the evidence goes to show that the northern species of Echinus have all oculars exsert, or occasionally one or two plates insert as progressive variants. On the other hand, the far southern species have one, two, or more to all plates insert as a frequent variant or as a typical species character (table, p. 160). The genus Gymnechinus is closely allied to Echinus, and* two species have been studied which present extraordinary characters. Of Gymnechinus robillardi I have studied nine speci- mens, seven of which are in de Loriol's collection, in the Geneva Museum. Eight of these, or 89%, have oculars I, II insert and V, IV, III exsert (text-fig. 179, p. 165). One specimen in de Loriol's collection has ocular I only insert as an arrested variant. The essential structure of the apical disc in this species is similar to that of the next. Of Gymnechinus pulchellus Dr. Mortensen most generously sent me ten specimens from the Gulf of Siam and Singapore. The periproct is quite eccentric (text-figs. 177, 178, p. 165), so that a line drawn through ocular III and genital 5 barely cuts the periproct; the genitals are much larger on the left than on the right of this line. In fourteen specimens seen, oculars I, II are insert and V, IV, III exsert in all cases, and Dr. Mortensen writes me that this is always the case in this species. These are the only species of Echini seen (except Strongylocentrotus gibbosus) in which an aberrant arrange- ment of ocular plates is a typical species character. When two oculars reach the periproct, it is typically I and V in all other Echini in over 99% of the 35,184 cases observed. For oculars I, II to be insert is a relatively rare character seen in only thirty-four specimens other than Gymnechinus, and all of these are in the families of the Echinidae or Strongylocentrotidae. Another extraordinary character common in these species of Gymnechinus is for genital 3 or 4 to be exsert or excluded from the periproct (text-figs. 177-179, p. 165), as discussed under consideration of genital plates. OCULAR AND GENITAL I'L.VIT.S 121 The five species of Toxopneustes all have typically ocular* I, V in-ert , hut tl,. ,,,i.|- erable variation shown. Toxopneustes maculatus (five specimens) has 80', with ocular- I. V insert and 20 % with I only insert as an arrested variant. Toxopneiutes pileolus in .is -penmen- has 92% with oculars I, V insert and 8% as arrested variants with I only insert. T«r»pneutte» semituberculatus in 25 specimens has 96% with oculars I, V insert and -I ' , am-.- ted with I only insert, thus being more progressive than pikolus. The next two specie- -how arre.-ted variant-, but also progressive variants, and in an increasing degree. Toxopneustes variegatus, from the West Indies and Florida (1,04:5 specimen-, all adult- . has as the species character 90% with oculars I, V insert (text-fig. 184, p. 165). An arrested variants, 1% have ocular I only insert, one specimen has V only in-ert. As progn variants, 8% have oculars I, V, IV insert and 0.2% have I, V, IV, II insert; 0.8% are aberrant variants. Of the eight aberrant variants, two have oculars I, IV in-ert. \ heing excluded by the fusion of genitals 4, 5 as in text-fig. 144, p. 134; one has oculars V, II in I being excluded by the fusion of genitals 5, 1 as in text-fig. 146, p. 134; and five speci- mens have oculars I, V, II insert as in text-fig. 145, p. 134, a right-handed equivalent of Un- typical progressive variant I, V, IV. The comparison of this species with the next. \vlii<-li i- a close ally, is interesting. Toxopneustes atlanticus (A. Agassiz), from Bermuda, has been considered a synonym of T. variegatus (Lamarck), but it is here considered a distinct species.1 In Toxopneustes atlanticus the species character of oculars I, V insert is taken on early, as usual, but the number of pro- gressive variants typical of adults is taken on at a later stage than in any other sea-urchin studied. I have therefore divided the material into three series: the smallest, 35 to l~> mm. in diameter, which is still developing; a larger series, 45 to 60 mm., which is developed as regards ocular arrangement; and a third series, 60 to 77 mm. in diameter, which includes the largest specimens seen (table, p. 161). In the smallest series, 35 to 45 mm. in diameter (5S7 .-pcci- mens), 81% have oculars I, V insert, a much higher percent than in adults. Of arrest. •. I fused, which mechanically prevented ocular I from reaching the periproct, as in text-fin-. 140 and 148, p. 134. The one specimen with oculars I, IV insert has genitals 4, 5 fused whirl, mechanically prevented ocular V from reaching the periproct, as in text-fig. Ill, p. |:u. This accounts for a trifle over half of the 59 aberrant variants seen in the -peri.- (p. \i\4). Of the remaining 27 aberrants, 25 are cases of I, V, II insert, as in text-fig. I i:(. which ia a right-handed equivalent of I, V, IV, and one specimen is a case of I, V, IV, III in-ert. which is considered as reversionary to the character common in the Cidamida, as in text-fig. 69, p. 98. There is therefore only one variant, which has oculars I, V, III insert, that could in any sense be considered as sporadic, a small number in so large a series. Thi> -peri.- -ho\\- almost exactly the same range of characters as Toxopneustes variegalus, but is markedly more progressive than that species. The immature series as above described p<(- far toward bridging the gap between the two, and a still younger would probably do so completely. In this regard it may be noted that a small lot of 37 specimens of 30 to 35 mm. in diameter, and not listed in the tables, has 92% with oculars I, V insert, no arrested variants, but 5.4% with I, V, IV insert. This shows that at this age it is fully developed as regards the bivium. but has relatively few of the progressive variants, less even than adult T. variegalus. The genus Tripneustes presents interesting characters with a considerable range. Of Tripneustes depressus only 16 specimens were seen, but typically, 75%, oculars I, V arc in 6% are arrested with I only insert; and 19% are progressive variants with I, V, IV insert. In Tripneustes variegalus (72 specimens) oculars I, V are insert in 68% as the species character. Of arrested variants, 7 % have I only, and one specimen has V only insert. Progressive variants are more common, 8% with I, V, IV and 11% with I, V, IV, II insert, Three specimens are aberrant, two with I, II insert as in Gymnechinus pulchellus, and one with V, II insert as in text-fig. 146, p. 134. Tripneustes esculentus is an interesting species on account of its range of characters in ocular plates, both within a locality and in two widely separated areas (table, p. 101). In 193 specimens from Bermuda 61 % have oculars I, V insert as the typical character for that locality. In 2% ocular I only is insert as an arrested variant (text-fig. 123). It is noteworthy that the three specimens showing this character are large individuals, the one figured being the lai. seen in the species. Of progressive variants, 35 % have oculars I, V, IV insert. 2' ", I. V. I\ . II. 124 ROBERT TRACY JACKSON ON ECHINI. and 0.5% all oculars insert. Two specimens are aberrant variants, one with I, V, II and one with V, IV, II insert (text-fig. 196, p. 169); as genitals 5, 1 are fused, this may be considered 127 TEXT-FIGS. 123-127. — Ocular plate arrangement in Tripnemles esculentus (Leske). All figures X 2.7. 123. Bermuda. Diam. 145 mm. R. T. J. Coll., 896. Ocular I only insert, an extreme arrested variant, but the largest specimen seen in the species. 124. Nassau, Bahamas. Diam. 100 mm. R. T. J. Coll., 675. Oculars I, V insert, an arrested variant for the West Indies. 125. Nassau, Bahamas. Diam. 95 mm. R. T. J. Coll., 677. Oculars I, V, IV insert, the typical character for the West Indies. 126. Nassau, Bahamas. Diam. 81 mm. R. T. J. Coll., 653. Oculars I, V, IV, II insert, a progressive variant (p. 94). 127. Bahamas. Diam. 95 mm. R. T. J. Coll., 676. All oculars insert, an extreme progressive variant. an incomplete I, V, IV, II. The species is abundant in Bermuda and attains a large size. The range of variation of Bermuda specimens is similar to that of the southern form, but the percentages are radically different. Tripneustes esculentus from the West Indies and Florida as regards oculars is much more progressive than the Bermuda form. I have divided the specimens into an immature develop- OCULAR AND GENITAL I'LATKS. |j:, ing and a developed series. In the developing series of 55 specimens, varying fro.,, 19 to 60 mm. in diameter, 76% have the bivium insert, quite near to the character <.f adult, from lier- muda. In 9% ocular I only is insert. Of progressive variants, 13% have oculars I, V, I\ insert. This is much below the percentage of adults, in which I, \ . IV in-.-n ,- tin- character in this region. One aberrant has oculars I, V, II insert. In the developed series of 50 to 127 mm. diameter from the \\V-t Indie.- ami Florida specimens), in 38% oculars I, V, IV are insert as the typical character (tcxt-lig. H.V»i. Tin- is the only species of the family in which I, V, IV has been found as a dominant character, although it is a frequent variant in many species. As arrested variants two specimen*, large adults, have V only insert. In 36% oculars I, V are insert (text-fig. 124). Thi- i- an arrested variant for the southern, while it is the typical character for the Bermuda form of the SIXHJMB. As progressive variants 18% have oculars I, V, IV, II insert (text-fig. n>n). Thi- variant i* important as it includes the bivium and posterior pair of the trivium, thus marking the bilateral symmetry in regular Echini as indicated by the incoming of ocular plates. In 1',' all the oculars are insert (text-fig. 127). The aberrant variants of the southern form of Tri/>nru*te* esculentus are rather frequent, 6%. Of the 27 aberrants, one has oculars I. IV in-ert. a- in text-fig. 144, and 24 have oculars I, V, II insert, which is the bivium and right posterior plate of the trivium instead of the left as usual. One specimen has V, IV, II insert , in which ocular I is excluded by the fusion of genitals 5, 1 (text-fig. 1%); and one ha- I, V, IV, III in-ert. a rare variant in the order but common in the Cidaroida. The difference in TripneusU-* > M-I//< ///H* from Bermuda and the West Indian area appears to be marked only in the arrangement of the ocular plates, no other distinction being observed. It is the same difference noted in -everal other species where series from widely separated areas are tabulated. It shows differential character- developing, not distinguishable in a single specimen, but obvious in a large series. Such may l>e considered as incipient species in the process of making. In the total number of 7(K5 specimens tabulated, it is interesting to note that of 30 aberrants, 26 are cases of I, V, II insert, and of tin- other four cases in three (p. 164) the aberration was due to the fusion of two uenitaU mechanically shutting out an ocular. Of Evechinus chloroticus (20 specimens) in 90% oculars I, V are insert, one specimen is a progressive variant with I, V, IV insert, and one specimen is aberrant with I, IV insert. Considering the family Echinidae as a whole, many species of the genus Kchinus have all oculars exsert as a character. One species, Echinus magellanicus, has ocular I only in-ert. and many species in the family have typically oculars I, V insert. Only one specie-. Tn/>nnutes esculentus, has typically oculars I, V, IV insert and this only in its southern localities, or five plates insert are rare in the family except in the southern form of Tn/>neustes csculrntu* and the Antarctic species of Echinus (table, pp. 160, 161). The Strongylocentrotidae includes genera in which the test is circular in outline, with 12G ROBERT TRACY JACKSON ON ECHINI. more than three elements in each ambulacral plate and other characters as discussed in the section on Systematic Classification. Of this family Pseudoboktia indiana (ten specimens) has in all the bivium insert. Sphaerechinus pulcherrimus (48 specimens) has 98 % with oculars I, V insert and 2% with I only insert as an arrested variant. Sphaerechinus granularis (291 specimens) has typically, 89 %, oculars I, V insert. Two specimens are arrested variants with I only insert; three are progressive variants with I, V, IV and three with I, V, IV, II insert. It is rather remarkable that this wide range of characters should be represented by so few specimens, but the same limited occurrence of a typical variation occurs in many species. The aberrant variants of Sphaerechinus granularis are relatively very numerous, 9 % ; two of these have oculars V, IV insert, but the 23 others all have oculars I, V, II insert, a case of the bivium and right hand instead of left hand of the trivium as usual. The frequence of this character suggests that some species might typically have I, V, II insert, but such is unknown (pp. 93, 141). Strongylocentrotus, on account of the number of pore-pairs and plate elements in its compound ambulacral plates, is the most specialized genus of the family in this important structure. It belongs with this family rather than with the Echinometridae (in which it has been placed) on account of the circular, not oval form, and because the oculars become insert in the sequence I, V, not V, I as in that family. I have been fortunate in studying a good series of most of the species and their mutual relations are very interesting (table, p. 162). Strongylocentrotus lividus as regards ocular arrangement is the most primitive species of the genus, as it is also as regards the number of elements entering into the compound ambulacral plates. Of this species I have examined 1,163 specimens, mostly from the Naples Station. Of these, as the species character, 75 % have all the oculars exsert (text-fig. 128). This includes the largest specimens seen (68.5 mm.) as well as smaller individuals. All oculars exsert is also the character of very young specimens of S. drobachiensis (text-fig. 131). In lividus in 17% ocular I is insert as a progressive variant (text-figs. 129, 129a). This character is like the typical feature of young S. drobachiensis when 4 to 5 mm. in diameter (text-fig. 133) and also like arrested variants of the same species (text-fig. 136). In lividus 2% have ocular V alone insert. This is a relatively rare character in the Echinidae, but is more frequent in some species of the Strongylocentrotidae, and in the Echinometridae it is the dominant character when only one ocular reaches the periproct. In lividus 4 % have oculars I, V insert (text-fig. 130), which is a progressive variant for the species, but is the dominant character of S. dro- bachiensis and most species of the genus. One specimen only, 0.1%, has oculars I, V, IV insert. This specimen has ocular IV fused with genital 3, like the ocular IV fused with geni- tal 4 in text-fig. 143, p. 134. The character of oculars I, V, IV insert which is an extreme and very rare progressive variant in lividus is a relatively common progressive variant and frequent in an increasing degree in the higher species of the genus, as shown in the table. The progressive variants in S. lividus occur in small or medium sized individuals, and only OCULAR AND GKNITAI. IM.ATIS 127 occasionally in large' ones, demonstrating as elsewhere claimed that tin- incoming of oculars in a matter of individual variation and not of age. There are 15 atarrants, 1%; of the*- one specimen has ocular III alone insert, a very rare variant in Echini, seen in only two other specimens. Five specimens have ocular II alone insert, also a rare variant. I i>ur -|M'cimen- have I, IV insert, two have I, II, and three have V, II insert. These are aberrant* that occur in species of the Echinidae and especially Strongylocenlrutux drolxichiensit, as shown in the table of aberrants. A large number of specimens of lividus were received after the diagram (text-fig. 176) was drawn and these altered the percentages considerably from what is there shown. Mr. Agassiz (1873, p. 446) said of this species, that one ocular IMflllM the periproct in medium sized specimens, and two oculars in large specimen-. II. did not mention all oculars exsert, which in those I have seen is the dominant character; al-«> two oculars insert is quite as frequent in small specimens as it is in larger one-. Slr»ngyl<>- centrolus lividus is exceptionally interesting as in its dominant character and progressive variant - it presents features in arrangement of oculars precisely like those seen in the development of S. drobachiensis (text-figs. 131-134); also its typical character and progressive variants are directly comparable to the arrested variants or typical character and progressive variai adult drobachiensis (text-figs. 135-138, p. 132). m mm 128 130 TEXT-FIGS. 128-130.— Ocular plate arrangement in SlTongyloccntTotits lindu* (Lamarck). Naplo*, Italy. All X 4.5. 128. Diam. 65mm. R. T. J. Coll., 697. All oculars exsert, tin- typical character. 129. Diam. 37 mm. R. T. J. Coll., 765. Ocular I insert, a progressive variant . Compare text-fi^.. 129a. Diam. 24 mm. R. T. J. Coll., 698. Ocular I insert. 130. Diam. 53 mm. R. T. J. Coll., 766. Oculars I, V insert, a progressive variant. Strongylocentrotus albus from the west coast of South America is an interesting ip In 60 specimens, 53% have all oculars exsert like the typical character in > 128 ROBERT TRACY JACKSON ON ECHINI. siderable range is shown, however, and as all exsert is the typical feature, variants are therefore all progressive. In 2 % ocular I is insert, in 5 % V, in 25 % I, V, and in 2 % I, V, IV are insert. Aberrant variants are frequent, 13%. Of these, one specimen has ocular III alone insert, a variant seen in only two other sea-urchins, four specimens have V, III insert, a unique variation, two have V, IV, III insert, which is the dominant character of Strongylocentrotus gibbosus (text-fig. 156, p. 145), and one specimen has oculars I, V, IV, III insert. It is striking that so many and such peculiar aberrant variants occur in this species, and the same is true of other species from the west coast of South America as noted (table, p. 164). Mr. Agassiz (1873, p. 438) says of this species that all oculars except one are excluded from the periproct, but I find that there is much variation and that all oculars exsert is the specific character. Strongylocentrotus fragilis sp. nov. This new species is striking for its size and the extreme thinness of the test. In shape it is strongly depressed, almost flat ventrally, the ambitus almost coinciding with the base. The color is reddish claret; young specimens are orange red; spines are short, 10 to 20 mm. long, light colored. Ambulacral plates have five elements each. Interambulacral plates ventrally have a row of primary tubercles up to six in number to each plate. At and above the ambitus there is a vertical series of one prominent primary tubercle to a plate in both interambulacral and ambulacral areas. Secondary and miliary tubercles are very small. Pedicellariae are similar to those of S. drobachiensis. In the type the diameter of the apical disc through III, 5 is 18 mm.; of the peristome in the same plane 27 mm. The test is very thin and correspondingly fragile, 0.6 mm. thick at the mid-zone. Of seven specimens in my collection all are of about the same size, but that selected as the type (R. T. J. Coll., 838) measures 94 mm. in diameter at the ambitus and 44 mm. in height. The specimens were collected at Catalina Island, off the south- ern California coast, and were sent me by Ward's Natural Science Establishment at Rochester, New York. A number of specimens are in the collection of the United States National Museum, dredged off the coast of southern California and Oregon in depths of 124 to 339 fathoms. These are smaller, about half grown, and are included in the tabulation of ocular plates. Of this species (55 specimens) 56% have oculars I, V insert as the typical character. Of arrested variants 13 % have all the oculars exsert, 29 % have I only insert, and 2 % have V only insert. There are no progressive variants or aberrants. Photographic figures, in dorsal and side view of the holotype of this species will appear in Part 4 of Agassiz and Clark's Hawaiian and other Pacific Ephini, Memoirs of the Museum of Comparative Zoology, Vol.34; Plate 113, figs. 3, 4. Of Strongylocentrotus mexicanus only six specimens were seen; five have oculars I, V and one has V only insert. In Strongylocentrotus tuberculatus (39 specimens) 92 % have oculars I, (HTLAR AND GENITAL I'l.ATKS. 129 V insert as the character, one specimen is arrested with ocular I only inwrt, one i- progressive with oculars I, V, IV and one aberrant with I, IV insert. Of Strongylocentrolu* depressu* in the few specimens seen all have oculars I, V insert. In such a study as here undertaken it is desirable to work out as fully us po.--.iblr the devel- opment and variation of some one species. I have attempted to do this with Stnmffyloctntrotux drobachiensis as a good representative type and the only one of which I h;id tin- opportunity to accumulate a very large number of observations. A study wa- Mimic of the dcvi-lopMicut and variation in many localities of 33,000 specimens. In handling material and makinn ": vations in large numbers one is likely to make an occasional mistake, so I went over moat of th«> material a second time when a few variants were found that escaped notice on the first count. The character of this species is strongly to have oculars I, V insert, but there is considerable variation in all localities and also there is considerable difference in the range of variat ion bet ween localities. This is set forth in the text and in tabular form on p. 143. The aberrant variant < of this species are all given together in the table of aberrants of the Ontrechitioida, p. I HI. 134 TEXT-FIGS 131-134 — Development of ocular plate arrangement in StrongylocenlTolw drdbachifnti* « I M < : I : 131. Diam.l.2mm. Adapted from Loven, 1892, Plate 4, fig. 27. X about 22. All ocular, t madreporic pore only; the suranal plate fills the i>eriproet (p. 172) 132 Salem Harbor, Massachusetts. Diam. 4 mm. R. T. J. Coll., 767. 133 York Harbor, Maine. Diam. 4.5 mm. II. T. J. Coll., 679. Or,,l:,r I ins,r, , ,,*,-«„. 1 134 York Harbor, Maine. Diam. 7 mm. R. T. J. Coll., 680. In text-figures 132 to 134 the madreporic pores progressively inm,»r in n.n..lM-r »i decreases in size; no genital pores exist (pp. 170, 176). Taking up the development first, Loven (1892) showed that in a very you,,* spmn.™ all the oculars are strongly exsert (text-fig. 131); a suranal plate fill* do not exist, and the madreporite has one large madreporic pore instead older specimen (text-fig. 132) has still all the oculars exsert, although , nearest to the periproct and it compares favorably with the adult character of ; 130 ROBERT TRACY JACKSON ON ECHINI. lividus (text-fig. 128). The suranal plate does not fill the periproct as in the earlier stage after Lov&i, but it lies opposite genital 3, as in Salenia (Plate 4, fig. 1). A few secondary periproctal plates have developed as seen also in the next two figures. No genital pores have appeared, but instead of a single pore in the madreporite, as in text-fig. 131, there are several pores and these increase in later stages (text-figs. 133, 134). At a later stage (text-fig. 133) ocular I has entered the periproct, but all other oculars are exsert. This stage may fairly be compared with progressive variants of S. lividus (text-figs. 129, 129a) that also have ocular I insert. In a still later stage (text-fig. 134) ocular I is fully insert and V is narrowly insert. This specimen, though only 7 mm. in diameter, has taken on the adult character of the bivium insert. In its detail it can be aptly compared with the extreme progressive variant of S. lividus (text-fig. 130). The specimen from which text-fig. 132 was drawn is 4 mm. in diameter, while that from which text-fig. 134 was drawn is 7 mm. in diameter, not far from twice as large, yet the apical disc of text-fig. 134 is only a little larger than that of text-fig. 132. This shows, what was earlier stated (p. 87), that the apical disc proportionally does not keep pace with the size of the test during growth but with development becomes relatively smaller. This relative change is more marked in early than in later stages of growth in which the relative reduction in this species is very slight. In order to test the age at which characters are taken on and to see what might be the range of variation at different ages, a large series of young and adult specimens was collected. The youngest series of 2.5 to 5 mm. in diameter came from several localities on the Maine and Massa- chusetts coasts, but were mostly collected on Chelsea Beach, Massachusetts, by Mr. J. Henry Blake, who kindly gave them to me. Succeeding this age, a series of specimens was collected at Dumpling Islands, North Haven, Maine. This locality is a favorable spot as specimens are abundant and attain an exceptionally large size, so that the range of size and presumably age is quite full. The specimens were collected at spring tides, when with exceptionally low water they could be easily picked off the rocks. All were taken from within a radius of about two hundred feet and all were from as uniform conditions as possible. The specimens were meas- ured with a steel caliper rule; 11,500 specimens from this locality were thus measured and observed, and are divided into two series : what I call a developing series under 30 mm. in diameter, and a developed series over 30 mm. in diameter. This is based on the fact that when over 30 mm., the typical adult character for that locality was established by the percentage having the bivium insert. Younger series of specimens in a progressively increasing degree have less of the full character developed and a greater percentage of individuals of immature character as shown in the table, p. 142. Taking up the developing series, it is safe to assume that at a very early stage all specimens would have all oculars exsert, as in text-fig. 131. Specimens (51) 2.5 to 4 mm. in diameter, the youngest I found, have 29 % with oculars all exsert and 71 % with I only insert. Of these latter, many specimens had the ocular only barely reaching the periproct, indicating that it OCULAR AND GENITAL PLATKS. had but just taken on this position. Specimens (82) 4 to 5 mm. in diameter have 4% with all oculars exsert and 96 % with ocular I only insert. All the specimen up t«, this U|P- lack genital pores. Specimens (800). 5 to 10 mm. in diameter have 0.1 % with all oculars exsert, 4nally in these younger stages. In this 5 to 10 mm. series the aberrant* are: e in only MX other nSrOretilM, namely in Strongylocentrolus lividus and a Microcyphus maculatus. Three specimens have ocular- I l\ . one V, IV, two V, II, and eight I, V, II insert. Before considering the developed series from Dumpling Islands, the variation of the specie* as a whole may be briefly stated. Omitting the developing scries as above drsrrilx-d. 27,417 specimens have been examined from various localities. Of these, thn oculars I, V are insert in 25,766 specimens, 94%, as a strong species character (text-fig. 137). AM an arrested variant only one specimen, 0.004 %, has all oculars exsert (text-fig. 135), as in the young. It is rather remarkable that this variant should be so very rare, as it is the character in two species of the genus. The arrested variant of ocular I insert is rather common, existing in 74<» .specimen-, or 3% (text-fig. 136). When one plate alone is insert in development or as an arrested variant, it is almost always ocular I, for while in the total recorded in this sjMJcies 1,758 cases of ocular I insert occur, there are only eleven cases of ocular V alone insert and these all occur in adults, as shown in the table. As progressive variants, 545 specimens, or 2% have oculars I, V, IV insert (text-fig. 138). Very rarely, in eight specimens, or 0.03%, oculars I, V, IV, II are insert (text-figs. 139, 139a). This is the extreme range of regular variants found in tin- species. Of adults there are 340 aberrants, or 1.2%. The aberrant variants in the species reach 1.2% and, as shown in the table of aberrant- (p. 164), cover a wide range of characters, but more than one half of the total are cases of I, V, II insert. The principal aberrant variants are shown in text-figs. 140 to 149, which figures also serve to show the principal aberrant variants of the order Centrechinoida. Taking up tin- aberrant variants of Strongylocentrotus drobachiensis, and here including the whole lot of 33,000 specimens, both young and adult, we find that very rarely ocular IV alone may be insert text - fig. 140); this was found in only three cases, while still more rarely (two cases) ocular II alone was insert. In no case was III alone insert. Oculars I, II alone are occasionally insert (29 cases) (text-fig. 141). This character is typical of Gymnechinus pulchellux (text-figs. 177, 178). As a left-handed equivalent of this last, oculars V, IV alone may be insert, 33 cases (text-fig. 11 J . This character is more frequent in the Arbaciidae, as there noted. An ocular occa.-ionally fuses with a genital (text-fig. 143). This has been found in 103 cases and may occur between any of the oculars with either of its adjacent genitals. Oculars I, IV may be insert i text-fig. 141'. In the great majority of the 81 cases of this aberrant seen in this species, genitals 4, 5 are fused as in the figure, mechanically shutting out ocular V, so that it may reasonably be considered an imperfect I, V, IV insert. Oculars V, II may be insert (text-fig. 146), and in all the 34 cases of this variant seen genitals 5, 1 are fused, mechanically shutting out ocular 1. so that this variation may be considered an incomplete I, V, II insert. Oculars I. V. II may be insert, 215 cases (text-fig. 145), and this is the commonest aberrant variant found in the species 134 ROBERT TRACY JACKSON ON ECHINI. ffi I n TEXT-FIGS. 140-149. — Principal aberrant variants in ocular plate arrangement of Strong yloccnlrolus drobachiensis (O. F. Mtiller) (see pp. 93, 94, 164). 140. Calderwood Island, Maine. Diam. 32 mm. R. T. J. Coll., 878. X 3. Ocular IV only insert, a rare variant. 141. Dumpling Islands, Maine. Diam. 64 mm. R. T. J. Coll., 849. X 3. Oculars I, II insert; compare Gyinnechi- nus, text-figs. 177-179, p. 165. 142. Dumpling Islands, Maine. Diam. 60 mm. R. T. J. Coll., 850. X 3. Oculars V, IV insert, a left-handed equivalent of text-fig. 141. Madreporic pores in genitals 2 and 1 (p. 172). 143. Dumpling Islands, Maine. Diam. 42 mm. R. T. J. Coll., 867. X 3. Oculars I, V, IV insert, but ocular IV and genital 4 are fused (p. 168). 144. Dumpling Islands, Maine. Diam. 47 mm. R. T. J. Coll., 852. X 3. Oculars I, IV insert, an incomplete I, V, IV, due to the exclusion of V by the fusion of genitals 4, 5 (p. 167). 145. Dumpling Islands, Maine. Diam. 56 mm. R. T. J. Coll., 851. X 3. Oculars I,. V, II insert, the commonest aberrant variant, a right-handed equivalent of the normal progressive variant, I, V, IV insert (pp. 93, 141). OCULAR AND GENITAL I'LATKS. 135 146. Dumpling Islands, Maine. Diam.58mm. R. T. J.Coll., H.W. x .T 0,-ulnn. V, II iiwrrt, an incomplrt* I \ II, due to the exclusion of ocular I by the fusion of gcnitalo 5, 1. Madrcporic porw are in grnital 2 and ocular 111 (p. 172). 147. Dumpling Islands, Maine. Diam. 54 mm. It. T. .). Coll., 864. X 3. Ocular* I, IV. II irwert, an incompfet* I) V, IV, II, due to the exclusion of ocular V by the fusion of genitals 4, .1; very "***• variant. Ocular III w opposite Coi- tal 2 only, not at the junction of genitals 2 and 3, as usual (p. 167). 148. Calderwood Island, Maine. Diam. 50 mm. R. T. J. Coll., 855. X 3. Ocular* V, IV, II inaert, an incomplete I> V, IV, II, as in text-fig. 147, but due to the exclusion of ocular I by the fusion of genital* 5, 1, a very rare variant (p. 167). 149. Dumpling Islands, Maine. Diam. 9.5 mm. R. T. J. Coll., 856. X 12. Ocular* I, V, IV, III inm-rt, a very rare variant. Genitals 3 and 4 split by secondary sutures (compare text-fig. 09, p. 98). and family. It is a right-handed development of three plates insert, which is usually expressed as I, V, IV insert. One case of I, IV, II (text-fig. 147) and two of V, IV, II insert (text-fig. 148) were found, both very rare variants; in these an ocular of the bivium is mechanically shut out by the fusion of the adjacent genitals. In two cases oculars I, V, IV, III are insert (text- fig. 149), and these were the only cases found in which ocular III entered the periproct in this species. From the above it is seen that in the 33,000 specimens there are 402 aberrants, which i- 1.2 % as stated. Of these, 215, or more than half, have I, V, II insert, and 92 are cases in which the fusion of two genitals excluded an ocular causing the irregularity. This leaves only 92 or 0.28 % as somewhat scattered aberrant variants. Returning to the Dumpling Islands series, we find that those exceeding 30 mm. in le irregularities of a small series are eliminated. The series of 30 to 40 mm. in diameter (1,750 specimens) has 2.4% with ocular I ii 95% have I, V; and 0.9% have I, V, IV insert. The aberrants are unusually frequent in this lot, 36 specimens or 2%. Of these variants, ten specimens have oculars I, IV insert: three have V, II; five V, IV; and eighteen I, V, II insert. The series of 40 to 50 mm. in diameter are about the size of the larger specimen^ met with in most localities. Of this size (2,900 specimens) 2.8% have ocular I only insert, a relatively high number, but on the principle of chances some fluctuation must be expected. One speci- men has V only insert, being one of two such found in the whole lot. In 95% oculars I, V. and in 1.2% oculars I, V, IV are insert. The aberrants are 2%. Of these, three sj>eeimens have oculars I, II insert; nine have I, IV, three have V, II, two have V, IV, and 27 have ocul;« V, II insert. The series of 50 to 60 mm. in diameter may be considered large specimens. Of this sue (1,272 specimens) 2.4 % have ocular I only insert; 94 % have I, V, and 1.3 ' , have I. V.I \ i. The arrested and progressive variants are practically the same as in the :«) to 40 mm. x-ri and the progressive variants as in the 20 to 30 mm. series. The aberrant variants are J 136 ROBERT TRACY JACKSON ON ECHINI. They are: two specimens with oculars I, II insert; two, I, IV; three, V, IV; two, V, II; six- teen, I, V, II (text-fig. 145) ; and one with I, IV, II insert and V, III exsert. In this last case genitals 4, 5 are fused (text-fig. 147), shutting out ocular V, so that it is evidently a case of incomplete I, V, IV, II. It is the only instance found of just this combination in any sea-urchin. At Dumpling Islands this species attains an exceptionally large size, and the next two sizes could not be collected often at other localities with which I am acquainted. The series 60 to 70 mm. in diameter is a small one (121 specimens) compared with the preceding. One specimen, 0.8%, has ocular I only insert, 95% have I, V, and two specimens, 1.6%, have I, V, IV insert. The second specimen was found in the last few examined. This is mentioned as, if by chance it had not been found, the percentage of progressive variants would have been much less, smaller even than in specimens 20 to 30 mm. in diameter. The generally expressed view that more oculars are insert in large specimens is quite without foundation in any species as far as my observations go. The aberrant variants of this series are 2%. Two specimens have oculars I, II insert (text-fig. 141), and one has I, V, II insert. The last series, 70 to 75 mm. in diameter (seven specimens), has 100 % with oculars I, V insert. In a larger series prob- ably some variants would have been found, but as far as it goes, it emphasizes the fact borne out by other species that the largest specimens have the species character, and that variants, both arrested and progressive, are more frequent in smaller individuals. This large series from Dumpling Islands demonstrates that very young specimens show the passage from all exsert to ocular I insert and then to the bivium insert in ontogeny; older but yet young specimens show that progressive variants may appear even to the full specific proportion before the full percentage of the specific character is established. Specimens half- grown (30 mm. or more) have about the same percentage and range of the arrested, typical, and progressive characters as in fully adult specimens. Large individuals have no greater number of oculars insert than smaller individuals, excluding youthful stages. Through the kind help of friends and from personal collecting, series of Strongylocentrotus drobachiensis have been obtained from a number of localities for study, to see what the specific range might be. In all localities the character is for oculars I, V to be insert, but the percentage of this character varies with locality, and also the relative proportion of arrested and progressive variants varies very widely. The localities represented are arranged in the table on the basis of these characters (p. 143). The most primitive type of the species seen is from Gullmar Fjord on the Swedish coast of Skagerrak. From this locality Dr. Mortensen kindly sent me fifty specimens. On inquiry he informs me that this fjord receives a considerable volume of fresh water from a river, so that the water is at times distinctly brackish. The specimens are medium sized individuals. Thirty percent have ocular I insert and only 58 % oculars I, V insert. There are no typical progressive variants, but a high percentage of aberrants, 12 %. Of these, one specimen has oculars I, II, OCULAR AND (JENITAI. IM 137 one has I, IV, and four have I, V, II insert. Specimens from this locality make an approach in primitiveness of structure to that shown in the 5 to 10 mm. series from Dumpling I-land«, an regards the percentage of I, and I, V insert; also in both there arc n<» ca*os of I, \ . IV iiutert, but a considerable number of I, V, II. The Gullmar specimens arc peculiar sis in all individual* the spines are of a light purplish color with only an indication of tho usual green. At Dumpling Islands the specimens are typically bright green; but in eight or ten out of the .-eric, then- collected the spines are light purplish, so close to the Gullmar typical color that a tecimon placed with them could not again be selected by its difference. The next step in advance is found in a series which I collected at Pulpit Harbor, North Haven, Maine. This locality is a deep, very narrow bay, well removed from the OJM-II ocean. It receives fresh water from a considerable lake at the head of the bay and also by leaching from the shores, so that the water is distinctly brackish. The water is shallow, ami the Kchini, which are extremely abundant, were collected at low tide near the bridge which crosses thi* narrow bay. All individuals below 30 mm. in diameter were eliminated, and tho-e tabulated ranged from this size up to 58 mm. in diameter. In this series (1,700 specimens > 10' , have ocular I only insert, one specimen has ocular V alone insert; 88% have oculars I, V, and 0.5% have I, V, IV insert. This is a large percent of arrested and small percent of progressive variants for the species. The aberrants are 1%. Of these, three specimens have oculars I, II ii four have I, IV; one has V, IV; and six I, V, II insert. As a whole, the Pulpit Harbor scrie^ makes a fairly close approach to the character seen in the immature 15 to 20 mm. -eri« - from Dumpling Islands, the similarity being in the percentages of the several characters and tin- relatively high number of aberrants with oculars I, V, II insert (table, pp. 1 1_. 1 i:< A number of Strongylocentrotus drobachiensis dredged off St. Pierre, south of Newfoundland, at the mouth of the St. Lawrence River, were kindly given to me by Mr. Owen Bryant . ( )f t his lot (194 specimens), all good sized individuals, 6% have ocular I only insert. '.»•_>' , I. V, and 0.5% I, V, IV insert. The aberrants are 2%, one specimen having I, IV and two I. V. II ii The specimens of this locality are closely equivalent to the 20 to 30 mm. series from Dumpling Islands, as regards the percentage of insertness of oculars. A number of the St. Pierre speci- mens (22) are of a light cream color, both tests and spines, giving them a very peculiar appear- ance. Specimens of a similar color occur also in material from Puget Sound, Washington, but I have not seen such from any other localities. As regards structural characters, the series described from Dumpling Islands. North Haven, Maine, would fall in place at this point, as indicated in the table (p. 143) The Dumpling Islands and the Calderwood Island next considered are both situated in the F,,\ Nand Thoroughfare, at the mouth of Penobscot Bay, into which empties the large river of tho same name. At Calderwood Island, when visited at extremely low eoune of tides, the Kehini are vastly abundant, so numerous that in one morning before breakfast, with the help of an ass 138 ROBERT TRACY JACKSON ON ECHINI. tant, I collected the 7,600 specimens here described. At this locality individuals do not attain a very large size, and observations were on various sizes without measurements, though none was very young. Of arrested variants, 3.2 % have ocular I only and 0.07 % have V only insert; 94 % have I, V; 1.6 % have I, V, IV; and 0.03 % have I, V, IV, II insert, thus presenting a wide range of characters. Aberrant variants are of many characters as might reasonably be expected in a large series, yet are relatively not numerous, only 76 specimens, or 1 %. Of these, one specimen has ocular IV only insert (text-fig. 140), a very rare variant in Echini; six specimens have oculars I, II insert; seventeen I, IV; nine V, IV; and eight V, II insert. Thirty-two specimens have oculars I, V, II, and two have V, IV, II insert, the latter a very rare variant (text-fig. 148). One specimen has oculars I, V, IV, III insert, II exsert. This very rare variant was seen in only one other specimen of this species (text-fig. 149, p. 134). The character of the Echini as regards ocular plates from the Calderwood locality is practically the same as in the Dumpling Island specimens, but is slightly more progressive. At York, Maine, a series was collected in tide pools. The conditions are rocky shores exposed to the open ocean. The specimens (2,700) varied in size from small to large, but none was very young. Only 0.9 % have ocular I alone insert, a smaller proportion than in any locality previously considered. Oculars I, V are insert in 97 %, the highest average of any locality studied. As this is the species character, specimens from this locality may in a sense be considered as the nearest approach to the ideal of the species. As progressive variants, 1.4 % have oculars I, V, IV insert and one specimen (text-fig. 139, p. 132) has oculars I, V, IV, II insert. The aberrants are relatively few, 0.9 %. They are two specimens with oculars I, IV insert; six with V, IV; six with V, II; and eleven with I, V, II insert. It is interesting to see that in these later series, as the relative frequency of oculars I, V, IV insert increases, con- currently the number of the aberrant variant I, V, II insert proportionately decreases. Up to this point the series from the several localities have gradually decreased in the prim- itive character of ocular I only insert and gained in the species character, the bivium insert, finding its maximum of 97 % in the York locality. There has also been a slight gain gradually in the progressive character of oculars I, V, IV insert. From here on in the succeeding locali- ties considered, with slight fluctuations, the bivium gradually decreases its dominance and the progressive variants concurrently increase, thus approaching other species of the genus which are further evolved in this character (compare pp. 143 and 162). Mr. A. P. Romine very kindly sent me a fine series of this species from Friday Harbor, Puget Sound, Washington. The locality is at the entrance to the Sound, and the water is presumably typically salt. The specimens average large, those tabulated ranging from 40 to 85 mm. in diameter. A specimen of S. drobachiensis from Alaska, in the United States Fish Commission Collection, measures 90 mm. in diameter, but otherwise the maximum Puget Sound specimens are the largest seen or recorded. Of this series, in 1,200 specimens, 96% OCULAR AND GENITAL PLATKS. 139 have the typical character of oculars I, V insert. In 0.9%, ocular I only is in-ert. and in 2.6 % oculars I, V, IV are insert; one specimen, 0.1 %, has I, V, IV, II in-ert. It i- int. ing to see how regularly this rare progressive variant crops out in almoHt every large series. The aberrant variants are few, eight specimens, or 0.8%. Of tin-,., tw., have \ I\ . ami six I, V, II insert. In the percentage of typical arrangement also of arrested, pn>nr<- and aberrant variants, the Puget Sound specimens are extremely close to those from York. Maine, but are slightly more progressive. In this lot there are ten specimens, 1 <;; , which arc light cream color, similar to the color commonly seen in Echinus aculus or affinis. Thi- peculiar color was also seen in specimens from St. Pierre, Newfoundland, as noted, but from no other locality. It is interesting to see how closely one can correlate not only the typical character but also -the relative frequence of variations in specimens collected at such widely distant localities. From Massachusetts Bay, mostly in tide pools at Nahant, a series of 5SX .-pecimen.- \\:i- examined. Of these, 1.4 % have ocular I only insert; 95 % have I, V; and 2.2 ' , have ocular- I, V, IV insert. One specimen (text-fig. 139a, p. 132) has oculars I, V, IV, II insert, the extreme progressive variant of the species. The aberrant variants, 1.5%, are one >pecimcn with oculars I, IV insert; one with V, IV; and seven with I, V, II insert. This is an unusually large proportion of I, V, II for a locality where I, V, IV is at all common. Through the kindness of Mr. Dwight Blaney of Boston, and from my own collecting, a series of specimens was obtained from Frenchman's Bay, Maine. They were all from -hallow water, and varied from small to large, though none was very young. Of this serie- 1. (MX) specimens) one, 0.03%, has all oculars exsert, an extreme and very rare arrested variant text- fig. 135, p. 132). It is the only one found in the species except as it occurs in a very early stage as a developing character. In 1.9% ocular I only is insert; in 94'',' ocular- [. V; and in 3.3% oculars I, V, IV are insert. In two specimens, or 0.05% oculars I. V. IV. II are insert. This shows a distinct gain in progressive variants over those previously rnn>idcred. In several of the following series there are no cases of I, V, IV, II insort, but this is so rare a character, that it cannot be expected in small series. In large series it appear-, how- ever, with marked regularity as shown in the table. The aberrant variants of Frenchman's Bay are 47 specimens, or 1 %. They are in detail, one specimen with ocular II only insert, a very rare variant; eight have oculars I, IV insert; four have I, II; five V. II; and twenty- nine have I, V, II insert. From Harpswell, Maine, through the kindness of Dr. F. D. Lambert, of Tufts College. I have 300 specimens. They are all large individuals. Of arrested variant-, ocular I only insert, one has V only, 92 % have I, V, and 3.7 % I, V, IV insert. The alx-rrant> are 1 %. Of these, two specimens have oculars V, II insert and one I, V, II insort. Through the kindness of Mr. J. Henry Blake, specimens were obtained from Truro, Massa- 140 ROBERT TRACY JACKSON ON ECHINI. chusetts. This is of interest as the most southern locality represented. The specimens were dredged in shallow water under open ocean conditions. In this series there are many small us well as large specimens, so for comparison they are divided into two sets. The first from the Truro locality, is composed of small specimens, 20 to 30 mm. in diameter. In this set (1,100 specimens) only 0.3 % have ocular I only insert. This is a smaller proportion than in the larger series, doubtless a mere coincidence, but it shows that the specimens are fully developed in regard to this character, whereas the 20 to 30 mm. series from Dumpling Islands (see table, p. 142) is less developed in this character than larger individuals of that locality. The Truro specimens of this series have 96 % with oculars I, V insert, a higher percent than the larger. On the other hand, of the progressive variant I, V, IV insert, there are only 2.9 % instead of 4.3 % as in the larger series, indicating that this character develops in later growth. Of aber- rant variants there is 1 %, consisting of five specimens with oculars I, IV and eight with I, V, II insert. The second set from the Truro locality consists of larger specimens ranging from 30 to 60 mm. in diameter. In this series (1,700 specimens) 0.6 % have ocular I only insert, 94 % have I, V, and 4.3 % are progressive variants with I, V, IV insert. One specimen, 0.06 %, has I, V, IV, II insert. The aberrant variants are 1 %, of which there are six specimens with oculars I, IV insert; two with V, IV; two with V, II; and ten with I, V, II insert. This series has gained in I, V, IV insert at the expense of the I, V as compared with the smaller series. It is of interest as it is marked by the least number of arrested variants and the greatest number of progressive variants of any locality on the New England coast (table, p. 143). A series of 200 specimens from Labrador is interesting as representing a northern locality. Arrested variants with ocular I only insert are rather frequent, 2.5 %. The specimens are so small that it is possible that some of them are developing individuals and a series of larger specimens might show fewer arrested variants. The same statement also applies to the next series considered. The Labrador lot has 87.5 % with ocular I, V insert, and 7.5 % of progres- sive variants with oculars I, V, IV insert. Aberrants are 2 %, being three specimens with oculars I, IV, and one with I, V, II insert. Through the kindness of Dr. Mortensen I have a series of 35 specimens from Iceland and the Faroe Islands. These both show practically identical characters, so are treated together. They are of special interest as being the most northern locality represented and also as showing the most progressive character seen in the species. The specimens are medium sized, a few are small. Of arrested variants 11 % have ocular I only insert, a strikingly high percentage for the species and especially as the progressive variants are frequent. Only 60 % have oculars I, V insert, almost the lowest percentage known in the species, and 20 % have as progressive variants oculars I, V, IV insert. This is way ahead of that known from any other locality and is directly comparable to the progressive variants of Strongylocentrotus purpuratus from Cali- fornia, which in this respect is the most progressive species of the genus. The aberrant variants OCULAR AND GENITAL PLATES. 1 1 1 are relatively numerous, three specimens, or 9 %. Of these, one has oculars I, IV ami i wo have I, V, II insert. A large series from that region would be well worth studying. The study of Strongylocentrolus drobachiensia from different loc-alitir- \\a- mad.- on thi- species as an available form, to gather what might be the range in differential development under various conditions and in different areas. The result >h<>\\s that tin-re is a very con- siderable difference with locality, and the same fact is borne out by observations on ot her >p. as shown in Cidaris affinis, Arbacia punctulata, Tripneustes esculentus, and Echinometra lucunter. It opens up a line of inquiry which would be worth following further in these or other Krhini. To ascertain what is the cause of variation is difficult, so many factors enter into such a problem. The localities, however, represent certain groups of conditions, and percentages of arrested or progressive variants have a certain approximation to those groups, so that tenta- tively they may be ascribed to these conditions. The most primitive scries occurred in deep reentrant fjords, or bays, well removed from the open sea, which receive a considerable incre- ment of fresh water. Such are Gullmar Fjord and Pulpit Harbor. The next more advanced group occurred near the mouths of large rivers, St. Pierre, Dumpling Islands, and Calderwood Island. Up to this point the arrested variants are in all localities more numerous than the progressive. The third group occurred in open sea water well removed from large rivers, the Truro locality being the purest open ocean conditions of the group; such are York, Pi i get Sound, Massachusetts Bay, Frenchman's Bay, South Harpswell, and Truro. In all of tin •-«• the progressive variants are more numerous than the arrested variants. The last group is far northern, and as far as known, from pure open ocean conditions, Labrador, Iceland and Faroe Islands. Here the progressive variants are markedly in advance of arrested variant > and also of the localities farther south. In the series considered a curious relation is brought out in regard to which plates meet the periproct when three are insert. The normal progressive variant for the species, family, and order is for oculars I, V, IV to be insert, and the equivalent right-handed aberrant i- I. V, II. If the I, V, IV is rare, then the I, V, II is relatively frequent, as in the Dumpling Islands series of 5 to 20 mm. in diameter; or in the adults of that locality, Gullmar Fjord, anil Pulpit Harbor. On the other hand, if the I, V, IV is relatively more common, then the I. V. II in.-ert becomes much less frequent, as seen in the series from Frenchman's Bay, Truro, and Labrador. This same relative preponderance is brought out also by other species. A striking case is Sphaerechinus granularis, in which (p. 126) I, V, IV is rare, 1 %, whereas I, V. II is common. 8 %. On the other hand, in Toxopneustes atlanticus, I, V, IV is common, 28 %, but I. V. II is rare, only 1 % (p. 122). Returning to the consideration of other species of Echini, in Slrongylocentrotus eurylhro- grammus, a southern species from Australia, of 56 specimens, 93% have oculars I. V i; As an arrested variant, 2 % have ocular I only insert and, as progressive variant-. :> ' , have 142 ROBERT TRACY JACKSON ON ECHINI. oculars I, V, IV insert. It is interesting to see that in this far distant locality the same laws of ocular arrangement hold as on the New England coast. In Strongylocentrotus franciscanus a very young specimen (text-fig. 150) has no genital Table of Development of Ocular Plate Arrangement in Strongylocentrotus drobachicnsis, find Variation of the same in one Locality (text-figs. 131-149, pp. 129, 132, 134). ^ t tj t ti 0) * Si 8 B £ O i <£ s h-H *-« ^ H-I fc M H-T I-H >— r M g a* > C a s | 1 | c 1 HH HH tf CD i •8 E .§ c > > > • -4-i C 6 1 § "3 HH 1 5 M HH "3 i fc o 6 1 1 o 1 = a 51 specimens 29* 71 133 Developing series, Maine and 2.5—4 mm. diam. 15* 36 Massachusetts 82 specimens 4 96 4-5 mm. diam. 3 79 SOO specimens 0.1 46 53 ; - 5-10 mm. diam. 1 369 419 11 2,000 specimens 19 80 o.s j 5,450 Developing series, Dumpling 10-15 mm. diam. 371 1,596 6 87 Islands, North Haven, Maine 1,400 specimens 7 92 0.4 ; 15—20 mm. diam. 97 1,289 5 9 1,250 specimens 5 95 ; O./ ^ 20-30 mm. diam. 60 1,161 T3 1 15 1,750 specimens t.4 95 0.9 1 30-40 mm. diam. 42 1,657 15 36 2,900 specimens 8.8 O.OS 95 /.* ; , 40-50 mm. diam. 80 1 2,74 i 34 44 6,050 Developed series, Dumpling }.'2~'2 specimens *-4 0.08 94 /.* i Islands, North Haven, Maine 50-60 mm. diam. 31 1 1,198 16 26 121 specimens 0.8 95 1.6 I 60-70 mm. diam. 1 115 2 3 7 specimens 100 70-75 mm. diam. 7 •Italic numerals represent percentages, Arabic numerals the number of specimens observed. OCn.AR AXirr.KXITAL PI.ATi ] j;t Table of Ocular Plate Arrangement and Variation in Strongylocentrotu* drobachientu from Different Localities (text-figs. 135-149, 178, pp. 132, 134, 153). - = ~ z a 1 -- -- d £ — ;- • e ^ ± - - •= ^ - - : 1 j3 | > | 1 - ; . sE = ! 1 I : = -^ 50 Gullmar Fjord on the Swedish coast of Skagerrak 30 « 15 6 1,700 Pulpit Harbor, North Haven, Me., 30-58 mm. diam In 0.09 «8 I 17:{ 1 1^03 9 14 194 St. Pierre, Newfoundland g a? m a i> 1 Dumpling Islands, North Haven, Maine. (This t.e 0.05 96 / / ' series, given above, belongs here.) 6,060 developed specimens, 30-75 mm. diam. 7,600 Calderwood Island, Fox Island Thoroughfare, Maine S.8 0.07 »4 1.8 0.05 1 24.' 5 7,157 118 2 •J.TCO York, Maine (text-fig. 176, p. 153) 0.9 0.0^ »7 ' ^ 0.04 I 25 1 2.610 38 1 25 1,200 Friday Harbor, Puget Sound, Washington, 40-85 0.9 96 «.ff O.I ; mm. diam. 11 1,1* 31 1 8 M Massachusetts Bay, mostly from Nahant, Mass. 1-4 «5 t.S o.« ff 8 557 13 1 9 4,000 Frenchman's Bay, Maine OJ08* 1^9 94 5.5 0.05 f 1* 75 3,745 130 2 47 300 South Harpsweil, Maine t.7 0.5 M / 9 1 .-:; 11 3 Truro. Massachusetts, series 20-30 mm diam. (1 100 0.3 as 1.9 \ ; specimens) 3 1,062 : MOO Sum* locality, Httif-n 30-60 mm diam (1 700 speci- 0.8 ! 0.05 / mens) 11 1.595 73 1 20 M Labrador f-f 0.6 87.5 5 5 1 175 15 4 35 Irclxnrl and FanV- Idamfc 11 00 K 9 4 n 7 | 3 33,000 20 ,758 11 W.231 • 0 ^ •Italic numerals represent percentages, Arabic numerals the number of specie 144 ROBERT TRACY JACKSON ON ECHINI. pores and ocular I only is insert; an older, but still very young specimen, 22 mm. in diameter, has the bivium insert, the species character. Of adults, 179 were examined, including a superb series of 61 specimens from Friday Harbor, Puget Sound, Washington, kindly sent me by Mr. A. P. Romine. Of this species, in 87 %, oculars I, V are insert (text-fig. 152). In 1 % ocular I alone is insert as an arrested variant. Both of the two specimens showing this character are adults, one being very large, 145 mm. in diameter (text-fig. 151). Of progressive variants n v 152 153 TEXT-FIGS. 150-153. — Ocular plate arrangement in Strongylocentrolus franciscanus A. Agassiz. 150. Monterey Bay, California. Young. Diam. 5.5 mm. R. T. J. Coll., 552. X 6.5. Ocular I alone insert as a developing character, no genital pores. 151. Friday Harbor, Puget Sound, Washington. Diam. 145 mm. R. T. J. Coll., 906. X 1.6. Ocular I alone insert, an arrested variant. 152. California. Diam. 154 mm. R. T. J. Coll., 724. X 1.6. Oculars I, V insert, the typical character. An exceptionally large specimen (text-figs. 166, p. 149; 199, p. 171). 153. Vancouver, British Columbia. Diam. 126 mm. R. T. J. Coll., 725. X 1.6. Oculars I, V, IV insert, a progres- sive variant. 11 % have oculars I, V, IV insert. The specimen from which text-fig. 152 was drawn is ex- ceptionally large, 154 mm. in diameter, the largest seen, yet it has only the bivium insert; the progressive variants were all considerably smaller. One specimen only is aberrant with oculars V, II insert, ocular I being excluded from the periproct by the fusion of genitals 5, 1 as in text-fig. 146. Of the three adults here figured it is noteworthy that the largest specimen (text-fig. 152) has the smallest apical disc and the next smaller specimen, which is an arrested variant (text-fig. 151), has the largest apical disc (p. 87). The most progressive species of the genus is Strongylocentrotus purpuratus from California. Through the kindness of Dr. W. K. Fisher, I received a fine series of specimens; with others, 120 have been studied. In this species 77 % have oculars I, V insert, 1 % is arrested with I only insert, and 22 % are progressive variants with I, V, IV insert. The species eury- throgrammus, franciscanus, and purpuratus, although they have oculars I, V insert as a typical OCULAR AND GENITAL I'l.ATKS. I ,- character, have a larger number of progressive variants as r,.Kar,N oeute plates than anv other species of the genus (table, p. 162). Strongylocentrotus gibbosus is a most unusual sea-urchin in that it ha* deeply bedded in the periproct a commensal crab, Fabia chilensis Dana. This mil, i, a v, , „„ Mwebtoj but one specimen in 24 studied has no trace of a crab (text-fig. 155). Tl,,- Utomaloai MM tion of the crab very deeply modifies the relative position of (!„• o,,,lar plate-. The crab in the cases seen occupies a position close to ocular IV and genital : how., in the figures, and no variation was noted in this position. This spe,-ie> :,,„! (lyin.H-.-hi.Mi.- an- the only Echini studied in which an aberrant arrangement of ocular plat,-, i. th,- dominant ,,i,,.. In 24 specimens one has I, V, IV insert (text-fig. 154), and four hav,- all th.- .,,-nlar. fa TEXT-PIGS. 154-157. — Ocular plate arrangement in Slrongylocmtrotux gibbosus (Agassi*). I':iy(:i. IVni. Tin- typir.-il commensal crab, Fabia chilensis, in all but text-fig. 155. All figures X4. 154. Diana. 31 mm. R. T. J. Coll., 704. Oculars I, V, IV insert. 155. Diam. 28 mm. R. T. J. Coll., 702. Oculars V, IV insert. Crab wanting. 150. Diam. 42 mm. R. T. J. Coll., 703. Oculars V, IV, III insert, the typical rhararlrr in this alx-rr.int np«-. the periproct meets the interambulacra at the points marked X. The commensal rnili is vrry rlrar and in it< lypir.-tl [op- tion (pp. 94, 128, 177). 157. Diam. 40 mm. R. T. J. Coll., 705. Ocular plates all insert. (text-fig. 157). These are the only cases of all oculars insert seen in the genus. It is also interesting that in text-fig. 157 there is an interspace between ocular III and genital .'$. where the periproct reaches the interambulacrum, and the same feature is shown in three arras in fig. 156. This is comparable as a parallelism to a similar condition of separation of ocular and genital plates in Phormosoma (p. 110). All the other specimens, 79 %, are alx>rrant in ocular arrangement. In five, oculars V, IV are insert; one of these has no associated crab (text-fig. 146 ROBERT TRACY JACKSON ON ECHINI. 155), but yet retains the specific irregularity. Eight have V, IV, III insert (text-fig. 156), a very unusual arrangement, seen in only three other cases in the order Centrechinoida, yet it is the dominant character, 33 %, in S. gibbosus. This arrangement of oculars with V, IV, III insert was found as an aberrant variation in six cases in the Cidaroida, as described in Cidaris affinis and Eucidaris tribuloides (pp. 96, 97, 99). Six specimens, 25%, have oculars I, V, IV, III insert, again a rare arrangement in the order, but frequent in the Cidaroida. In young specimens of gibbosus a few mm. in diameter all oculars are exsert. In the Strongy- locentrotidae, of the species studied, two are characterized by having oculars all exsert; all others have typically the bivium insert except the aberrant S. gibbosus (pp. 162, 164). The Echinometridae as here restricted includes Echinometra and allies, which are elliptical in outline through a sidewise axis, a character peculiar to this group of Echini only. In this family, as in the Arbaciidae, when ocular plates enter the periproct, it is in the sequence V, I, not I, V, as in the Echinidae and Strongylocentrotidae. On this basis, when only one ocular is insert, it should be V, and this is true as a dominant rule; occasionally, however, ocular I alone is insert. Such cases may be considered variants toward the character of the associated families in which, if only one plate is insert, that plate is typically ocular I. The rule is not quite so constant as in the Arbaciidae, in which, if one plate is insert, it is ocular V with very rare exceptions. The most primitive species of Echinometra on the basis of ocular plate arrangement is E. oblonga. Of this species (44 specimens) in 98 % all the oculars are exsert, and in 2 % ocular V is insert as a progressive variant. In Echinometra viridis (25 specimens), 96% have all oculars exsert, and 4% ocular V insert. Echinometra mathaei(15Q specimens) has typically, 79 %, all oculars exsert; of progressive variants 19 % have V, and 1 % have V, 1 insert; 1 % is aberrant with oculars V, II insert. Of Echinometra lucunter a large series was studied, and it shows different facies in two widely separated localities. In the West Indian area (578 specimens) typically, 57 %, ocular V alone is insert (text-fig. 159). As arrested variants 17 % have all oculars exsert (text-fig. 158), the typical character of E. oblonga. As progressive variants 25 % have oculars V, I insert (text-fig. 160), like the typical character of E. van brunti, and 0.3 % have V, I, IV insert (text-fig. 161). In Echinometra lucunter from Bermuda considerable difference exists. In 176 specimens from that locality ocular V is typically insert in 46 %. The arrested variants, however, are less frequent, only 9 % having all oculars exsert. Also the progressive variants are much more frequent than in the West Indian form, there being 43 % with V, I, and 0.6 % with V, I, IV insert. The Bermudan form, while having typically ocular V insert as in the West Indian, is therefore distinctly more progressive as shown by its variants, and makes a closer approach to the character seen in the next higher species, E. van brunti. The Bermudan form of E. lucunter is notable for its large size and robust character. One specimen in my collection from that locality measures 90 mm. through the long axis. While in Echinometra OCULAR AND GKMTAI, I'l.ATKS. 117 lucunter 413 specimens have ocular V alone insert, only four h»* ocular I alone in-,n . -Uwi,,g the strong dominance of this character. In the whole m,ml,,r (7M) ,-x:,i,,i,,,.,|. then BN l..n two specimens, 0.3%, with an aberrant arrange.n,-,,t of ocular-. I,, one, oeillttl \ . IV are insert, and in the other V, II alone reach the pi-riproH ftahles, pp. n;:<, n, i n Dl 158- TEXT-FIGS. 158-161.— Ocular plate arrangement in Echinometra lucunter (Linn<5). Hayti, West Imiini. All figures X4. (Compare text-figs. 111-114, p. 115.) 158. Length 41 mm., through 3, 1. R. T. J. Coll., 768. Oculars all exsert, an arrested variant. 159. Length 55 mm., through 3, 1. R. T. J. Coll., 769. Ocular V insert, the typical charartrr. 160. Length 52 mm., through 3, I. R. T. J. Coll., 770. Oculars V, I insert, a progressive variant. 161. Length 41 mm, through 3, 1. R. T. J. Coll., 771. Oculars V, I, IV insert, an extreme prograwve variant. Echinometra van brunti is an interesting form as it is apparently the highest specie- of the genus, judging from the ocular plates. In 76 specimens the typical character is to have oculars V, I insert, which occurs in 72%. As arrested variants only 11 % have ocular- nil e\ which is the character of E. mathaei; in 12 % V only is insert, which is the character of K. lucunter; and in 4 % ocular I only is insert. As a progressive variant, 1 % have V. I. IV i; It would be most interesting to get a large series of this species for comparative .study, hut it is felt that the number seen is enough to give a fair basis for comparison. In Heterocentrotus mammillatus (35 specimens) 80 % have oculars all exsert .11% are pro- gressive variants with ocular V insert; in one specimen ocular I, and in one oculars V. 1 are insert. One specimen is aberrant with oculars V, II insert. In the nearly allied Hclcrocentrotus trigonarius (47 specimens) typically, 60 %, all oculars are exsert; in 28 % ocular V is insert, in 4 % ocular I and in 9 % oculars V, I are insert. In Colobocentrotus alratus (82 specimens , !< have all oculars exsert, and in 1 % ocular V is insert, as a progressive variant. The Echinometridae as a family is characterized by very close adherence to the rub ocular arrangement. In the whole 1,222 specimens examined, only four aberrant- were found; of these, three have oculars V, II and one has V, IV insert (tables, pp. 163, 164). Having considered the character of ocular plates in their relation to the genitals and to 148 ROBERT TRACY JACKSON ON ECHINI. the periproct as typical developing and adult features, and as variants in many species of fossil and living Echini, the characters may be summarized as follows. In the Ordovician Bothrio- cidaris archaica the 'oculars form a continuous ring with genitals on their dorsal border (text- fig. 162). In the Devonian to Carboniferous usually, as in Melonechinus (text-fig. 163), oculars and genitals all reach the periproct and the corona. In the Mesozoic usually, as in Cidaris coronata (text-fig. 164), the genitals alone reach the periproct and oculars are all exsert. In the Recent, oculars are all exsert in the young individual. In the adult typically all oculars may still be exsert, or one, or more to all plates may travel in so as to reach the periproct, and the incoming, barring relatively rare exceptions, is in a perfectly definite order. Different species or genera attain as a character definite points along this line of differential development, and selected cases of coming in are shown in text-figs. 165 to 169. All plates may be typically exsert, as in Echinus esculentus (text-fig. 116, p. 117). One plate may be typically insert, when it is either ocular I, as in Echinus magellanicus (text-fig. 165), or ocular V, as in Echino- TEXT-FIGS. 162-175. — Ocular plate arrangement in typical Echini. Each figure represents the typical character of the several species represented. 1C2. Bolhriocidaris archaica sp. nov. Ordovician, Russia. From Plate 1, fig. 2. X 7. Oculars very largo, mooting in a ring, genitals small, dorsal to the oculars (p. 87). 163. Melonechinus multiporus (Norwood and Owen). Lower Carboniferous, St. Louis, Missouri. From Plalo ">(>, fig. 6. X 3. Oculars and genitals all meet the periproct and corona. Compare text-fig. 169. Genitals have many pores. 164. Cidaris coronala Goldfuss. White Jura, Sonntheim. Stuttgart Museum 9,782. Enlarged. All oculars exsert. Plates of periproct in place, very rare for fossils of the genus (pp. 96, 174). 165. Echinus magellanicus Philippi. Patagonia. Diam. 26 mm. R.T.J. Coll. ,773. X 2.7. Ocular I insert (p. 119). 166. Strongylocentrotus franciscanus A. Agassiz. California. Diam. 112 mm. R. T. J. Coll., 699. X 1.7. Oculars I, V insert (p. 144). 167. Arbacia nigra (Molina). Chili. Diam. 92 mm. R. T. J. Coll., 796. X 2.6. Oculars I, V, IV insert (p. 116). 168. Acrosalenia pseudodecorata Cotteau. Bathonien, France. (After Cotteau, 1875-'80, Plate 246, fig. 6.) Oculars I, V, IV, II insert. Suranal plate is dorsal to genital 3 (p. 112). 169. Phyllacanlhus baculosa (Lamarck) . Mauritius. Diam. 41 mm. R. T. J. Coll., 695. X 2.7. All oculars insert. (Compare text-fig. 163, p. 102; Plate 3, figs. 3, 4.) 170. Phormosoma placenta Wyville Thomson. Off Cape Sable to Cape May, 956 fath. Diam. 56 mm. R. T. J. Coll., 707. X 3.5. All oculars insert and interspaces exist between oculars and genitals so that the periproct reaches the interambulacra. Genitals are split ventrally. Ambulacral plates are simple primaries in the placogenous zone. Intcr- ambulacral plates originate against oculars as usual (pp. 63, 110, 177; Plate 3, fig. 8). 171. Holectypus hemisphericus Desor. Inferior Oolite, Leckhampton Hill, England. Diam. 28 mm. R. T. J. Coll., 738. X 9. Oculars all excluded from the center by genitals (p. 170). 172. Cassidulus subqiiadralus Conrad. Upper Cretaceous, Holly Springs, Mississippi. After W. B. Clark, 1893, Plate 31, fig. Ih. Enlarged. Oculars I, V reach the center, other oculars are excluded from the center by the genitals. 173. Toxobrissus pacificus A. Agassiz. Adapted from A. Agassiz, 1904, text-fig. 279, p. 193. Enlarged. Oculars I, V are virtually insert, although actually ocular I is shut out by the posterior extension of genital 2. 174. Micraster coranguineum (Lamarck). Cretaceous, England. Length 55 mm. R. T. J. Coll. ,521. X 6.7. Ocu- lars I, V, IV reach the center, others excluded from the center by the genitals. Compare text-fig. 167 (p. 92). 175. Ananchytes ovatus (Leske). Cretaceous, Sussex, England. Length 67 mm. Student Laboratory Coll., 172, Harvard University. X 2.4. Oculars I, V, IV, II reach the center, III only being excluded from the center by the genii als. Compare text-figs. 126 and 168 (pp. 92, 167). OCULAR AND GKNITAI. I'I.\TI> ll'.l 0 150 ROBERT TRACY JACKSON ON ECHINI. metra lucunter (text-fig. 159, p. 147). Two plates may be insert, when it is typically the bivium, as in Strongylocentrotus franciscanus (text-fig. 166). Three plates may be insert, when it is the bivium and left posterior plate of the trivium, as in Arbacia nigra (text-fig. 167). When four plates are insert, it is typically the bivium and posterior pair of the trivium, as in Acrosalenia pseudodecorata (text-fig. 168). I have shown this character in many cases as a variant but have not seen a species in which it is the character, so have copied the figure from Cotteau (1875-'80), as he says that four plates are typically insert in that species. All ocular plates may be insert, as in Phyllacanthus baculosa (text-fig. 169), when we have a character which is a close approach to that dominant in the Upper Palaeozoic (text-fig. 163). The next differential character to appear is for interspaces to develop between the ocular and genital plates, so that the periproct comes in contact with the interambulacra, as in Phormo- soma placenta (text-fig. 170). Turning to the irregular Echini, we find in part a parallel series to that seen in the regular Echini. As the periproct is eccentric, of course oculars cannot reach that structure, but if oculars reach the center line, they may be considered insert, or if excluded from the center line by junction of the genital plates, they may be regarded as exsert. Oculars may be all exsert, as in Holectypus (text-fig. 171; compare text-fig. 164). The bivium alone may be insert, as in Cassidulus (text-fig. 172; compare text-fig. 166). In some species, as Toxobrissus (text-fig. 173), the plates of the bivium may be separated by the posterior extension of the madreporite, but as this plate radially speaking is out of place, the oculars I, V may still be considered as morphologically insert. Or it could be looked at from another point of view and ocular V alone regarded as insert (as is common in the Arbaciidae), the other four oculars being shut out from the center by the contact of the genitals. Three ocular plates may be insert, when it is the bivium and left posterior plate of the trivium, as in Micraster (text-fig. 174; compare text- fig. 167). Or, finally, four ocular plates may be insert, when it is the bivium and posterior pair of the trivium, as in Ananchytes (text-fig. 175; compare text-fig. 168). The typical character of arrangement of ocular plates and the range of variation are ex- pressed diagrammatically by block lines in text-fig. 176. Each block represents the frequency of the character in the species, as given in the tables (pp. 100, 101, 143, 154-163). An excep- tion to this statement is in the cases of Strongylocentrotus lividus (p. 126) and Phyllacanthus annulifera (p. 102) in which additional specimens, tabulated after this diagram was drawn, somewhat altered the facts and percentages, but it was not deemed of sufficient importance to omit the observations, and there was no opportunity to alter the diagram. The characters are all given correctly to scale excepting that when one exists in less than 1 % of the specimens, it is represented by a line the thickness of which has no relation to the frequency of the same. On the left of the diagram is given the character o, all oculars exsert. This is an invariable feature in the specimens of Echinus affinis observed (p. 118). It is also the character of the OCULAR AND GENITAL I'LAT! \-\ adults of most Mesozoic and the young of all modern species of regular Echini. IWing to Echinus esculentus, all exsert is still strongly the character, but one plate may be insert a* an infrequent progressive variant (p. 118). In Arbacia pundulntn, „ .similar con.li.,,,,, prevail*, but one plate insert is a more frequent variant and rarely two or three plates are in Strongylocentrotus Uvidus has typically all oculars exsert, but one bMrl is a frequent an.l insert a rarer progressive variant (p. 126).' Echinometra mathaei has a lower percent.^,, of all exsert and a consequent, gain of progressive variants (p. 146). In Echinus angulotus the progressive variants become more strongly marked, especially as compared will, th.- northern species of the genus shown (p. 119). In Salenoddaris varispina, instead of all exsert, one ocular insert is the species character, and the feature of oculars all exsert passes into the phase of an arrested variant (p. 1 u . Echinus magellanicus has typically one ocular insert; all oculars are exsert as an occa-ional arrested variant, or. I, V insert as an occasional progressive variant. In no case seen were oculars I, V, IV insert, the space for which is indicated in the diagram at X, but in one >pe<-i- men oculars I, V, IV, II are insert, as an extreme progressive variant (p. 1 19). EchinotnHm lucunter from the West Indian fauna (p. 146) has one ocular insert as the species character, but all exsert is a frequent arrested variant and two insert a more frequent progressive variant, with rarely three plates insert. In the same species from Bermuda (p. 146) a different condition prevails, as arrested variants are rarer and progressive variants are much commoner than in the southern form. With Strongylocentrotus fragilis two oculars insert becomes the dominant character, with all exsert or one insert as frequent arrested variants (p. 128). In Echinometra van briinli two plates insert is strongly the dominant character with all oculars exsert or one insert as rela- tively infrequent arrested variants; and three oculars insert as a somewhat rare progre> variant (p. 147). Strongylocentrotus drobachiensis from York, Maine, has very strongly two oculars insert, with but few arrested and progressive variants (p. 138). From here on, the species shown have less of the bivium insert, few arrested variants with all exsert or one insert, and progressively more with three or four plates insert. Toxopneustes variegatus shows a distinct gain of progressive variants over the last species considered, and a consequent dropping of the bivium insert character (p. 121). In Strongylocentrotus purpuratus there is a still further reduction of the I, V insert and gain of the I, V, IV insert. A striking case is the Toxo- pneustes atlanticus in which progressive variants are much in excess of what is found in the closely allied T. variegatus (p. 122). With Tripneustes esculentus from the West Indian fauna (p. 124), three oculars inx-rt becomes the dominant character. In this species from this area two oculars insert is a very 1 In the diagram (text-fig. 176) the first 170 specimens only of Strongylocentrolus lii-idus are included. Recently, and too late to alter the diagram, this number was increased to 1,163 specimens. In this larger scries the pereentagiv (pp. 126, 162) are altered somewhat from that shown in the diagram and one specimen, 0. 1% has oculars I, V, IV insert, a feature not given in this diagram. 152 ROBERT TRACY JACKSON ON ECHINI. common arrested variant in frequency closely approaching the dominant character, and four oculars insert is a common progressive variant; rarely all oculars are insert. Arbacia nigra has strongly three oculars insert with no progressive variants, but occasional arrested variants of all exsert, and frequent arrested variants with one or two oculars insert (p. 116). This species covers the same range of characters as shown in Arbacia punctulata, but in very different pro- portions. Centrechinus setosus has strongly . three oculars insert as the species feature and is almost the only species in the order in which the variation covers six characters. All exsert or one or two oculars insert occur as rare arrested variants, and four oculars or all insert are frequent progressive variants (p. 108). Of Centrostephanus rodgersi there are few observations, but as far as they may be trusted, it is the strongest three oculars insert of any species known, with frequent progressive variants having four or all oculars insert (p. 110). Eucidaris tribu- loides has strongly three oculars insert as a dominant character (p. 97). Its range of varia- tion covers practically all the characters known in regular Echini from the Lower Carboniferous up. The only exceptions to this statement are cases of Echini that typically have an aberrant ocular arrangement, as Gymnechinus pulchellus (p. 120) and Strongylocentrotus gibbosus (p. 145). The arrested variants of Eucidaris tribuloides are few, with all oculars exsert, or one or two insert. Progressive variants are common with four or much oftener five oculars insert. In no sea-urchin studied is four oculars insert a typical species character, though this is said (Cotteau, 1875-'80) to be the case in Acrosaknia pseudodecorata Cotteau. With Phyllacanthus annulifera all oculars insert is the character with three or four oculars insert as frequent arrested variants (p. 102). In Phyllacanthus baculosa all oculars are insert as a strong species feature (p. 102). The only possible variants on this line of development are arrested, and such occur with three or four plates insert as rare arrested variants. In Aspido- diadema nicobaricum all oculars are strongly insert and no variation is known (p. 104). Those cases given in the diagram are selected, but almost any of the species shown in the tables of ocular plate arrangement could be intercalated in the diagram and there find an harmonious place in the scheme of differential structure. \, The accompanying tables show the characters of ocular plates in the species studied. The table for the Cidaroida is on pp. 100, 101 and for Strongylocentrotus drobachiensis on pp. 142, 143. In tabulating characters the only specimens omitted were those that had no locality, where this was an important item; also 71 that had three, four, or six areas, and some eight speci- mens that were so distorted that they could not properly be included. The general relation of percentages is considered on p. 93. All aberrant variations in the Centrechinoida are given in the last table (p. 164). As the relation of ocular plates to the genitals and periproct plays such a distinct and definite part in geological sequence, in ontogeny, in variation, and in geographical distribution, it seems that they may be accepted as a feature of importance in the study of Echini. It seems also that they make a reasonable basis where differences occur on which to arrange the systematic sequence of species within the genus. OCULAR AND GENITAL PLATKS 153 2 OR § 9 II 3 D en 2. ~ -TT o O OR g -a £. CO £ 3 3 C5 >— I z, -t "g. o I' ii P 5" 3 § i-i "g. If 5 O m g S £ a. •-' SJ 2 J% &. -^ B ~ o — o O Cn f o Q cr CD Q. o cr ro O cr CD Q CX Cl cr CJ- O X CT O CX CJ cr rs ex cr cs ro cs 8- cf ex 1 CD er- rs O o o iiniiiii CO pTTTTTT Cn O S O § 8 lililL § (in 1 1 11' i iiiumj ininiii 1U1111U U111111J mnnn mum mm mm 2 1 1, 1, J 1 Illllllll auul L — IIII!.!li mu 1 1 1 1 i 1 1 1 1 ! _L1 1 1 i I i 1 iiiiiii 1 1 1 1 1 1 1 1 1 1 1 1 1 ill 1 11 11 1 1 1 1 1 11 1 II Illlllll] iMiniii • CT— v/v-^ 1 IIIMIIM IlllILILl limn h^N/X^X^N, •s-^^N^v "v/N^\/\. \/N^~S^N. N/'s/'^x" ysxs/s^ 3 1 ! IHI 1 1 1 ! Illllli fV^ f^~> •*~f^j~*~>~*+*~ -. •^^s^r*^' /\/N**^TN r^r^_y-N^» \ iimmn j-^~^^^~- ,^s~*s*^**^ iiinun n 1 1 ! 1 1 ! 1 1 ! T ? &»— 3 1 111 ' 'I 3 1 — «3 0 3 g i^^^^^^ • 3 Q cr • 0 i //////, ....| ///////, 2 f-X I a> ..-I 1 b '////A Q_ | o" •• c§"L i — *> Y /////, S/' /'//// ^a ex ct> \ °"R V//////: SSSSS^fffff • \ s /V/V / / S//1(S/////. 005 fcVlimii- .Mini* 'JfM) Krhinim •J.KIO Arli i. i.i |ni!iri i, 170 SinniK.vl»«-fiiiri,ii|. I, l'«'l i:i-liiiiriini-ir;i in . UN) Kc 28 S^enoeidarM varMpina l-'-l l»iirm* m.ij:i-l| ir. \\ .--i lii.li--. :nnl Murii i:rliiiimii.-lr:i liiciintiT, Bcnnoda frufflia 7I> Ki-liitioiiH-tra van l>niiiti •_',7(K) icnsis. York, M 1,(M3 TuxoiHifiislfH varii-a - I'Jll BtRMtgjrioMBtntlM iiiinnir.i'ii-. 1,403 Ti>\i>|>niMiNtn* .lioin.*. \\ . -t Imlifri ami 455 Mfl 1,168 ('<-iiin-.-lniiiis setomw 12 Ccntrostcphaous rodgeni S49 Kiirularis tribukwka 12 l'hyll:ir:inthus annulifrrm 106 Phyllaranthua baculon 47 A.xpiiltxliaileiiia nicobaricura 154 ROBERT TRACY JACKSON ON ECHINI. Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida. I Mri M 1 $ 0) M M 6 1 m M M •fcl b 0) M M z V HH »-H rrant. Number of specimens. Order CENTRECHINOIDA. Suborder AUWDONTA; All oculars exsert. H- 1 M > i~ •—* "a 6 0 H- T M > HH f > 1 1 M hH M V 1 > M S J5 1 HH" *H i > M > HH" 13 B o « i _g HH HH > HH > HH" "a B O All oculars insert. Arrangement of oculars abe 15 Hemicidaridae. Hemitidaris cartieri d'Orbigny. 100* 6 Jurassic, Europe. H emicidaris hojfnujnni Agassiz. 15* 100 169 Jurassic, Europe. Hemicidaris intermedia (Fleming). 6 89 s S 58 Jurassic, Europe. (Text-fig. 75.) Hemicidaris crenularis (Lamarck). I5i 81 13 16 5 « 2 16 Jurassic, Europe. Hemicidaris luciensis d'Orbigny. 47 13 9 SI 1 56' » 1 18 Jurassic, Europe. (Text-figs. 76, 77.) Hemicidaris langrunensis Cotteau. 2 11 5 M 9 67 10 Jurassic, Europe. Hemidwdema stramonium Agassiz 2 90 4 10 12 16 Jurassic, Europe. Asterocidaris minor Cotteau. 9 100 1 43 Jurassic, Sollies, France. (Text-fig. 78.) Goniopygus peltatus Agassiz 16 100 75 Jurassic, Europe. ^3 100 Jurassic, Europe. (Text-fig. 79.) 75 426 366 32 0 27 0 0 0 1 44 Asp i do diade matidae . Aspidodiodcma, meijerei Doderlcin. 100 47 Hawaiian Islands, 241-294 fathoms. Aspidodiadema nicobaricum Doderlein. 44 100 10 Hawaiian Islands, 165-500 fathoms. (Text-fig. 176.) 47 100 22 West Indies, 687-955 fathoms. (Text-fig. 80.) DeTtnatodiademfi horridum A. Agassiz. 10 100 Galapagos Islands, 812 fathoms. 22 123 0 0 0 0 0 0 123 0 * Italic numerals represent percentages, Arabic numerals the number of specimens observed. OCULAR AND GENITAL PLATES. I :,:, Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida (continued). - • \ ** ! Q 1 i jimens. fm M NH N-J" g — ' £ | ] OJ o. cc "8 I f I | — — 1 •8 1 1 HH 1 IE •J ~" | a Suborder A ULDDONT A (continued). | 1 1 | | | = Centrechinidae. 18 Pseudodiadema pseudodiadema (Lamarck). 89* // Jurassic, Trouville; Yonne. (Text-figs. 81, 82.) 16* 2 1 Magnosia punclata Quenstedt. 100 Jurassic, Nattheim. (Text-fig. 83.) 1 3 Cottaldia granulosa (Miinster). 100 Cretaceous, Chamboy. 3 4 Phymechinus mirabilis (Agassiz). 75 ,; Jurassic, Europe. (Text-fig. 84.) 3 1 7 Pedina rotala Wright. 100 Oolite, England. 7 4 Slomechinus granularis Agassiz. 100 Jurassic, Europe. 4 28 Slomechinus perlatus Desmoulins. 100 Jurassic, Europe. 28 50 Slomechinus bigranularis (Lamarck). 88 2 2 8 Jurassic, Europe. (Text-figs. 85, 86.) 44 1 1 i 14 Polycyphus normannus Desor. 93 7 Oolite, Europe. 13 1 37 Orthopsis miliaris (d'Archiac). 100 Cretaceous, Algiers; Europe. (Text-fig. 87.) 37 Centrcchinus setosus (Leske). Atlantic and Pacific Oceans several localities. De- 23 5 9 55 1 veloping series, 8-40 mm. diam. (110 specimens). 25 5 10 IK) 5 3 2 1,278 (Text-figs. 88-92.) The same. Atlantic and Pacific Oceans, many localities. Devel- 0.2 O.I 0.1 / 77 tS oped series, 40-108 mm. diam. (1,168 specimens). 2 •1 1 n 671 194 -J.M *{ (Text-figs. 93-95, 176.) 11 Echinothrix calamaris (Leske). 9 .' 1— 1 > 1 M 1 o t-4" t—t M HH > 1 3 u o i-T HH > HH ti" o cr.' _C > h— T 1 O ^-T M i > ^H > I 1 t— t HH > HH > H- T 1 1 All oculars insert. Arrangement of oculars abe 2 Centrechinidae (continued). Centrostephanus asleriscus A. Agassiz and Clark. 100* 12 Hawaiian Islands. Centroslephanus rodgersi A. Agassiz. 2* e» 25 8 4 Parramalta, N. S. W.; Port Jackson. (Text-figs. 96, 176.) Centrostephanus lanffispinus (Philippi). 8 3 1 100 9 Mediterranean. (Text-fig. 97.) Aslropyga pulvinala (Lamarck). 4 100 12 Gulf of California. (Text-fig. 99.) Aslropyga radiala (Leske). 9 /OO 36 Hawaiian Islands. Chaetodiadema pallidum A. Agassiz and Clark. 12 /CO Hawaiian Islands. (Text-fig. 98.) 36 1,548 185 11 2 26 740 202 347 35 4 Echinothur iidae . Aslhenosoma hystrix (Wyville Thomson). 100 1 Off Cape Hatteras to Charleston, S. C., 258 fathoms. Asthenosoma ijimai Mortensen. 4 100 3 Off Tokio, Japan, 55 fathoms. (Text-fig. 101.) Asthenosoma owstoni Mortensen. 1 100 11 Sagami Sea, Japan. Phormosoma placenta Wyville Thomson. 3 /oo Off Cape Sable to Cape May, 956 fathoms. (Text-fig. 170.) 11 19 0 0 0 0 0 0 19 0 57 Suborder STIRODONTA. Saleniidae. Peltasles stellulala Agassiz. 100 Cretaceous, Europe. 57 * Italic numerals represent percentages, Arabic numerals the number of specimens observed. OCULAR AND GENITAL I'l.vri Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida I. -7 B i | | I M M Q ~ = | bJ *— i d - ri .0 V) a > > > :-" I B S ^, M ^J" — 9 en 1 6 1 | 1 •^ es • i •8 n 8 2 •• :~ ^ ^ "* . 1 s J 1 j ^ 5 1 1 fc Suborder STIRODONTA (continued). 3 1 | J = 1 Saleniidae (continued). 70 I'i'l/dsles wrighti Desor. 1(K>* Cretaceous, Farrington, England. (Plate 4, fig. 7.) 70* 16 Salenia scutigera Agassiz. too Cretaceous, Europe. 16 20 Salenia petalifera Agassiz. 96 5 Cretaceous, Europe and Algiers. 19 1 16 Salenia pntlernoni A. Agassiz. Off Cuba, 300 fathoms; Barbados, etc. (Plate 4, 81 m figs. 1, 2.) 5 11 2 Salenia cincta A. Agassiz and Clark. too Near Goto Island, Japan, 95 fathoms. 2 10 Salenocidaris profundi (Duncan). 30 70 North of Tristan da Cunha, 1,425 fathoms. (Text- 3 7 fig. 102.) 26 Salenocidaris varispina A. Agassiz. _•; 73 West Indies, 270-687 fathoms. (Text-fig. 176; Plate 7 l!l 4, fig- 6.) 16 Salenocidaris miliaris A. Agassiz. IB S/ Galapagos Islands; Japan. 3 13 10 Acrosalenia aspera Agassiz. 100 Jurassic, Europe. 10 5 Acrosalenia decorata (Haime). till 40 Oolite, England. a 2 101 Acrosalenia spinosa Agassiz. / r Jurassic, Europe. (Text-fig. 103.) i 7 93 58 Acrosalenia hemicidaroides Wright. 0 5 Jurassic, Europe. (Text-fig. 104.) i 3 50 \ 16 Acrosalenia pustulata Forbes 0 19 Jurassic, England. 1 Id 3 i 1 12 8 j 17 j Jurassic, near Cirenccster and Wilts, England. 1 7 1 a i (Text-fig. 105.) 435 105 65 0 162 4 3 i -• * Italic numerals represent percentages, Arabic numerals the number of spccin* 158 ROBERT TRACY JACKSON ON ECHINI. Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida (continued). t 1 1 S 1 HH H- 1 | B HH W M W M i f M — HH h-T M if 03 . > > > y 1 i s "i 1—1 .- ^ "™ 3 1 •g 1 & 1 ;> HH ^H 1 s •8 •5 2 03 c M .s NH ^ HH i 1 i E £ £ £ C a 1 £ C.) • oS • • J2 § Bj £• * 3 3 2 2 | Suborder STIRODONTA (continued). < ^H Oculars V insert; I. IV. 11, III exacrt. i ^^ w ^^ - £ > i-T i I ] H -' I ES > I = i a -- - -r A 11 ocular* bum. •5 •g 7 Temnopleuriclae . Glyphocyphus radiatus Desor. 1U» 11 Cretaceous, Europe. Trigonocidaris albida A. Agassiz. 100 ;• 7 West Indies. Temnopleurus hardwickii (Gray). 11 100 34 Japan; Ceylon. Temnopleurus toreumaticus (Leske). 1 100 19 China Seas; Japan; India. Temnopleurus reevesii Gray. 34 63 47 22 Japan; Siam. Salmons alexandri Bell. 10 KXI 9 14 Australia. Salmacis bicolor Agassiz. 22 too 12 Japan; Mauritius; Red Sea. Salmacis sphaeroides (Linn6). 14 100 34 Australia; Philippines; and loc. (?) Mespilia globula (Linn6). 12 97 3 139 Samoa; Japan; and loc. (?) Microcyphus maculalus Agassiz. 33 98 1 i / 8 Mauritius; Japan, etc. Amblypneusles formosus Valentin. 136 100 i i 12 Australia; Tasmania. Amblypneustes griseus (Blainville). 8 100 10 Australia. Amblypneusles pallidus (Lamarck). 12 100 38 Australia. Amblypneustes ovum (Lamarck). 10 97 5 33 Australia. 37 97 1 s Australia. 32 i 400 378 11 i i 0 0 7 -• * Italic numerals represent percentages, Arabic numerals the number of specimens observed. 160 ROBERT TRACY JACKSON ON ECHINI. Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida (continued). i 1 1 •fi t: § i 1 0) 8 I M I M I-H £5 HH i— < H ^ E M " M HH I n" h-T hH — »— 1 t— I t a . > >" >" if .S J "3 1 1J > i-T 0) I > ^H fe" I o 0 IM O V 0 1 a a ^ >" > q 1 •S e 53 M > HH* i— T HH" 1 E 9 "3 £ £ £ £ £ ~3 §i B • a y. Suborder CAMARODONTA (continued). O 3 1 J 1 O 1 O J O I Echinidae. 605 Echinus affinis Mortensen. KM* ( MT c:ust coast of United States. 1,022-1,106 fathoms. 605* (Text-figs. 115, 176.) S Echinus elegans Diiben and Koren. 100 < )ff Cape Romain and loc. (?) 8 10 Echinus gracilis A. Agassiz. 100 Off Carolina and Martha's Vineyard. 10 200 Kchinus esculentus I.iinu'. 97 3 Plymouth, England; Isle of Man; Mediterranean. 195 5 (Text-figs. 116, 117, 176.) 129 Erhimts mil-inris \fiillor 98 1 2 Norway; England; Isle of Man. 126 1 2 299 Echinus microluberculatus Blainvillc. 96 2 ^ O.S i Mediterranean. 287 5 4 1 2 10 Echinus melo Lamarck. 90 10 Mediterranean; England. 9 1 127 Echinus acutus Lamarck. 82 18 Plymouth, England; Norway; Bergen; Mediterranean. 104 23 100 Echinus angulosus Leske. 54 30 4 9 « ; Algoa pay; Cape Colony; South Africa. (Text-fig. 54 30 4 9 2 1 176.) Echinus magellanicus Philippi. 97 3 Patagonia; Straits of Magellan. Developing series, 35 1 200 2.5-5 mm. diam. (36 specimens). (Plate 3, fig. 14.) The same. 5 88 4 0.0 I Falkland Islands; Straits of Magellan. Developed 9 145 7 i 2 series (164 specimens). (Text-figs. 165, 176.) 16 Echinus margurilaceus Lamarck. 6 6 ff 5(? e BS v W •3 IM O 8 i .5 > > _, •1 o 1 i M > ~" « « 1 1 a V ~ 9 Jj S - 2 y I Suborder CAMARODONTA (continued). 5 1 1 J 1 J 5 1 Echinidae (continued). 5 Toxopneustes maculatus (Lamarck). HO* so Fiji Islands; Mauritius. 1* 4 38 Toxopneustes pileolus (Lamarck). 8 M Acapulco; Panama; Mauritius. 3 35 25 Toxopneustes semituberculatus Valentin. 4 00 Galapagos Islands. 1 24 1,043 Toxopneustes variegatus (Lamarck). ! 0.1 SO s 0.* o.s West Indies and Florida. (Text-figs. 176, 184.) 11 1 937 84 2 8 Toxopneustes atlanticus (A. Agassiz). 0.9 O.i «/ Iff 0.5 § Bermuda. Developing series, 35-45 mm. diam. 5 1 475 92 2 12 (587 specimens). The same. 0.1 0.5 0.1 67 18 7.5 t.B 2,643 Developed series, 45-60 mm. diam. (1,463 speci- 1 8 2 983 415 Is 36 mens). (Text-figs. 118-122, 176.) The same. 0.7 0.5 68 *0 0.7 / .S Developed series, 60-77 mm. diam. (593 specimens). 4 2 401 171 4 11 16 Tripneustes depressus A. Agassiz. e 75 19 La Paz, California; and loc. (?) 1 12 3 72 Tripneustes variegatus (Leske). 7 / 68 S H ^ Mauritius; Jeddah, Red Sea; Durban; Natal; Samoa; 5 1 49 6 1 3 Indo-Pacific; Lord Howe Island; Hawaiian Islands. Tripneustes esculentus (Leske). 2 61 f / Bermuda. Developed series, 50-145 mm. diam. (193 3 117 67 3 i i specimens). (Text-figs. 123, 196.) The same. 9 76 IS § 703 West Indies and Florida. Developing series, 19-50 5 42 1 i mm. diam. (55 specimens). The same. 0.4 SO 38 18 / 0 West Indies and Florida. Developed series, 50-127 2 166 172 84 5 mm. diam. (455 specimens). (Text-figs. 124-127, 176.) 20 $v€chinus chlorolicus (Viilcntin). 50 5 5 !*Jew Zealand. 18 1 1 6,292 1,444 259 19 3,290 ,021 123 7 129 * Italic numerals represent percentages, Arabic numerals the number of specimens observed. 162 ROBERT TRACY JACKSON ON ECHINI. Table of Typical Ocular Plate Arrangement and Variation in the Centrechinoida (continued). Number of specimens. Suborder CAMARODONTA (continued). All oculars exsert. u B H- 1 t-H HH •g i— i t-H I HH All oculars insert. Arrangement of oculars aberrant. >— i is i h-T t— 1 1— 1 i— T i 9 1 HH* H-( 1 3 B O t-H i" HH HH* 1 M 1-H t-H O 10 48 291 1,163 60 55 6 39 12 56 179 120 24 Strongylocentrotidae. Pseudobolelia indiana (Michelin). Mauritius; Isle de la Reunion. Sphaerechinus pulcherrimus A. Agassiz. Japan. Sphaerechinus granularis (Lamarck). Mediterranean; Azores. Strongylocentrotus Hindus (Lamarck). Mediterranean; Fayal; England. (Text-figs. 128-130, 176.) Strongylocentrotus albus (Molina). Patagonia. Strongylocentrotus fragilis sp. nov. Catalina Islands, California; off California and Ore- gon coasts. (Text-fig. 176.) Strongylocentrolus mexicanus A. Agassiz. Cape St. Lucas. Strongylocentrotus tuberculalus (Lamarck). Japan; Sidney, Australia. Strongylocentrotus depressus A. Agassiz. Japan and loc. (?) Strongylocentrolus drobachiensis (O. F. Muller). See tabulation of 27, 417 specimens exclusive of devel- oping series, p. 143. The percentages only are given here. (Text-figs. 135-149.) Slrongylocenlrotus eurythrogrammus (Valentin). Australia. Strongylocentrolus franciscanus A. Agassiz. California; Washington. (Text-figs. 151-153, 166.) Strongylocentrotus purpuratus (Stimpson). California; Puget Sound. (Text-fig. 176.) Strongylocentrotus gibbosus (Valentin). Payta, Peru. (Text-figs. 154-157.) 100* 10* 47 258 4 50 15 56 31 T 92 36 100 12 94 75 876 53 32 13 7 2 i 2 17 195 2 1 29 16 3 o./ 1 1 3 9 25 15 IS 8 2 26 B 3 1 17 1 3 1 3 1 3 1 0.004 2.7 0.04 a 0.03 1.2 2 1 i 2 1 1 93 52 156 77 93 5 3 20 £8 26 4 1 1 17 4 79 19 1 2,063 53- 220 31 765 56 3 4 69 * Italic numerals represent percentages, Arabic numerals the number of specimens observed. OCULAR AND GENITAL PLATES. !<;:; Table of Typical Ocular Plate Arrangement and Variation in the Cenlrechinoida (continued). | 1 | I i M a D M M a I 8 — fc" NH" £ a" E: 1 I J i B | t f I b = - : •5 "o B I J > - > •J •* B • 1-1 ^ "-T — i-T I _c s 1 I 1 1 J 5 | ' £ Suborder CAMARODONTA (continued). 3 | 1 5 : | 5 ^ E chin ome t rid ae . 44 Echinometra oblonga Blainville. 98* i Samoa; Hawaiian Islands; South Africa. 43* i 25 Echinomelra viridis A. Agassi z. 96 ^ West Indies. 24 i 159 Echinomelra malhaei Blainville. 79 /9 , 7 Red Sea; Durban; Natal; Mauritius; Bonin; Hawai- 126 31 1 1 ian Islands. (Text-fig. 176.) Echinometra lucunter (Linn<5). 17 O.S r,r 25 West Indies and Florida (578 specimens). (Text- 97 2 332 Ml a 1 754 figs. 158-161, 176.) The same. 9_ / #? ^5 O.ff 0.0 Bermuda (176 specimens). (Text-fig. 176.) 15 2 81 76 i 1 76 Echinomelra van brunli A. Agassiz. // 4 18 72 / Lower California; La Union; South America. (Text- 8 3 {T 55 i fig. 176.) 35 Heterocenlrotus mammillatus (Leske). 80 3 // » a Mauritius; Indian Ocean; Bonin Island; and loc. (?) 28 1 4 1 i 47 Heterocenlrotus trigonarius (Lamarck). 90 4 2S 9 Hawaiian Islands; Mauritius; Tahiti; Palmyra Is- 28 2 13 4 land. 82 Colobocentrolus atratus (Linn£). 99 / Hawaiian Islands; Mauritius; Zanzibar; and loc. (?) 81 1 1,222 450 10 473 281 4 0 0 4 * Italic numerals represent percentages, Arabic numerals the number of specimens observed. ROBERT TRACY JACKSON ON ECHINI. Table of Aberrant Ocular Plate Arrangement in 48,541 Specimens of the Centrechinoida.1 Total number of specimen*. Percentage of aberrants. i I exsert. £ B V B i i 1 I X 4) \ 0) £ I X V -*•> I HH 1 3 U O 1 1 1 — 1 — i— T -*-> H- 1 > I c HH" HH — « f *~i % .a — — HH I HH HH — H-T .1 — HH 2 I n 5 HH _g HH e I •— > 1. HH •M i Oculars 1 1 Oculars 1 1 Oculars 1 1 = o 3 0 o 1 1 58 1,278 58 16 64 141 2,329 67 76 246 139 299 100 200 16 9 14 1,043 2,643 72 703 20 291 1,163 60 39 33,000 179 24 159 754 35 Hemicidaris crenularis (Lamarck). Centrechinus setosus (Leske). Acrosalenia hemicidaroides Wright. Acrosalenia pustulata Forbes. Stomopneustes variolaris (Lamarck). Arbacia lijcula (Linn6). Arbacia punctulata (Lamarck). Arbacia dufresni Blainville. Arbacia spatuligera Agassiz. Arbacia nigra (Molina). Microcyphus maculalus Agassiz. Echinus microluberculatus Blainville. Echinus angulosus Leske. Echinus magellanicus Philippi. Echinus margarUaceus Lamarck. Gymnechinus robillardi (Loriol). Gymnechinus pulchettus Mbrtensen. Toxopneustes variegatus (Lamarck). Toxopneustes atlanticus (A. Agassiz). Tripneustes variegatus (Leske). Tripneusles esculentus (Leske). Evechinus chloroticus (Valentin). Sphaerechinus granularis (Lamarck). Strongylocentrotus lividus (Lamarck). Strongylocentrotus albus (Molina). Strongylocentrotus tuberculatus (Lamarck). Strongylocentrotus drobachiensis (O. F. Miiller) Strongylocentrotus franciscanus A. Agassiz. Strongylocentrotus gibbosus (Valentin). Echinometra mathaei Blainville. Echinometra lucunter (Linne1). Heterocentrotus mammillatus (Leske). 2 3 7 6 6 1 0.6 7 13 8 1 1 1 1 6 89 100 0.8 f i t I 9 13 1.2 79 o.; 1 1 1 1 32 1 1 1 2 1 1 2 2 3 1 1 14 3 10 1 13 1 4 1 1 2 1 i 1 1 8 14 2 1 1 18 1 1 5 25 13 1 2 1 1 26 2 1 2 23 1 1 K 4 2 3 4 2 1 2 1 81 3 29 33 34 1 215 1 2 2 5 8 6 1 1 1 1 Total number of aberrants 704 = 10 3 8 97 1 56 82 4 63 4 300 i 11 17 47 'This table includes all aberrant variants of the Centrechinoida listed in the tables, pp. 142, 143, 154 to 163. See text- figs. HO, p. 114; 140-149, p. 134; 155, 156, p. 145; 177-179, p. 165; 182, p. 165; 196, p. 169. SPECIAL CHARACTKUS OF (JKXITAI. 1'I.ATKS. Hi.-, SPECIAL CHARACTERS OF GENITAL PLATES. Certain characters of genital plates are here taken up aside from th.-ir n-hti,,,,, .,, .!„• oculars, that have just been considered. The characters in genitals are subject to a great deal of variation. While the bearing of these variations is often obscure, for thr most part th.-y follow very definite lines. In my studies of post-Palaeozoic fossil and H.-m.t Echini, over TEXT-FIGS. 177-184.— Showing genital plates excluded from the periproct. 177. Gymnechinus pulchellus Mortensen. Gulf of Siam. Diam. 15 mm. R. T. J. Coll., 863. X 8.2. Genital 3 exsert by the contact of genitals 2 and 4. Oculars I, II insert, the species character (pp. 93, 120). 178. The same. Diam. 10 mm. R. T. J. Coll., 864. X 8.7. Genital 4 exsert by the contact of genitals 3 and 5. 179. Gymnechinus robittardi (Loriol). Mauritius? Diam. 26 mm. R. T. J. Coll., 811. X 4.5. Genital 3 exsert. Oculars I, II insert, the species character (p. 120). 180. Strongylocentrotus drobachiensis (O.F. Muller). York Harbor, Maine. Diam. 44 mm. R. T. J. Coll., 782. X 2.81. Genital 3 exsert by the contact of genitals 2 and 4, as in text-figs. 177, 179, 184. 181. The same. Chelsea Beach, Massachusetts. Diam. 3 mm. R. T. J. Coll., 880. X 28. Genital 4 exsert by the contact of genitals 3 and 5 as in text-fig. 178. No genital pores (compare text-fig. 133, p. 129). 182. The same. Dumpling Island, North Haven, Maine. Diam. 50 mm. R. T. J. Coll., 866. X 2.7. Genital 4 exsert by the contact of genital 5 and ocular IV (compare text-fig. 144, p. 134). 183. The same. Calderwood Island, Maine. Diam. 32 mm. R. T. J. Coll., 865. X 2. 8. Genital 4 exsert by the contact of genital 3 and ocular V. 184. Toxopneustes variegaius (Lamarck). Boca Ceiga Bay, Florida. Diam. 58 mm. R. T. J. Coll., 872. X 3.7. Genital 3 exsert (p. 121). 166 ROBERT TRACY JACKSON ON ECHINI. 250,000 genital plates have been examined, and the principal striking variations noted. In the 33,000 specimens of Strongylocentrotus drobachiensis studied, detailed lists of the variations of genital plates were kept as a basis for determining the numerical frequency of occurrence. Under ocular plates it is shown that there is great diversity as to whether these meet the periproct or are shut out from it. On the other hand, genital plates show great uniformity in that all the plates meet the periproct. No exception to this is known in fossil regular Echini; in Recent Echini, however, some exceptions have been found as individual variations. Dr. Mortensen (1904, p. 114) says of Gymnechinus pulchellus that sometimes one of the genitals, mostly 3, is excluded from the periproct. He writes me that in about thirty percent of the specimens genital 3 and more rarely 4 is exsert. In ten selected specimens of G. pulchellus that Dr. Mortensen generously sent me, four have genital 3 exsert (text-fig. 177), two have genital 4 exsert (text-fig. 178), and four have all genital plates reaching the periproct. In a specimen of Gymnechinus robillardi (text-fig. 179) genital 3 is exsert. De Loriol (1883) figures the same species with genital 4 exsert. In his collection I saw two specimens with genital 4 exsert, as in text-fig. 178. It is striking that this very exceptional character is common in two related species. Specimens with exsert genitals have been found in a few other species. One specimen in 139 Microcyphus maculatus (this is in de Loriol's collection in Geneva), one in 1,043 Toxopneustes variegatus (text-fig. 184), and two in 2,643 Toxopneustes atlanticus have genital 3 exsert. In 33,000 Strongylocentrotus drobachiensis 37 specimens have genital 3 exsert (text- fig. 180). In all the cases seen of genital 3 exsert in the several species, this plate was similarly excluded by the contact of genitals 2 and 4 as figured. In S. drobachiensis eight specimens have genital 4 exsert. This, however, is not excluded by the same plates in all cases. In a very young individual (text-fig. 181) genital 4 is excluded by the contact of genitals 3 and 5, as in Gymnechinus pulchellus (text-fig. 178). Another method of exclusion of genital 4 is by the contact of genital 5 and ocular IV (text-fig. 182) ; and in a third method, which may be considered more normal for the species, genital 4 is excluded by the contact of ocular V and genital 3 (text-fig. 183). In the Museum of Comparative Zoology, a Microcyphus maculatus from Mauritius has genital 4 excluded by the contact of ocular V and genital 3, as in text-fig. 183; also a Heterocentrotus irigonarius from the same locality has genital 3 excluded by the contact of genitals 2 and 4, as in text-fig. 184; and a Microcyphus annulatus Mortensen, from Bass Straits, Australia, has genital 1 excluded from the periproct by the contact of genitals 5 and 2. The oculars of this specimen are all exsert, as usual in the genus. In a.11, 61 cases have been seen in 50,000 specimens with a genital excluded from the peri- proct, 47 of the cases being of genital 3, thirteen of genital 4, and one case of genital 1. Why genital 3 or 4 should be excluded and almost no others is not obvious, but it shows how definite even a very rare variation can be. While genitals are rarely excluded from the periproct as variants, they are still more con- SPECIAL CHARACTERS OF GENITAL I'LATKS. 107 stantly in contact with the interambulacrum ventrally. In Bolhriocidaru archaica (Plate 1, fig. 2) the genitals lie wholly dorsal to the oculars, and in B. pahlcn, < IM.-.i,- I , fig. 6) they do *o in part. In one specimen of Slrongylocentrolus drobachiensis (Plate 5, fig. 10) genital I li.-.~ dorsal to the oculars, as in Bothriocidaris archaica; but in this peculiar specimen inleramUla- crum 1 is wanting (p. 42), which accounts for this exceptional genital exclusion. Otherwise, as far as seen, a genital, when existent, always extends to the inleraml.ulacnun of ii> area. Genital plates are of secondary importance. One may be absent wit liout visibly affecting the corona (spatangoids, text-figs. 174, 175, p. 149). Rarely a genital may be wanting in regular Echini (p. 45), when the other portions of the test have the usual pentamerous system. Such a case is seen in Eucidaris (text-fig. 185). In this specimen there are five oculars, I aixl 1 1 being in contact from the absence of genital 1. In interambulacrum 1 there an- two young plates lying against oculars I and II; the next older plate belonging to column 2 is large and extends across the area, whereas the third older plate i- small. Otherwise the corona is quite as usual. In two specimens of Arbacia (Plate 4, figs. 11, 12) and in a Strongylocentrotus (Plate 6, fig. 7), genital 4 is want- ing and interambulacrum 4 is narrowed, consisting in part of only a single column of plates. In Tripneustes esculenlus (Plate 6, fig. 4) there are six oculars, but no. additional genital, so that the extra genital may theoretically be considered as wanting, and there is only a single column of interambulacral plates through- out the added area as far as developed. In all of these specimens in the area where the genital is wanting, the interambulacrum dorsally abuts against the two over- II 755 TEXT-FIG. 185.— Eucidaris tribuloides (La- marck). Jamaica. Diam. 34 mm. R. T. J. Coll., 802. Genital i wanting. Young interam- lying ocular plates in a similar manner to that of bulacral plates originate against oculars I and Bothriocidaris and the posterior area in spatangoids II, as usual (p. 45). (text-figs. 162, 174, 175 p. 149). Genital and ocular plates are fused in a mass in clypeastroids, and two genitals may be fused in spatangoids (A. Agassiz, 1904, p. 161), but in regular Echini these plates are typically separate. Occasionally, however, in regular Echini two genitals or a genital and an ocular are fused. In a specimen of Centrechinus setosus (text-fig. 186) genitals 2, 3 and ocular III are fused into a perfectly symmetrical mass, no trace of sutures being visible. A similar fusion of two genitals, or a genital and an ocular, has been seen in many cases in the Echinidae and Strongylocentrotidae. In Strongylocentrotus drobachiensis genitals 2, 3 were fused in 30 • 3, 4 in 32 cases (text-fig. 195) ; 4, 5 in 68 cases (text-fig. 147, p. 134) ; and 5, 1 were fused in 19 cases (text-fig. 148, p. 134). Genitals 1, 2 were fused in only five cases. The fusion of genitals 168 ROBERT TRACY JACKSON ON ECHINI. was seen in other species also, as Tripneustes esculentus (text-fig. 196). In 103 cases of S. drobachiensis an ocular was fused with a genital (text-fig. 143, p. 134), any ocular of the five fusing with one or rarely two of the associated genitals. As far as the fusion of genitals, or genitals with an ocular goes, it may be considered a parallel variation to the typical condition in certain irregular Echini, where such fusion normally occurs. While fusion of genitals is rare, splitting on lines of solution to make divided plates is more common. This splitting of genitals by secondary sutures is a typical character in the Echino- thuriidae only (Asthenosoma, text-fig. 101, p. 109, and Phormosoma, text-fig. 170, p. 149). Such splitting is shown fully by Mr. Agassiz (1904) in many of this family. The splitting is 186 TEXT-FIGS. 186-189.— Fusion, or splitting of genital plates in Cenlrechinus setosus (Leske). 186. Jamaica. Diam. 49 mm. R. T. J. Coll., 803. X 2.8. Genitals 2, 3 and ocular III are fused in a mass; oculars I, V, IV, II insert, bilaterally symmetrical through III, 5. 187. Bahamas. Diam. 85 mm. R. T. J. Coll., 714. X 2.8. Genitals split by secondary sutures. 188. Bahamas. Diam. 85 mm. R. T. J. Coll., 689. X 2.8. Madreporic pores in genitals 2, 3, and ocular III. 189. Jamaica. Diam. 71 mm. R. T. J. Coll., 772. X 2.8. Madreporite split by secondary sutures. especially marked on the ventral border of genital plates or may pass directly through the plate. I have seen no splitting of genitals in fossil Echini, but it is rather common as a variant in Recent species. Such secondary division of genitals is seen in Centrechinus (text-figs. 187, 189). In Strongylocentrotus drobachiensis many cases of split genitals were found. In 275 cases genital 3 is split by a transverse suture parallel to the base, as in text-fig. 190. This seems to be a family peculiarity, as it was observed in several species of the Echinidae as in Tripneustes esculentus (Plate 6, fig. 4), and in the Strongylocentrotidae. Instead of splitting by one trans- verse suture, as in text-fig. 190, genital 3 may be divided by one or more sutures in other planes, as in text-fig. 190a and 190b; such were noted in 90 cases. Genital 3 is split much more SI'KCIAI, CIIAHACTKIJS OF CKNITAI. 1'I.ATKS. in*.) HI 755 755 TEXT-FIGS. 190-196. — Splitting, fusion, etc., of genital and ocular plates, in Strongylocrnt rot us and Tripririi-.! 190. Strongylocentrotusdrobachiensis(O.F. Mutter). York Harbor, Maine. Diani. 51 rum. H. T. .1. Coll.. 77:3. X 3. Genital 3 split by one horizontal suture (compare Plate 6, fig. 4). 190a. The same. Diam. 38 mm. R. T. J. Coll., 774. X 3. Genital 3 split by one vertical suture. 190b. The same. Diam. 49 mm. R. T. J. Coll., 775. X 3. Genital 3 split by three sutures. 191. The same. Calderwood Island, Maine. Diam. 46 mm. R. T. J. Coll., 879. X 3. Genital _' split. 192. The same. Harpswell, Maine. Diam. 43 mm. R. T. J. Coll., 776. X 3. Several genitals split by secondary sutures. 193. The same. York Harbor, Maine. Diam. 46 mm. R. T. J. Coll., 711. X 4. Genitals 2,3, and oculars III. V are split by secondary sutures; the splitting of oculars is a very rare variation (Plate 6, fig. 6). 194. The same. Diam. 42 mm. R. T. J. Coll., 700. X 4. Genitals 1 and 2 much split up; ocular V split; t-xtra genital pores, but there is no genital pore in the madreporite (compare text-figs. 197-199, p. 171). 195. Thesame. Diam. 41 mm. R. T. J. Coll., 777. X 3. Genitals 3, 4 fused (compare Plate 0. fin. -: Plate 7. lv 196. Tripneustes esculentus (Leske). Bermuda. Diam. 138 mm. R. T. J. Coll., 787. X 2. Genitals 5, 1 fused; oculars V, IV, II insert (pp. 93, 124). 170 ROBERT TRACY JACKSON ON ECHINI. frequently than any other plate in the families of the Echinidae and Strongylocentrotidae. ( icnital 2 is also frequently divided in S. drobachiensis by secondary sutures (text-figs. 191- 194.) Divisions of this plate were found in 120 cases in this species. Genitals 1, 4, and 5 are occasionally divided by secondary sutures, as seen in 134 cases, but 2 and 3 take the lead by a strong majority. Very rarely oculars are split (text-figs. 193, 194), but only ten cases were noted; otherwise, genitals divided by secondary sutures are the only cases I have seen in Echini of plates derived by the fission of preexisting plates. In the young of echinothuriids, genitals are not split, and in Strongylocentrotus the splitting was very rare in young specimens, while rather frequent in adults. It is evident, as in echinothuriids, that this is a character that comes in with increasing age. Occasionally a line of secondary suture only goes partially through a plate, demonstrating that these are true cases of splitting and not cases of accessory plates. In very young Echini genital pores do not exist, as shown fully by Loven (1892) and A. Agassiz (1904). As seen in Strongylocentrotus drobachiensis (p. 131, text-figs. 131-134), no genital pores were found in specimens up to 5 mm. in diameter, after which age they come in rapidly, and only 128 in 800 were without such pores in the series 5 to 10 mm. diameter; only six in 2,000 were without genital pores in the series 10 to 15 mm. diameter, and no larger specimen was wholly imperforate. Occasionally, one, more rarely two, and in three cases three genitals were imperforate in adults. In a fresh Toxopneustes atlanticus examined, in which a genital was imperforate, the corresponding genital gland was absent. The absence of a genital pore as a variant may be compared with Holectypus (text-fig. 171, p. 149), and some spatangoids (A. Agassiz, 1904) in which one or more genitals are typically imperforate. Typically, in post-Palaeozoic regular Echini there is a single genital pore within the con- fines of each genital plate. In Goniocidaris nutrix and canaliculata (text- figs. 72-74, p. 99) the ventral border of the genitals is open, doubtless resorbed so that the genital pores impinge on the interambulacra. This character has been seen as a variant in Centrechinus setosus, Arbacia nigra, and Strongylocentrotus drobachiensis, but is of uncommon occurrence. Mr. Agassiz (1873) shows that in the clypeastroid Peronella peronii (Agassiz) the genital pores lie in the interambulacra widely removed from their usual position. In an Arbacia punctulata in one area the genital pore is not in its usual plate, but passes through the third interambula- cral plate from the apical disc. In Strongylocentrotus the genital pores very rarely perforate an interambulacral plate, and in four cases found perforated an ocular plate. While genital pores are usually found in genital plates, it seems that there is no necessary correlation, and the pore when developed may perforate any portion of the test. Genital pores are usually perfectly visible in dorsal view, are even salient features, but in Salenia paltersoni they are invisible externally though plainly seen in an internal view of the same specimen (Plate 4, figs. 1, 2). While a single genital pore to a plate is the character in Recent regular Echini, supplementary pores are not rare. They are especially common in Arbacia SPECIAL CHARACTERS OK (iMMTAJ, IM.ATKS. 171 pundulata (text-figs. 197, 198), in which I previously described them Mai-Urn. Is'.Mt, p. |.;n Similar extra genital pores have been seen in Kurltlnrix //•//»///„/,/,*, /•>////,te«l but do not show in external view, as noted in Salenia pattersoni (p. 112). In an ancient fossil it would be easy for small genital and madreporic pores to be so filled up as not to be recognizable, for frequently in fossils pores cannot be seen when we know from other specimens that such existed. In Lepidechinus (Plate 63, figs. 7, 8) there is one pore in each genital plate in tin- only species of the genus in which the apical disc is known. In other Palaeozoic Echini genital plates typically have more than one pore \« ;\ plate. There may be two or three, as in Lepidesthes (Plate 68, fig. 5), or there may be three to live in a plate, as in Palaeechinus (Plate 29, fig. 6; Plate 30, fig. 4), Lovenechimis i Plate 11, fig. 3), and Melonechinus (Plate 56, fig. 6). Instead of a few pores there may be numeruu- genital pores to a plate, even as many as ten or eleven, as shown in Lepidooentnu (Plate 21, fi- Pholidechinus (Plate 28, fig. 10), and Perischocidaris (Plate 67, fig. 3). It is possible that in types where fine madreporic pores are unknown, some of the larger pores served as madreporic 172 UOHKHT TRACY JACKSON ON ECHINI. openings. Otherwise all the pores in genital plates doubtless connected with genital glands, as in Recent Echini with accessory pores. In very young Recent Echini, as shown by Love"n (1892), there is a single madreporic opening in genital 2 (Plate 2, fig. 3; Plate 3, fig. 14; text-fig. 131, p. 129). Fine madreporic pores soon appear, and in the adult are usually numerous (Strongylocentrotus, text-figs. 132- 139, p. 132). In some types there are few madreporic pores in the adult, a primitive character (Salenia, Plate 4, fig. 1). Usually the madreporite is perforated by many pores, as seen from the interior as well as from the exterior. In the Cidaridae, however (text-figs. 59,60; 70, 71, pp. 95, 98), while there are many on the exterior of the plate, there is only a single large madreporic pore on the interior, so that at this part of the plate the youthful character is retained in the adult. The same condition exists in Salenia pattersoni (Plate 4, figs. 1,2). In Echinocyamus (Love"n, 1874) there is a single external madreporic pore. In Habrocidaris scutata (text-fig. 206), as shown by Messrs. A. Agassi z and Clark (1908), no fine madreporic pores exist in genital 2, but, instead, there is a single pore in the middle of the plate, which appears to be a retention in the adult of the single madreporic opening characteristic of the young. This is the only case known in an adult regular echinoid. In Palaeozoic Echini a typical madreporite with numerous fine pores is known in a few species. It exists in Lovenechinus lacazei, as observed by Bather (text-fig. 243); also, it has been found in Lepidesthes formosa (Plate 68, fig. 5), L. colletti (Plate 71, fig. 1), Meekechinus elegans (Plate 76, fig. 6), and Echinocy stiles pomum (Plate 18, fig. 6). In a number of Palaeo- zoic genera the apical disc is not known well enough to enable one to state anything with assur- ance. In the Palaeechinidae the apical disc is known in many species and yet the madreporite has been seen in Lovenechinus only, as above noted, and reported in Melonechinus multiporus by Keyes (1894). I have not seen a specimen of Melonechinus with madreporic pores. In post-Palaeozoic regular Echini the madreporic pores exist in genital 2, and are typically limited to that plate. In examining large series of specimens, it is frequently found that the madreporic pores extend beyond genital 2. When this occurs, in the great majority of such variants, they extend to genital 3 and frequently ocular III as well (Centrechinus, text-fig. 188) ; or they may extend to ocular III without invading genital 3 (text-fig. 146, p. 134). This extension of madreporic pores has been seen in many species, but in Strongylocentrotus dro- bachiensis, on account of the number examined, a greater range is known than in others studied. Of this species in 33,000 specimens, 928 cases were noted in which madreporic pores extended from genital 2 to 3 (Plate 5, fig. 13). In 128 cases madreporic pores occur in genital 2 and ocular III (text-fig. 146, p. 134), and in 64 cases in genitals 2, 3 and ocular III, as in Centre- chinus (text-fig. 188). In 80 cases, madreporic pores are in genitals 1, 2, 3, and in 60 cases in genitals 2 and 1 (text-fig. 142, p. 134). Other variations in the extension of madreporic pores beyond genital 2 are only rarely found. In 15 cases, they exist in genital 2 and ocular II; in THE PERIPROCT. 173 six cases in 2, III, II; in three cases in 2, 3, III, and II; in four cases in 2, 3, II (text-fig. 148, p. 134). In seven cases madreporic pores occur in genitals 1, 2, 3, and ocular III ; in four in 1, 2, 3, and II; and in eleven in 1, 2, 3, and II, III (Plate 5, fig. 14). The most extreme range observed was one specimen in which the madreporic pores extended from genital 2 to genitals 1, 3, 4, and oculars III, IV, V. A similar range of variation in the distribution of madr<'fx>ric pores and in about the same proportions has been found in other specie-, especially in the families Echinidae and Strongylocentrotidae. In the young, madreporic p<>n- very rarely extend beyond genital 2, whereas they frequently do in the adult. This change evidently i» taken on as the animal increases in size to the adult condition. Occasionally madreporic pores invade interambulacrum 2, and in one somewhat distorted Strongylocentrotus drobachiensis this invasion was extensive. All this goes to show that while typically madreporic pores are limited to genital 2, they may extend from this plate to adjacent genitals, oculars, or interambulacrum, but apparently never to plates of the periproct. They seem never to be absent from genital 2 in Recent regular Echini. When madreporic pnn- extend beyond genital 2, in the great proportion of cases they move to the left of the atitero- posterior axis, emphasizing by this a bilateral axis or plane of symmetry through III, 5. As seen from these studies, the genital plates have nothing to do with the interambulacrum, which develops on either side of the oculars (p. 62). The genitals typically possess genital pores, and one of them possesses madreporic pores, but both of these structures may pierce other parts of the test. Genital plates may, therefore, be considered as structures of secondary importance, of much less morphological value than are the oculars. THE PERIPROCT. The periproct is an area of considerable interest. Unfortunately in fossils it is rarely preserved, as the plates easily drop out and are frequently wanting, even in museum specimens of Recent Echini. It is worth noting that in Recent Echini periprocts and peristomes may be rendered strong and safely fastened in place by dipping the specimens in dilute shellac dissolved in alcohol, or gelatine dissolved in water. The same treatment is very effective in >trength- ening the thin tests of delicate Echini and in keeping the spines firmly in place. In Palaeozoic Echini the plates of the periproct are small, angular, and completely fill the area, as in cidarids. In Bothriocidaris archaica there are nine small plates that fill the area dorsal to the genitals (Plate 1, fig. 2). In Hyaltechinus beecheri (Plate •_':•. fig. 5) a few peri- proctal plates are preserved (others restored in the figure), indicating a periproct «— entially as in Cidaris. In Palaeechinus (Plate 31, fig. 4), Maccoya (Plate 34, fig. 6), I.ovcncchinus (Plate 42, fig. 6), and Melonechinus (Plate 56, fig. 1) the periprocts as far as preserved are made up of many polygonal, rather thick plates filling the area, that are essentially like those of 174 ROBERT TRACY JACKSON ON ECHINI. Eucidari.f tribtiloides in structure (text-figs. 62-69, p. 98). In the Lepidesthidac, the peri- proctal plat os in the known types are essentially the same, like cidarids, but are rather thinner and more scale-like; such are shown in Lepidesthes formosa (Plate 68, fig. 5), L. collelti (Plate 71, fig. 1), and Meekechinus elegans (Plate 76, fig. 6). Palaeozoic types as far as known do not throw any light on the suranal plate, which is such a prominent feature in the young of some Recent Echini and the adults of certain genera. There is no evidence that a suranal plate was differentiated in the Palaeozoic, and, as it is apparently wanting in the Cidaroida and Aulodonta, both young and adult, it is also doubtless wanting in the Palaeozoic. In the Cidaroida, periproctal plates are thick and angular, filling the area, with the anus central. They are essentially like those known in the Palaeozoic and in so far may be con- sidered primitive. These plates are shown in representative cidarids in text-figs. 59-74, 164 (pp. 94-99, 149). Love'n (1892) figures a young Goniocidaris with a single plate filling the periproct (Plate 2, fig. 3); but Mortensen (1911) thinks this a mistake, as in a specimen of a similar stage he found three plates. Mr. Agassiz's (1904) figures of young cidarids, and those young specimens which I have studied, show no indication of a dominance of a first, over later added plates. It seems, then, that we have here no suranal such as exists in the Saleniidae and in young Echinidae and Strongylocentrotidae, in which groups alone has it been demon- strated. The existence of a suranal plate is apparently a secondary and specialized rather than a primitive character. Dr. Mortensen wrote me in effect that he concurs in this view, and he expresses the same in a recently published paper (1911). In the Centrechinoida the character of periproctal plates presents wide differences in various genera. Of the Aulodonta there are large plates on the periphery of the periproct with small Isolated plates within, as seen in Chaetodiadema, Centrostephanus, Astropyga (text-figs. 96-99, pp. 108, 109), or young Centrechinus (text-fig. ^88) ; or there may be small, isolated plates only, with tissue largely leathery, as in adult Centrechinus (text-figs. 93-95, p. 107). Of the Stirodonta in Salenia and Salenocidaris (Plate 4, figs. 1, 6; text-fig. 102, p. Ill) we find a prominent suranal plate lying dorsal to genital 3 and with small anal plates in addition. In the fossil Peltastes (Plate 4, fig. 7) the suranal occupies a prominent place but lies dorsal to ocular III, thus differing from Salenia and young Strongylocentrotus and Echinus, in which the suranal lies dorsal to genital 3. In a series of 74 specimens of Peltastes wrighti one speci- men has two large plates, as in Aerosalenia hemicidaroides (text-fig. 104, p. Ill), and as in that figure the larger plate, which may be considered the suranal, lies against genital 3, as in Salenia. This is a striking difference from the other specimens, in which there is only a single plate lying dorsal to ocular III, as shown in Plate 4, fig. 7, which is the generic character. The fact that the suranal may occupy one of two positions has a certain bearing on other genera. In Acrosalenia spinosa (text-fig. 103, p. Ill) the suranal lies dorsal to ocular III, as in Peltastes, but in A. hemicidaroides (text-fig. 104, p. lit) there are two large plates; the larger THE I'KHIPIKMT. 175 of these two, which appears to be the suranal, lies dorsal to genital 3, a* in Salenia. In Acro- salenia wiltoni (text-fig. 105, p. Ill) there are four large periproeial plati- !>• -ides a vacant space, doubtless for small anal plates as in Salenia. The largest of these four is probably the suranal and lies dorsal to ocular III, as in Acrosaknia spinosa and Peltastes. In Arbacia there are typically four plates in the periproct, but as variant- there may l>e fewer or more than this number. Bell (1879) notes that there may l>e a> few a- thn< or an many as ten, and Mr. Agassiz (1881, p. 57) notes that there may he more than four up to thir- teen periproctal plates. I noted (1899, p. 131) that in Arbacia punctulala there may be as few as three or as many as nine plates as variants from the typical four. In Arliaeia the typiral four periproctal plates lie in such planes that two are in the antcro-posterior axis III, 5, and two are on each side of this axis (text-figs. 111-114, p. 115; text-figs. 1G7, p. 149; 202). The m TEXT-PIGS. 200-206.— Variation of periproctal plates in Arbacia with the typical rhanirtrr in II:ibrocidaris. 200. Arbacia punctulata (Lamarck). Woods Hole, Massachusetts. Diam. 25 mm. R. T. J. Coll.. 7J7. Only two periproctal plates; suranal dorsal to genital 3. X3. 201 202 203 204 205 205a. The same. Diam. 45 mm. R. T. J. Coll., 728. The same. Diam. 47 mm. R. T. J. Coll., 729. Diam. 31 mm. R. T. J. Coll., 730. Diam. 36mm. R. T. J. Coll., 731. Diam. 43 mm. R. T. J. Coll., 732. The same. The same. The same. The same. X 3. Only throe periprortal plates. X 3. Four periprortal plali-s, tin- typiral character (p. 115.) X 3. Five ]x>riproctal plates; rompan- trxt-fiK.206. X 3. Six periproctal plates. X 3. Many prriproct:il platrs. a __...„. Florida. Diam. 32 mm. R. T. J. Coll., 890. X 4. One large and about fifty small periprocUl PlateT""The7P~eci"men is so distorted its ocular arrangement is omitted in tabulation of il.- M-" '-. pp. 206. Habrocidaris scutala (A. Agassiz). Santa Cruz, West Indies. Di,,m. 17.5 ,,,m. A,laPt,-l Clark, 1908, Plate 54, fig. 5. X 3. Five periproctal plates; compare text-f,K. 21M. pore in genital 2 (compare Plate 3, fig. 14). The genital pores lie very far dorsally (p. I.-1) 176 ROBERT TRACY JACKSON ON ECHINI. plate lying dorsal to ocular III is apparently the equivalent of the suranal, as in Acrosaknia wiltoni (text-fig. 105), which also has four large plates. In examining some 2,300 specimens of Arbacia punctulata, considerable variation was found in the periproctal plates, and they varied in adults from two to many (text-figs. 200-205). Two specimens were found with only two plates and many with three. In both of these forms what I take to be the suranal overlaid jit'intal 3, as in Salenia, not ocular III as usual. A number of specimens were found with five plates and several with more than five, one being shown with six and one with thirteen (text- figs. 204, 205). In one abnormal specimen from Florida (text-fig. 205a) there is one large peri- proctal plate facing ocular III, as usual, and, in addition, some fifty small rounded periproctal plates of a character similar to those usual in the Echinidae. When there are five periproctal plates in Arbacia, as in text-fig. 203, the condition is exactly like that of Habrocidaris (text- fig. 206). In Parasalenia gratiosa A. Agassiz, as shown by Mr. Agassiz (1873, p. 435), there are four periproctal plates, as in Arbacia, but they lie in a different plane so that two are on each side of the antero-posterior axis through III, 5. Of five specimens of Parasalenia gratiosa seen in de Loriol's collection, in the Geneva Museum, four have the typical four plates in the periproct, but one has only three. Variations of periproctal plates in Arbacia dufresni were also noted as described, p. 115. In the young of the Echinidae and Strongylocentrotidae a suranal plate fills the periproct, as shown by Mr. Agassiz (1874, p. 732). This is typically developed in young Echinus (Plate 3, fig. 14) and Strongylocentrotus (text-figs. 131-134, p. 129). As the animal grows, the suranal gradually loses its prominence, new plates forming along its right posterior border and the suranal retaining while recognizable a position dorsal to genital 3. In the adult of Strongylo- centrotus drobachiensis a plate is often found dorsal to genital 3 somewhat larger than other periproctal plates (text-figs. 135-139, p. 132). It seems that this may be recognized as the suranal still holding a slight supremacy in size. A similar plate similarly located is frequently recognizable in other genera, as Toxopneustes (text-fig. 122, p. 122) and Echinus (text-fig. 115, p. 117), and may fairly be considered as the suranal. There is considerable individual variation, some specimens having no such larger plate at this area and others possessing one. Dr. Mortensen (1911) expresses the view that the suranal is not a primitive structure form- ing an essential part of echinoid morphology, but is a specialized structure found only in certain groups of Echini. I heartily agree with this view. It seems that the suranal is simply one of the plates of the periproct which has attained exceptional prominence and which in youth entirely fills this area in those families in which it is a marked feature (Saleni- idae, Echinidae, Strongylocentrotidae). In the adults of the Temnopleuridae, Echinidae, Strongylocentrotidae, and Echinometridae (text-figs. 115-1G1) the periproctal plates are usually relatively large and solid, more or less numerous, but not definitely limited to a small number (except in Genocidaris and Parasalenia), ARISTOTLE'S LANTERN AND PERIGNATHIC GIRDLE. 177 and fill the periproctal area. In irregular Echini periproctal plates are relatively numerous and always fill the area completely. As clearly shown by Mortensen (1907, I 'Into i:jj in Hriaatter (Schizaster) fragilis, the periproct in the very young individuals is within the apical disc, as in regular Echini. It early travels out and soon assumes its adult position in the posterior inti-r- ambulacrum. In regular Echini the periproct is typically enclosed by a ring of genital, or genital and ocular plates. In the Echinothuriidae, on account of the separation of genitals and o.-nlure, the periproct may come in contact with the interambulacra (text-fig. 170, p. 149). As a rela- tively rare variation, a similar condition may exist in other regular Echini, as Rtrongylocenlrolus gibbosus (text-fig. 156, p. 145), 8. drobachiensis (Plate 5, fig. 15), and S. Hindus (Plate 6, fig. 5). In such types the young interambulacral plates develop in contact with the oculars as usual, and the periproct has no relation with the interambulacra excepting that of mechanical contact (pp. 63, 110). In the Exocycloida the periproct lies in interambulacrum 5; it is therefore separated from the ocular and genital plates of the apical disc and completely surrounded by interambulacral plates. THE ARISTOTLE'S LANTERN AND PERIGNATHIC GIRDLE. Comparatively little has been published in regard to the Aristotle's lantern in Palaeozoic Echini. Trautschold (1868) figured complete lanterns in Archaeocidaris rossica, Sollas (1899a) figured a lantern in Palaeodiscus, and Meek and Worthen (1873) in Lepidocidaris in part. The lantern and its muscles in living Echini have been worked out quite fully by a number of authors, the most important being Valentin (1841), A. Agassiz (1872-74, 1904, 1908, 1909), T. H. Stewart (1861), and Love~n (1892). The jaws and muscles are often very inadequately or incorrectly given in text-books. For comparison with fossils, a lantern with soft parts was worked out in Strongylocentrotu- (Plate 5) as a basis for comparison. The lantern of this genus and a number of others not previously described were studied, and are given more or less fully in the following pages. The perignathic girdle might properly be described with the lantern in the several types, but it seemed best to treat it separately (pp. 189-198). It is believed that the structure of the lantern is of great value in systematic classification, and that the structure of its several parts presents characters that are of ordinal or subordinal value. As Dr. Mortensen pointed out (1904, p. 54), the structure of the teeth, keeled or un- keeled, is "a very important character, though it has hitherto received verylittle attention." Besides the teeth there are other features of value. Briefly stated, the essential points are: teeth grooved or keeled ; epiphyses narrow, or wide and united by suture ; the top of the pyramids, as seen when the epiphyses are removed, a smooth floor, or pitted ; foramen magnum deep, or shallow; angle of outline of the lantern depressed or erect; compasses present or absent. 178 ROBERT TRACY JACKSON ON ECHINI. The lantern of Strongylocentrolus drobachiensis is taken up first as a type of structure, because opportunity offered to study living material and abundant fresh specimens for dis- section. The structure has not been published in this type excepting in so far as Loven (1892) described the jaws and muscles in the young; the study has, therefore, interest from making known the structure in a common type and adds some features not previously recorded. In Strongylocentrotus there are five keeled teeth lying free about the mouth. The tooth is hold in place by the two half-pyramids which ventrally enclose it closely by an inward extension of the base of the lateral wings (Plate 5, fig. 5). The tooth rests against the dental slide (s. d.) on the inner face of the pyramids. On each side the dental slide is produced dorsally as a guid- ing or styloid process, which in face view is seen projecting above the base of the foramen mag- num (Plate 5, figs. 4, 7). After traversing freely the space of the foramen magnum, in this type the tooth rests against two guiding processes, the crests of the epiphyses (Plate 5, figs. 2-5, 7, 9). The tooth then curves inward, takes a second sharp curve on itself and in the same plane, and terminates in a free point in the dental capsule (Plate 5, fig. 6). From the mouth to a point just above the crests the tooth is calcified; beyond this point to the proximal tip the tooth is soft and pulpy and easily destroyed. In area 1 of Plate 5, fig. 9, the soft part of the tooth has been removed, whereas it is in place in areas 2 and 3. The calcified part is that usually shown in figures of lanterns, and is the only portion preserved in fossils, as in Archaeocidaris (Plate 12, figs. 4-8) and Pholidechinus (Plate 27, figs. 4-6). An entire tooth spread out flat is shown in Plate 5, fig. 8; it is seen that at the dorsal, young or growing portion of the tooth it is grooved, but, passing ventrally, the character of the keel is soon taken on. That is, the young, last added portion of the tooth as a localized stage in development is grooved, as is the whole tooth in the Aulodonta, Cidaroida, and Palaeozoic forms; whereas the older or earlier formed portion of the tooth has taken on the full specific and subordinal character of a keel. The pyramids are each composed of two pieces joined by a median or pyramidal suture (Plate 5, figs. 4, 7, p. s.), and each piece is spoken of as a half-pyramid. Dorsally the pyramid in- cludes a wide angle, the foramen magnum, which in this and allied species is rather deep. On the inner side at the base (Plate 5, fig. 5) the wings of the pyramid curve around so as to embrace the tooth tightly at its point of exit. Each half-pyramid consists of a peripheral portion, the outer face of which gives rise to two muscles, and the inner bears one of the two dental slides which support each tooth, and a lateral wing which is strongly ridged horizontally for attach- ment of the interpyramidal muscles. The dorsal face of the half-pyramid, seen only when the epiphysis is removed (Plate 5, figs. 9, 10), presents a series of pits of considerable size and depth. These pits have apparently been overlooked by previous observers. They are important, as they are characteristic of the order of the Centrechinoida, but are not found in other orders of Echini. In 100 specimens of Strongylocentrotus drobachiensis from Frenchman's Bay, Maine, examined for this character, pits exist in all the pyramids, but there is considerable variation as regards the pattern and depth of the pits; occasionally they are very shallow. ARISTOTLE'S LANTKKX AND I'HHKJN ATHK (ilUDI.i: 179 An epiphysis surmounts each half-pyramid to which it is joined |>v ,•],,.,• Mit,ire < Plate 5, figs. 2-7, 9). The epiphysis extends proximally, capping tho half-pyramid, and lateral! tends over the foramen magnum and meets its fellow of tho opponte -id.- in a median Each epiphysis presents a glenoid cavity and an internal and an external tnlx-rde I'l.it.- :,. figs. 3, 5, 9), which serve in articulation with the brace. It also hear- an elevated processor crest which is apposed to the tooth and dorsally supports that organ. The extension of the epiphyses over the foramen magnum so as to unite in suture and the cn-t- developed on the same, are important characters seen in the four families of the Temnopleiiridae, i;,.|,jMidae, Strongylocentrotidae, and Echinometridac, comprising the new suborder ('aman.donta. but are absent in other Echini (p. 183). The brace is a block-shaped plate, often called rotula, which rests on and interlocks with the two opposed epiphyses (Plate 5, figs. 9, 11, 12). On its outer lateral borders it present* two condyles which fit into the glenoid cavities of the epiphyses. The compass (Plate 5, figs. 2, 9) rests on top of the brace, extends over its whole length, is attached to the brace on li- mner proximal end by a tiny ligament, and is bifurcated on its outer end. Each compass consists of two parts, a suture just within the circular compass muscles separating the compass into an inner and an outer piece. The structure of the compass and brace is quite uniform in Echini, excepting the clypeastroids. There are thus forty pieces in the lantern of Strongylo- centrotus, and in all other Echini that possess a lantern, excepting the clypeastroids. These parts are in brief: five teeth; ten half-pyramids ; ten epiphyses; five braces; ten pieces making up the five compasses. Next taking up the soft parts associated with the lantern of Slrongylocenlrolus drobachiensis, we find that each tooth at its basal portion is enclosed in a voluminous, very delicate tr parent sac that may be called the dental capsule. A dental capsule is figured by the Sara>in> (1888) in Asthenosoma,1 and is mentioned in Cidaris by T. H. Stewart (186'1) and in Echinus by Chadwick (1900), but I think it has not been adequately shown before. In order to see the sac properly, a specimen should be opened alive, right out of the sea. It is so delicate and sen>i- tive, that if opened a few hours later, though the animal be still active, the sac has shrunk to small proportions. In alcoholic material as far as observed it is always collapsed. When opened thus alive, the capsules are so inflated that they look like five bladders radially arranged, and so large that they actually touch one another at the area nearest the oesophagus 1 1 Ma- fig. 1). The sac envelops the base of the tooth completely, lies free, but on its outer lx>rder passes over the epiphyses and some distance down the face of the area of the foramen magnum (Plate 5, fig. 6). Similar capsules were seen in fresh specimens of Arbacia punclulata, Sphaer- echinus granularis, and Strongylocenlrotus lividus, and very small ones inEchiiuirticlinius It would be interesting to study the capsules in perfectly fresh material of other Echini. 1 Unfortunately in Lang's (1896) copy of this figure, the dental capsule U labeled Polian vesicle. 180 ROBERT TRACY JACKSON ON ECHINI. The muscles of the lantern are very complex. They have not been described in adult Strongylocentrotus, though Loven (1892) showed them in a very young one and in exquisite detail in the adult of several types. There are sixty muscles in Strongylocentrotus and other regular Echini. There are ten protractors (Plate 5, figs. 1, 4, pr.; text-fig. 229), which take origin on the upper outer face of the half-pyramids and epiphyses and are inserted at the base of the two half-interambulacra which are associated with the intervening ambulacrum (compare text-figs. 218, 219, p. 191). The protractors serve to extend the mouthparts, which the animal actively does when in good condition. The ten retractors (Plate 5, figs. 1, 4, re.), which serve ta open the jaws, take origin on the lower outer face of the half-pyramids and are inserted on the auricles. The retractors of the two half-pyramids that are united by the interpyramidal muscle pass to the two auricles of the same ambulacrum (compare text-fig. 219, p. 191). Ten radial compass muscles take origin from the bifurcated termini of the compasses and are in- serted at the base of the two next adjacent half-interambulacral areas. From studying their motions in life, and from their position and wide divergence, it seems that the function of the radial compass muscles is to maintain and restore the vertical position of the lantern. When alive, the mouth with the peristome is freely and actively extended and retracted, and not in a vertical plane only, but with much sidewise or inclined motion, so that the radial compass muscles are in just the position to effect the motion and restore the perpendicular. It is note- worthy that in clypeastroids, where the lantern is in almost immediate contact with the base of the test and little motion is possible, the protractor muscles are very small and the compasses with their muscles are absent. The distribution of protractor, retractor, and radial compass muscles is immediately con- nected with the view expressed (pp. 62, 190), that the corona may be considered as made up of five rather than ten areas. Five large but short interpyramidal muscles (Plate 5, fig. 2, ip.), extend from the corrugated lateral wing of each half-pyramid to the similar wing of the next adjacent half-pyramid. These muscles serve to close the jaws and from their size must be very powerful. Ten tiny internal brace muscles (Plate 5, fig. 12, i. b.) extend from the brace to the two associated epiphyses, and ten similar external brace muscles, (e. 6.), extend also from the brace to the epiphyses, binding these parts together and doubtless giving some mobility. Five circular compass muscles (Plate 5, fig. 1, i.) extend between the compasses, being inserted at the proximal end of the outer of the two pieces of which each compass is composed. Their function is not evident. In brief the sixty lantern muscles of Strongylocentrotus and other regular Echini are as follows: ten protractors; ten retractors; five interpyramidal muscles; ten internal brace muscles; ten external brace muscles; five circular compass muscles; ten radial compass muscles. Such being the character of the lantern of the adult, it is important to see what is the ARISTOTLK'S I,\\TKKX AM) I'KIIICN ATIIK (JIKDI.i; 181 character in the young. Lov<§n (1892, p. 13, Plate 4) described the lantern of a young Mrongy- locentrotus drobachiensis only 1.2 mm. in diameter. At this stage the pyramids arc \vi.le-.-ingled, so that the whole lantern is broadly inclined instead of being nearly perpendicular, an in tin- adult; also the sides of the half-pyramids bearing the interpyramidal muscles are curved instead of being in a nearly vertical plane as in the adult, and as a result the interpyramidal muscles are relatively longer than in the adult. In these several characters the lantern of young Strongylocentrotus point for point agrees with the typical Palaeozoic lantern as seen in Arehaeo- cidaris (Plate 12, figs. 4-6) and Pholidechinus (Plate 27, figs. 4-6). The same agreement with the Palaeozoic characters is seen in the lantern of young Goniocidaris (Plate 2, fig. 17). Having considered the lantern and muscles of Strongylocentrotus, representative lanterns of Echini will be taken up in the sequence of their structural differentiation. Of Bothriocidaris nothing is known but the tips of the teeth, or pyramids. They lie opposite -the ambulacra (Plate 1, fig. 1). That they occupy this anomalous position is without explanation unless by an accidental twist they have come to assume it. It is the most ambiguous feature of this important type. I have been so fortunate as to secure for study some excellent lanterns of Palaeozoic genera. These are described under their several species, but are briefly considered here. The essential character of the lantern in the Echinocystoida and Perischoechinoida is represented by Archaeocidaris (Plate 12) and Pholidechinus (Plate 27) ; other genera as far as known present only slight differences. Of other genera it is known more or less completely in Palaeodiscus, Oligoporus (Plate 50, figs. 11, 12), Melonechinus (Plate 56, figs. 9, 10), Lepidesthes (Plate 68, figs. 9-14), Pholidocidaris (Plate 74, figs. 2, 6, 7), and Meekechinus (Plate 76, fig. 7). In t he- Palaeozoic genera the teeth are grooved, and when in place, extend slightly above the base of the foramen magnum (Pholidechinus, text-fig. 207, Plate 27, figs. 5, 6). While the teet h are usually obtusely acuminate orally, as in Pholidechinus and Lepidesthes (Plate 68, fig. 9), in one genus, Meekechinus (Plate 76, fig. 7), the teeth are deeply serrate distally, a unique cham The pyramids are wide-angled in outline and as a result the lantern is inclined at an angle of about 45 degrees instead of being nearly perpendicular as in the adults of most living regular Echini; also the lateral wings of the pyramids are curved, indicating quite long interpyra- midal muscles (Plate 27, figs. 4, 6). In these characters the Palaeozoic lantern approaches closely that in the young of modern types (Goniocidaris, Plate 2, fig. 17), and also the adult of Recent echinothuriids (Plate 2, figs. 19-21). The foramen magnum is moderately deep (Archaeocidaris, text-fig. 208, Plate 12, fig. 4). It appears very shallow in Pholidechinus (Plate 27, fig. 6), but this is in part due to the position in which the specimen was drawn. The lateral wings of the pyramids present a corrugated surface for attachment of interpyra- midal muscles (Plate 12, fig. 8; Plate 13, fig. 13; Plate 68, fig. 12). The dorsal surface of the half-pyramids, seen when the epiphyses are removed, is smooth, as in the Cidaroida 182 ROBERT TRACY JACKSON ON ECHINI. (Plate 2, fig. 9), not pitted as in the Centrechinoida. The half-pyramid seen from within shows a dental slide for the support of the tooth (Plate 13, fig. 14; Plate 50, fig. 12), as in Recent Echini. The styloid processes do not extend above the base of the foramen magnum, in this feature being like the Cidaroida, but unlike the Centrechinoida, where the styloid processes are visible in face view (text-fig. 211). The epiphyses cap the half-pyra- mids and are narrow, projecting only slightly beyond the limits of the outline of the half- pyramids (text-figs. 207, 208; Plate 12, figs. 1, 7; Plate 27, figs. 4-6). Each epiphysis pos- sesses a glenoid cavity for the interlocking of the brace (Plate 12, fig. 8; Plate 08, fig. 12). The brace is a block-shaped plate, practically identical with that of living regular Echini. It rests on the epiphyses, and its condyles fit into their glenoid cavities (Plate 12, figs. 3, 6, 7; Plate 27, figs. 4-6). A compass is such a delicate structure that it is rarely preserved, but one was found in Archaeocidaris (Plate 12, figs. 1, 2) resting on the brace and with the typical bifid outer end. A compass is also shown in Pholidechinus (Plate 27, fig. 5), butHhe bifid end is gone, or possibly it did not have such a bifurcation, as it is not existent in all Recent compasses. These are the first cases of compasses described from Palaeozoic species. It is seen that in the Palaeozoic Echinocystoida and Perischoechinoida the lantern is made up of forty pieces, as in Recent regular Echini. In structure it approaches closest to that of Cidaris. There were doubtless the same sixty muscles as described in Strongylocen- trotus. It is interesting to see how near the characters of these ancient genera are to those of living forms, and also that their closest comparison is with the young of the latter. In the Cidaroida the lantern is the most primitive of any Recent Echini. Loven (1892) showed the character in the young of Goniocidaris ; here at a very early stage the pyramids are very wide-angled, with long interpyramidal muscles and a deep foramen magnum (text- fig. 209; Plate 2, fig. 17). In these characters it differs from the adult, but is practically identi- cal with the Perischoechinoida. According to Loven, at this early stage the protractor and retractor muscles are inserted directly on the primordial interambulacral plates, which are still in place. This condition again by inference is close to that in the Palaeozoic genera where (excepting Miocidaris) apophyses and auricles are apparently always absent, and the pro- tractor and retractor muscles were without doubt attached directly to the basicoronal inter- ambulacral plates (text-fig. 221, p. 193). Lov6n (1892) described the lantern and muscles of "Cidaris papillata" (Cidaris cidaris (Linne1)) with his usual care. To show another type and to bring out certain points, the lan- tern of Eucidaris iribuloides is here shown in text-fig. 210 and Plate 2, figs. 7-16. In this species the teeth are grooved and extend far beyond the pyramids ventrally (Plate 2, figs. 7, 8). The tooth rests against dental slides on the inner face of the pyramids, but the styloid processes are slight and do not extend above the foramen magnum so as to be seen in face view (Plate 2, fig. 10), as they do in the Centrechinoida. The pyramids are comparatively narrow-angled, stand- * ARISTOTLK'S LVNTKHN AM) I'l.UK-N \TIIK (JIIUH.K 183 ing erect, and the foramen magnum is extremely shallow, t l.r pyramidal suture extending m-arly the length of the outer face (Plate 2, figs. 8, 10). Th<- pyramid ha- the n-nal corrugation- ..., the lateral wings (Plate 2, fig. 7). When the epiphyses are remove,!, the do,-al faces of tin- pyramids present a smooth surface (Plate 2, fig. <), area II). This is an important cha. in which it resembles Palaeozoic genera, but differs from the ( Vnirerhinoida j,, which pjt, typically occur in this area. The epiphyses are narrow, extending only .-lightly l>eyond the upper face of the half-pyramids. Each presents a glenoid cavity and internal ami external tubercles for articulation with the brace (Plate 2, figs. 7, 9, 14, 15). The hraee i- of the n-ual shape with rather strongly marked condyles and external and internal foramina for articulation with the glenoid cavities and tubercles of the epiphyses. Each ossicle of the compa- i- eompooed of two pieces and is strongly arched, with a bifid outer end (Plate 2, fig. 12). A lantern i- -h..wn on Plate 2, fig. 9, drawn to give the full characters from the dorsal view. In area I all the part- are in place; in V the compass is removed to show the brace; in IV the compass and brace are removed to show the epiphyses; and in area II the epiphyses also are removed. -<> a- to .-how the dorsal face of the half-pyramids. This figure may be compared with similar druwing- of Phormosoma (Plate 2, fig. 20), Salenia (Plate 4, fig. 4), and Strongylocentrotus (Plate 5, fig. 9). These figures bring out essential differences in their several separate groups. The lantern of Eucidaris as shown has the character of its order and is essentially similar to that of the Perischoechinoida. The chief differences are the angles of the pyramid and the .-hallow foramen magnum. These differences, however, are bridged by the young. In the Centrechinoida the structure of the lantern is extremely interesting and afford- data for grouping the families in three distinct suborders on the basis of the characters of the teeth and the epiphyses. The order as a whole differs from other orders in that the dorsal face of the half-pyramids (seen when the epiphyses are removed) shows a .-erie- of pit- instead of plane surfaces. The order is characterized by having a deep foramen magnum instead of a very shallow one, as in the Cidaroida, or a moderately deep one, as in the Perischoechinoida. The first suborder, which I would call the Aulodonta, (avXdj, a groove, and 68ous, tooth) is characterized by grooved teeth and narrow epiphyses, not meeting in suture over the foramen magnum (Centrechinus, text-fig. 211; Phormosoma, Plate 2, figs. 19-21). The second sul>- order or Stirodonta (crreipa, a keel, and 68ou's, tooth) is characterized by keeled teeth and narrow epiphyses, not meeting in suture over the foramen magnum (Salenia, Plate 4, figs. 3, 4; Glyptocidaris; Stomopneustes, Plate 4, figs. 8-10; Arbacia, text-fig. 212). The third suborder or Camarodonta (Ka^dpa, anything with an arched covering, and 0801/5, tooth) is characterized by keeled teeth and wide epiphyses, meeting in suture over the foramen magnum (Tripneustes, text-fig. 213; Strongylocentrotus, Plate 5, figs. 1-12). A more detailed consider- ation of these suborders and their characters follows. Aulodonta.— In Centrechinus seiosus (text-fig. 211, text-figs. 219, 220, p. 191) the teeth IS I ROBERT TRACY JACKSON ON ECHINI. 213 212 TEXT-FIOS. 207-216. — Essential features of the lantern in representative Echini. In each species figured are shown a pyramid with associated parts in place seen in face view, with a cross section of the tooth; also an epiphysis (A) seen from above, and a top view of a half-pyramid (B) from which the epiphysis has been removed. 207. Pholidechinus brauni sp. nov. Lower Carboniferous, Crawfordsville, Indiana. Yale University Museum Coll., 321. X 3.4. (Compare Plate 27.) Tip of compass restored as indicated by dotted lines. Tooth grooved and epi- physes narrow, foramen magnum moderately deep. 208. Archaeocidaris rossica (Buch). Lower Carboniferous, Miatschkowa, Province of Moscow, Russia. Mus. Comp. Zo6l. Coll., 3,181. X 3.2. (Compare Plate 12.) Top of pyramid smooth, tooth grooved, epiphyses narrow, foramen mag- num moderately deep. Tip of the tooth restored as indicated by dotted lines. 209. Goniocidaris canaliculata A. Agassiz. (Adapted from Plate 2, fig. 17.) Young lantern, epiphyses narrow, fora- men magnum moderately deep. 210. Eucidaris tribuloides (Lamarck). Bahamas. R. T. J. Coll., 694. X 3.2. Top of pyramid smooth, tooth grooved, cpiphyses narrow, foramen magnum very shallow. (Compare text-fig. 218, p. 191; Plate 2, figs 7-16.) ARISTOTLE'S LANTERN AND PERIGNATIIIC (MUDI.E. IV, 211. Cenlrechinus setosua (Leskc). Bermuda. R. T. J. Coll., 788. X 1.6. Top of pyramid pill.-d, i.x.th xruoved, cpiphyscs narrow, foramen magnum deep (compare text-figs. 219, 220, p. 1!)1). 212. Arbacia punctulata (Lamarck). Woods Hole, MassachuKetm. II. T. J. Coll , sM. -I. T..p..fp>. pitted, tooth keeled, cpiphyses narrow, foramen magnum deep. 213. Tripneustes esculentus (Leskc). Florida. R. T. J. Coll., 884. X 2.1. Tup of pyramid pin,-.|, I.H,I|, knip:in- I'luir ."., li«-. I 214. Clypeasterrosaceus(Lmn6). Bahamas. K.T.J. Coll., 885. X I.«. Top of pynimid nimiotli, pyramid* later- ally flaring, epiphyses narrow, compass wanting, foramen magnum very sliall, top of pyramid; st., styloid process; t, tooth. are grooved and continue calcified high above the base of the foramen magnum. They arc supported by the dental slides, as usual, and the long styloid processes, typical of the order, are a prominent feature in face view. The pyramids are narrow-angled, with a deep foramen magnum, and the upper borders of the pyramids curve inward over the space of the foramen magnum and a slight distance beyond the epiphyses. The top of the pyramids has deep pits seen when the epiphyses are removed (text-fig. 2115). The epiphyses are narrow, not quite covering the dorsal face of the half-pyramids. The brace and compass are as IIMKI! except that the compass may be outwardly rounded instead of bifid as in most Echini. In text-fi^. 219 (p. 191), the protractor and radial compass muscles are shown passing from the lantern to the two half-interambulacra associated with ambulacrum III and the retractor muscle.- passing to the auricles that originate on ambulacrum III. The genus Phormosoma is most interesting as representing the remarkable Echinothuriidae. Mr. Agassiz (1904, Plate 47) figured the structure of the lantern in Echinosoma hispi Agassiz), and I show it in another species, Phormosoma placenta. The teeth are grooved, narrowly acuminate distally (Plate 2, figs. 19-21). They are supported by the dental slides and styloid processes as usual. The pyramids are very wide-angled with long interpyramidal muscles. As the angles are wide, the lantern is inclined instead of nearly perpendicular, tin- usual character of the suborder, and in this respect it is closely like that in the adult of Palaeo- zoic and the young of Recent species. This is best seen by comparing the dorsal view of Phoriuo- soma (Plate 2, fig. 20) with that of Pholidechinus (Plate 27, fig. 5). The foramen magnum is deep and widely curving, a very distinctive character. The dorsal face of the pyramid* ha- the pitting seen in all the order when the epiphyses are removed, as shown in Plate : area II. In side view (Plate 2, fig. 21) the lateral wing of the pyramid is corrugated as usual, and is strongly bowed on its outer line. The epiphysis is very narrow with the usual glenoid cavity (Plate 2, figs. 19, 21, and 20, area IV). Duncan (1889a, p. 40) is mistaken in saying of the Echinothuriidae that epiphyses are wanting; they doubtless ,.xi>i in all regular Echini 186 UOHKRT TRACY JACKSON ON ECHINI. possessing jaws. The brace is of the usual shape, and the compasses are strongly arched, curving over the outer border of the braces (Plate 2, fig. 19). The muscles of Phormosoma are of the usual number in lanterns of regular Echini, but in addition extra muscles are given off from the auricles radially. These muscles (text-fig. 226, p. 193) are very delicate and may fairly be called radial peristomal and radial somatic muscles, as they extend like tent-roprs from the auricles radially to these two areas. They have been described in Asthenosoma as longitudinal muscles (Lang, 1896, p. 471), but this name seems inappropriate. These muscles apparently cause movements of the highly flexible test of the corona and peristome (p. 195). The Aulodonta have the primitive structure of grooved teeth and narrow epiphyses seen in the Echinocystoida, Perischoechinoida and Cidaroida. With this they have the deep foramen magnum, prominent styloid processes, and especially pits in the top of the pyramids character- istic of the Centrechinoida. Slirodonta. — Salenia is a type of much interest. Duncan (1889a) gives the characters of the lantern, but I believe they have not been shown in detail or figured. The teeth are keeled and supported by the dental slides and styloid processes as usual (Plate 4, figs. 3, 4). The pyramids are rather wide-angled, have a deep foramen magnum (Plate 4, fig. 3), and when the epiphyses are removed, show pits in their dorsal faces (Plate 4, fig. 4, area I). The epi- physes are very narrow, only slightly more than covering the dorsal faces of the half-pyramids (Plate 4, fig. 4, area I). The foramen magnum is therefore open dorsally. The braces and compasses have the usual shape. The protractor and radial compass muscles pass from their origin in the half-pyramids and compasses to the basicoronal plates of the half-interambulacra associated with the area in which they originate (Plate 4, figs. 4, 5). The retractor muscles pass from the half-pyramids to auricles developed from the ambulacra. In Salenia the keeled teeth, deep foramen magnum, pits in the dorsal face of the pyramids, and the auricles are all characters which unquestionably locate this type as one of the Centrechinoida and equally separate it from the Cidaroida with which group Salenia was formerly associated (p. 195). The lantern of Stomopneustes variolaris, I believe, has not been described. It is erect, with teeth keeled, epiphyses narrow, not meeting in suture over the foramen magnum (Plate 4, figs. 8-10). The dorsal ends of the half-pyramids extend inward over the foramen and at their free ends are produced ventrally as spurs which meet and give support to the teeth. The function of these pyramidal spurs is similar to that of the crests developed on the epiphyses of the Camarodonta (text-fig. 213), but they cannot be homologized with them as they arise from a different structural part. I believe this is a feature which has not hitherto been noted in the lantern of Echini. Stomopneustes has been placed in the Echinometridae, but the structure of the lantern would locate it in this suborder, and it seems that it may be safely followed as a basis of classification. In Glyptocidaris (Phymosoma) crenulare, the only living representative of its family, the Phymosomatidae, the structure of the lantern is as in Stom- ARISTOTLK'S I.AXTKKX AND I'KUKJNATIIK MitiH.K. 187 opneustes, teeth keeled, foramen magnum open, epiphyses n.-irn.w, .-mil -pur- fn.m tin- produced dorsal tips of the pyramids supporting II,,. teeth. TbCM character! link tl. i fam.he- together and equally separate them from other familie.- ..f regular Kdiini. In Arbacia, as in Salenia, the teeth arc keeled (text-fin. -'I'.'i. Th- pyramid- have a rather deep foramen magnum, and the upper fares <,f the half-pyramids seen when the epipl removed, show a pitted surface. The epiphyses are narrow, little mure than rapping 1 1..- half- pyramids, SO that the foramen magnum is open dorsally. The brace-, of Arl.acia an- ..f the usual type, but the compasses are distally rounded instead of bifi.l a- in mo-t Kchini. Tin- feature was found in Arbacia lixula, A. pundulata, and A. liigrn. .-o that it i.- pn.babh generic. The Stirodonta as regards the lantern present features intermediate in rharaeter, having narrow epiphyses as in the Aulodonta and still more primitive types but keeled teeth like the Camarodonta. Keeled teeth are evidently mechanically more powerful than grooved teeth (text-figs. 207-212, p. 184). Therefore this structure can be considered a mechanical a> well as a structural advance over what obtains in the lower groups of Echini. Camarodonta. — Tripneustes represents the most complex structure known in the ('entre- chinoida. The teeth are keeled (text-fig. 213), and are supported by the dental slide-. The epiphyses are wide and meet in a median suture over the foramen magnum. In addition, the epiphyses bear crests, which are strongly developed in Tripneustes, and the-e p< against and give support to the teeth at their upper portion. The pyramid- are nearly IMT- pendicular and have a deep foramen magnum, which is roofed over by the joined cpiphyws. The dorsal face of the half-pyramids, seen when the epiphyse.- are removed, -ho\\s the pits characteristic of the order. The styloid processes are strongly developed, a- seen in fare view. The epiphyses have the usual glenoid cavity and tubercles for articulation with the ]>• The brace is of the usual character, and the ossicles of the coinpa-s are divided into two p and are distally cleft as usual. Strongylocentrotus as previously described il'lat' tially like Tripneustes. A peculiar variation was found in a specimen of Tripnetutet <-xcnl. from Bermuda. In this there are no pits in the top of the pyramids, and a- Midi it may be considered a regressive variant. It is the only case seen in the Centrechmotda in which th. -e characteristic pits are wanting. The character of the Camarodonta as described is to have keeled teeth and wide epiphyses meeting in suture over the foramen magnum; also the epiphyses bear cn-ts which give support to the teeth. This is the feature of the Temnopleuridae as ascertained in Temnopleurus, Microcyphus, and Amblypneustes. It is the character of the Echinidae as ascertained in Echinus, Toxopneustes, and Tripneustes, and of the Strongyloeentn>tid:i' D in Sph chinusand Strongylocentrotus. Finally, it is the character of the Echinoinctridae, as ascertained in Echinometra and shown by Mr. Agassiz (1908) in Coloborentrotus. The lantern of the Camarodonta is mechanically as well as structurally the most highly evolved known in Echini. 188 ROBERT TRACY JACKSON ON ECHINI. The keeled teeth as in the Stirodonta are a mechanical advance over grooved teeth (text-figs. 207-213, p. 184). In addition the confluence of the epiphyses (text-fig. 213, p. 184; Plate 5, figs. 2, 5, 9) is a mechanical advance, as, besides supporting the teeth, it makes with the braces a continuous rigid base as fulcra for the action of the interpyramidal muscles, instead of a distinct continuous base as occurs in all lower Echini (text-figs. 207-212, p. 184; Plate 2, figs. 19, 20; Plate 27, figs. 5, 6). Turning to the irregular Echini, Love"n (1892) and Hawkins (1909) showed that in Discoidea, representing the Holectypina, the pyramids are wide-angled. This is like the character in the young of Recent regular Echini and in the adult of Palaeozoic species, so that in Dis- coidea it may be considered a regressive type of lantern (p. 218). Loven (1892) worked out the lantern and muscles of several of the Clypeastrina with minute care. The lantern in this suborder is highly flattened, broadened, and specialized in character, being very different from the same structure in any regular Echini. A representative portion of a lantern of Clypeaster is shown in text-figs. 214-216 for comparison. The tooth is short and narrow, and the keel, which is relatively very wide (text-fig. 215), makes up a large part of the mass of the tooth. A little depression in the tip of the tooth, represented in section, is probably due to mechanical wear. The keeled teeth of the Clypeastrina indicate a relation of this group to regular Echini with keeled teeth. When the lantern is held in its natural plane (text-fig. 214), only the dorsal tip of the tooth is visible, but if rotated upward (text-fig. 216), the ventral tip is seen as well. The pyramids are broadly triangular and procumbent with a lateral expansion into great wings which are deeply plicate on their outer faces. The median suture exists as usual ; the foramen magnum is extremely shallow, almost a straight line. On the lateral wings of the half-pyramids there are no corrugations, as in regular Echini, for the attachment of interpyramidal muscles, although these are well developed. On the dorsal face of the half-pyramid seen when the epiphysis is removed (text-fig. 2145), there are no pits as in the Centrechinoida, but the sur- face is smooth. The epiphyses are very small and the brace is a small, narrow, block-shaped plate quite different from that of the regular Echini. The compasses are wanting, apparently an ordinal character. The Aristotle's lantern is an internal structure and as such is not so likely to be affected by external conditions as the more superficial parts of an urchin. It seems, therefore, that its structure as a complicated mechanism should yield data of classificatory value, binding together the larger groups, and I believe that the facts fully support this view. Summing up the characters briefly: in the Palaeozoic Echinocystoida and Perischoechi- noida (text-figs. 207, 208), the lantern is inclined at an angle of about 45 degrees, not erect. The teeth are grooved, pyramids wide-angled, foramen magnum moderately deep, epiphyses narrow, and there are no pits in the top of the pyramids. In the ancient Cidaroida (text-fig. 210) the structure is similar, but the lantern is erect, the foramen magnum very shallow, and there are no pits in the top of the pyramids. ARISTOTLE'S LANTERN AND I'KKKIX .\TIIK CIIUU.K is-.. In the Centrechinoida, as an order, there are pita in the top of the pyramid* beneath the epiphyses, the foramen magnum is always deep, styloid processes are visible in face view, and the lantern is erect excepting in Astropyga and the Echinothuriidae, when- it is inclined as in the young, and the adult of Palaeozoic types. Other characters of (he lantern in this ,,rd.-r are sufficiently distinctive to justify the formation of three suborders, as shown (p. is:{,. I,, all the above the lantern is made up of forty pieces, braces and compasses an- nearly alike, and corrugations exist on the pyramidal wings for attachment of interpyratnidal muscle*. In the Holectypina the structure of the lantern in Discoidea was shown in part by I»\ en (1892), and has recently been shown very completely by Hawkins (1909) in LKscoidea cylin- drica. As Hawkins shows, the teeth are narrow, elongate, and keeled; pyramids are wide- angled with a rather deep foramen magnum and laterally with corrugations for the attachment of interpyramidal muscles; the epiphyses are relatively large but narrow and closely resemble those of the Stirodonta. In the whole structure the lantern approaches much nearer to that of the Stirodonta than of any other group of Echini. Of course it may differ in other genera of the Holectypina where it is at present unknown (see p. 218). In the Clypeastrina the lantern is procumbent, but is more erect in the young, as I have seen in Echinarachnius parma. The teeth are keeled, the foramen magnum is extremely shallow (text-figs. 214-216), pyramids are highly modified with wing-like exten-i..ns without ridges for the attachment of interpyramidal muscles, or pits in the top of the pyramids; brace and epiphyses are very small, and compasses are absent. The whole lantern is much specialized, the keeled teeth presenting the best connecting character (see p. 218). The Spatangina as a suborder are characterized by the absence of the lantern, and it is of highest interest that a lantern exists in young Echinoneus, as shown by Mr. Agassiz (1909). In a very early stage this type has a lantern with keeled teeth, deep, open foramen magnum and bifid compasses, the retractor muscles are attached to the ambulacral auricles, and the protractor and radial compass muscles are attached to the base of the single primordial inter- ambulacral plates. It is interesting and suggestive that this combination of characters shown by Mr. Agassiz in young Echinoneus finds an exact parallel in adult Arbacia (text-fig. 212, p. 184; text-fig. 227, p. 193), and further, the Stirodonta, as here defined, is the only group of regular Echini that does possess such a combination of characters (p. 217). Before considering the perignathic girdle and the relation of the lantern muscles to the same, I would call attention to the relation of the lantern and muscles to the test as a whole. In the Centrechinoida, as Love'n (1892, p. 44) said, "the retractors of every pyramid ar. tached on different ambulacra, each on a rising auricular branch." He considered the mu- arising from a single pyramid, the halves of which are united by suture, whereas I take the two half-pyramids united by the interpyramidal muscles as the basis of consideration. The dis- tinction is purely a morphological one. In other words, a pyramid may be considered as inter- 190 ROBERT TRACY JACKSON ON ECHINI. radial in position, its two halves united by suture and embracing the tooth (text-fig. 210). This is the usual way of considering it, and undoubtedly the best for description of the lantern itself. Or a pyramid may be considered as radial in position, the two halves united by the interpyramidal muscle being the unit, and the halves thus considered are the point of origin of all the lantern muscles that are inserted in one radial coronal element (text-figs. 218, 219). As stated (pp. 43, 62), the corona of a sea-urchin may be considered as made up of five ele- mental radial parts, each of which is developed in relation to one of the ocular plates, as it is at this point that all new coronal plates originate. Any one of these five parts consists of an ambulacrum and on each side a half-interambulacrum, as these originate on the ventral border of the overlying ocular plate. The genitals are omitted from this consideration as coronal plates do not originate in relation to them and one may be absent (spatangoids) without affecting the corona (p. 167.) This relation is shown in Palaeechinus drawn from the exterior (text-fig. 217), and Eucidaris drawn from the interior (text-fig. 218). The other half-interambulacra not figured would be associated with the next adjacent ambulacra and ocular plates on either side. The compass, brace, and two half-pyramids face this ideal radial area, as in text-figs. 218-220, but the teeth would be interradial in position. In Eucidaris (text-fig. 218) the radial compass muscles, protractors, and retractors pass to the apophyses of the two half-interambula- cra on either side. In Centrechinus (text-fig. 219) the radial compass muscles and protractors, as in Eucidaris, pass to the apophyses of the two associated half-interambulacra, but the re- tractors have been transferred to the two auricles that develop on the ambulacrum (compare text-fig. 225). This divides the sea-urchin more naturally than to consider the ambulacrum as one and the interambulacrum as a second and independent part. The perignathic girdle has been studied by Duncan (1885a) and critically by Loven (1892). I have little to add to their studies except a correlation with fossils and a general summing up of relations. In text-figs. 221-236 is shown the base of two ambulacral and two interambulacral areas of the corona, seen from within, with one set of those lantern muscles that are inserted on the base of the corona. Thus the structure is shown both with and without the associated muscles in the leading orders and representative families of Echini. Bather (1909) has shown that in the Permian Miocidaris keyserlingi there are apophyses (text-fig. 238 bis) as in the Recent cidarids, but in other Palaeozoic genera no perignathic girdle has been found in any type, and all the evidence goes to prove that no such structure existed. I have seen as actual tests or internal molds the interior of the basicoronal plates in Lepidocentrus, Hyattechinus, Palaeechinus, Lovenechinus and Perischodomus, and in none of these was there a trace of any supports for the attachments of lantern muscles. Moreover, as Loven (1892) showed in very young Cidaris, the muscles are attached directly to the base of the primordial interambulacral plates, no apophyses having at that stage developed. From the structure of the lantern in Palaeozoic genera (Plate 27) it is evident that muscles existed, and it is assumed that the ARISTOTLE'S LANTERN AND I'KHKJNATIIIC CIIMM.K. I'.M in TEXT-PIGS. 217-220. — Morphology of radii in Echini. The corona consists of five parts, each including an ambulacrum and two half-interambulacra originating beneath an ocular (pp.35, 43, 62, 86). 217. Palaeechinus quadriserialis Wright. Lower Carboniferous. Adapted from Plate 30, Tig. 3. X '-' irom the exterior. 218. Eucidaris Iribiiloides (Lamarck). Bahamas. R. T. J. Coll., 754. X 2.7. Seen from the ini.rinr with thai portion of the lantern and muscles associated with this coronal element (compare lcxt-ti«^. 'Jill. 1 219. Centrechimus setosus (Leske). Florida. R. T. J. Coll., 790. X 1.9. Base of a coronal cli-nifiit arnl that por- tion of the lantern and muscles that are associated with this element (compare text-l'ujs. 21 1. p. Is I; JJ.'i. p. 193). 220. The same. Face view of the two radial half-pyramids, etc., that are associated with om- i-..ruii:il i-N-nn-ni I..-II.T- ing: ip., interpyramidal muscles; r. p., right half of pyramid '_'. and /. /)., left half of pyramid .'!. Letters of text-figs. 218-220 as in text-figs. 221-230 (p. 193). 192 ROBERT TRACY JACKSON ON ECHINI. protractor, retractor, and radial compass muscles were attached directly to the base of the intcTumbulacral plates, as restored diagrammatically in Lovenechinus (text-fig. 221). This is almost exactly the condition of young Cidaris, and is virtually like that of Arbacia (text-fig. 227), as far as protractor and compass muscles are concerned. Muscles are not attached to ambulacral areas in any known sea-urchin unless special processes, the auricles, are there existent as in Centrechinoida. Such being the structure of the skeleton and probable position of muscles in the Perischo- cchinoida, the next step in advance is seen in the Cidaridae (text-fig. 222). As Love"n (1892) showed in this group, there is a direct vertical growth of the edges of the interambulacral plates on the peristomal border. These growths produce wing-like expansions to which all the perig- nathic muscles are attached. This arrangement is known only in the Cidaroida. As these processes are a direct outgrowth of the interambulacral plates, they may properly be called apophyses. They are very distinct from the separate pieces occurring on the ambulacral areas of the Centrechinoida, and these may well retain the name of auricles, previously applied to both. Love'n (1892, p. 38) recognized clearly the morphological distinction of apophyses and auricles, but did not give any distinguishing name to differentiate them. In Eucidaris (text-fig. 222) the radial compass muscles, protractors, and retractors are attached to the two apophyses. The ambulacra are quite free of muscles and the character of the apophyses freed TEXT-FIGS. 221-230. — Base of corona with attachment of lantern muscles in representative regular Echini. 221. Lovenechinus missouriensis (Jackson). Lower Carboniferous, Missouri. X 2.2. No perignathic girdle, muscles restored schematically. 222. Eucidaris Iribuhides (Lamarck). Bahamas. R. T. J. Coll., 742. X 3. All muscles inserted on high apophyses- 223. Phyllacanthtis baculosa (Lamarck). Mauritius. R. T. J. Coll., 753. X 2.2. Apophyses arched over the ambu- lacrum, a rare aberrant variant (compare text-fig. 229). 224. The same. R. T. J. Coll., 900. X G.5. Vertical growths on the proximal side of ambulacral plates; further dorsally these growths exist as fine separate spines extending into the body cavity (compare Plate 3, fig. 12). 225. Centrechinus setosus (Leske). Bermuda. R. T. J. Coll., 691. X 2.3. Apophyses high, auricles high, centrally confluent. In this and succeeding figures protractor and radial compass muscles are inserted on more or less developed apophyses, but the retractors are inserted on auricles (compare text-figs. 211, 219, 220). 226. Phormosoma placenta Wyville Thomson. Off Cape Sable to Cape May, 956 fathoms. R. T. J. Coll., 778. X 2.2. The apophysis is single, not double, as the single primordial interambulacral plate is retained; auricles have secondary sutures (s). Radial peristomal (per.) and somatic (so.) muscles extend from the auricles to the peristome and corona (compare text-fig. 43, p. 80). 227. Arbacia lixula (Linnd). Naples Station. R. T. J. Coll., 886. X 2.2. Apophysis very reduced and consists of a single piece as the primordial interambulacral plate is retained. Auricles are separate slender styles. 228. Arbacia nigra (Molina). Chili. R. T. J. Coll., 797. X 2.2. Auricles meet in an arch (p. 116). 220. Ntnmgylocentrolus drobachiensis (O. F. Miiller). Eastport, Maine. X 2.2. Apophyses low, auricles meeting in an arch (compare Plate 5, figs. 1-12). 230. Kchinometra lucunter (Linn6). Bahamas. X 2.2. Apophyses high, auricles extravagantly developed in a high spoon-sha]>ed arch. Lettering: a, b, left and right ambulacral columns; op., apophyses; ou., auricles; pr., protractor muscles; r, radial com- pass muscles; re., retractor muscles; s, suture of auricle with ambulacral plate. ARISTOTLE'S LANTERN AND I'KllKiN'ATIlIC MHIU.K I'.i:; re. 728 230 194 ROBERT TRACY JACKSON ON ECHINI. from muscles is shown in one area. The ambulacral plates ventrally and throughout the area passing dorsally bear very fine delicate spines that lie near the middle of the area and extend into the body cavity (Plate 3, fig. 13). Ventrally near the peristome these spines may com- bine into continuous ridges, as in Phyllacanthus (text-fig. 224). Similar spines occur in some Palaeozoic Echini, as Hyattechinus (Plate 24, fig. 6); but I have not seen them in the Centrechinoida (p. 61). The apophyses in the Cidaroida in the several species seen are typically as in text-fig. 222, high, broad, and flaring over the ambulacral areas. In one area of a specimen of Phyllacanthus baadosa (text-fig. 223) the apophyses meet in a suture over the ambulacral area, and Duncan (1885a) shows a similar case in Phyllacanthus imperialis (Lamarck). In these aberrant variants the retractor muscles come to occupy a position over the ambulacrum just as they do in Cen- trechinus (text-fig. 225), but with the radical difference that in Centrechinus they are inserted on auricles, not on apophyses. In the Centrechinoida a different condition exists in the perignathic girdle. Apophyses may develop on the interambulacral plates to a considerable extent (Centrechinus, text-fig. 225; Echinometra, text-fig. 230), or apophyses may be much reduced (Strongylocentrotus, text-fig. 229; Arbacia, text-fig. 227). On the other hand a new character exists not seen in the Perischoechinoida nor the Cidaroida. This feature is auricles, which, as shown by Loven (1892), are two pillars, or flattened plates arising from the base of the ambulacra, but separated from the ambulacral plates by sutures. They are not a continuation of the ambulacral plates as apophyses are of the interambulacral plates. Auricles originate on either side of the ambu- lacrum with an open space between; they may exist as perpendicular isolated pillars (Arbacia lixula, text-fig. 227; Salenia, Plate 4, fig. 5), or they may arch over the ambulacrum, joining in suture (Arbacia nigra, text-fig. 228; Strongylocentrotus, text-fig. 229). The joining is a feature of development, as they are apparently always separate in the young. It is also a species differential and subject to individual variation, as well as to radial variation within the individual. Auricles may form high and wide arching plates (Centrechinus, text-fig. 225; Echinometra, text-fig. 230). When apophyses are developed, the auricles present a suture line at their point of mutual contact (Centrechinus, text-fig. 225). The auricles in this order are the points of insertion of the retractor muscles of the lantern, which are thus located instead of being inserted on the apophyses as in the Cidaroida, a marked ordinal distinction. The protractor and radial compass muscles, however, are inserted on the apophyses, as in the Cidaroida. Taking up the representative types shown, in Centrechinus (text-fig. 225) the apophyses are high and auricles very high, broad, and meeting in an arch over the ambulacra. The pro- tractor muscles are powerful and with the radial compass muscles are attached to the apophyses. The retractors are also powerful and are inserted high up on the arch of the auricles. ARISTOTLE'S LANTERN AND I'KKKiNATIIIC (JIHDI.K. 195 In Phormosoma (text-fig. 220) the primordial interambulacral plate w retained in the adult in the basicoronal row (text-fig. 43, p. 80), so that the apophysis consists of the upward growth of one plate, instead of two plates as in Centrechinus; therefore there in no median miturr. The apophysis is low and bears the radial compass and rather .-lender pmtnirtor muscles. The auricles are exceptional in that each consists of two pieces joined by suture instead of one piece, as in all other families of the order. The retractor muscles are inserted on the upper of these two pieces. Another striking character of the auricles is that muscles extend from t hem radially in two directions. The radial peristomal muscles extend inward, and the radial somatic muscles outward, being inserted on the plates of the peristome and corona respectively. Such muscles have been described in Asthenosoma (Lovdn, 1892, p. 45). Bell (1889, p. 438) says that these radial or " Langsmuskeln " are altogether wanting in Phormosoma, but he is quite mistaken. In Salenia (Plate 4, figs. 4, 5) the apophyses are low and on them are inserted the protractor and radial compass muscles. The auricles are slender, not meeting in an arch, and bear the retractor muscles. This structure as well as the lantern of Salenia is entirely characteri-tir of its order, not showing any features of the Cidaridae with which the Saleniidae were formerly associated (p. 186). In Arbacia lixula (text-fig. 227) the primordial interambulacral plate exists in the basi- coronal row, and the apophysis of this single plate is so slight that it can hardly be considered more than a thickening of the same. To it the protractor and radial compass muscles are attached, as usual. The auricles are simple isolated columns standing quite free and bearing the retractor muscles. In Arbacia nigra (text-fig. 228) the auricles may join in an arch over the ambulacrum, though frequently they do not join, and there is considerable diversity in this character in different specimens or in different areas of the same specimen. This joinii the auricles in an arch is a progressive character and A. nigra has other progressive feature-, as previously discussed (p. 116), marking it as a specialized species in its genus. Strongijlocentrotits drobachiensis (text-fig. 229) has low but well marked apophyses, to whirh are attached the protractor and radial compass muscles. The auricles are arched, meet in a median suture, and bear the retractor muscles. In young specimens the auricles are separate. As a matter of individual variation, in adults occasionally the auricles do not join in an an-h. but retain the youthful and more primitive character of separate pillars. In Echinometra lumnter (text-fig. 230) the perignathic girdle is a very striking structure. The apophyses are high, strongly developed, and bear powerful protractor and compass muscles. The auricles are thick, solid, extraordinarily high, and meet as spoon-shaped plates, arching above the ambulacrum, with a long median suture. The retractor muscles are situated high up on the auricles and are very powerful. Loven (1892) gives the characters of the perignathic girdle in Discoidea and Galerites 196 ROBERT TRACY JACKSON ON ECHINI. representing the Holectypina, but I have had no opportunity to study them. In these genera low apophyses and auricles exist, and this structure with others affiliates the Holectypina with the Centrechinoida (p. 218). In the Clypeastrina the perignathic girdle was described by Love'n (1892) in representative types. It presents striking ordinal characters. Apophyses are wanting, but auricles are developed, and on these are inserted both the retractor and the protractor muscles, whereas in regular Echini the protractors are always attached to the apophyses, or directly on the basi- coronal interambulacral plates. As compasses are absent in the Clypeastrina, their muscles, of course, are also absent. In Clypeaster subdepressus (text-figs. 231, 232) the ambulacral plates of the basicoronal row roof over the primordial interambulacral plates so as nearly to «over them, but the inter- ambulacral plates as far as visible are shaded, as seen in areas 2 and 3. The auricles are erect pillars situated on either side of the ambulacrum, and, as the ambulacra arch over the inter- ambulacra, therefore the auricles of two separate ambulacral areas come in juxtaposition, a character seen only in this order. The four retractor muscles of each area are situated on the inner and lateral upper faces of the auricles, and the two protractors, which are very small, are situated on the bases of the same (text-fig. 231). Four retractors are not seen in all cly- peastroids, and in other orders there are only two such muscles in each area. The degree to which the ambulacral plates roof over the primordial interambulacrals in the basicoronal row varies in specimens and in different areas of the same individual. In Clypeaster rosacens (text-figs. 233-235) the beveling is considerable, but the whole length of the interambulacral plate is seen from within, whereas in Clypeaster subdepressus (text-figs. 231, 232) the same plate is visible only at intervals. In this beveling of ambulacral plates it is to be distinctly understood that we are considering the interior of the test. As viewed from the exterior, it is a case of the interambulacra beveling over the ambulacrum, as discussed (p. 73). In Echinarachnius parma (text-fig. 23G), as shown by Loven (1892, p. 67), a very remark- able condition obtains; the auricles occur on the primordial interambulacral plates instead of on the ambulacrals, and the small retractor and protractor muscles are inserted on the auricles. In this type, therefore, the retractor and protractor muscles occupy the same interradial posi- tion that they do in the Cidaroida, but instead of being inserted on apophyses, as in that group, they are inserted on transposed auricles, a distinct morphological part. The case stated in brief is as follows : in the Echinocystoida and Perischoechinoida, as far as known, no perignathic girdle existed, and the muscles were doubtless attached directly on the base of the interambulacral plates. In the Cidaroida, apophyses are developed as upward growths of the basicoronal interambulacral plates, and on these apophyses are inserted pro- tractor, radial compass, and retractor muscles. In the Centrechinoida, apophyses are well or feebly developed, and to them protractors and radial compass muscles are attached, but in this re. 2 ARISTOTLE'S LANTERN AND I'KHHJNATIIlr (ilKDI I ni -ait: . ,-v re.2 I '.17 236 TEXT-FIGS. 231-236. — Base of corona with attachment of lantern muscles in the Clypeastrina. 231. Clypeasler subdepressus (Gray). West Indies. H. T. J. Coll., 887. X 2.8. Ambulacra! plates nearly roof OMT the primordial interambulacral plates. Auricles are high, bearing the insertion of the protractor and two pain of retractor muscles. 232. The same. X 4.7. Showing the relation of primordial ambulacra! and intcrambularral platen, the latter shicl' •! 233. Clypeaxter rosaccus (Linne). Bahamas. R.T.J. Coll., 888. X 5.7. The primordial intcrambulacral pl:r less completely covered by the ambulacrals than in text -fig. 232. 234. The same. Plates separated, inner view (p. 74). 235. The same. Plates separated, viewed from peristomc. 236. Echinarachnius panna (Lamarck). Eastport, Maine. X about 5.7. Auricles are transferred to the primordial interambulacral plate and bear the insertion of protractor and one pair of retractor muscles. Lettering as in text-figs. 221-230, p. 193. 198 HOUEKT TRACY JACKSON ON ECHINI. order a new part appears, auricles, which arise from the ambulacra as separate pieces, and to them the retractor muscles are attached. In the Holectypina apophyses and auricles are both existent. In the Clypeastrina, apophyses are wanting, but auricles are developed, and to them protractor and retractor muscles are attached (radial compass muscles are wanting). Further, the auricles in this suborder may arise from the ambulacra, as in the Centrechinoida, or may, as Lovdn showed, be transferred to the interambulacral plates occupying an interradial instead of a radial position. In the Spatangina in adults the perignathic girdle is wanting as the lantern is absent. In the young of Echinoneus, however, as shown by Mr. Agassiz (1909) and Westergren (1911) auricles are developed on the ambulacra as separate styles, similar to those in the Centrechinoida, as in Arbacia (text-fig. 227). Mr. Agassiz (1883, p. 50) has shown that there are small knobs on the interior of the test in the spatangoid Conolampas sigsbei A. Agassiz. These knobs are on the base of the ambulacra and appear to be remnants of auricles which typically occupy this position. Not uncommonly in the Spatangina a process with a suture at its base arises from the interior of an ambulacral plate near the peristomal border. Such processes may be considered cases in which an auricle is retained as a reversionary variation. It is seen that the perignathic girdle presents characters that differ very definitely in the several larger groups of Echini, so that this structure as well as the Aristotle's lantern yields characters of high interest and importance in the comparative morphology and systematic classification of the Echinoidea. PART II. SYSTEMATIC CLASSIFICATION OF E< 1 1 1 \ I . As urged by Hyatt, a natural classification of organisms should be based on a comparative study of the young and adult, fossil and living forms; the young because through stag, development they throw light on ancestry; the adult because such are the full expression of generic and specific characters; the fossil because as an essential part of a group they cannot be ignored, and also because to the past one must look for the ancestors of the living. The living representatives as an essential part of a group need consideration, and if one's work is largely palaeontological, a study of the living is of first importance, as the study of soft parts throws great light on the structure of hard parts, as I showed (1890) in studie- of Pelecypoda. Variation is only second to development as a basis for studying genetic rela- tions, as variants, both arrested and progressive, have a direct relation to the characters of more primitive or more specialized species or genera in a systematic serit •-. Echini are classified almost entirely on the structure of skeletal parts, so that well pre>' fossils can be studied with almost as much accuracy as living forms. Morten-en has urged the importance of pedicellariae and also spicules in the tube-feet as a basis of clarification. I believe no one has shown that these structures have a differential value in ontogeny or in evolu- tionary series. Moreover, they are minute and difficult structures to ascertain. If one attempts to follow Mortensen's splitting of genera on these characters, it seems that it is neces- sary to be a specialist on these particular parts in order to perceive the fine distinctions that he draws. Every part of an organism is surely worthy of careful study; but to base classifica- tion on such minutiae of no known evolutionary value is undesirable. The classification here offered conforms for the most part with what I gave in 18%, differing from it only in minor details and going further in certain groups. It is based essentially on the structure of the adult and the development of the same. While no single character has been followed, the characters taken into consideration are: the ambulacrum, interamlmlacrum, coronal imbrication, basicoronal plates, ventral resorption of corona, ocular and genital plates, periproct, peristome, Aristotle's lantern, perignathic girdle, spines and tubercles, gills and sphaeridia. The relative value of these parts naturally differs in different groups of the Echini. Of Palaeozoic Echini all the genera, except those imperfectly known, are here briefly con- sidered, but of post-Palaeozoic forms only the larger groups are taken into account. It may be said with truth that all Echini belong distinctly to this class and make no . (199) 200 ROBERT TRACY JACKSON ON ECHINI. approach to other classes of the Echinodermata. Attempts have been made to connect the Echini with the Asteroidea, especially through the genus Palaeodiscus, as later discussed, but the present evidence is opposed to this view. Mr. A. H. Clark (1909) has recently attempted to connect the Echini with the Crinoidea. In Echini all plates of the corona originate beneath a permanent plate, the ocular, as they do not in crinoids. The reproductive bodies of Echini are internal and interradial in position, whereas in crinoids they are situated on the arms. The peristome of Echini (excepting the Exocycloida) bears ten or more ambulacral plates, as the oral region of crinoids does not. Clark has attempted to correlate the auricles of Echini with ambulacral plates of crinoids. Auricles are unknown in Palaeozoic Echini and the Cida- roida; they exist only in the Centrechinoida and some Exocycloida, both specialized types. Moreover, they do not occur (Centrechinoida) at the ventral end of the ambulacra as Clark's theory calls for, but very far from the ventral termination of the ambulacra, which is the row of primordial ambulacral plates around the mouth. This is best seen in Phormosoma (text- fig. 226, p. 193), or other echinothuriids, where many rows of ambulacral plates exist between the auricles and the mouth. What the ancestor of the Echini as a class was is unknown, but it might fairly be sought amongst the Cystoidea. The Echini, though possessing a wide range of structure, may be described as animals possessing alimentary, reproductive, nerve, and water vascular systems within an enclosing superficial pentamerous skeleton which bears movable spines. There are from two to twenty columns of plates in each of the five ambulacral areas and from one to fourteen columns of plates in each interambulacral area. New coronal plates are formed at the ventral border of the five ocular plates, ambulacral pores pass through ambulacral plates, rarely (clypeastroids) in part between plates. The peristome in all but the Exocycloida bears from one to many rows of ambulacral plates, with or without non-ambulacral plates. There are five oculars (apparently in part or wholly wanting in some of the Pourtalesiidae), and five genitals or fewer, the whole being fused into a mass in certain types of Exocycloida. The genitals typically have each one or more pores as exits of the five interradially situated reproductive glands. In addition, typically, madreporic pores exist in genital 2, but are not recognizable in most Palaeozoic forms. The periproct is more or less plated, situated within the oculo-genital ring, or in irregular types outside of that area; the anus is in the periproct. The masticatory lantern is composed of forty pieces (or clypeastroids thirty pieces) ; it is wanting in adult spatangoids. Respiratory organs consist of Stewart's organs, peristomal or ambulacral gills. Locomotion is effected by ambulacral feet or by spines, or both. Such being the character of the class as a whole, the following key presents the characters by which the several groups may be divided. It is too much to hope that errors of diagnosis will have been entirely overcome, but it is felt that it is an approximation to the real affinities as gathered from a comparative study of the characters of young, adult, fossil, and living types. SYSTEMATIC CLASSIFICATION OK K< HIM 201 In Palaeozoic types the given characters, especially of the peri-tome, may be known in only one or a few cases, and further study may require modification in detail-. A table is given (p. 209) that presents in a tree form the relation- :i> iindcrntood, ami following this, as briefly as possible, a consideration of each of the several division.-, the full. being given of the Palaeozoic forms. Post-Palaeozoic genera of the regular Echini, and tin- families of the Exocycloida are not included. Key to the Classification of the Echinoidea. I. Two columns of high hexagonal plates in each ambulacra! urea, and one column of plate* in r»« li int.-r- ambulacral area .................... Onlcr HOTUUKX IDAUOIO S With characters of the order ................ Family H.HIIKI.M IIMHIIMI Ambulacra! pores superposed in the center of plates. I'lates not imliricate. Primordial ambulacra! plates around mouth in the peristome. Primordial intcramluilacral plates in basicoronal row. Base of corona not resorbed. Oculars very large, genitals very small. Pcriproct with many small plates. Peristome with two rows of ainhulacral plate^ only. Jaws. Bathriociitarit (three special). II. Two or more columns of plates in each ainhulacral area, and two <>r more columns of platen in cmch inicr- ambulacral area. A. Two columns of simple or compound plates in each ainhulacral ami. and two colmiui-> of platnt in each interamhulacral area (for A A, see p. J05). B. Periproct within oculo-genital ring (for BB, sec p. 204). C. Ainhulacral plates low, simple; two (in one genus, Tetracidark partly four) columns of plates in each interamhulacral area. Coronal plates rarely imbricate ( Miocidaris'. Prim- ordial ambulacral plates around the mouth in the peristome. Primordial interambulacral plates resorbed. Base of corona resorbed. Oculars all exsert, or becoming insert in the sequence V, I, IV, II, III, or V, I, IV7, III, II. Periproct covered with many thick plates. Peristome with many rows of ambulacral and interradial non-ambulacral platen, or rarely ambulacral plates only. I-antern erect, teeth gnxned, foramen magnum very shallow; epiphyses narrow. No pits in the top of pyramids. Pyramids with ridges on lateral wiop. Perignathie girdle consisting of apopli\scs only. Stewart's organs pn-*-nt. Primary spinet with a cortical layer. Primary tubercles perforate. Sphaeridia absent. Order < IDAKOIhA With characters of the order. (Onl.\ one assured genus of this family <«vurs in the Palaeo- zoic, therefore other genera are omitted.) . . Family CIDAI Interambulacral plates beveling over the ambulacral on the adraclial sin species only of this.order and genus are definitely known in the Palaro? Miiicidarii. CC. Ambulacral plates compound, rarely simple; two columns of plates in each intrramhulacral area. Coronal plates not imbricate or imbricate. Primordial ambulacral plates around the 202 ROBERT TRACY JACKSON ON ECHINI. mouth in the peristome. Primordial interambulacral plates in the basicoronal row, or usually resorbed. Base of corona not resorbed, or usually resorbed. Oculars all exsert or becoming insert in the sequence I, V, or V, I, IV, II, III. Periproct plated with few or many plates, or granules, or largely leathery. Peristome with ten primordial ambulacra!, also non-ambula- cral plates, or in one family many rows of ambulacral plates only. Lantern erect or rarely inclined; teeth grooved, or keeled; foramen magnum deep; epiphyses narrow, or else wide and uniting in suture over the foramen magnum. Pits in the top of pyramids. Pyramids with ridges on lateral wings. Perignathic girdle consisting of low or high apophyses, and auricles. Peristomal gills, rarely with Stewart's organs in addition. Primary spines without a cortical layer. Primary tubercles perforate or imperforate. Sphaeridia present. Order CENTRECHINOIDA. D. Teeth grooved. Epiphyses narrow, not meeting in suture over the foramen magnum. Ambulacral plates simple or compound. Coronal plates imbricate or not. Primordial interambulacral plates resorbed or retained in the basicoronal row. Base of corona resorbed or not. Oculars all exsert, or becoming insert in the sequence I, V, IV, II, III. Periproct with many plates or granules, or largely leathery. Lantern erect or inclined. Primary tubercles usually perforate Suborder AULODONTA. Ambulacral plates compound ventrally, simple above the mid-zone, or in some genera compound throughout. Coronal plates thick, not imbricating. Base of corona resorbed. Oculars all exsert, or one, or two may be insert. Periproct unknown. Peristome unknown. Lantern erect Family HEMICIDARIDAE. Ambulacral plates simple. Coronal plates thin, not imbricating. Base of corona resorbed. Oculars large, insert. Periproct leathery, but partially plated. Peristome with ten very large primordial ambulacral plates. Lantern erect. Family ASPIDODIADEMATIDAE. Ambulacral plates compound. Coronal plates not imbricate (Mesozoic), or more or less imbricate (Recent). Base of corona resorbed. Oculars exsert, or one to all insert. Periproct, more or less plated, to nearly leathery. Peristome with ten prim- ordial ambulacral, also non-ambulacral plates. Lantern erect, or (Astropyga) inclined. Stewart's organs slight, or absent Family CENTBECHINIDAE. Ambulacral plates compound. Coronal plates very thin, imbricate. Primordial interambulacral plates in basicoronal row. Base of corona not resorbed. Oculars insert, often separated from the genitals by interspaces. Genitals more or less split by secondary sutures. Periproct leathery but partially plated. Peristome with many rows of ambulacral plates only. Lantern inclined. Radial peristomal and somatic muscles. Stewart's organs Family ECHINOTHURIIDAE. DD. Teeth keeled. E. Epiphyses narrow, not meeting in suture over the foramen magnum. Ambulacral plates compound or largely simple. Coronal plates not imbricate. Primordial inter- ambulacral plates resorbed or retained in the basicoronal row. Base of corona resorbed or not. Oculars all exsert or becoming insert in the sequence I, V or V, I, IV, II, III. Periproct with prominent suranal, or with many small plates, or SYSTEMATIC CLASS IF I (ATI ON OF ECHINI. four, or five large plutes only. IVristomc with ten priinonlinl iiiiiluilarriil. alvi n-.n- amhulacral plates. Lmtern erect. I'riumry tubercle, impcrforatc, or exceptionally perforate . Sul.or.ler .S Tl Hl>lH>ST.\. Ambulacral plates compound, or largely simple. Primordial ititcrumluilacral plates resorbed. Base of corona resorbed. Oculars exsert or becoming i- in the sequence I, V, IV, II, III. IVriproct with u permanent large suranal, or more large plates, with small anal plates. Primary tubercles imjx-rforate, or perforate. No spurs from pyramids supporting teeth. Family SM.I.MIUAK. Ambulacral plates compound. Primordial interatnbulacrul plates resortx-d. Base of corona resorbed. Oculars becoming insert in the sequence I, V . [V, II, III. Periproct with numerous small plates only. Primary tubercles imperfnrate. Spurs from pyramids support the teeth dorsally. . Family PHYMOHOMATIDM Ambulacral plates compound, composed of three elements each, at the mid-zone every four or five ambulacra! plates are Ixnmd together and grown over by one primary tubercle. Primordial interambulacral plates resorbed. Base of corona resorbed. Oculars becoming insert in the sequence I, V, IV. Periproct with many small plates only. Primary tubercles imperforate. Spurs from pyramids support the teeth dorsally Family STOMMI-NKI MIHAK. Ambulacral plates compound. Primordial interambulacral plates in the I coronal row. Base of corona not resorbed. Oculars all cxscrt nr lx-<-oniing in-.cn in the sequence V, I, IV. Periproct with four or five large plates only. Primary tubercles imperforate. No spurs from pyramids supporting teeth. Family ARHAI HUM.. EE. Epiphyses wide, meeting in suture over the foramen magnum. Ambulacral plates compound. Coronal plates not imbricate. Ambitus circular, or elliptical through a sidewise axis. Primordial interambulacral plates resorbed. Base of corona resorbed. Oculars all exsert or becoming insert in the sequence V, I or I, V, IV, II, III. Periproct usually plated with many small plates (in one genus, Parasalenia, with four large plates). Peristome with ten (in one species five) primordial ambulacra! plates and more or fewer non-aml>ulucral plates; rarely the latter are absent. Lantern erect. Primary tiilx-rdes impcrforate. Suborder CAM .11«>1><>.\ T.I. Ambitus circular. Pits, or sculpturing in coronal plates dorsally. Ambulacral plates at mid-zone composed of three elements each. Oculars usually all exsert . Family TKM \oi-i KIKIUM. Ambitus circular. No pits or sculpturing in coronal plates dorsally. Ambula- cral plates at mid-zone composed of three elements cadi, rarely dorsally of two elements. Oculars all exsert, or becoming i"*<-rt in the sequence I. \ . IV II III. Family F.c IIIMDAE. Ambitus circular. No pits or sculpturing in the coronal plates. Ambulacral 204 ROBERT TRACY JACKSON ON ECHINI. plates at mid-zone composed of from four to ten dements each, rarely (some Echinostrephus) of three elements each. Oculars all exsert or becoming insert in the sequence I, V, IV, II. . . . Family STRONGYLOCENTROTIDAK. Ambitus elliptical in a sidewise axis. No pits or sculpturing in coronal plates dorsally. Ambulacral plates at mid-zone composed of four or more elements each, rarely (Parasalenia) of three elements each. Oculars all exsert, or be- coming insert in the sequence V, I, IV. . . . Family ECHINOMETRIDAE. BB. Periproct outside of oculo-genital ring, in interambulacrum 5. Regular in form, or more fre- quently more or less markedly bilaterally symmetrical through the axis III, 5. Slight or no resorption of base of corona by the advance of the peristome. Lantern present or absent. Peri- stomal gills, or ambulacral gills only. Sphaeridia present. . . Order EXOCYCLOIDA. Ambulacral plates compound, or largely simple, areas not petaloid dorsally. Primordial ambulacral plates unknown. Primordial interambulacral plates in basicoronal row, or in part resorbed. Base of corona slightly resorbed. Oculars and genitals all present and dis- tinct, or fused, or genital 5 absent; when present, it is imperforate. Periproct unknown. Peristome central, structure unknown. Lantern inclined so far as known. Teeth keeled, epiphyses narrow. Foramen magnum moderately deep. Pyramids with ridges on lateral wings. Perignathic girdle consisting of low apophyses and auricles. Peristomal gills present Suborder HOLECTYPINA. Ambulacral plates simple, areas petaloid dorsally. Ventrally ambulacral pores are minute and specialized. Primordial ambulacral plates in basicoronal row. Primordial inter- ambulacral plates in basicoronal row, or exceptionally (Arachnoides, p. 72) pushed dorsally and in part resorbed by intracoronal resorption. Base of corona not resorbed. Ocular and genital plates fused in a mass, usually no genital pore in area 5. Genital pores within the fused mass or outside in interambulacra 1, 2, 3, 4. Periproct plated. Peristome central, leathery. Lantern procumbent, highly modified, teeth keeled, foramen magnum very shallow, small epiphyses and braces, but no compasses. Pyramids usually without ridges on lateral wings. Perignathic girdle consisting of auricles only, on ambulacral, or on inter- ambulacral plates. No peristomal, but ambulacral gills only. Suborder CL YPEAS TRL\. I . Ambulacral plates simple, areas commonly petaloid dorsally; in some types pores are absent in part of the plates. Ambulacrum III often differs markedly in character from other areas. Ambulacral plates often highly specialized in form and size. Primordial ambulacral plates in the basicoronal row, or (Pourtalesia) in part pushed dorsally. The basicoronal plates la, Ho, III6, IVa, Vb are larger and with two pairs of pores or two separate single pores, whereas the 16, lib, Ilia, IVb, Va are smaller with one pore-pair or one single pore. Primordial interambulacral plates in basicoronal row or (Lovenia, Pourtalesia) pushed dorsally. Base of corona not resorbed. Oculars and genitals separate, or genitals partially fused. Oculars apparently absent in some Pourtalesias. Genital 5 absent, and some additional genitals rarely absent. Periproct plated. Peristome eccentric, plated with non-ambulacral plates only. Lantern and perignathic girdle absent (present in the young of Echinoneus, pp. 189, 217). No peristomal, but ambulacral gills only. Suborder SPAT AN GIN A. SYSTEMATIC CLASSIFICATION OF l.< HIM _'li:, AA. Two or more columns of simple- plates in each ambulacra! ar.-a, ami ilir.-,- or more mluiniu of plate* in each interambuhuTiil urea (for A, set- p. 201). H. Genitals largely covering the dorsal surface. Two columns of low plat.-, in ,-uch ami.ulacral area and three columns of plates in cadi inicraml.iilacral an-a. Platrs n..t imbricate. Prini- ordial interamlmlacral plates in liasicoronal row. Base of eorona n..i resorlx-d. Oculars *mall. strongly exsert by the contact of large genitals. IVriprocl central, structure unknown. iVri- stome central, structure unknown. Lantern and perignathic girdle unknown. Order PLKSHX IDAKOII.V KB. Genitals small. Two to twenty columns of plates in each amlmlacrul area and three to four- teen columns of plates in each interainlmlacral area. Plates not imbricating, or imbricating; when the latter, ambulacra! plates imbricate ventrally and interambulaeral plates dorsally and from the center laterally and over the ambulacra on the adradial sutures. Primordial ambulacral plates on the peristome. Base of corona resorbed or not. I'eristonir central with many row* of ambulacral plates only, or the same with non-ambulacral plates. I jintcrn inclined, composed of 40 pieces, teeth grooved. Foramen magnum moderately deep, epiphytes narrow. No pits in top of pyramids. No perignathic girdle. No peristomal gills. Primary spiue-i and |>erforate tulHTcles with secondary spines and imperforate tubercles, or secondaries only. C. Irregular, periproct apparently in nn interambulacrum. Two to four columns of plate* in an ambulacral area, and eight to nine columns of plates in an interambulaeral art-a. Plates thin, imbricating. Oculars and genitals doubtful. . . . Order KCHI.VX 'VSTOIDA. Two columns of plates in an ambulacral area and eight to nine columns of plates in an interambulaeral area. Primordial interainlmlacral plates in basieoronal row. Base of corona not resorbed. Peristome with ambulacral plates only. Ijinteni typically echinoid. Numerous fine spines. (One genus and species.) Family PALAEODUCIDAK. Four columns of plates in an ambulacral area, and eight columns of plates in an interam- bulaeral area. Small primary spines and tubercles. (One genus and species.) Family KCIIIMM ^IIDAE. CC. Regular, periproct within oculo-genital ring. Two to twenty columns of plates in each ambulacral area, and three to fourteen columns of plates in each interambulaeral are*. Plates imbricate or not. Primordial interainlmlacral plates in basicoronal row, or resorl»ed. Base of corona not resorbed or resorbed. Oculars usually all insert. Genitals typically with more than one pore each; rarely (Lepidechinus) with one pore each. Madreporite usually not recognizable. Periproct covered with many thick plates. Peristome with many rows of ambulacral plates only, or in addition with interradial non-ambulacral plates. Spines primary and secondary, or the latter only. Primary tubercles perforate, secondary tubercles imperforate Order PKIUSCHOKt HI NOIDA. D. Two columns of plates in each ambulacral area, four to fourteen columns of plates in each interambulaeral area. Plates thin, imbricating. E. Four to eight columns of plates in an interambulaeral area. Primordial and additional interambulaeral plates rcsorbed in the advance of |x'ristome. Ocu- lars, genitals, and periproct imperfectly known. Peristome with many rows of 206 ROBERT TRACY JACKSON ON ECHINI. ambulacral and interradial non-ambulacral plates. Spines large primaries with perforate tubercles in the center of each interambulacral plate, also secondary spines and imperforate tubercles Family ARCHAEOCIDARIDAE. Fragmentarily known from dissociated interambulacral plates and spines. Plates similar to those of Archaeocidaris but primary tubercles without a basal terrace Eocidaris (one species). Ambulacral plates all alike, of equal height. Four columns of plates in an interambulacral area. Primary spines large, tapering, or inflated, smooth, or with lateral spinules. Primary tubercles with basal terrace and scrobicular ring Archaeocidaris (many species). Ambulacral plates low, with also higher, wider and wedge-shaped plates. Six to eight columns of plates in an interambulacral area. Primary spines cylin- drical. Primary tubercles with no basal terrace, but with scrobicular ring. Lepidocidaris (one species). EE. Five to fourteen columns of plates in an interambulacral area. Primordial interambulacral plates in basicoronal row. Base of corona not resorbed. Ocu- lars insert. Genitals with many pores each. Peristome with many rows of ambulacral plates only. Spines small eccentrically placed primaries with secon- daries, or the latter only Family LEPIDOCENTRIDAE. Test high, probably spheroidal; ambulacral plates high, two or three equaling the height of an adambulacral plate, pore-pairs uniserial. Seven to eight columns of nearly rhombic plates in an interambulacral area. Koninckocidaris (two species). Test high, spheroidal, ambulacral areas narrow throughout; ambulacral plates low, about eight equaling the height of an adambulacral plate, pore-pairs uniserial. Five to eleven columns of plates in an interambulacral area. Small primary spines and tubercles with secondaries on interambulacral plates. Lepidocenirus (five species). Test depressed to flattened; through the ambitus circular, pentagonal, or cly- peastriform. Ambulacral areas broad, petaloid ventrally, narrow dorsally, pore-pairs uniserial. Eleven to fourteen columns of plates in an interambula- cral area. Small primary and secondary tubercles on interambulacral plates. Hyattechinus (three species). Test high, spheroidal, ambulacral areas narrow throughout, pore-pairs mod- erately biserial. Nine to ten columns of plates in an interambulacral area. Secondary spines and tubercles only. . . . Pholidechinus (one species). DD. Two to twenty (usually more than two) columns of plates in each ambulacral area, three to eleven columns of plates in each interambulacral area. Plates not imbricate or imbricate. E. Test elliptical, obovate, spherical or subspheroidal. Two to twelve col- umns of plates in each ambulacral area, three to eleven columns of plates in each SYSTEMATIC CLASSIFICATION OF WIIINI. 207 interamhulacrul urea. Plates not imbricate, Inn ambulacra! plat.-i I. the interambulacra! on adradial sutures. Primordial interariiluilucrul plate* retort One row only of interambulacral plates rcsorbcd in advance of the peris t. Oculars usually all insert, genitals usually with tlir.-.- in five porn e»rli. I stome with many rows of ambulacra! ami somr inierradial non-ambulacra! platen (Plate 5(5, figs. 7, 8). Secondary spines and im|M-rforat<- tubrrcli-* only. Funiily I'M.M K insn.o Two columns of plates in each ambulacra! area. c..n.,i-,ting of pl.it.-, which un- all primaries; pore-pairs uniserial. Four tc. si\ column^ of plate* in • interambulacral area I'nlm-.rhimu (four species). Two columns of plates in each ambnlacrul an... ...noting of plates which «rr alternately primaries and partially or completely occluded; pore-pain biscriul Four to eight, or nine columns of plates in each iiitcramhulacral area. Mnccoya (six species). Four columns of plates in each ambulacra! area. ron-.i.sting of demi- ami occluded plates; pore-pairs hiserial. Four to seven column-, of plati--. in eucli intcr- ambulacraJ area Lorrn<-rhinu* (six species). Four columns of plates in each ambulacra! area, consisting of demi-. ix-cluded, and in addition scattered isolated plates; pore-pair-, multi^-rial l-'mir to nin<- columns of plates in each interainhulacral area. . Oligoportu (five species). Six to twelve columns of plates in each amhularral area. coiiM-sting of demi-. occluded, and one to four irregular columns of isolated plati-> in i-arli half-area at the mid-zone; jxire-pairs multiseriiil. Thre<- to ••!.-.. ,-n mlumns of plates in each interambulacral area. . . . .Miluni'rhiniu (fourteen species). EE. Test elliptical, obovatc, spherical, or subspheroidal. Two to twenty columns of plates in each ambulacral area. Three to thirteen columns of plates in each it ambulacra! area. Plates imbricate. Primordial interambulacral plates in Iwsi- coronal row. Base of corona not resorbed. Oculars usually all iiiM-rt. genitals with one to many pores each. Periproct plated with many thick plates. I'eri- stome witli many rows of ambulacra! plates only. Primary .-.pines with [K-rforate tubercles, usually eccentric and irregularly distributed on interambulacral pl;r with secondary spines and tubercles, or the latter only. . Family L>:rii>t>nii. Two columns of plates in each ambulacral area. Four to eight columns of plates in each interambulacral area. Plates quite thick, imbricating iiHxlera' Secondary tubercles only, (icnital plates as far as known with only one pore each, the only instance known in the Palaeozoic. Resembles Palaeechinus excepting for the imbrication /x/W.rAi'nw.. (four Two columns of plates in each ambulacral area. Five columns of plates in each interambulacral area. Plates imbricating strongly. Kccentric perforate primary with secondary tubercles on interambulacral plat.->. Genital plates with many pores 1'eritckodomus 208 ROBERT TRACY JACKSON ON ECHINI. Six columns of plates in each ambulacra! area. Five columns of plates in each interambulacral area. Plates apparently imbricating moderately. Eccen- tric primary tubercles on certain adradial plates, with secondary tubercles on the same and alone on other interambulacral plates. Perischocidaris (one species). Four columns of plates in each ambulacra! area. Eleven to thirteen columns of plates in each interambulacral area. Plates strongly imbricating. Small primary with secondary spines and tubercles on interambulacral plates. Proterocidaris (one species). Eight to sixteen columns of plates in each ambulacra! area. Three to seven columns of plates in each interambulacral area. Plates strongly imbricat- ing; plates all of uniform size. Secondary spines and tubercles only. Test elliptical, obovate, or spherical Lepidcsthes (ten species). Four to six columns of plates in each ambulacra! area. Five to six columns of plates in each interambulacral area. Plates strongly imbricating. Ambu- lacra! plates large ventrally, small dorsally; interambulacral plates dorsally very large in adambulacral columns, smaller within. Eccentric primary spines and tubercles with secondaries on dorsal adambulacral plates, and secondaries only on interambulacral plates of dorsal median columns. Pholidocidaris (four species). Twenty columns of plates in each ambulacral area. Three columns of plates in each interambulacral area. Plates of uniform size, imbricating strongly. Small central primary spines and tubercles with secondary spines and tubercles on ambulacral and interambulacral plates. Teeth distally serrate, a unique character Meekechimis (one species). Having considered the systematic relations of the Echini in the form of a key and in a genealogical table I will give briefly the reasons for the several steps which will be more com- pletely gathered from the morphological studies, and from the systematic description of Palaeo- zoic Echini. The geological distribution of the several groups of Echini as given in the table (p. 209) is taken from the systematic part of this memoir excepting the groups of the Centre- chinoida and Exocycloida which are taken from Duncan (ISSQa).1 The most primitive type of Echini, I believe emphatically, is Bothriocidaris. This view is based on the simplicity of its structure, and especially on the close comparison of this struc- ture with that seen in the very young of all geologically later Echini known and the youthful characters retained at the ventral border in the adults of many types. In Bothriocidaris 1 1 differ from Duncan in regard to the Hemicidaridae which I date from the Trias whereas Duncan (1889a, p. 50) says that Hemicidaris occurs in the Zechstein. Dr. Bather (1909a, p. 250) expresses himself very positively that none of the Ectobranchiata appear before the Trias and I prefer to follpw this most accurate authority. I differ also in extending the Holectypina only to the Eocene, as the Recent Pygastrides (Duncan, 1889a, p. 138) is very doubtful. w p I HH W O w w fe o I H < U u 210 ROBERT TRACY JACKSON ON ECHINI. (Plate 1, fig. 1), in the corona each ambulacrum consists of two columns of high hexagonal plates, each with two pores, superposed, surrounded by a peripodium, and situated in the middle of the plate. Such a structure is not known in any other adult regular echinoid, but is almost identical with that seen in young Goniocidaris (Plate 2, figs. 1-3), Strongylocentrotus (Lov6n, 1892), and Phormosoma (Mortensen, 1904, p. 54). Each interambulacrum of Bothriocidaris consists of a single column of plates, which is represented by a single plate at the ventral border of the interambulacra in the young of all other Echini (Goniocidaris, Plate 2, fig. 1 ; Strongylo- centrotus, Plate 3, fig. 11; Phormosoma, Plate 3, fig. 10). This single plate is also seen in adults where resorption has not removed the base of the corona, as in the Palaeozoic Hyattechinus rarispinus (Plate 23, fig. 1), H. pentagonus (Plate 25, fig. 1), H. beecheri (Plate 26), Perischo- domus (Plate 64, fig. 2). Again, the single ventral plate is seen in adult Recent Phormosoma (text-fig. 43, p. 80), Arbacia (text-fig. 227, p. 193), in the Triassic Tiarechinus (text-fig. 31, p. 70), and in nearly all clypeastroids and spatangoids (text-figs. 27-29, p. 70, and 52, 54, p. 80; Plate 3, fig. 15). It seems that there is ample proof that the interambulacrum begins with a single plate, as shown by Love"n (1874), and Mortensen (1903) in Hypsiechinus (Plate 3, fig. 6). This structure with less evidence I correlated (Jackson, 1896, p. 233) as a stage in development with the single column of plates in Bothriocidaris, naming it the protechinus stage. As Palaeozoic types with many columns of interambulacral plates begin at the ventral border, the young, with a single plate representing a single column, and later add their several columns during development (Plate 26), it seems that Bothriocidaris throws great light on the numerous columns there existent (p. 64). In Bothriocidaris a row of primordial ambulacral plates forms a continuous ring around the mouth, as in all succeeding regular Echini, and they are relatively large, as in the young of modern Echini, Goniocidaris (Plate 2, fig. 1). In Bothriocidaris a second row of plates sur- rounds the first, completing the peristome. This second row was probably derived by flowing down from the corona, and is closely comparable to the second stage in development of Phor- mosoma (Plate 3, fig. 10), as pointed out by Mr. Agassiz (1904, p. 79). A striking feature of Bothriocidaris is the great size of the oculars and the very small genitals (Plate 1, fig. 2). This may fairly be compared with the similar condition in very young Echinus microtubercu- latus (Plate 3, fig. 5), as shown by Bury (1895), though the adult of the same species has large genitals which exclude the oculars from the periproct. The most difficult thing to account for in Bothriocidaris is the fact that the teeth seem to be radial in position, as discussed (p. 242). Of the three species of Bothriocidaris, the salient features are, briefly, as follows. In B. archaica sp. nov. the oculars meet in a continuous ring with genitals dorsal to the same (Plate 1, figs. 1, 2), interambulacral plates bear spines. In B. pahleni Schmidt (Plate 1, figs. 3-6), part of the genitals lie dorsal to the oculars, and part separate the oculars, reaching the inter- ambulacra; interambulacral plates are without spines. In B. globulus Eichwald (Plate 1, figs. SYSTEMATIC CLASSIFICATION <>l l-i HIM. 211 7-9) all of the genitals separate the oculars and meet the inti-rnmhularra; interamlmlacral plates bear spines. These several species occur in the Ordoviciaii of Russia (p. L' The feature of Palaeozoic Echini is that they have more than t«, ,.-„!, „„„. ,,f plate* in each interambulacral area. This is true of all known forms excepting Bott.riocidaris and Miocidan- as far as the latter occurs in the upper Palaeozoic. Gregory (1897), Sollas t 1899), and other- have assumed that the most primitive form of Echini had many column- of int.Tamlmlacral plates in an area, and several authors have considered I'alacodi.-cu.- a- tin- most primitive- known type. On this basis evolution would entail a loss of such parts, as our modern i all have two columns of interambulacral plates in an area. The evidence of development and adult structure is opposed to this view. At the ventral border of the young of all known modern types, and at the ventral border of the adult where not removed by resorption, \ve find a .-inKle primordial plate in each interambulacral area succeeded in the second row by two plates. There is no evidence in development of a larger number of columns dropping out to two in any known living form, or indeed, in any fossil form excepting as seen in sone.-cence ! I'eri-chociduris, Plate 65, figs. 1, 2; Plate 67, figs. 2, 3), and in the little known Tetracidaris of the ( 'retnrcoua. I, therefore, consider the Echini usually classed as the Euechinoida, with a geological range from the Lower Carboniferous to Recent inclusive, and comprising the orders Cidaroidn. < Vn- trechinoida, and Exocycloida as next related to Bothriocidaris. This view is based on >tructure and development. I am well aware of the intervening geological gap, but can only appeal to the rarity of all forms in the Silurian and Devonian to account for the absence of intermediate types. While the Palaeozoic orders Echinocystoida and Perischoechinoida are not con-i-: as in the direct line of ancestry of modern forms, they yet show many primitive chara<" especially as regards the peristome and lantern, which can well be compared with the condition in the young of later types. The order Cidaroida is placed as directly derived from the Bothriocidaroida without known intermediate forms. The Cidaridae as regards the structure of the young and adult are the least removed from Bothriocidaris of any known echinoid, living or fos-il. The young (Plate 2, figs. 1-3, 6) have high hexagonal ambulacral plates with the pores of the pore-pairs superposed. Each interambulacrum has a single plate ventrally, succeeded by two plates in the next row. The peristome has a single row of primordial ambulacral plates which are like those of Bothriocidaris excepting that in that type there are two peristomal rows. The base of the corona has not yet been resorbed, exactly like adult Bothriocidaris. In young cidarids the genitals are large and oculars small and exsert, unlike Bothriocidaris. The young lantern is inclined (Plate 2, fig. 17), with deep foramen magnum, long interpyramidal muscles i Lov.'n. 1892) as in the Perischoechinoida, and the lantern muscles are attached directly to the ! coronal interambulacral plates without apophyses (Love"n, 1892), as is the apparent condition in the Perischoechinoida (text-fig. 221, p. 193). 212 ROBERT TRACY JACKSON ON ECHINI. Adult cidarids differ from the young principally in having low instead of high ambulacral plates, the ventral border of the corona resorbed, many rows of ambulacral, also (with rare exception) interradial non-ambulacral plates in the peristome. Many rows of ambulacral peri- stomal plates is distinctly a Palaeozoic character (Plate 23, fig. 1), and some genera as Archae- ocidaris have non-ambulacral plates as well. The oculars of adult cidarids may be all exsert as in the young, or one or more to all insert, as shown here. The periproct is plated with numer- ous heavy plates as in the Perischoechinoida. The lantern of the adult is nearly vertical (Plate 2, figs. 7-10), instead of inclined, with a very shallow foramen, and short interpyramidal muscles. The perignathic lantern muscles are all inserted on the elevated apophyses, a feature peculiar to this order only (text-fig. 222, p. 193). The absence of pits in the top of the pyra- mids is a feature like the Perischoechinoida but unlike the Centrechinoida. Teeth are grooved as in the Echinocystoida, Perischoechinoida, and Aulodonta. Primary spines are strikingly developed, naked of epidermis, with a cortical layer and a collar about the base, thus differing from the next order. The presence of frondescent Stewart's organs and the absence of peri- stomal gills and sphaeridia are distinctive characters of the order. The Cidaroida present distinctly a combination of Palaeozoic with modern characters. Apparently only two species in the Palaeozoic are definitely referable to the Cidaridae, the Lower Carboniferous Miocidaris cannoni sp. nov. from America (p. 247), and the Permian Miocidaris keyserlingi (Geinitz) from Europe (p. 245). The Centrechinoida as an order differs from the Cidaroida in that the ambulacral plates are usually compound; the peristome (excepting the Echinothuriidae) has only one row of primordial ambulacral plates, with non-ambulacral plates. The lantern has a deep foramen magnum, the tops of the pyramids are pitted, and auricles are developed, on which are inserted the retractor muscles of the lantern. Peristomal gills and sphaeridia are developed. The young of the Centrechinoida (Plate 3, figs. 9-11) make a close approach to cidarids in having simple ambulacral plates, and large central spines and tubercles in the middle of the inter- ambulacral plates. Further, the young have a single primordial interambulacral plate in each area, peristome covered with ambulacral plates only, inclined lanterns with long interpyramidal muscles recalling young cidarids, and the characters seen in the adults of certain Palaeozoic types, as previously discussed. Of the three suborders of the Centrechinoida, the first has the most characters like the Cidaroida, and the last has the fewest (p. 183). The suborder Aulodonta, while having the characters of its order, makes an approach to the Cidaroida in that the teeth are grooved, epiphyses narrow (text-fig. 211, p. 184), and primary tubercles perforate. Some members also approach the Cidaroida in possessing simple ambulacral plates, or Stewart's organs, or many rows of ambulacral plates in the peristome. The Hemicidaridae being wholly a fossil group, some characters are wanting. The peri- stome is unknown. They are primitive in that oculars are mostly all exsert, regressive in that SYSTEMATIC CLASSIKK ATION < >l !•:< HIM. 213 Hemicidaris in the upper half of its test has returned to wimple ambulacral plates. In my tables of ocular plates (pp. 154-159) Duncan is followed in the grouping of f.,»il genera in families, and it is possible that some genera placed in this family may have other affiniti.-.-. The plates are thick and most genera have perforate tubercles. The Aspidodiadematidae are essentially characterized by simple ambulacral plates, large primordial ambulacral plates which nearly cover the peristome (text-fig. 51, p. 80), and a very large apical disc, all of which are primitive characters. There are very wide insert oculars (text-fig. 80, p. 104). The test is thin and fragile. The Centrechinidae have compound ambulacral plates of usually three elements each. The Mesozoic species have relatively thick plates, not imbricate, oculars usually all exsert. The living species have thin tests more or less imbricate, three or more oculars usually insert (text-figs. 81-99, pp. 105-109); while the sequence of incoming of oculars is typically I, V, IV, II, it is not rarely (Centrechinus setosus) I, V, IV, III, a feature rare in the order as a whole, but a typical variation of many cidarids (p. 96). There are only ten primordial ambulacral plates of moderate size on the peristome with non-ambulacral plates (Lov6n, 1892, Plate 12, figs. 153, 154), a strong distinction from the Echinothuriidae. While the lantern is typically erect, it is inclined in Astropyga, as in the next family. In the Echinothuriidae the test is remarkably thin and strongly imbricating, and ambu- lacral plates are compound, composed of three elements each. The primordial interambulacral plates are retained in the basicoronal row (text-fig. 43, p. 80). It is remarkable that a peri- stome of the size attained in this group comes about by the growth of the plates and not by resorption of the base of the corona. Perhaps the most distinctive character of the family is the fact that the peristome is plated with many rows of ambulacral plates only, a feature rarely seen in the Cidaroida and in no other post-Palaeozoic group ; but a character of many Palaeo- zoic genera, as Palaeodiscus (Plate 18, fig. 2), Hyattechinus (Plate 23, fig. 1), and Lepidestht - (Plate 68, fig. 3). Mortensen (1904, p. 53) on the strength of my observations classed the Echinothuriidae with the Lepidocentridae because of the similarity of the peristome. I cannot agree with this view; the ambulacra and interambulacra differ radically from those of the Lepidocentridae. In addition, the auricles, peristomal gills, and pits in the top of the pyramids class this family with the Centrechinoida and with close affinities to the Centrechinidae ex- cepting for the peristome. This is the relationship recently adopted by Messrs. Agassiz and Clark (1909). The character of the peristome with many rows of ambulacral plates only may perhaps be best considered a localized reversion, or parallelism to some ancient type. Such is seen, in fact, in the young of all regular Echini where the peristome for a time is covered with ambulacral plates only. The oculars of the echinothuriids are exsert in the young (Plate 3, fig. 8), but in the adult are all insert and often are separated from the genitals (text-fig. 170, p. 149), a 214 ROI5KRT TRACY .JACKSON ON ECHINI. feature characteristic of this family only. The lantern is inclined, with long interpyramidal muscles (Plate 2, figs. 19-21), a feature like the Palaeozoic, and also the young of types that have erect lanterns in the adult. It may be considered a retention in the adult of a youthful character, seen also in Astropyga. Stewart's organs, more or less developed, are a feature of this family, as of the Cidaroida, although they differ markedly, being vermiform or sausage- shaped rather than frondescent as in the Cidaroida. Radial peristomal and somatic muscles (text-fig. 226, p. 193) are peculiar features of the Echinothuriidae and known in no other Echini. The suborder Stirodonta differs from the Aulodonta in that the teeth are keeled, but agrees with it in that the epiphyses are narrow (text-fig. 212, p. 184). In some the primary tubercles are perforate as in the Aulodonta, but in most genera tubercles are imperforate as in all the Camarodonta. This group, as most others, occupies an intermediate position, possess- ing in some genera characters like the preceding, and in others characters like the succeeding group. Such is found to be true of any classification if the groups are at all nearly related. The Saleniidae is one of the most interesting groups of Echini. The permanence in the adult of the suranal is one of the most striking features (text-figs. 102-105, p. 111). It may lie against genital 3 as in Salenia or facing ocular III (Peltastes), or may be one of several large plates as in some Acrosalenias. This is apparently the first appearance of the suranal plate in Echini, as discussed (p. 174). The ambulacral plates may be compound throughout, or only ventrally and simple above, indicating extreme reversion. The large primary spines and prominent central tubercle like Cidaris may fairly be considered a retention in the adult of characters common to the young of the whole order, indicating with the simple ambulacral plates, when they occur, a reversionary rather than a progressive type. The retention of a single madreporic opening on the proximal side of genital 2 (Plate 4, figs. 1, 2) is a fact in accordance with the same line of reasoning. Ocular plates are exsert or reach the periproct in the sequence I, V, IV, II, III, a contrast to the Arbaciidae where the sequence is V, I, IV. The Phymosomatidae Mortensen (1904, p. 55) classes with the Saleniidae and Arbaciidae, expressing closer relations with the latter. Duncan (1889a) also places this family next to the Arbaciidae. Ambulacral plates are compound, of five elements each in the Recent Glypto- cidaris crenulare, or with more or fewer elements in some fossils. One or more to all oculars may be insert (text-fig. 106, p. 113). Mr. Agassiz's photographic figure (1873, Plate 7a, fig. 8) of Recent Glyptoddaris crenulare shows ocular I only insert. This character, with the somewhat prominent suranal plate opposite genital 3 in the figure cited, inclines one to affiliate the family rather more closely with the Saleniidae than the Arbaciidae. The teeth are keeled, epiphyses narrow, and spurs from the dorsal tips of the pyramids support the teeth as in Stomopneustes (Plate 4, figs. 8-10). This structure is peculiar to these two families only, as far as known. The Stomopneustidae contains only the Stomopneustes variolaris. This genus has been classed with the Echinometridae, but Mortensen (1903, p. 133) separated it as a distinct family SYSTEMATIC CLASSIFICATION OK l-( HIM 21.', on account of differences in spicules of the tube-feel whirl, an- vi-ry law and ,^-uliur, HIM! on differences of the pedicellariae. It differs from the Kchinometndae al-o i,, that tin- ocular* enter the periproct in the sequence I, V, IV (p. 1 13), not V, I, I \ . M in that family Th- mo* important character, however, is that the teeth arc keeled and rpiphys.^ narrow, not m.-..in,K in suture over the foramen magnum (Plate 4, figs. 8-10). Other important ix-niliariti,-* exist as described (p. 186). The character of the lantern places this genus and family a> a member of the Stirodonta. Its affinities are nearest to the I'liym.^omatidae a- indicate,! l>y «pur- from the dorsal tips of the pyramids, which support the teeth Plate J. figs, s 111). Th,. ambu- lacral plates are composed of three elements each, and where fully developed, a- at the mid- zone, four or five plates are combined and grown over by a large primary tubercle, a very strik- ing character. The periproct has numerous small plates, as in Phymosoma. The orular plates of the bivium are typically insert in Slomopneusles variolaris, but I only or I. V. IV may be insert as described (p. 113). Also, as an aberrant variation, three specimen- in a total of 64 have oculars I, V, II insert. This is an essential character of the Kchinidae and Strongylu- centrotidae, and suggests a connection between the families. The small suranal plate of <;iiji»l»- cidaris crenulare, as figured by Mr. Agassiz (1873, Plate 7a, fig. 8). suggest., the sum- affinity, and it seems that in one of these two families may lie the ancestral stock <>i tin- Kchinidae and allies. Of the Arbaciidae the most striking feature is that there are only four, or five, nearly equal plates in the periproct, a feature otherwise known only in Parasalenia. Another important feature not so readily ascertained is the retention of the primordial interambulacral plates in the basicoronal row, as pointed out by Mr. Agassiz (1904, p. 54). A third unusual character is that ocular plates, when they enter the periproct, do so in the sequence V. I. IV p. 158). This is known elsewhere only in the Echinometridae, as here shown. The auricl .|ely separate styloid processes (text-fig. 227, p. 193) or slightly arched and joined by suture 228). Tube-feet are dorsally modified as ambulacral gills in Arbacia (A. Agassiz, 1872, p. 204). In the genera Habrocidaris and Podocidaris, as shown by A. Agassiz and Clark 1 1908, p. 77), and Pygmaeocidaris, as shown by Doderlein l (1906), the primordial interambulacral plate is retained as in Arbacia. The suborder Camarodonta may be considered the most specialized of modern regular Echini on the basis of the lantern, and also in various genera by the sculptured test, the degree of specialization of the ambulacrum, peristome, perignathic girdle, or the elliptical form through a sidewise axis. The essential feature is the fact, that while the teeth are keeled as in the last 1 Doderlein figures (190G, p. 184, fig. 36e) a third median pl:il«- in the third coronal row of t'yicmarocidaris. As this genus so closely resembles Habrocidaris, in which there i* a im-diaii tubercle but no median third plutp, it is powihlr that Doderlein was misled in introducing thesutures of I his plate, a point difficult to ascertain in such a small specimen (4.8mm.) as he had. If Doderlein is correct, it is a unique ease in the Ontrwhinoida. 216 ROBERT TRACY JACKSON ON ECHINI. suborder, the epiphyses are wide and meet in a medium suture over the foramen magnum (text- fig. 213, p. 184; Plate 5, fig. 2). The epiphyses further develop crests that serve as supports for the upper part of the tooth. These features are known in no other Echini and express the fullest differentiation attained in the lantern of regular Echini (p. 187). In the Temnopleuridae, the circular, form of the test, the ambulacral plates of three ele- ments each, with the curious pitting or sculpturing developed on at least the upper part of the test are the most distinctive features. The peristome is mostly naked except for the primordial ambulacral plates. Of Pleurechinus doederleini, Mortensen (1904, p. 78) says that there are only five, instead of ten, buccal plates, a unique character. This is a very remarkable departure, as the ambulacrum, both in the peristome and in the corona of Echini, so constantly consists of a right and a left half for each area. The ocular plates are mostly exsert in modern types, a primitive character, but one or more are said to be insert (Duncan, 1889) in some fossil types. In the Cretaceous Glyphocyphus radiatus all oculars are insert, p. 117. This family on account of its peculiarities represents probably a side branch rather than the basal series of its suborder. The Echinidae is a large family including many genera and species; the test is circular or slightly pentagonal; ambulacral plates have three elements each. Plates with two elements each occur in Echinus affinis, but this is exceptional, and they exist dorsally only (p. 118). The peristome has ten primordial ambulacral plates of moderate size (Lov6n, 1892, Plate 12, fig. 156) with more or fewer large or small to granular non-ambulacral plates. Exceptionally there is a dense covering of non-ambulacral plates (Toxopneustes, text-fig. 57, p. 84). The oculars may be all exsert, or ocular I, or very frequently I, V, or rarely I, V, IV may be insert as a species character; as progressive variants, oculars I, V, IV, II, or all plates may be insert. The range of variation is wide in many species, but with rare exceptions oculars reach the periproct in the sequence I, V, IV, II, III (text-figs. 115-127; pp. 160, 161). The commonest aberrant variant for oculars is for I, V, II to be insert, a combination seen only in this family, the Strongylocentrotidae, Stomopneustidae, and Saleniidae (p. 164). In Gymne- chinus (p. 120) typically an abnormal arrangement of oculars occurs as described. The periproct is plated with many larger or smaller plates, and in adults frequently a somewhat larger plate, which is apparently the suranal, lies against or near genital 3 (text-fig. 122, p. 122). The size which renders this plate distinguishable is subject to much individual variation. It is markedly developed in some, as Toxopneustes variegatus. Of the perignathic girdle the auricles are moderately developed and commonly meet in an arch over the ambula- rum; apophyses are usually only slightly developed. The Strongylocentrotidae (Gregory, 1900, p. 313) includes the large genus Strongylocen- trotus and a few others. The test is circular as in the Echinidae, but, with the exception of some species of Echinostrephus, there are from four to ten elements to an ambulacral plate. As in the Echinidae, oculars may be all exsert or otherwise reach the periproct in the sequence SYSTEMATIC CLASSIFICATION OF K< 1 1 1 M 217 I, V, IV, II (text-figs. 128-153). Many species typically have the bivium iiwert, and one, Strongylocentrotus gibbosus (p. 145), typically has an aberrant arrangement of onilars. Slrongy- locenlrotus albus is peculiar in having frequent and also very rare forms of aberrant arrange- ment of ocular plates (pp. 127, 162, 164). The Echinometridae, as here restricted, includes genera which are elliptical through a sidewise axis, not through III, 5. As a secondary character, the ocular plates, when readiin^ the periproct, do so in the sequence V, I, IV, not I, V, IV, as in the Echinidae and Strongy- locentrotidae. This sequence is strongly held as shown in the table (p. 163), but occasionally ocular I comes in first as a variant. These characters eliminate StrongylocentrotUH and it- allies, which have usually been included here, but which I include in Gregory's (1900) family Strongylocentrotidae placed next to and associated with the Echinidae. The Ecliinotnctridae besides the above have in some genera other striking and very specialized characters. In Echinometra lucunter the auricles are extraordinarily developed as high spoon-shaped arches (text-fig. 230, p. 193). In Heterocentrotus the primary spines attain excessive size and bulk, and in another direction the spines of Colobocentrotus are most abbreviated, truncate; and in C. atratus the spines are polygonal from mutual pressure, so as to resemble angular plates. The Exocycloida present a remarkable series of forms of Echini, all characterized by having the periproct eccentric in interambulacrum 5. Assuming a monophyletic origin for the group, the three suborders present a striking series of structural departures from the regular Echini from which they doubtless originated. Considering the characters of the group as a whole in brief, the compound ambulacral plates and peristomal gills of the Holectypina and the auricles of that group and the Clypeastrina, the existence of keeled teeth, where teeth are known, and the presence of sphaeridia, are all characters which unquestionably asso* the Exocycloida with the Centrechinoida and not with the Cidaroida, where these structures are non-existent. Mr. Agassiz (1909) has shown that in the young of the spatangoid Kchino- neus a well developed lantern exists. This discovery is of the greatest interest and import :i as previously teeth were unknown in this group. On examining his figures and description, it is seen that the lantern is erect, teeth are keeled and epiphyses narrow, not extending over the foramen magnum. Further, the interpyramidal muscles are short, the protractor and compass muscles are inserted on the primordial interambulacral plates, and the retract <>r> are inserted on the auricles which are situated on the ambulacra. These details are shown more fully by Westergren (1911), in a monograph on the genus Echinoneus, which death pre- vented Mr. Agassiz from writing. Looking back to the Centrechinoida, we find that this tyj>o of lantern exists only in the suborder Stirodonta. Further, the attachment of muscles, as stated, occurs only in Arbacia and probably other members of its family. Looking at the matter from the view-point of Arbacia, in that genus the teeth are keeled, epiphyses narrow (text-fig. 212, p. 184); the primordial interambulacral plates are retained in the basicoronal 218 ROBERT TRACY JACKSON ON ECHINI. row; auricles exist as usually separate styles (text-fig. 227, p. 193); ambulacral tube-feet dorsally are modified as ambulacral gills, and locomotion is effected in considerable part (A. Agassiz, 1872, p. 264) by the spines. Any one of these characters might well be a case of parallelism, but the sum of them gives strong evidence of kinship with the Exocycloida. I therefore consider the Exocycloida as connected with the Arbaciidae, probably through some early common ancestral stock. The suborder Holectypina is nearest akin to the Centrechinoida as it possesses compound ambulacral plates and peristomal gills. The ambulacra are not petaloid dorsally as they usually are in clypeastroids and spatangoids. The lantern is inclined with moderately deep foramen magnum, and the wings of the pyramids are horizontally striated for attachment of inter- pyramidal muscles as in regular Echini (Love"n, 1892). The teeth are narrow, elongate, and keeled, and the epiphyses are large, but narrow (Hawkins, 1909). These characters make a near approach to those of the Stirodonta, but in part are like those of the clypeastroids. In addition, in the Holectypina auricles exist on the ambulacra and there are low interambulacral apophyses, both of which occur in the Centrechinoida, but auricles only exist in the clypeas- troids. In the Holectypina the base of the corona is only partially resorbed so that one or more primordial interambulacral plates are retained in the basicoronal row of the adult (Loven, 1874). In this suborder there are usually five genital plates with the madreporic pores in genital 2, but in genital 5 there is no pore (text-fig. 171, p. 149), or genital 5 may be absent. The test is usually circular and not specially modified as in the two following sub- orders. In the suborder Clypeastrina the test is more or less flattened to discoid, circular, penta- gonal, or other shape, and elongate and bilaterally symmetrical through III, 5. Internal pillars and stalactitic growths are peculiar to the group, also lunules, or reentrant emargina- tions may develop. Ambulacral plates are simple with the typical ambulacral pores limited to a petaloid area dorsally; ventrally there are numerous very minute pores, described by Mr. Agassiz (1874, p. 695). They are so small as to be recognizable only with difficulty. Both the primordial ambulacral and interambulacral plates are in the basicoronal row (text-fig. 52, p. 80) a character not known in regular Echini at any stage in life. Rarely (Arachnoides, p. 72, according to Loven, 1874), one interambulacral plate is pushed dorsally and the other four are resorbed by intracoronal resorption so that the basicoronal row may be composed of ten ambulacral plates only, a unique condition for Echini. The peristome is leathery without plates, as far as I have been able to ascertain, a condition unknown in other Echini. Oculars and genitals are fused into a mass; comparable to this is the partial fusion of genitals typical of some spatangoids, and the partial fusion of genitals or genitals and oculars occurring as variants in regular Echini (p. 167). There are four or five genital pores, but the posterior is usually wanting. In Laganum diploporum, described by Messrs. Agassiz and Clark (1907), curiously enough there are six genital pores, two being in area 5. The lantern is usually SVSTKMATIC ( LASSIKICATIO.V OF |.;< |||N| procumbent (text-figs. 214-216, p. 184) though inclined in Kchinocyamu^ ' Uven, 1892). The teeth are keeled, foramen magnum shallow, cpiphyses small and narrow, h™.-.- -mail, wanting in Laganum (Loven, 1892), compasses wanting. The pyramids an- more or le*s highly modi- fied (least in Echinocyamus, Love"n, 1892) with wing-like lateral expan-io,,- and without , for the attachment of interpyramidal muscles. The perignathic girdle con.-i-t- ,,f auridi- only, which are situated on the ambulacral plates (text-fig. 231, p. 197) a.- in tin- (Vntrcchinoida. or may be transferred to the primordial interambulacnil plat.- t.At-di;. -j: u-ually densely covered with small non-ambulacral plates (text-figs. 27- 2S, p. 70. and .VI. p. Mh. Ocular plates may be all exsert, that is, do not reach the center line, or ocular> I. V, or I. V. IV. or I, V, IV, II may be insert (text-figs. 172-175, p. 149). In certain specialized l\ in some species of Pourtalesia (LovSn, 1883; A. Agassiz, 1904), the oculars an- apparently partially or wholly absent in adults. Four genitals are typically present, but 5 is absent and more genitals may be wanting. Genitals 2, 3 may be typically fused (( 'yst echinus. A 1904), as seen in variants of regular Echini (p. 167). The madreporic pores are in genital 2 or extend to 3 where these two plates are fused. An extension to :* i- a common variant in some regular Echini (p. 172). Genital 2 may be much enlarged and extended posteriorly so as to reach interambulacrum 5 (text-fig. 173, p. 149). The lantern is wanting in adults, but occurs in young Echinoneus (pp. 189, 217), as shown recently by Mr. Agassiz ll'.MH)). - are short and undifferentiated, or may be highly produced and with marked arenl differentia- tion. Tubercles in some genera are subject to much areal differentiation, making pattern- on the test. The primary tubercles in Metalia, Meoma, and Brissus are [xrforate and cronu- 220 ROBERT TRACY JACKSON ON ECHINI. late, and in Metalia even the secondary tubercles are perforate. This perforate character is a parallelism or a reversion to a feature typical of Palaeozoic species, the Cidaroida and Aulo- donta, but is not known in other regular Echini excepting a few of the Saleniidae. Respiration is apparently by ambulacral gills only. Sphaeridia are present. All the orders thus far considered have two columns of plates in each ambulacral area; and one column (Bothriocidaroida) or two columns (Cidaroida, Centrechinoida, Exocycloida) in each interambulacral area. In the latter the two columns succeed a single column repre- sented by a single plate in the basicoronal row, seen in the young and also in the adult if not resorbed. In succeeding orders we find two or more columns of ambulacral plates, and three or more columns of interambulacral plates in each area respectively, and on this basis they are considered a further remove from the primitive than any of the above types (p. 70). Of the Plesiocidaroida the type is Tiarechinus, which presents certain extraordinary characters as shown by Lov^n (1883). The ambulacra in each area are composed of two columns of low simple plates. The interambulacra in each area retain the primordial inter- ambulacral plates in the basicoronal row, but in the second row there are three plates (text-fig. 31, p. 70). For a row of three plates to follow immediately the primordial interambulacral plate of the first row is a character known in no other Echini. In Tiarechinus the three plates of the second row are elongate, reaching the apical disc, so that each area consists of but two rows of plates, a unique condition. The genitals are exceptionally large, nearly covering the dorsal field of the urchin, and oculars are small and strongly exsert. With present knowledge it is not closely affiliated with any other group. The three columns of plates in an inter- ambulacral area, the retention of the primordial interambulacral plates, and the imperforate and peculiarly distributed primary tubercles are all objections to including Tiarechinus in the Cidaroida as done by Bather (1909a, p. 66). The Palaeozoic Echini included in the orders Echinocystoida and Perischoechinoida structurally are more removed from the primitive as regards the ambulacrum and interambula- crum than any Recent form. Further, there is no evidence in the development of modern types that they were derived from these more complex forms. Following the facts there is no alternative, as I see it, except to consider the Palaeozoic genera of the Echinocystoida and Perischoechinoida as structurally differentiated on independent lines from later known forms and on those lines further removed from the primitive than are the types now living. A some- what comparable case is seen in Cephalopoda in which the extinct Devonian to Cretaceous Ammonoidea are further removed structurally from the primitive Cephalopoda than are the species of living Nautilus. Certain broad characters of these Palaeozoic orders may be considered first as they are features of the group as a whole and can thus be disposed of and save repetition. Ambulacral plates are always simple, with two pores each. There may be two columns of such plates in SYSTEMATIC CLASSIFICATION OF K< '111X1. 221 each area or more than two up to twenty, but with an equal number in each half-ambulacrum. The primordial interambulacral plates may be retained in the basicoronal row, or may be re- sorbed in the advance of the peristome. There are three or more, usually more, col um: plates in each interambulacral area, and there may be as many as fourteen, the highest numlxT at present known. The plates may be imbricate or not, but when imbricate, the ambulacrabi imbricate adorally and the interambulacrals aborally and from ftje center laterally and over the ambulacrals (text-figs. 32-38, p. 75). The primordial ambulacra! plates arc »iiu:itr order, and i.- -trikinnly uniform in character. Mr. Agassiz (1881, p. 80) suggested and Duncan (1889a, p. 1 1 tated that there are passages for peristomal gills in Archaeocidaris, but such have not been (inured. A- th.-n- was no indication of such slits in the best specimens which I studied i Plate '.», fin. (i and Plato 11, fig. 1) and as such structures are otherwise known only in the ( Vntrerhinoida and Holee- typina, I think this is a mistake, and peristomal gills may be considered a- \\ anting in Archaeocidaris and other Palaeozoic genera as well (p. 253). The Archaeocidaridae is a family with only three genera, Eocidaris, Archaeocidark and Lepidocidaris. Eliminating Eocidaris, which is most imperfectly known, there are two column* of ambulacral plates and four, or six to eight of interambulacral plates in each area resort ively. The plates are rather strongly imbricate, and each interambulacral plate bears a central pri- mary perforate tubercle and large spine, also secondary spines and tubercle-. The base of tin- corona is extensively resorbed, there being four plates in the basicomnal row in each interambu- lacral area. The peristome has many rows of ambulacral plates with iion-ainbularral plate- in Archaeocidaris (Plate 9, figs. 6, 7) and probably was similar though unknown in Ix-pido- cidaris. The apical system is doubtfully known, which is rather remarkable with so many species. The lantern is well known in Archaeocidaris (Plate 12) and con-i-ts of forty | as in modern regular Echini (p. 254). The genus Eocidaris has large interambulacral plates which bear a central perforate tubercle, as in Archaeocidaris; there is a scrobicular area but no basal terrace. Thi> genus i- most imperfectly known, but Bather (1909), who has studied the question and material crit ically . feels that it should be retained. Only one species is recognized, the Devonian K. Inerifirinn (Sandberger), Plate 15, figs. 11, 12. The absence of a basal terrace, which is the essential difference from Archaeocidaris, could easily be accounted for by wear as it is not always ob- servable in true Archaeocidaris. The young dorsal plates of Archaeocidaris have no basal terrace (Plate 11, fig. 2), so that a genus founded on this character should be considered the more primitive of the two (p. 254). In Archaeocidaris the ambulacral plates are narrow and low, with pore-pairs uniserial (Plate 12, fig. 9). In the few species where the corona is fairly known, there are four columns of large plates in each interambulacral area (Plate 10, fig. 10). Each plate bears a large mitral perforate tubercle with a basal terrace and scrobicular ring (Plate 11, fig. 4). The basal terrace is so slight an eminence that it is often worn off, and this feature can only \»> ascertained in fairly well preserved specimens. From the center rises a primary spine of ronsiderabl. and various ornamentation; in addition, secondary and miliary spines and tubercle- occur on the periphery of the plates. The young plates dorsally i Plate 1 1 . fig. 2) are at first smooth, then an imperforate tubercle arises (as in developing plates of cidarids, Plate 3, figs. 1, 224 ROBERT TRACY JACKSON ON ECHINI. but without a basal terrace, a feature which, with the perforation, developed later as the plate was pushed ventrally by younger newly added plates. The base of the corona is extensively resorbed so that several rows of plates have evidently been cut away in the advance of the peri- stome (Plate 9, figs. 7, 8). This is the most extensive resorption definitely known in any Echini, though it may have been as much, or more, in Recent regular Echini, where data are not avail- able to measure the amount of resorption (p. 256). The species of Archaeocidaris are numerous but are largely described from isolated spines and plates. With available material perhaps the best way to group the species is on the basis of the character of the spines, as is done under the description of species. The smooth-spined forms are considered first, as smoothness is in general a primitive character; next are grouped the species with spines bearing short small spinules, then those with long thorn-like spinules, etc., associating the species on the similarity of characters in these respects (p. 258). Only six species are known with a more or less complete test, and of these the best material occurs in Archaeocidaris wortheni (Plate 8, figs. 5, 6; Plate 9, figs. 6-11) and A. rossica (Plate 10, fig. 10; Plates 11, 12). The species of Archaeocidaris occur in the Lower Carboniferous, Carbon- iferous or Coal Measures, and Permian. The genus Lepidocidaris is known only from L. squamosa Meek and Worthen (Plate 16, figs. 1-3; Plate 17). The ambulacral plates are not all alike, but every third plate is larger and more or less completely abuts against two smaller plates of the opposite half -area (Plate 17, figs. 1, 3, 8). There are six or eight columns of plates in an interambulacral area; these are high, rounded, with a scrobicular area, but no basal terrace. The margin is thickly studded with secondary tubercles. The primary spines are feebly striate longitudinally and very cylindrical (p. 282). The Lepidocentridae is a family of Silurian, Devonian, and Lower Carboniferous Echini that have strongly imbricate plates and includes most striking and interesting species. There are but two columns of plates in each ambulacral area, and from five to fourteen columns of plates in each interambulacral area; the latter is the extreme limit of known Echini. The primordial interambulacral plates are in place in the basicoronal row (Plate 23, fig. 1), as ascer- tained in five species. The peristome is covered with many rows of ambulacral plates only (Plate 23, fig. 1). Oculars where known are small, all insert, and the genitals where known, are wide with many (eight or nine) genital pores (Plate 28, fig. 10). The periproct has numerous plates (Plate 25, figs. 3, 5) and an exceptionally perfect lantern is known in one species (Plate 27), presenting the typical Palaeozoic character. The spines are small, eccentrically placed primaries, with secondaries, or the latter only (p. 284). The genus Koninckocidaris Dollo and Buisseret was based on K. cotteaui Dollo and Buis- seret, which has not been figured. The most important character is that the ambulacral plates are high, two or three equaling the height of an adjacent interambulacral plate; pore-pairs SYSTEMATIC CLASSIFICATION OF WHIM. 225 are uniserial. The interambulacra have seven or eight columns of Mrongly imbricate |M>!VK- onal plates in an area. As high ambulacral plates are a primitive character, Kotiinckocidaru is considered a lower genus than Lepidocentrus which has low amliulaeral plate- p. 284). In Koninckocidaris cotteaui as described, two ambulacral pint.- equal tin- height of an interambulacral ; there are seven columns of interambulacral plates in an area, tin- median column being the narrowest; spines and tubercles are of two sizes. Thi-. tin- type of tin- genus, is from the Lower Carboniferous of Belgium (p. 285). Koninckocidaris silurica sp. nov. (Plate 19, fig. 1 ; Plate 20, figs. 5, 6) has three ambulacra! plates equaling the height of one adambulacral. There are eight columns of rhombic inter- ambulacral plates in an area, the plates of column 7 in each area being very narrow in the t \ \»-. This species is from the Niagara Group, of Rochester, New York, and is of interest as by far the oldest echinoid yet found in America and also the oldest known in the family ip. '_>* Lepidocentrus is characterized by relatively high spheroidal tests, ambulacral areas narrow throughout, ambulacral plates low, interambulacrals with small eccentric primary and second- ary tubercles. The species are from the Devonian or Lower Carboniferous, and the best known is L. mulleri (Plate 19, figs. 2-5; Plate 20, figs. 8-13), (p. 286). Hyattechinus gen. nov. — This genus includes some of the most striking of known Echini. The test is depressed or flattened. Horizontally the outline is circular, pentagonal, or clypeas- triform. The most distinctive character is that the ambulacra are broad, almost petaloiil ventrally, narrow dorsally, ambulacral plates are low, pore-pairs uniserial. Interambulacra have from eleven to fourteen columns of plates in each area and a very accelerated development so that new columns are added early and rapidly during development. There are small primary and secondary tubercles on the interambulacral plates. As the species of Hyattechinus pr« very exceptional characters, these may be briefly stated. In Hyattechinus rarispinus (Hall) (Plate 21, fig. 6; Plates 22, 23) the test is nearly circular, and flattened probably as much as in Recent Phormosoma; ambulacra ventrally are twice as broad as dorsally, with ventral internal spurs as in beecheri. Interambulacra have eleven to thirteen columns of plate- in each area, varying within these limits in different areas of the same specimen (Plate 2:1, fig. 3). This species was described as a Lepidechinus by Hall, but is very different from that genus. In Hyattechinus pentagonus sp. nov. (Plate 24, figs. 1-4; Plate 25, figs. l-4i the t- compressed, strongly pentagonal, the most so of any known regular echinoid. Ambulacra are ventrally twice as broad as dorsally. Interambulacra have fourteen columns of plates in each area, the highest number known in any echinoid. Dorsally, the adambulacral and some addi- tional columns drop out and therefore fail to reach the apical disc, an indication of senesc. In the remarkable Hyattechinus beecheri sp. nov. (Plate 24, figs. 5-8; Plate 25, fig. 5; Plat. the test is depressed with a flat base, moderately pentagonal and elongate, and bilaterally symmetrical through the axis of an ambulacrum and opposite interamlmlacrum which I take 226 ROBERT TRACY JACKSON ON ECHINI. to be the axis III, 5. This is the only known case of a regular sea-urchin with centrally placed periproct that is bilaterally symmetrical through an antero-posterior axis. The ambulacra ventrally are twice as wide as dorsally and the ventral ambulacral plates develop a series of short spurs which extend into the body of the animal. Somewhat comparable proximal growths are known in Recent cidarids (p. 61; text-fig. 224; Plate 3, figs. 12, 13), but excepting Hyatt- echinus are unknown in other Echini. There are eleven columns of plates in each inter- ambulacrum in beecheri. The plates by their incoming show an accelerated development, and dorsally the adradial columns and some others drop out, showing senescence. The only known specimen is an internal mold so that the exterior of the plates is unknown, yet so perfect is the specimen that it is represented spread out by the Loven method (Plate 26), (p. 291). Pholidechinus gen. nov. is known only from a single species, P. brauni sp. nov. (Plates 27, 28). The test is high and spheroidal, ambulacra narrow throughout; at the mid-zone alternate plates are somewhat pinched off at the suture with the interambulacrum, by the broadening of the plates between. Occasionally a plate is quite cut off from the interambula- crum and thus becomes occluded, but this is exceptional. There are nine or ten columns of plates in each interambulacral area. The plates are scale-like and imbricate strongly. Spines and tubercles are secondaries only, on both ambulacra and interambulacra. Genitals are very wide with many genital pores. A very perfect lantern is known, as figured (p. 299). The family of the Palaeechinidae (commonly known as the Melonitidae) contains the most species, and as a whole is the best known of the Palaeozoic groups of Echini. The test is sphe- roidal or occasionally elliptical and in one species obovate. There are from two to twelve columns of plates in each ambulacral area according to the genus or species. It must be urged that this character should be ascertained at or near the mid-zone, as ventral or dorsal to this zone the number of plates may differ (text-fig. 237, p. 231), and it is at this area that the full differential specific characters are evinced, as elsewhere discussed (p. 55). In the interambul- acra there are from three to eleven columns of plates in each area varying with the species, also varying somewhat in the species and even somewhat in different areas of the same indi- vidual. The plates of the corona are not imbricate, but in all species the ambulacral plates bevel over the interambulacral on the adradial sutures (Plate 38, fig. 9). A reverse condition exists in all Echini with imbricate plates, for in these the interambulacrals are beveled over the ambulacrals on the adradial suture (text-fig. 32, p. 75). Coronal plates are very thick, more so than hi any other group of Echini, the thickness often exceeding the width or height of a plate, a distinctly specialized character. The primordial interambulacral plates are resorbed, and apparently these only, as there are two interambulacral plates in each interambulacral area in the basicoronal row (text-fig. 25, p. 70). The peristome is known only in Melon- echinus multiporus (text-fig. 48, p. 80). On the basis of this species there are many rows of ambulacral with some interradial non-ambulacral plates on the peristome. Ocular plates are SYSTEMATIC CLASSIFICATION OF K< HIM 227 imperforate in the known species. They are typically all insert, or reaching the periproct, but exceptionally one or more to all may be exsert (Plate 33, figs. 11, 12). Genitals have from two to five pores each, and a madreporite is rarely recognizable (h-xt-fig. 243, p. 331). The periproct is plated with numerous thick plates (Plate 34, fig. 6), u.s in the Gidaroida, but these plates are rarely preserved. The lantern is imperfectly known, but has the eawntial Palae- ozoic characters as far as preserved. The spines in the whole family are enwritially alike, small secondaries on ambulacral and interambulacral areas; tubercles are imperforate and evenly distributed over the corona (Plate 61, fig. 8). The existence of secondary spines and impi-r- forate tubercles only may both be considered specialized characters. One species, Maccoya phillipsiae, is said to be Silurian, but all others in the family are Lower Carboniferous (p. 302). The family characters are of course understood in the brief description of generic characters given here. Palaeechinus M'Coy has only two columns of plates throughout each ambulacral area, all plates are primaries of equal height, pore-pairs uniserial. Interambulacra with four to six columns of plates in each area. The best known species are Palaeechinus quadriseriali* (Plate 29, fig. 1; Plate 30, figs. 1-7) and Palaeechinus elegans (text-fig. 237; Plate 29, figs. 3, 4, 6; Plate 31, figs. 1-5), (p. 304). The genus Maccoya Pomel differs from Palaeechinus in that at the mid-zone pore-pairs are biserial. All ambulacral plates extend to the middle of the area, but marginally alternate plates meet the interambulacrum, or are nearly or quite cut off from it by the outer enlargement of their fellows (M. intermedia, Plate 34, fig. 2). This makes alternate plates primaries and occluded instead of all primaries as in Palaeechinus. In some species the alternate plate may weakly reach the interambulacrum instead of being cut off, M. sphaerica (Plate 34, fig. 5). Such make an approach to the character of Palaeechinus, but, as the pore-pairs are biserial, it seems best to consider them in this genus. On the interior of the test the plates all cross the half-areas and pore-pairs are uniserial, a radical difference from the exterior of the same structures (Plate 33, figs. 4, 5). The interambulacra have from four to nine columns of p! in each area in the several species. A very perfect periproct is known in M . sphaerica. The best known species are Maccoya burlingtonensis (Plate 32, figs. 1-3; Plate 33, figs. 1-5), M. intermedia (Plate 33, figs. 6-12; Plate 34, figs. 1-3), and M. sphaerica (Plate 32, figs. 4, 5; Plate 34, figs. 4-10), (p. 311). The genus Lovenechinus gen. nov. includes species in which at the mid-zone the ambula- crum consists of four columns of plates. In each half-area there is a vertical series of demi- plates which extend from the interambulacrum inward and a similar series of occluded plates that extend from the middle of the ambulacrum outward, but neither series crosses' the half- area (Plate 42, fig. 2). Ventrally and dorsally the plates for a brief space are all prim:, and, between these and the character plates, are plates which are alternately primaries and occluded (Plate 42, figs. 1, 3 and 4; text-fig. 237). In this genus there are no isolated plates 228 ROBERT TRACY JACKSON ON ECHINI. such as are present in Oligoporus (Plate 50, fig. 7), this being the distinction between the two genera. In the interambulacra of Lovenechinus in the known species there are from four to seven columns of plates in an area. Of the several species the most completely known are Lovenechinus missouriensis and L. septies (Plates 39-45 and 46, fig. 4), (p. 324). The genus Oligoporus Meek and Worthen is characterized by the fact that the ambulacrum at the mid-zone has four columns of plates and, in addition, in the middle line of each half-area isolated plates at intervals, but not in a continuous series so as to make an additional column (Plate 50, fig. 7). This structure is distinctly intermediate between that of Lovenechinus and the simplest species of Melonechinus. The youthful Oligoporus (Plate 50, fig. 8) has exactly the structure of adult Lovenechinus, and the youthful Melonechinus as a second stage in devel- opment (Plate 56, fig. 3) has exactly the structure of adult Oligoporus. In the interambula- crum of Oligoporus there are from four to nine columns of plates in an area according to the species. All known species are American, from the Lower Carboniferous, and the best known is Oligoporus danae (text-fig. 237; Plate 47, fig. 13; Plate 49, figs. 4, 5; Plate 50), (p. 350). The genus Melonechinus Meek and Worthen has many species with a very wide range of characters. The ambulacrum at the mid-zone has from six to twelve somewhat irregular col- umns of plates. The two median columns of occluded plates that extend from the middle of the ambulacrum outward are wider than other plates of the area, and are principally involved in the more or less high ridge that usually marks the central line of the ambulacrum. The demi-plates which extend from the interambulacrum inward do not differ externally from others of the area except the occluded plates, with the exception of the fact that they bevel over the interambulacra. On the outer face of the plates the pore-pairs are surrounded by a peripodium which occupies that part of the plate nearest the next adjacent interambula- crum. On the other hand, on the internal face of the plates the pore-pairs are very near the center of the isolated plates but in demi- and occluded plates, the pore-pairs lie nearer to the center of the half-area than to the middle of the plates (Plate 56, figs. 4, 5) . The ambulacrum of Melonechinus on the ventral border has four columns of plates like the typical character at the mid-zone of Lovenechinus. Passing from this area dorsally, scattered isolated plates appear, the generic character of Oligoporus; further dorsally the isolated plates are more fre- quent and fall into columns which are more or less in number according to the species in hand. This is shown in text-fig. 245, p. 382; Plate 56, fig. 3; Plate 57, fig. 1 ; and others. In one area of a specimen of M . multiporus, as a regressive variant there are simple primary plates ventrally (Plate 57, fig. 3). This shows that while the genus typically has four columns ventrally, it may revert to two columns as a variation, repeating the character seen at this area in the lower genera of the family, and likewise the character seen at the mid-zone in Palaeechinus, the lowest genus of the family. In the dorsal region of Melonechinus near the apical disc, in the region of young last added plates, the ambulacrum is also simpler. As few as two plates may SYSTEMATIC CLASSIFICATION OF FCIIINI. be found next the ocular (Plate 56, fig. .6), and passing ventrally, a progressively increasing number of plates occurs until the full species character is Attained. This i- shown in outline in text-fig. 237. The interambulacra at or near the mid-zone have from three to eleven column* of plates in each area varying with the species, and somewhat in tin- qweiM, -T indeed in differ- ent areas of the same specimen. As in other genera where there is a difference in thi- re-pert, the ambulacrum is considered the more essential part and of first consideration in classifica- tion; the species are therefore erected first on the basis of specialization of the ambulacrum and secondarily on that of the interambulacrum. Other characters are for the most part essentially similar in all species of the genus. The best known species is Melonechinus multi- porus (Plate 54, fig. 5; Plate 55; Plate 56, figs. 2-13; Plate 57; text-figs. 237, 245, 246, p. 382; Plate 60, figs.,1, 2), (p. 359). Having considered briefly the family of the Palaeechinidae, it is seen that the genera, and in addition in Melonechinus the species, present a progressive series as regards differential evolution of ambulacral characters; also, where a complex ambulacrum is attained as a character gathered from the mid-zone, the ventral plates built in the youth of the individual are simpler. The young last added dorsal plates as a localized stage in development also present a simpler condition. This relation is expressed diagrammatically in text-fig. 237. This is not a schematic diagram, as each of the several figures is taken directly from the Plates as indicated. In the figure the species characters are given in the middle horizontal row representing the mid-zone. In the lowest row are given the characters taken at or close to the ventral border of the corona; in the uppermost row are given the characters of plates at or close to the ocular plates. Between the lowest row or the uppermost row and the mid-zone are given the intermediate characters, both ventral and dorsal. In Palaeechinus elegans and other species of the genus the plates are simple priin throughout the length of the ambulacrum, the simplest condition in the family. The plates are wanting at the ventral border in the known specimens of this species, t herefore in t he diagram a gap occurs at this point. In Maccoya burlingtonensis the plates ventrally are simple pri- maries, at the mid-zone primaries and occluded plates alternating, and dorsally simple primaries In Lovenechinus missouriensis ventrally the plates are simple primaries, higher up alternately primaries and occluded, and at the mid-zone demi- and occluded plates. Passing dorsally, we find primary and occluded plates alternating, and close to the dorsal border primaries only. In Oligoporus danae again, the plates ventrally are simple primaries, above that alternately primaries and occluded, above that demi- and occluded plates. At the mid-zone there arc in addition scattered isolated plates which is the generic feature. Passing dorsally we find demi- and occluded plates only, which doubtless were succeeded near the oculars by primaries only, but such are not preserved in available specimens. In Melonechinus we jiave the most specialized genus with from six to twelve columns of 230 ROBERT TRACY JACKSON ON ECHINI. ambulacral plates at the mid-zone. In this genus ventrally there are four plates in each area instead of two as in the preceding genera, although exceptionally in one known case, as a re- gressive variant, in one area simple primaries occur (Plate 57, fig. 3). In Melonechinus springeri ventrally the plates are demi- and occluded, higher up isolated plates appear; at the mid-zone there are three definite columns in a half-area. Above the mid-zone we pass into an area of demi-, occluded, and scattered isolated plates, then demi- and occluded only, and near the ocular primaries only. We see in this and other species of the genus that dorsally a simpler condition exists than that found at the ventral border of the corona, emphasizing the value of localized stages in studies of development. In Melonechinus indianensis ventrally the plates are demi- and occluded, higher up demi- and occluded, with scattered isolated plates; higher again three columns, and at the mid-zone four columns of plates in a half-area, the species character. Passing dorsally we find three col- umns, then two, and near the ocular primaries only. In Melonechinus multiporus the same condition occurs, but a little more complex. At the ventral border plates are demi- and occluded, higher up the same with scattered isolated plates, then three columns, then four, and at the mid-zone five columns in a half-area as the full specific differential. Passing dorsally, we fall into four columns, then three, two, and near the ocular primaries only may occur as in the same area in all lower species and associated genera. The extreme condition of the family occurs in Melonechinus giganteus. Here from conditions of preservation certain stages are wanting, but ventrally there are demi- and occluded plates, next as far as preserved an area with three columns, then one with five, and at the mid-zone there are six columns in the half-area. Melonechinus keepingi at the mid-zone has six columns in the half-area as in giganteus, and the dorsal area of this species was therefore used to complete the diagram, which I could not do in the case of giganteus. Passing dorsally from the mid-zone, we find a condition of five columns, then four, three, two, and finally primary plates only close to the dorsal border of the area. TEXT-FIG. 237. — Illustrating the structure of the ambulacrum in representatives of the Palaeechinidae as seen at the mid-zone, with the phylogenesis of the same as shown by ventral youthful stages and dorsal localized stages of the species shown. Numerals indicate number of columns of ambulacral plates in a half-area. (Compare text-figs, on pp. 54, 59). Palaeechinus elegans M'Coy (from Plate 31, fig. 1). Maceoya burlingtonensis (Meek and Worthen) (from Plate 33, figs. 1,2). Lovenechinus missouriensis (Jackson) (from Plate 42, figs. \-V). Oligoporus danae Meek and Worthen (from Plate 50, figs. 1, 7, 8). Melonechinus springeri sp. nov. (from Plate 52, figs. 2, 3). Melonechinus indianensis (Miller and Gurley) (from Plate 53, figs. 1-3). Melonechinus muUiporus (Norwood and Owen) (from Plate 56, figs. 2, 3, 4, 6; Plate 57, fig. 1, and text-fig. 245, p. 382. Melonechinus giganteus (Jackson). Of this species the structure from the ventral border to the mid-zone is repre- sented below the black line (from Plate 59, figs. 12, 13, and Plate 61, fig. 8). Melonechinus keepingi sp. nov. at the mid-zone has the same character as giganleus, and its dorsal area is represented above the black line (from Plate 59, fig. 1). »~ 3 I f §" II SYSTEMATIC CLASSIFICATION OK KrillXI. 23] II II o •o 3 N § § 3 -<" g I r I! Maccoya liurliiiKionctuM. '--.T inimourieiuw. ()ligo|K>ru8 daiute. NS ) Melonechinus gpringrri. Mrliilirrhinil.x iixliaiioilMB. \Go Mi'l rhinu.1 multiporua. 0 gigantpua below the heavy line, and Melon- ochinus keeping! above the heavy line. *>. co N> 232 KOHKKT TRACY JACKSON ON ECHINI. As shown in the diagram by connecting dotted lines, each type in the development of its ambulacrum presents a series of stages, either ventrally as youthful or dorsally as localized stages or both, which are directly comparable to the adult (mid-zone) character of all the simpler preceding types of the family. As the result, a complete genealogical history of the family can be read from the study of the ambulacrum. It is also seen how completely developing plates as localized stages repeat the characters seen as stages in the developing individual gathered from the plates from the ventral border up to the mid-zone. This is comparable to the developing characters occurring in successively added septa in ammonites, as shown by Hyatt and others, where also localized stages occur, as I showed (Jackson, 1899, p. 134). The family Lepidesthidae is enlarged over what it was when I first published it (1896) to include certain old genera and one new one. It presents a wide range of characters, yet it is difficult with present knowledge to make two distinct families for the included genera. The sum of the characters affiliates the group as an offshoot from the Palaeechinidae, and the extreme characters seen in several species mark this as one of the most specialized of all groups of Echini. There are from two to twenty columns of plates in each ambulacral area and from three to twelve columns of plates in each interambulacral area. The plates are moderately or more usually strongly imbricate, and bear secondary spines with imperforate tubercles only, or in some genera part or all of the interambulacral plates bear also a primary spine with a perforate tubercle. Where the ventral border of the corona is known, the primordial interambulacral plates are in place, but this area is unknown in some of the genera. In Lepidechinus and Lepi- desthes the peristome is covered with ambulacral plates only, and the same condition probably exists in the other genera. Oculars are all insert or may be exsert. Genitals have from one to many pores each, and the periproct is heavily plated. The lantern has the usual Palaeozoic characters, but in one genus the teeth are distally denticulate. The simplest of the Lepides- thidae are so similar to the simplest members of the Palaeechinidae that the Lepidesthidae may well have been derived from that stock (p. 393). The genus Lepidechinus Hall makes a close approach to Palaeechinus. It differs from it mainly in that the plates imbricate moderately, and that interambulacral plates bevel over the ambulacrals instead of the ambulacral plates beveling over the interambulacrals, as in Palaeechinus and all of its family. The ambulacral plates are all primaries, nearly uniform in height, or with a slight tendency for alternate plates to become enlarged against the interam- bulacral suture, pore-pairs are nearly or quite uniserial. Interambulacral plates are in four to eight columns in each area. These plates are rounded hexagonal, with curved surfaces bearing secondary spines and tubercles only. Oculars are all exsert and genitals with a single pore each as far as preserved in L. tessellatus, the only species of the genus in which they are known (Plate 63, figs. 7, 8). The species are all known from fairly complete specimens (Plate 62, figs. 1-5; Plate 63; Plate 64, fig. 1), (p. 394). SYSTEMATIC CLASSIFICATION OF KCJIIM The characters of the genus Perischodomus M'Coy (Plate (12, (in-, i, 7 I'l.-.i,- i,|. liu-. 2-8) are taken from P. biserialis M'Coy, the only satisfactorily known Bpedw. Tin- ambulacra have two columns of plates in each area at the niiores. The periproct is covered with many moderately thick plates. This is one of the most extreme 234 ROBERT TRACY JACKSON ON ECHINI. genera of Echini for ambulacral differentiation. The best known species are Lepidesthes for- mosa (Plate 66, figs. 4-7; Plate 68, figs. 3-14) and L. colktti (text-figs. 14, p. 54; 32-38, p. 75; 251; Plates 69, 70; Plate 71, fig. 1). Pholidocidaris Meek and Worthen is one of the most specialized in certain respects of Palaeozoic genera. There are from four to six columns of plates in each ambulacral area, but the plates are very large ventrally and small dorsally. A peculiarity is that the pores are situated in the middle of the plates, a primitive character. The interambulacra as far as known have five or six columns of plates in an area and the plates are rounded polygonal. The adambulacral plates dorsally are very much larger than the intermediate plates, one equaling in height the distance of two or three of the adjacent interambulacral plates. This is a character known in no other Echini. In addition the adambulacral plates bear each one eccentric primary spine and perforate tubercle, with secondary tubercles. The intermediate plates dorsally bear secondary tubercles only. The primordial interambulacral plates are in the basicoronal row, and the imbrication of coronal plates is extreme. The genital plates have many pores. No species is known perfectly, but the best known is the genotype, Pholidocidaris irregularis (Plate 73, figs. 3-7; Plate 74, figs. 1-7; Plate 75, figs. 1-5). Meekechinus gen. nov. (Plate 75, figs. 6-8; Plate 76) is in some respects the most specialized of known Echini, and is based on the single species M . elegans sp. nov. There are twenty columns of low rhombic plates at the mid-zone in each ambulacral area, the highest number known in any sea-urchin. With this great expanse of ambulacrum there are only three columns of small plates in each interambulacral area. All plates are strongly imbricate, all interam- bulacral plates bear a small primary spine and tubercle, with secondary tubercles, with the same on the ambulacral plates. Ocular plates are apparently all exsert, and genitals are large, the madreporite being exceptionally large and with distinct madreporic pores, the clearest seen in any Palaeozoic species. Pedicellariae were found in this remarkable species, and are the only ones yet known from the Palaeozoic. The lantern has the typical Palaeozoic characters except that the teeth are distally denticulate, a unique character for Echini. This species is the highest geologically and the most specialized structurally of any known Palaeozoic echinoid. If this classification is adopted the names Palaeechinoida and Euechinoida will naturally lapse as the major divisions of the Echini are ordinal only as shown in the table, p. 209. PART III. PALAEOZOIC ECHINI. In considering the systematic part of this memoir, attention is railed to the general state- ments of the history of the subject, sources of material, methods of work, etc., as given in the Preface and Introduction. The morphological part of this memoir is based in considerable part on the study of Palaeozoic species, so that considerations of these older forms and their relations are scattered all through the morphological sections. As references to the pages of these earlier considerations of Palaeozoic genera and species can be gathered from the index they are largely omitted in the descriptions. A key to the classification of Palaeozoic Echini is given in the last section (p. 201-208), and a systematic table (p. 209), showing the genealogical relations, as understood, of the Palaeo- zoic Echini to each other and to the larger groups of the post-Palaeozoic Echini. An asteri>k before the name of a species indicates that specimens have been studied. Under each species the synonymy is given in full as far as ascertained, and references to the principal literature. Miss Klem (1904) has recently published so full a list of references in her Revision of Palaeozoic species, that it seems unnecessary to repeat minor references. All text-books are omitted unless there is special need of comment, also works in which species are simply listed without description or discussion, as Miller's Catalogue of North American Geology and Palaeontology, Etheridge's and Morris's Catalogues of British Fossils, d'Orbigny's Prodrome, Dujardin and Hupe's Echinodermes, etc. Where species are simply listed without description or discussion, as in parts of LoveVs (1874) and Miss Klem's (1904) memoirs, no reference is deemed necessary. Messrs. Lambert and Thie'ry's Essai de Nomenclature (1910) has recently come to hand (March, 1911). Their distribution of Palaeozoic species in genera and their generic synonyms do not appear to me well considered. While there are no descriptions of species in Lambert and Thiery's Essai, names from this work are included as a matter of synonymy. In my descrip- tions of species I have given what are considered the essential features with new matter. Where further information is desired, it may be obtained from the authors cited. GEOLOGICAL DISTRIBUTION. Considering in brief and in a broadly inclusive way the geological distribution of Palaeozoic Echini, their occurrence in formations is as follows. In the Ordovician, Echini are known only from Russia where the primitive genus Bothriocidaris is represented by three spe (235) 236 ROBERT TRACY JACKSON ON ECHINI. In the Silurian, Echini are represented thus far only in America and England. In t he- Niagara Group of New York State is found the oldest known representative of the Lepidocen- tridae, Koninckocidaris silurica sp. nov. The position of the Niagara is about in the middle of the Silurian. In England, Maccoya phillipsiae (Forbes) is ascribed to the Llandovery which is at the base of the Silurian, but this horizon for the species may be doubted. In the British Museum there is an excellent echinoid lantern from the Wenlock Limestone of Dudley,1 the oldest assured horizon from which an echinoid is known in Great Britain. In the Lower Ludlow, which is the upper part of the Silurian, just below the Devonian, occur in England Palaeodiscus ferox Salter, and Echinocystites pomum Wyville Thomson, the sole representatives of the order Echinocystoida. In the Devonian, as in the Silurian, only a few Echini are known. In the Devonian of Germany Eocidaris laevispina (Sandberger) is fragmentarily known. This is the only species here ascribed to that genus and it is the earliest, also the only known representative of the Archaeocidaridae in the Devonian. In the Devonian of Germany also are found Lepidocentrus rhenanus (Beyrich), L. mulleri Schultze, and L. eifelianus Miiller. Lepidocentrus drydenensis is found in the Upper Devonian of America, in New York State. All species of Lepidocentrus are Devonian excepting one, which is found in the base of the American Lower Carboniferous. In England Lepidesthes devonicans Whidborne and Pholidocidaris acuaria (Whidborne) occur in the Devonian; they are the oldest representatives of their genera and of the family Lepi- desthidae. The imperfectly known Xenocidaris, with three species, is found in the Devonian of Germany. The term Subcarboniferous is commonly used in America for the lower part of the Carboni- ferous, below the Coal Measures. I use here the term Lower Carboniferous. This is a more nearly correct name for the horizon and has the advantage of coinciding with foreign usage. The Lower Carboniferous is the period of greatest development of Palaeozoic Echini and it is in America that the most species are found. Here occurs the Miocidaris cannoni sp. nov. which is important as the geologically oldest known member of the Cidaridae, which family is a salient feature of the Echinoid fauna from Mesozoic to Recent times. The genus Archaeocidaris also first appears in the Lower Carboniferous, and in this formation there are many species in both America and Europe. The genus Lepidocidaris, structurally the highest member of the Archaeocidaridae, 1 Tliis lantern, which was recently discovered in the matrix and developed by Dr. Bather, is well preserved. It has wide-angled pyramids, a moderately deep foramen magnum, and a brace in place. The sides of the pyramids have ridges for the attachment of interpyramidal muscles. It has the essential characters of lanterns, as seen in the Lower Carboni- ferous. As there is no portion of the test in association with the lantern, its generic position is unknown, but it is quite probable that it is a Lepidocentrus or a near ally of that genus. 1 Dr. Bather called my attention to the fact that Austin (1848) reported that a large species of Echinocrinus [Archaeo- cidaris] occurs in the Wenlock Limestone, Silurian, of Glidden Hill, which is near Coalbrookdale in Shropshire. There is no recognizable description, and the specimen is unknown. If this observation should be confirmed, it would greatly ex- tend the geological range of the genus. GEOLOGICAL DISTRIBUTION. 237 is known from one species in the American Ix>wer Carbomfen.u-. The Lepi.lncentridae ix represented in America by Lepidocentrus whilfieldi sp. nov., also llu«tl,<>nnu* ram/,'""1' Hall), H. pentagonm sp. nov., and H. beecheri sp. nov., all fn.m tin- Waverly ( irnup. tin- l.a-al m.-mlx-r of the Lower Carboniferous. The Lepidocentridae also i- represented in America by /'/./,//,/- echinus brauni gen. et sp. nov., from the Keokuk zone, and in Kurope l>y KiminrL-.H-iiltiri* cotteaui Dollo and Buisseret, from Belgium, and Tornquistellus gracilis (Tormnii-t t from ' many. Of the Palaeechinidae, Maccoya phillipsiae is attributed to tin- Silurian of England, but with this exception the family of the Palaeechinidae is known only from the Lower « -ar- boniferous of America and Europe. Of this family the genera Palaoechinus, Marcnya and Lovenechinus are represented by both American and European -pr« ,,-s, but Oligoporu-. i- American only. Of the highest genus of the family, Melonechinus, eleven species are American, two are British, and one Russian. Of the Lepidesthidae, most of the species are from tin- Low IT Carboniferous, but two are found in the Devonian as above noted, and two occur in later hori- zons. Lepidechinus, the lowest genus of the family, is known wholly from the LOW.T boniferous, three species, L. iowensis sp. nov., L. tessellatus sp. nov., and L. imbricatus Hall, being found in America, and one species, L. irregularis (Keeping), in Ireland and France. Perischodomus is represented by one well known species, P. biserialis M'Coy, in the Lower Carboniferous of Ireland and England, and one imperfectly known species in America. IVri-- chocidaris is known only from P. harteiana (Baily) in the Lower Carboniferous of Ireland. Proterocidaris is known from the striking species, P. giganteus Koninck, from the Lower Car- boniferous of Belgium. The relatively large genus Lepidesthes has one species in the British Devonian and one in the American Coal Measures, but all others are from the Lower Car- boniferous. Of these, six species are American, one British, and one Russian. As above stated, one species of Pholidocidaris is from the Devonian, but the others known are from the Ixnver Carboniferous. One species, P. irregularis Meek and Worthen, the best known is American. P. tennis Tornquist is known in England and Germany and P. gaudryi Julien in France. In the Upper Carboniferous, or Coal Measures, the Palaeozoic Echini have dropped out with extreme suddenness and relatively few species are known. The genus Archaeooidaris is represented by 19 species recorded from the Coal Measures, all known fragmentary only from spines and plates. Seventeen of these have been recorded from America and two from Europe.1 Besides Archaeocidaris in the Coal Measures of America is found Lepidesthes extremis sp. nov., structurally and geologically the highest known species of this very interesting genus. 1 The following species of Archaeocidaris have been found in the Coal Measures of North America its recorded by various authors: A. longispina Newberry, A. agassizi Hall, A. coloradeiixis noin. nov., .1. graeilu Nrwl>,>rry, A. arulraia Shumard and Swallow, A. edgarensis Worthen and Miller, A.trtulifcr Whilr, A.|x> there are only twospeciea recorded: A. jxiriuloia (Eichwald) in Russia, and specimens which arc hen- referral to A. acanthi/era TrauUchold in England. 238 ROBERT TRACY JACKSON ON ECHINI. In the Permian, very few forms of Echini are known. In England and Germany Mioddaris keyserlingi (Geinitz) occurs, and is important as the geologically second species known in the Palaeozoic with two columns of plates in an interambulacral area. As far as at present defi- nitely known, it and the new Mioddaris cannoni from the American Lower Carboniferous are the geologically oldest members of the Cidaroida. In America, Archaeocidaris aculeala Shumard and Swallow is reported as occurring in the Permian, and in India Archaeocidaris is doubtfully represented by one species, A. forbesiana (Koninck), which is imperfectly known, but is provisionally referred to this genus. Archaeocidaris selwyni occurs in the Permian of Australia. In the American Permian is found Meekechinus ekgans gen. et sp. nov., which is a very interesting type, as it has twenty columns of ambulacral plates in an area at the mid-zone, being in this respect the most specialized of known Echini. It is the highest of the Lepides- thidae and geologically the last of the series with more than two columns of ambulacral and interambulacral plates in an area which is the essential feature of most Palaeozoic Echini. SYSTEMATIC DESCRIPTIONS. Order BOTHRIOCIDAROIDA Jackson. Schmidt, 1874, p. 37. Bothriocidaridae Zittel, 1879, p. 480 Bothriocidaroida Jackson, 1896, p. 238. Regular Echini, with periproct enclosed by the oculo-genital ring. Two columns of plates in each ambulacral area and one column of plates in each interambulacral area. Family BOTHRIOCIDARIDAE Klem. Bothriocidaridat (as an order) Zittel, 1879, p. 480; (as a family) Klem, 1904, p. 14. With characters of the order. BOTHRIOCIDARIS Eichwald. Bothriocidaris Eichwald, 1860, p. 654. Botriocidaris Neumayr, 1881, p. 4. Botryocidarut Love'n, 1883, p. 57. Small spherical or elliptical Echini. Ambulacral areas relatively wide, about twice as wide as the narrow interambulacra with their single columns of plates. Ambulacral plates high, hexagonal, the pores of each pore-pair superposed in a depression in the center of each plate. Interambulacral plates high, hexagonal, equaling the ambulacrals in height. Plates BOTHRIOCII)ARIS. of test not imbricate. Primordial interambulacral plates are in the basicoronal row. Baai- coronal ambulacral plates are not sharply distinguished from the perwtomal plates. Spines few on ambulacral and interambulacral, or on ambulacral plates only. IVri-tom.- will, rows of ambulacral plates only. Oculars very large, genitals small. IVripnx-t with man y small, angular plates, filling the area. Ordovician, Russia. This is the oldest known K.TIUS of Echini and also one of exceptional interest on account of its features which in many respect* resemble the young of later Echini. The type species is Bothriocidaris globulus Eichwald, from the Ordo- vician of Russia. (See pp. 54, 64, 70, 80, 87, 149, 208.) Key to the Species of Bothriocidaru. Oculars continuous, forming a closed ring; small genitals dorsal to the oculars; tubercles on ambulacral and interambulacral plates, . ... . H. arrhaicn sp. nov.. p. 239. Oculars in part continuous and in part separated by the small genitals; tubercles on ambulacra! plates only. • B. paA/rm Schmidt, p. iM_( Oculars all separated by the small genitals; tubercles on ambulacral and interambulacral plates, B. globulin Eichwald, p. 243. 'Bothriocidaris archaica sp. nov. Text-figs. 2, p. 54; 22, p. 70; 40, p. 80; 162, p. 149; Plate 1, figs. 1, 2. Bothriocidaris globulus (pars) Jaekel, 1894, text-figs. 1, 2: (pars) A. Agassiz, 1904, p. 79; (pars) Klem. 1904, p. 15. Bothriocidaris [globulus pars] Bather, 1902, p. 620, text-fig. 5B. The precious and only known specimen of this species is in the Museum fur Naturkunde in Berlin, and I am under greatest obligations to Dr. Otto Jaekel for the opportunity to study this which, I feel, is perhaps the most interesting of known Echini. The details of structure are remarkably clearly preserved, but are naturally difficult to study in such a small specimen. It is probably the best preserved specimen known in the genus, and is marvellously perfect when its age is considered. Its perfection is a tribute to Dr. Jacket's skill as a preparator. The test is slightly elliptical, 12 mm. in height, 11.2 mm. in diameter through the mid- zone. The circumference at the ambitus is 35.5 mm.; circumference in a vertical plane around the poles 36 mm., width of an ambulacrum at the mid-zone 4.2 mm., width of an interambula- crum at the same area 2.2 mm. Each ambulacrum consists of two columns of high hexagonal plates; at the mid-zone a plate measures 2.2 mm. in its greatest width. Ambulacral pores are superposed in a sunken area in the center of each plate. At the ambitus there are typically four, in some cases perhaps fewer, tubercles on each plate near the margin of the peripodium. Interambulacral plates are high, hexagonal, equaling the height of the ambulacrals. with from one to three tubercles on each plate at the mid-zone. The plates of the corona are not im- bricate. There are two rows of peristomal ambulacral plates. The diameter of the apical 240 ROBERT TRACY JACKSON ON ECHINI. disc through the plane III, 5 is 4 mm. This measurement includes from the adoral border of ocular III to the aboral tip of the youngest plate of interambulacrum 5. The apical disc measures proportionately 36 % of the diameter of the test. This proportion is about the same as in the modern Cidaridae and is relatively larger than in other known Palaeozoic species (pp. 87, 104). Oculars are large, forming a closed ring, thus covering the ambul- acra and inter-ambulacra completely, a unique character. Genitals are small and shut out from contact with the interambulacra by the continuous character of the oculars (p. 87). The periproct has many small angular plates filling the area. This species differs from B. pahleni in that there are perforate tubercles on both ambulacral and interambulacral plates, whereas in pahleni they are absent in the interambulacrals. It also differs in that the genitals are wholly dorsal to the oculars instead of part of them separating the oculars as in pahleni. Bothriocidaris archaica differs from globulus in that the oculars form a closed ring, whereas in globulus the oculars are separated by the genitals which meet the interambulacra of their several areas. Lyckholm Schicht, Ordovician, Hohenholm, Island of Dago, Russia. The type and only known specimen is in the Berlin Museum as above stated. In the morphological part of this memoir much attention is given to Bothriocidaris as a primitive type, and the consideration is largely based on the study of this species. The ambula- crum is a feature of particular interest. The whole of ambulacrum IV measured on the curve from the oral termination to the ocular is 15 mm. in length. The two ventral rows of ambula- cral plates are considered as peristomal, from which the basicoronal plates of the corona are not sharply defined. In the corona proper, and excluding the peristome, there are eight ambu- lacral plates in each column of each area excepting Ilia, in which there are nine plates, as a very young plate is in contact with the ocular, but so low that it does not quite reach the inter- ambulacrum. Pore-pairs are superposed in the middle of each plate, a condition known in the adult of regular Echini only in this genus (text-fig. 22, p. 70). At the mid-zone there are four perforate tubercles to a plate, or in some plates fewer; when fewer at this area, the differ- ence may be due to loss from erosion. Vent rally and dorsally there are fewer tubercles as a character. In the sixth plate from the base in ambulacrum II a, the tubercles were not seen, but are filled in by comparison with adjacent plates, otherwise the tubercles of ambulacral plates are figured as observed. The hexagonal shape and superposed pores are like the young of later Echini (pp. 54, 57). Interambulacrum 3 measures on the curve 12 mm. in length. In each interambulacrum there are nine plates, and the basicoronal plate of each area is a pentagon, the ventral apex of which impinges on the second row of peristomal ambulacral plates (compare Plate 2, fig. 1; Plate 3, figs. 9, 10). The tubercles of these plates are few in number, but striking. There is a single tubercle on the basicoronal plate in each area, also a single tubercle on the second BOTHRIOCIDARIS. 241 plate in each area excepting 2, where it is wanting, doubtless from erosion; in the third and succeeding plates to the mid-zone there may be one, two, or three tubercles varying with flu- areas, the highest number occurring in area 4. Dorsally, for one or more plates in an area, there is only one central tubercle to a plate like that in the basicoronal plates. In the youngest interambulacral plates in contact with the oculars, there are no tubercles, a common charu<-t.-r of plates next the apical disc. The characters of the tubercles on the intcniinlnilacra t and aborally is in contact with the basicoronal interambulacral and ambulacral plates. The plates of this second row are distinguished from the coronal plates only by their position and interambulacral relation,1 but the same thing is true of the young of some Recent types (Plate 2, fig. 6). The second row was probably derived by flowing down from the corona (pp. 79, 86). On some plates of this second row one or two tubercles were observed. The oculars are very large relatively, and are unique in that they meet in a continuous ring. Ocular III measures 1.4 mm. in height, but the others somewhat loss. All have three tubercles excepting II, which has only two. Ocular III has in addition two tiny sinuous ele- vations which appear to be part of the plate. Jaekel thought these indicated a madreporite; this may be correct, but it is doubtful. The small plates in the dorsal interradial angles of the oculars I consider as genitals (as discussed, p. 88). Genitals 1, 2 and 4, 3 are in contact ' By an error in making my drawing in Berlin, from which original Mr. Blake drew Plate 1, fig. 1, the initial plate of area 1 rests against the third plate of 16, instead of the second plate as it evidently should. 242 ROBERT TRACY JACKSON ON ECHINI. dorsally, as seen in Plate 1, fig. 2, but a periproctal plate separates genitals 2 and 3 and others separate genital 5 from 4 and 1 on either side. They thus present a certain bilateral symmetry, but this may be only a coincidence. All the genitals bear a tubercle excepting genital 2, where it is probably worn off, but if madreporic pores existed in 2, that might account for the absence of a tubercle. The small relative size of the genitals and their position dorsal to the oculars suggests a comparison with the somewhat similar condition in embryonic Echinus as seen in Plate 3, fig. 5. The periproct contains nine or ten minute angular plates, the sutures of which are difficult to make out, but apparently are as shown in the figure. They are similar to plates seen in other Palaeozoic periprocts and present no striking feature (p. 174). Teeth, or more probably, dental pyramids exist in areas I, II, IV, and V. Jaekel considered them parts of the dental system, and I agree with him, but Bather differs because of their radial position. No other known structure occurs at this area in Echini, and their position, it seems, may be accounted for by a possible accidental twist, as a considerable twist is occasionally found in dried Recent material. To accept a. radial position as normal in this type is opposed to morphological principles, and in so far I should entirely support Bather's opinion. Bothriocidaris pahleni Schmidt. Plate 1, figs. 3-6; Plate 8, fig. 1. Bothriocidaris pahleni Schmidt, 1874, p. 38, Plate 4, figs, la-lg; Zittel, 1879, p. 481, text-figs. 339a-339c; A. Agassiz, 1892, p. 72, Plate 29, fig. 1; Jaekel, 1894, p. 246; Jackson, 1896, pp. 233, 238, text-fig. 4; Gregory, 1900, p. 300, text-figs. 1-3; Lambert and Thiery, 1910, p. 118. Botriocidaris pahleni Neumayr, 1881, p. 152, Plate 1, fig. 6. Botryocidaris pahleni Loven, 1883, p. 57, 2 text-figs. Bothriocidaris palheni Pomel, 1883, p. 117. Bothriocidaris phaleni Klem, 1904, p. 15. The test is small and nearly spherical; according to Schmidt, the type is 15.5 mm. in height and 16 mm. in diameter. Ambulacral plates are high, hexagonal. Schmidt says there are ten plates in a column, and eliminating the two peristomal rows, we have, therefore, eight ambulacral plates in a column in the corona, as in B. archaica. The individual ambulacral plates at the ambitus are 3 mm. wide and 2 mm. high. The pits for pore-pairs are about 0.5 to 0.75 mm. broad, showing two pores which are superposed. There are two tubercles to a plate, and some of the spines are in place. They are longitudinally striate, up to 4 mm. long and about 0.5 mm. thick; these are the only spines known in the genus. The interambulacral plates are of the same height as the ambulacral, but narrower, 2.5 mm. wide at the ambitus. The primordial interambulacral plates are pentagonal, ventrally in contact with the dorsal border of the second row of peristomal ambulacral plates. The youngest plates dorsally against the apical disc are pentagonal, or so low that they are nearly triangular. There are eight or BOTHRIOCIDARIS. 243 nine plates in a column according to Schmidt, and nine as seen in Plate 8, fig. 1. The surface of these plates is finely granulated, but with no perforate tubercles, indicating that in this species there were no large spines, possibly no interambulacral spines at all. If the hitter, it is a unique condition in Echini. There are two rows of peristomal ambulacra! plates, the second being in contact with the ventral border of the primordial interambulacral plates. The oculars are large, of which the ocular considered III is the largest. Each plate bear- two or three tubercles. Oculars IV, V and I, II are in contact (Plate 1, fig. 0), but IV, III and II, III are separated so that genitals 2, 3 reach the interambulacra. Thus it is -tructurally bi- laterally symmetrical through the axis III, 5, but this may be a mere coincidence. Four -mall genitals are in place, but genital 5 is wanting; 2 and 3 reach the intcniinbiilacra a- in B. globulin, but the others are shut out by the contact of the oculars. Each genital bears a small per- forate tubercle. Considering these plates as genitals, there are three other plates within the apical disc that may be considered as plates of the periproct. This species differs from the other two in that there are no perforate tubercles on the interambulacral plates, and it is inter- mediate between B. archaica and B. globulus in the lateral contact of the ocular plate- p. 87). The type is from the Jeweschen Schicht, Ordovician, Nommis, Esthland; a second speci- men, the original of Plate 8, fig. 1, is from the Diluvial-Geschichte, Ordovician, Rostov, Russia. Love'n (1883, p. 57) described and figured in this species, presumably the type specimen, long cylindrical bodies having one end in close relation to the ambulacral pores. He took tin -«• for tube-feet, and said that they even showed traces of having their tubes strengthened by arcuate spicules. It certainly is a remarkable condition of fossilization if these are tube- feet. In the figure which I published (1896, text-fig. 4, p. 234) of this species, the error was made of taking the perforation of tubercles for ambulacral pores, so that tln-t u.re repre- sented incorrectly, in a horizontal plane instead of superposed. The same mistake was made by Gregory (1900). The photographic figure (Plate 8, fig. 1) is taken from a cast that was made by Dr. Jaekel and which he kindly gave me. It shows enlarged the general appearance of the species, relative width of plates, and the whole length of one interambulacrum. The interambulacral areas are colored to differentiate them. Bothriocidaris globulus Kit-hwaUl. Plate 1, figs. 7-9. - Aldrovandus, 1618, p. 136, fig. 5. Bothrioddaris globulus Eichwald, 1860, p. 55, Plate 32, figs. 22a, \>, l.ut not fig. 23; Si-hiiii.lt. 1: Plate 4, figs. 2a-2c; (pars) Jaekel, 1894; (pars) Jackson, 1896, p. 238; (pars) Kl.-m. 1904, p. 15; (pars) A. Agassiz, 1904, p. 79; Lambert and Thiery, 1910, p. US. Botriocidaris globulus Neumayr, 1881, p. 152. Eichwald's original figures and description are not very detailed, but Schmidt piv. excellent description and figures of this species, from which my account is taken. Test globular, 244 ROBERT TRACY JACKSON ON ECHINI. in Schmidt's specimen 18 mm. high, 18.5 mm. in diameter. Eichwald's type was smaller, only 12.5 mm. in diameter. There are two columns of high hexagonal plates in each ambulacra! area, and the plates at the ambitus are 4 mm. wide and 3 mm. high. Interambulacral plates are somewhat narrower, 3 mm. wide. Schmidt says that there are ten ambulacral plates in each column, which, subtracting two for the peristomal rows, leaves eight in a column for the corona, as in the two other species. The pore-pairs are superposed in the middle of each plate, and at the ambitus there are four perforate tubercles around the peripodia. The interambula- cral plates at the ambitus have two or three perforate tubercles, but ventrally and dorsally only one. Schmidt says that the spines attributed to this species by Eichwald have nothing to do with it, but appear to be small Bryozoa. The peristome consists of two rows of ambula- cral plates as in the other species; the dorsal border of the second row is in contact with the ventral border of the primordial interambulacral plates. The oculars are large, the largest of which I take to be III, as in B. archaica. They bear one, two, or five tubercles each, but ocular IV has no tubercle, probably worn off. Four genital plates are in place, but genital 4 is absent or displaced (Plate 1, fig. 9). The genitals are larger than in the other species; each bears a tubercle and separates the oculars, therefore reaching the interambulacra as they do in all later Echini, but in this feature differing entirely from archaica and partially from pahleni (p. 240). There are only two periproctal plates in place lying dorsal to oculars II and III and separating the associated genitals. Schmidt figures five minute plates ventral to the primordial ambulacral plates, and which I take to be teeth or dental pyramids, as in the other species (discussion, pp. 181, 242). Schmidt's specimen is from the Lyckholm Schicht, Ordovician, Hohenholm, Island of Dago, Russia. The type is from the same locality. It is very interesting historically that Aldrovandus in 1618 gave a figure that is recognizable as belonging to Bothriocidaris and probably to this species. The figure is entitled "Echinus lapis spoliatus a spinis," but there is no description. While somewhat rough, the figure shows two columns of high hexagonal ambulacral plates, with a cup-shaped depression in the center of each, and a single column of high hexagonal interambulacral plates which apparently meets the genitals. There are from one to three tubercles on the interambulacral plates; these features apply to this species and no other. It is remarkable that this excessively rare echinoid should have been found so early and then lost sight of until recent years. Order CIDAROIDA Duncan. Cidaraida Duncan, 1889a. Regular Echini with periproct enclosed by oculo-genital ring. Two columns of low, narrow ambulacral plates and two columns of pentagonal interambulacral plates, the latter with a large, central primary tubercle and spine, also marginal secondary tubercles and spines. Other MIOCIDARIS. characters are of importance if the whole order is to be considered (see pp. -Jill. •_>! 1 , but for the Palaeozoic, this is a sufficient diagnosis. It is quite possible thai the D.-vonian Xenocidaris, with three species, considered under Incertae Sedis, Ix-Iongs (,, th<- < 'idaroida. Family CIDARIDAE Gray. Cidaridac Gray, 1825, p. 4. With characters of the order. MIOCIDARIS Doderlein. Mioddaris Doderlein, 1887, p. 40; Bather, 1909, p. 61 ; 1909a, pp. 83, 251. Eotiaris Lambert, 1899, p. 82; Lambert and Thiery, 1910, p. 127. Pcrrnocidaris (pars) Lambert, 1899a, p. 39. Eondaris (pars) Lambert and ThieVy, 1910, p. 126. Test of moderate size, adradial margin of the interambulacral plates beveled over tho ambulacrals, interambulacral plates relatively few, or many in M. cunmmi, often wide, with scrobicules which are circular or elliptical, distinct or confluent. This genus contains Imt two Palaeozoic representatives, the other species being Triassic or Jurassic. The type—penes as selected by Bather (1909, p. 61) is the Triassic Miocidaris cassinim Hat her ,,-, I ),-,!,„ M,,M-,,,,,: near Posneck, Thuringia, Museum of Comparative Zoology 3,1<>.!; I', nman. X.-.-h,t,.ii,. Freiburg i. B. Museum; Permian, Humbleton Hill and Tunstall Hill, British * Miocidaris cannon! sp. nov. Text-figs. 239a— 239e This species is represented by a single specimen kindly sent to me by Mr. George I .. ( annon, instructor in geology and biology in the Denver High School, of Denver, Colorado. It «;,- received too late (August, 1911) to be figured otherwise than by insert cuts, which with the description are inserted in proof-sheets. e TEXT-FIGS. 239a-239e. — Miocidaris cannoni sp. nov. Millsap Formation, Lower Carboniferous, near Denver, Colorado. Holotype. Museum of Comparative Zoology Collection 3,201. a. View of the specimen. X 2. A few interambulacral plates are in place in interambulacra A, C, and E. The rest of the specimen consists of an internal siliceous mold. b. Outline of an internal impression of an interambulacral plate from area C. X 4. Showing elevated mamolon. c. View across the dorsal part of interambulacrum C. X 4. Showing fragments of three plates in place which • l he median suture; the outlines of the plates are restored, as indicated by dotted lines. d. Interambulacral plate from near the mid-zone in area E, with about four opposing ambulacra! plates, which arc indicated by siliceous casts of the pore-pairs. X 4. e. Section of an interambulacral plate in the dorsal part of area E, showing its beveled edge on the adradial suture. X 4. The outline of the ambulacrum is seen in section and siliceous molds of the pore-pairs exist as elevated plug*. The specimen is a siliceous internal mold and about half of it is embedded in a hard sili- ceous chert. A few fragmentary worn interambulacral plates are preserved. The specimen shows two ambulacral areas, one interambulacrum complete from the ventral border to the apex, and parts of two next adjacent interambulacra. The impressions of sutures on the mold are clear only in parts, but they are perfectly clear in the plates, as far as the>e are preserved. The test is depressed spheroidal, free from all distortion, and measures about 20 mm. in 248 ROBERT TRACY JACKSON ON ECHINI. height by 29 mm. in diameter. No ambulacral plates are preserved, so that the characters of the ambulacra are derived wholly from the mold. The ambulacra at the mid-zone measure about 7.5 mm. in width. As this is a measurement of the interior, on the exterior the width would be somewhat less, because the interambulacral plates bevel over the ambulacrals on the adradial sutures (text-fig. 239e). There are two columns of low plates in each ambulacrum. The position of the plates is indicated in part by rather obscure impressions of sutures, but mainly by the siliceous plugs which represent the casts of pores of the pore-pairs (text-fig. 239e). The pores of each pore-pair at the mid-zone are 1 mm. apart, and the distance from the outer pore of one plate in a right half-area to the outer pore of the adjacent plate in a left half -area is 6 mm. Four ambulacral plates equal the height of an interambulacral plate at the mid-zone, as gathered from the number of pore-pairs in the mold opposed to an interambulacral plate which is in place (text-fig. 239d). This number is similar to the number of ambulacral plates opposed to an interambulacral in Miocidaris keyserlingi, as stated above, but it is much smaller than the usual number in the adults of Recent cidarids (compare text-fig. 218, p. 191). In the young of Recent cidarids, however, the ambulacral plates are higher and in very young speci- mens may be even as high as the interambulacrals (Plate 2, fig. 2). The only interambulacrum which is entirely exposed to view measures 12 mm. in width at the mid-zone. In the same plane the width from the right outer pore of ambulacrum D across interambulacrum C to the left outer pore of ambulacrum B is 13 mm., this being only slightly more than the width given for the interambulacrum itself. There are two columns of plates throughout the interambulacral area, and, as gathered from the impressions on the mold, there are fourteen plates in each interambulacral column. In each of the two lateral inter- ambulacral areas, A and E, which are partially visible, there are five plates in place, and these from their height also indicate that there would be about fourteen plates in one column. This is a very large number for the genus and also for the family. In Recent Eucidaris tribuloides I have found fourteen plates in a column, but such a number is rarely attained in the Cidaridae. In the dorsal portion of interambulacrum C there are two fragmentary plates (text-fig. 239c) which meet in a median angular suture, as usual in cidarids. As seen at one point dorsally where the plates are preserved, the interambulacral plates bevel strongly over the ambulacrals on the adradial suture (text-fig. 239e). It is from this structure that I refer the species to the genus Miocidaris. The interambulacral plates at the mid-zone measure 2.5 mm. in height by about 6 mm. in width, measuring to the middle of the interambulacral area, and about 0.75 mm. in thickness. The measurement of the height and width is taken from the internal mold, as no plate preserved is complete in width, but the height as given is confirmed by the plates which are in place. The most complete plate preserved at the mid-zone in area E meas- ures 4 mm. in width, but its admedian portion is hidden beneath the hard siliceous matrix. Unfortunately the worn plates that exist do not show a complete outline nor surface characters, MIOCIDARIS. 249 excepting that one plate in area E shows the remains of the perforation of -a primary tubercle. In the mold the horizontal boundaries of the interambulacral plates are fairly well denned as depressed furrows extending from the adradial suture to near the middle of the interambula- crum, but the median sutures are mostly indistinct. On examining the interior of a half- grown Eucidaris tribuloides it is seen that the horizontal boundaries of the interambulacral plates stand out as prominent ridges, whereas the median boundaries do not, and this may well account for the differences seen in the mold. The mold of each plate presents a slightly convex form with a small mammillate elevation (text-figs. 239a, b) which corresponds with the concave form and deeper impression beneath the tubercle on the interior of the plate of a cida- rid, as seen well in an immature Eucidaris tribuloides. This species is of exceptional interest, as it is the first sea-urchin recorded from the Palaeo- zoic of America with two columns of plates in an interambulacrum ; also it extends the range of the genus Miocidaris and the order Cidaroida to the Lower Carboniferous, whereas previously they were not known below the Permian. The occurrence of this type with two columns of interambulacral plates in the Lower Carboniferous adds support to my view, as earlier pub- lished (1896, p. 237, table facing p. 242) and maintained in this memoir, that two columns of plates in an interambulacral area is a primitive structure and types having this structure are to be derived from an ancestor with one column of plates in an area, and not to be derived from an ancestor with many columns in an interambulacral area, as has been usually held (p. 211). Miocidaris cannoni, which I take pleasure in naming for Mr. Cannon, from whom I received the specimen, differs from other species of the genus in its large size and numerous interambula- cral plates in a column. The number of plates is perhaps sufficient to justify generic distinction, but as the surface characters are unknown, it seems best to place the species in the genus Mio- cidaris, to which at least it is very closely allied. While this species occurs in the Lower Carboni- ferous and is therefore very much older than Miocidaris keyserlingi of the Permian, it is placed higher than that species because, on account of having a large number of plates in an inter- ambulacral column, it is farther removed from the primitive than is keyserlingi with a smaller number of plates in a column. Mr. Cannon informs me that he recently obtained the specimen, and that it is from the Millsap Formation of the Rocky Mountain Lower Carboniferous, from near Denver, Colorado. The specimen was collected by Mr. George Day, and was found in one of the loose chert concre- tions in the Platte River drift. While not in place, material of this lithological character according to Mr. Cannon and other authorities is known in Colorado only from the Millsap Formation, which occurs as outcrops in the Front Range. Girty (1903, pp. 162, 167) ascribes the Millsap Formation to the Mississippian, or Lower Carboniferous. The specimen is now in the collection of the Museum of Comparative Zoology 3,201. 250 ROBERT TRACY JACKSON ON ECHINI. Order ECHINOCYSTOIDA nom. nov. Cystocidaridae Zittel, 1879, p. 480; A. Agassiz, 1881, p. 81. Cysiocidaroida Duncan, 1889a, p. 20; Jackson, 1896, p. 242; Gregory, 1900, p. 300. Cysticaroidea Tornquist, 1897, p. 730. Professor Zittel based his name of the order on the name Cystocidaris which he gave to replace the genus Echinocystites of Wyville Thomson. As Cystocidaris is a synonym and cannot stand, neither, by the rules of nomenclature, can the name of the order based on it; I therefore substitute a new name for this order. Test spheroidal or flattened, apparently irregular, with the anus in an interambulacral area. Ambulacra narrow, with two or four columns of low plates in an area. Interambulacra wide, with numerous, eight or more, columns of very thin, rather irregular polygonal plates in an area. Lantern well developed, typically echinoid in character. The known specimens of the two families and genera of this order are imperfectly preserved, therefore are incompletely known; further knowledge is much to be desired. Family PALAEODISCIDAE Gregory. Palaeodiscidae Gregory, 1897, p. 133; Lambert and Thiery, 1910, p. 117. Test depressed, nearly or quite circular. Gregory says pentagonal, but I think this is hardly correct. Ambulacra narrow, composed of two columns of low plates in each area, with pores throughout the areas, not imperforate ventrally, as Gregory says. Anus eccentric in an interambulacrum at a considerable distance from the apex and quite near the mid-zone, as figured by Spencer (1904, Plate 1, fig. 1). Earlier Gregory (1897) said that the anus is central, but he did not figure it. I have not seen a specimen showing this structure. A typical echinoid lantern exists. There is only one genus and species. PALAEODISCUS Salter. Palaeodiscus Salter, 1857, p. 332; Zittel, 1879, p. 453; Duncan, 1889a, p. 6; Gregory, 1900, p. 301; Lam- bert and Thiery, 1910, p. 117. With characters of the family. The type and only recognized species is P. ferox Salter, of the Silurian of England. Palaeodiscus gothicus is considered under Incertae Sedis. *Palaeodisaus ferox Salter. Plate 18, figs. 1-5. Palaeodiscus ferox Salter, 1857, p. 332, Plate 9, fig. 6; Wyville Thomson, 1861, p. 13, Plate 4, figs. 6, 7; Neumayr, 1881, p. 155, Plate 1, fig. 8; Gregory, 1897, p. 129, text-figs. 4, 5; Plate 7, figs. 5a-5b; Sollas, 1899, p. 701, text-figs. 6-11; 1899a, p. 277; Spencer, 1904, p. 31, text-figs. 1-8, Plate 1, fig. 1; Lambert and Thiery, 1910, p. 117. PALAEODISCUS. 251 The test is very much flattened in known specimens, as it probably was in life, and is nearly or quite circular in outline. Ambulacra are narrow with two columns of low plates, of which about four equal the height of an adambulacral plate. The pore-pairs are about in the middle of the plates and are clearly developed ventrally, as shown in my figures. I cannot understand why Dr. Gregory should say (1897, p. 129) that there are no pores through the plates, but that the podia must have been extended between the sutures. The specimens Dr. Bather kindly loaned me, from the British Museum, have pores distinctly through the plates as in other typical echinoids. Interambulacra with many, apparently about eight or nine columns of highly irregular plates, and, as pointed out by Spencer, the primordial plates are in the basi- coronal row. The plates were evidently extremely thin and bore numerous fine acicular spines. On the peristome there are ten columns of ambulacral plates only. The apical <1N<- i- unknown but I think Gregory is not justified in saying probably absent. It is not known to be absent in any echinoid. The lantern, as shown by Sollas, is of the typical character, inclined, with pyra- mids, epiphyses, braces, and even compasses, as figured by Sollas. Lower Ludlow, Silurian, near Ludlow, and Church Hill, Leintwardine, England; Hritish Museum, a number of specimens, including those described by Gregory (1897) ; Oxford Museum. This species, representing its genus and family, has been much discussed, and on account of imperfections of material, a number of points are still uncertain. Salter referred the type to starfishes, and Zittel (1879, p. 453) followed him. Several authors have considered the type as intermediate between starfishes and echinoids, and as a primitive type. I think recently published material distinctly shows that Palaeodiscus is an echinoid, has no connection with starfishes, and is not a primitive type. As regards the ambulacrum, I find no evidence of pores between the plates, as claimed by Gregory, but rather they are through the plates as usual in echinoids. As regards the roofing system of plates described by Sollas and Spencer, they claim that above the typical ambula- cral plates (Sollas, 1899, p. 705, fig. 9) there is a set of narrower plates roofing over the outer flooring plates. This narrower set is supposed to correspond with the ambulacral plates of a sea-urchin, superposed on those of a starfish, and thus the connection of the two groups is supposed to be solved. It is a somewhat novel morphological reasoning from the facts. It would require that we consider the wider or flooring ambulacral plates of Palaeodiscus which Sollas, 1899, pp. 705, 706, considers the equivalent of the ambulacral plates of later Echini), as equivalent to the adambulacral plates of a starfish grown across the area and meeting in the center line, but I see no basis for such an argument. I think the roofing plates of Sollas are the narrower ambulacral plates of the dorsal side brought in mechanical contact with the wider ventral plates by the flattening of the test, exactly as shown in area B of Hyaltechinua rnrispinus (Plate 23, fig. 1). The interambulacra are typically echinoid, and from the large number of columns of plates appear to me to indicate a specialized, not a primitive type. Ambulacral 252 ROBERT TRACY JACKSON ON ECHINI. plates on the peristome are a typical echinoid character. The inclined lantern is of the typical character seen in Palaeozoic species, is purely echinoid, and has no relation to the structure of any known starfish. There are grooved teeth, narrow epiphyses, braces, and even rather deeply forked compasses as shown by Sollas (1899, text-figs. 7, 8) whose figure 7 is in part reproduced in my Plate 18, fig. 5. Some knowledge of ocular and genital plates is much to be desired, and the position of the anus should be more positively settled. If Spencer is correct in showing the anus in an interambulacral area, we must consider Palaeodiscus a peculiar and irregular echinoid. If the anus is in the center dorsally, as Gregory says (1897, p. 129), then Palaeodiscus is not irregular, is wrongly placed in this order, and could properly find a place in the Lepidocentridae, from which it differs essentially in this character only. Family ECHINOCYSTIDAE Gregory. Echinocystidae Gregory, 1897, p. 133; Lambert and Thiery, 1910, p. 118. Test spheroidal, ambulacra narrow with at the mid-zone four columns of plates which are demi- and occluded. Interambulacra broad with many columns of irregular plates. Plates thin with small primary and secondary tubercles and spines. Apical plates doubtful, but the anus is eccentric in an interambulacrum. A well developed typical echinoid lantern exists. One genus and species. ECHINOCYSTITES Wyville Thomson. Echinocystites Wyville Thomson, 1861, p. 106; Duncan, 1889a, p. '20; non Hall, 1865; 1868a, p. 316. Cystocidaris Zittel, 1879, p. 480. Echinocystis Gregory, 1897, p. 124; Lambert and Thiery, 1910, p. 118. With characters of the family. The type-species is E. pomum Wyville Thomson, from the Silurian of England. "Echinocystites pomum Wyville Thomson. Plate 16, fig. 4; Plate 18, figs. 6-8; Plate 20, figs. 1-1. Echinocystites pomum Wyville Thomson, 1861, p. 109, Plate 3, figs. 1-3; Plate 4, figs. 1-5. Echirwcystites uva Wyville Thomson, 1861, p. 110, Plate 4, figs. 4,5. Cystocidaris pomum Zittel, 1879, p. 480. Cystocidaris uva Zittel, 1879, p. 480. Echinocystis pomum Gregory, 1897, p. 124, text-figs. 1-3, Plate 7, fig. 4; Sollas, 1899, p. 707, text-figs. 12-14; Klem, 1904, p. 13; Lambert and Thiery, 1910, p. 118. Echinocystis [pomum] Spencer, 1904, pp. 31, 34. Echinocystis uva Lambert and Thiery, 1910, p. 118. The test is spheroidal, ambulacra narrow with four columns of plates in an area, demi- and occluded, pore-pairs are biserial and pass through about the center of each plate. Inter- PERISCHOECHINOIDA. 253 ambulacra wide with in each area about eight columns of very irregular thin polygonal plates which bear small primary and secondary tubercles and spines. The apical plates are doubtful; but a madreporite is described by Wyville Thomson and Gregory in an interambulacrum. As this is a unique condition in Echini and morphologically difficult to understand, it may not be too much to suggest that in the squeezing of this rather badly preserved material, it may have got displaced. According to Wyville Thomson, the anus with apparently periproctal plates is in an interambulacrum, making it an irregular type. The lantern is well developed, and Gregory shows that it has typical echinoid pyramids. The material I have seen is so crushed and badly preserved that it is very difficult to make out much structure. There seems no reason for considering this type as presenting any possible connec- tion with starfishes, or as a primitive type. Its four columns of ambulacral plates, and especi- ally its eccentric anal area, would lead one to consider it a specialized and irregular rather than a primitive echinoid. Lower Ludlow, Silurian, Leintwardine, England; a very fine specimen is in the Museum of Practical Geology, London 7,385, one of Sir Wyville Thomson's originals. This is shown in Plate 16, fig. 4, from a photograph kindly sent me by Dr. Kitchin. There are several specimens in the British Museum, part of which Dr. Bather kindly loaned me for study. Oxford Museum (Sollas). Order PERISCHOECHINOIDA M'Coy. Perischoechinida M'Coy, 1849, p. 251; 1854, p. 114; Jackson, 1896, p. 239. Tessdati Desor, 1858, p. 152. Perischoechinidae Loven, 1874, p. 39; A. Agassiz, 1874, p. 644; 1881, p. 3; Zittel, 1879, p. 481. This large order consists of regular Palaeozoic Echini in which the periproct is within the oculo-genital ring. The test is of various shapes and horizontal outline throughout the ambitus, but is usually spheroidal. Ambulacral areas are narrow, or wide, with in each area from two to twenty columns of plates, all simple and all bearing one pore-pair each. There are from three to fourteen columns of plates in each interambulacral area. Usually the plates of the adambulacral columns are pentagonal, and those of the median columns hexagonal, except where new columns are introduced, and in young plates dorsally. Plates may be thick, or thin, and bear primary perforate tubercles and spines with secondaries, or the latter only. Plates of the corona may be imbricate or not; when imbricate, ambulacral plates imbricate adorally and bevel under the adambulacral plates laterally. Interambulacral plates imbricate aborally and from the center laterally and over the adjacent ambulacral plates. When plates are not imbricate, then the sides of the plates are as nearly parallel as is mechanically possible in a curved test, but they may be very far from parallel, as in the thick-plated Melonechinus. When there is no imbrication, the ambulacral plates may bevel over the adambulacrals, as is char- 254 ROBERT TRACY JACKSON ON ECHINI. acteristic of the Palaeechinidae. As far as the evidence goes, the primordial ambulacral plates are around the mouth on the peristome, and the primordial interambulacral plates are in the basicoronal row, or are resorbed in the advance of the peristome. The peristome is plated with many rows of ambulacral plates only, or may in addition have non-ambulacral plates situated interradially. Oculars are usually imperforate and all insert, but rarely are perforate, and exceptionally one or more to all may be exsert. Genitals usually have three or more to numer- ous genital pores; the madreporite is rarely distinguishable. The periproct is covered with many angular plates which fill the area. The lantern is inclined, subtending an angle of about 90 degrees, and as in modern regular Echini, is composed of forty pieces. The teeth are grooved, pyramids wide-angled, foramen magnum moderately deep, epiphyses narrow, capping the half-pyramids; brace and compass as in modern Echini. This group includes all Palaeozoic Echini excepting those already considered, and comprises the best known and, excepting Both- riocidaris, the most interesting genera of these ancient formations (pp. 361-363). Family ARCHAEOCIDARIDAE M'Coy. Echinocrinoidea T. and T. Austin, 1842, p. 111. Arckaeocidaridae M'Coy, 1849, p. 253; Loven, 1874, p. 42. Lepidocidaridae Bather, 1907, p. 456. The test is spheroidal or depressed; ambulacra are narrow, with in each area two columns of plates imbricating moderately adorally and beveled under the adambulacrals. Pore-pairs are uniserial or slightly biserial. There are from four to eight columns of plates in each inter- ambulacral area, plates are large, thin, imbricating moderately aborally and laterally and over the ambulacrals. . The interambulacral plates bear a large central perforate primary tubercle and large scrobicule, with a large primary spine, also secondary tubercles and spines. The base of the corona is resorbed in the advance of the peristome, strongly so in Archaeocidaris. The peristome has many rows of ambulacral and at least in Archaeocidaris interradial non-ambula- cral plates as well. Oculars and genitals unknown or very doubtful. There are three genera in the family. The name Lepidocidaridae was proposed by Dr. Bather to take the place of Archae- ocidaridae on the basis of giving up Archaeocidaris for the earlier but misleading name of Echinocrinus. As I have decided to cling to the old established name Archaeocidaris, pending possible consideration of the matter, I therefore retain also the name Archaeocidaridae. EOCIDARIS Desor. " Eocidaris Desor, 1858, p. 155; Lov6n, 1874, p. 42; Bather, 1909, p. 44; (pars) Lambert and Thi6ry, 1910, p. 126. This genus, most imperfectly known, is based on isolated interambulacral plates and primary spines. Interambulacral plates are probably hexagonal, or pentagonal in adradial EOCIDARIS. columns, as in Archaeocidaris, but the shape is not definitely known in the only species attri- buted to this genus. The plates have a large central perforate tub,-,-, -I,- and scrobicule and marginal secondary tubercles, like Archaeocidaris, but differ from that genus in that then- is no basal terrace within the scrobicular circle. Primary spines are stout. This genus has recently received most careful consideration from Dr. Bather, and ho concludes from all the evidence that of known species, only the Cidaria laevispina and scrobi- culata Sandberger are referable to it. Many species have been referred to the genus by various authors, but I agree with Bather that all excepting those noted, are clearly referable to other genera. This genus is closely related to Archaeocidaris, from which, so far as known, it differs only in the absence of the basal terrace. As the known species occur in the Devonian, it is older than Archaeocidaris, which first appears in the Lower Carboniferous. The youthful plates in the dorsal region in Archaeocidaris rossica have not acquired the basal terrace, and in this feature are therefore like the condition ascribed to the geologically older but closely related Eocidaris. The type species is E. laevispina (Sandberger) from the Devonian of Germany. *Eocidaris laevispina (Sandberger). Plate 15, figs, lla-d, 12. Cidaris laevispina Sandberger, 1850-'56, p. 382, Plate 35, figs. 2-2d. Cidaris scrobiculata Sandberger, 1850-'5G, p. 382, Plate 35, fig. 3. Eocidaris laevispina Desor, 1858, p. 156, Plate 21, figs. 18-21; Love"n, 1874, p. 43; Klem, 1904, p. 69; Bather, 1909, text-fig. 1, p. 51, Plate 1, figs. 1-4; Lambert and Thic'ry, 1910, p. li'ii. Eocidaris scrobiculata Desor, 1858, p. 157, Plate 21, fig. 17; Love"n, 1874, p. 43; Mem, 1904, p. 71 ; Bather, 1909, Plate 1, fig. 5; Lambert and Thiery, 1910, p. 126. This species, the only one which I recognize in the genus, is based on isolated mterambula- cral plates and spines. Bather recently borrowed Sandberger's original specimens from the Wiesbaden Museum and figured them, and my figures are based on his. The interambulacral plates show beveled edges, indicating strong imbrication. As the outlines of the plates are not preserved, their shape, hexagonal or otherwise, cannot be definitely stated. The central perforate mamelon is elongate, scrobicular area large, with no trace of a basal terrace; second- ary tubercles are rather widely and irregularly spaced on the extra-scrobicular area excepting the beveled edge, which apparently in life was overlapped by the next adjacent plate. Primary spines are stout, cylindrical, smooth, with a weakly developed annulus, which does not show vertical fluting as in the typical milled ring of Archaeocidaris. The holotype of Cidaris scrobiculata Sandberger is a single interambulacral plate (Plate 15, fig. 12), and is so close to laevispina in character, that it is here included as a synonym. A- Bather says (1909, p. 53), " The Sandbergers may have been right in regarding this specimen as 256 ROBERT TRACY JACKSON ON ECHINI. of a different species; but if one were to maintain that it came merely from a different part of the test of C. laevispina, I do not see how it could be disproved." Sandberger's material all came from the Middle Devonian, Stringocephalus Limestone of Villmar, and is in the Wiesbaden Museum as above noted. Two interambulacral plates from the Devonian of Villmar are in the Museum of Comparative Zoology 3,192, from the Schiiltze Collection. ARCHAEOCIDARIS M'Coy. Echinocrinus'L. Agassiz, 1841, p. 15; Bather, 1907; 1909; 1909a, p. 264. Archaeocidaris M'Coy Mss., 1844, p. 173; M'Coy, 1849, p. 252; Young, 1873; 1876; Loven, 1874, p. 43; Duncan, 1889a, p. 11; A. Agassiz, 1881, pp. 79, 80; Lambert and Thiery, 1910, p. 124. Palaeocidaris L. Agassiz and Desor, 1846-'47, p. 340. Cidarotropus Pomel, 1883, p. 113; Lambert and Thiery, 1910, p. 125. Permacidaris (pars) Lambert, 1899a, pp. 39, 47; Lambert and Thiery, 1910, p. 127. The test is depressed spheroidal, ambulacra narrow, sinuous in outline, conforming to the outline of the massive adradial plates. Ambulacral plates are low, of uniform character, imbricating moderately adorally and beveled strongly under the adradials; the pore-pairs are uniserial. Interambulacra, in all species where a fairly complete test is known, with four columns of plates in each interambulacral area. The adradial plates are pentagonal, but rounded on the adradial suture line; plates of the intermediate columns are hexagonal. Each plate bears a prominent perforate median tubercle with a wide scrobicular area and a basal terrace, though this terrace, being a slight feature, may be worn off in eroded plates and is absent (A. rossica) in young plates dorsally. Beyond the border of the scrobicular circle are secondary tubercles which differ in their number and in the extent of surface which they cover both in different species and somewhat in plates of different parts of the test in the same species (A. rossica). Primary spines are relatively large, often very large, with a concave base, marked milled ring, and a shaft tapering or enlarged, smooth or ornamented with striations, spinules, or rarely flange-like vertical ridges. The primordial ambulacral plates are on the peristome around the mouth, and the primordial interambulacral plates with additional rows are resorbed in the advance of the peristome, as there are four plates in the basicoronal row (Plate 9, figs. 7, 8). The peristome is covered with radially situated ambulacral and interradially situated non-ambulacral plates, all small and imbricating adorally (text-fig. 47, p. 80). Ocular and genital plates are doubtful, periproct with many small angular plates. The lantern is well developed, of the typical Palaeozoic character (Plate 12, figs. 1-8). Of this genus a few species are known fairly completely,1 but there are numerous species described from incomplete material, often only one or more dis- The best known species, especially as regards the test, are Archaeocidaris wortheni, legrandensis, rossica, agassizi, and i urti. ARCHAEOCIDARIS. 257 sociated plates and spines. Such are most unsatisfactory, often difficult to distinguish, and doubtless there are too many recognized species, of little interest except as expressing the geo- graphical distribution of the genus. With available material the best way, it seems, is to group the species on the basis of spine characters, associating those species that have smooth spin.--, those in which the spines bear low nodose spinules, and those with spinules more elevated and directed at right angles to the shaft of the spine, or pointing distally, or spines with lateral flanges, spines triangular in section, or spines inflated. This has at least some resemblance to a natural classification. The type species, as indicated by Bather (1907, p. 453), is A. urii (Fleming) from the Lower Carboniferous of Europe. The genus Archaeocidaris is structurally closely related to the Cidaridae, but is n ion- complex in that there are four columns of plates in an interambulacral area instead of two columns. Archaeocidaris may be derived from some early cidarid, perhaps Devonian or Silurian. The fact that I describe a true cidarid (Mioddaris cannoni) from the Lower Carboniferous, which is geologically as early as any species of Archaeocidaris known lends weight to this argument. (See pp. 70, 77, 80, 184, 223, 361, 363.) Lambert and Thiery (1910, pp. 124, 125) under what I consider as Archaeocidaris recognize two genera, Archaeocidaris, which they say has interambulacra formed of from five to eight columns of plates, and Cidarotropus, in which they say that the interambulacra are formed of four columns of plates. I know, no species of Archaeocidaris with more than four columns of plates in an interambulacral area, and many of the species which they list in one of their two definite genera are known only fragmentarily from isolated plates so that the number of columns in an area is quite unknown. The proper name to apply to this genus is open to question. As shown positively by my friend, Dr. Bather, on the basis of priority, Echinocrinus is the correct name. Thi- name, however, is misleading, was based by Professor Agassiz on a misconception of affinities, and has been abandoned for some sixty years in favor of the entirely appropriate Archaeocidaris of M 'Coy. It is not a case of Archaeocidaris being preoccupied but simply of priority. To revive the old name, Echinocrinus, in accordance with rules of nomenclature, will make confusion at present and in future, and no gain to any one. As Dr. Bather justly says (1909a, p. 264), "While there can be no doubt as to the conse- quences of the rules, this seems to me just one of those cases that should be settled by a properly constituted authority in defiance of the rules." Such being the case, pending the action of some formal authority, I feel it best to follow the conservative action of retaining the entirely satisfactory and thoroughly established name Archaeocidaris. The name Palaeocidaris Agassiz and Desor is a pure synonym, Cidarotropus Pomel with Archaeocidaris wotfheni Hall as the type, and Permocidaris Lambert with Archaeocidaris forbesiana (Koninck) as the type, I do not recognize as distinct genera. ROBERT TRACY JACKSON ON ECHINI. With present knowledge it is impracticable to make a key for distinguishing each of the numerous and imperfectly known species of Archaeocidaris. An attempt has been made, however, to give a key that will distinguish groups of species which have similar characters as regards the structure of the primary spines, and these will serve as an aid in identifying any case in hand in which the spines are in place. Key to the Groups of Species of Archaeocidaris.1 Spines circular in section, smooth, without spinules or nodose elevations: A. irorthmi Hall (America), p. 259. A. longispina Newberry (America), p. 261. A. legrandemi* Miller and Gurley (America), A. glahrispina (Phillips) (Europe), p. 261. p. 260. Spines circular or rarely elliptical in section, with numerous short spinules which are nearly uniform in size and are directed distally: A. nerei (Miinster) (Europe), p. 262. A. rossica (Buch) (Europe), p. 263. A. agassizi Hall (America), p. 266. A. illinoisensis Worthen and Miller (America), p. 266. A. coloradensis nom. nov. (America), p. 267. A. kcokuk Hall (America), p. 267. A. gracilis Newberry (America), p. 267. A. dfulcata Shumard and Swallow (America), p. 268. A. shumardana Hall (America), p. 268. A. edgarensw Worthen and Miller (America), p. 269. A. newberryi Hambach (America), p. 269. A. trudifer White (America), p. 269. Spines circular in section, with large thorn-like spinules directed distally : A. norwoodi Hall (America), p. 270. A. cratis White (America), p. 272. A. paradoxa (Eichwald) (Europe), p. 270. A. acanthi/era Trautschold (Europe), p. 272. A. mufronata Meek and Worthen (America), A. pizzulana Gortani (Europe), p. 272. p. 271. A. megastyla Shumard and Swallow (America), A. dininnii White (America), p. 271. p. 273. Spines with two lateral wing-like expansions: A. biangulata Shumard and Swallow (America), p. 273. Spines densely covered with long spinules directed distally: A. ornata (Eichwald) (Europe), p. 274. A. our ay crisis Girty (America), p. 274. Spines triangular in section, with spinules on the angles and directed distally: A. triplex White (America), p. 274. A. triserraia Meek (America), p. 275. A. triserialis (M'Coy) (Europe), p. 275. 1 A number of species of Archaeocidaris, or of species referable to that genus, which are not known well enough to intercalate in the systematic series are taken up later. These are: Archaeocidaris konincki, ladina, scotica, selwyni, sixi and trautscholdi, Cidarites lennesseae, Echinocrinus anceps, spinosus and striatus, considered under Incertae Sedis. Also Archaeocidaris tirolensis, Echinocrinus cidariformis and pomum considered under Nomina Nuda. ARCHAEOCIDAHIS. !>.-,«. t Spines with four vertical rows of spinuli-: A. rankini Young (Europe), p. 276. Spines with six vertical rows of spinules: A. prisca (Minister) (Europe), p. 276. Spines with many vertical ridges, which bear spinulcs directed diwtally: .1. trrnckn Tornquist (Europe), p. 276. A. halliana (Geinitz) (Europe), p. 279. A. urii (Fleming) (Europe), p. 276. .1. muensleriana (Koninck) ( KnnM,,->, p. 280. Spines inflated, club-shaped: A. forbesiana (Koninck) (India), p. 280. .1. .»/,. /,. Girty (America), p. 281. A. spinoclavata Worthen and Miller (America), A. ctavata (Eichwald) (Europe), p. 2M.'. p. 281. "Archaeocidaris wortheni Hall. Text-figs. 26, p. 70; 47, p. 80; Plate 8, figs. 5, 6; Plate 9, figs. 6-11. Archacocidaris wortheni Hall, 1858, p. 700, Plate 26, figs. 4a^tg; Love"n, 1874, p. 43; Quenstedt, 1875, p. 372, Plate 75, figs. 10-14; Zittel, 1879, p. 485, figs. 343a-343c (not 343d, which in tln\ ami -th.-r editions is evidently Archcwocidaris kcokuk Hall); (?) Walcott, 1884, p. 212; Keyes, 1894, p. 128, Plate 17, figs. 3a, 3b; 1895, p. 187, Plate 20, figs. 3a, 3b; Jackson, 1896, p. 214, Plate 8, figs. 43-16; Tornquist, 1897, p. 770, Plate 21, fig. 5; Klem, 1904, p. 61. Cidarotropus wortheni Pomel, 1883, p. 113; Lambert and ThieYy, 1910, p. 125. Test spheroidal, but flattened mechanically in the known specimens. The ambulacra are narrow, sinuous, conforming to the outline of the adambulacral plates. Ambulacral plates are low, imbricating moderately adorally, beveled under the adradials, with pore-pairs uni- serial. Interambulacra are broad, with four columns of plates in each area, imbricating mod- erately aborally and from center laterally and over the ambulacrals. There are four plates in the basicoronal row of each interambulacral area, indicating an extensive resorption of the corona in the advance of the peristome (p. 73). Interambulacral plates hexagonal, except the adradials, somewhat wider than high, with a wide scrobicular area as seen well in Plate 8, fig. 5, and Plate 9, fig. 9. Secondary tubercles are limited to a narrow border parallel to the edges of each plate. The primary spines are long, slender, slightly arcuate, from the milled ring tapering to the distal end. Small secondary spines are associated with the secondary tubercles. The peristome has ambulacral plates radially and numerous scale-like non-ambula- cral plates interradially situated, all imbricating adorally. The dorsal area is known only partially (Plate 8, fig. 6). The lantern is of the typical character of the genus (Plate 9, fig. 10). St. Louis Limestone, Lower Carboniferous, St. Louis, Missouri. The cotypes and several other specimens including one fine slab with ten tests are in the American Museum of Natural 260 ROBERT TRACY JACKSON ON ECHINI. History; specimens from the same locality in the Museum of Comparative Zoology; F. Springer Collection; (?) Lower Carboniferous, Eureka District, Nevada (Walcott). The type specimen in the American Museum of Natural History is one of the most nearly complete specimens known in the genus, and measures 53 mm. in diameter through J, E (Plate 8, figs. 5, 6; Plate 9, figs. 6-8). It is not quite complete in the basicoronal row, but excepting area I is very nearly so. In areas A and C, in the basicoronal row, the plates of columns 1 and 4 are nearly whole, whereas the plates of columns 3 and 2 are small, representing only the dorsal part of each plate, of which the ventral portion has been resorbed. In areas E, G, and probably I, in the basicoronal row, the plates of columns 1 and 3 are small, of which the greater part has been resorbed, whereas the basicoronal plates of columns 4 and 2 are nearly complete plates with slight ventral resorption. A similar condition is shown in A . rossica (text-fig. 239 bis, p. 264), and in part in A. urii (Plate 15, fig. 1). This alternation of large and small plates in the basi- coronal row is due to the cutting off of the ventral part of the plates by resorption in the advance of the peristome (text-fig. 26, p. 70). The relative position of the large and small plates differ- ing by the two arrangements I earlier ascribed (1896, p. 219) to the relative position of the in- troduction of column 4, as seen in the restoration (Plate 9, fig. 8). By restoring schematically the plates that have been resorbed, we see that if column 4 is introduced to the right of the center, then in the basicoronal row the plates of columns 1 and 4 are large; or if column 4 is in- troduced to the left of the center, then in the basicoronal row the plates of columns 1 and 3 are small. There are no gill-slits on the peristomal border (p. 223). The peristome in this fine specimen is the most nearly complete one known in the genus. There are two columns of ambulacral plates in an area, doubtless formed by flowing down from the corona as in Cidaris (text-figs. 46, 47, p. 80). There are also many irregular scale-like non-ambulacral plates imbricating strongly. These plates, it is believed, are formed in place, and are not derived from the corona, as discussed under consideration of the peristome (p. 86). It was in this specimen that secondary spines were first shown in the genus. A complete lantern is not known, but the essential parts are shown in Plate 8, fig. 6, and Plate 9, fig. 10. The pyramid is wide-angled with rather deep foramen, epiphyses narrow, capping the half- pyramids. *Archaeocidaris legrandensis Miller and Gurley. Plate 8, figs. 7, 8; Plate 9, figs. 12, 13; Plate 10, figs. 3, 4. Archaeocidaris legrandensis Miller and Gurley, 1889, p. 373, Plate 10, fig. 15; Keyes, 1895, p. 185; Mem, 1904, p. 50; Lambert and Thie"ry, 1910, p. 124. Eonduris blairi Miller, 1892, p. 683, Plate 22, fig. 1; Klem, 1904, p. 67. Test in side view (Plate 8, fig. 8) is only moderately compressed, and measures 26 mm. in diameter, and the ventral view (Plate 8, fig. 7) is of about the same size. The ambulacral plates are not preserved, but their position is located by the outlines of the adambulacrals. AHCHAEOCIDARIS. 261 There are four columns of plates in each interambulacrum; these plates arc low. wioV h« \:»gons, the basal terrace is clearly marked in the scrobicular area (Plate 8, fig. 7). Spines arc -month, tapering, slightly arcuate. Secondary spines are on the borders of plates associated with secondary tubercles (Plate 9, fig. 13). The type of A. legrandensis (Plate 10, fig. 4) is a very small and not well pre-crvcd speci- men, but it has low hexagonal plates and smooth, slightly arcuate spines. AH I cannot dis- tinguish this species from blairi, therefore legrandensis, which is the older name, has priority. Miller was mistaken in referring blairi to the genus Eocidaris, for since the basal terrace is perfectly clearly marked, this feature indicates that it is an Archaeocidaris. The type specimen of legrandensis is from the Kinderhook Group, Ixtwer Carboniferous, Le Grand, Iowa, now in Chicago University Collection 6,198. A second specimen from the same locality and collection is no. 12,314. The specimens originally described as Eocidari* blairi, here considered a synonym, are from the Keokuk Group of Boonville, Missouri, now in Chicago University Collection 8,855. Keokuk Group, Canton, Indiana, a ventral view, with some spines in place, Museum of Comparative Zoology 3,198; Keokuk Group, Bono, Lawrence County, Indiana, Museum of Comparative Zoology, two good specimens, one (3,199) showing four columns of plates in each interambulacral area and the other (3,200) spines in place. In the Springer Collection a specimen 8,024, from the Kaskaskia Group, Pulaski County, Kentucky, and one 8,083, from the Keokuk Limestone of Bono, Indiana, are referred to this species. * Archaeocidaris longispina Newbt-rry. Plate 10, fig. 1. Archaeocidaris longispina Newberry, 1861, p. 116, Plate 1, figs. 1, la; Keyes, 1895, p. 191; Klein, 1904, p. 51 ; Lambert and Thiery, 1910, p. 124. Known only from primary spines which are long, smooth, narrow above the milled ring, inflated in the lower half and thence tapering to a point, Newberry says 2.5 to 3.5 inche- in length. The longest of the three type specimens measures 63 mm. in length and 6 mm. in diameter at the widest part. Crinoidal Limestone, upper part of Carboniferous (Coal Measures), on the banks of the Colorado River. The type consists of three spines on one slab. It is in Columbia University Collection 6,419 G, and bears the label "Coal measure limestone, North Arizona." *Archaeocidaris glabrispina (Phillips). Plate 10, figs. 2a-2b, 8a-8e, 9. Cidaris glabrispina Phillips, 1836, p. 208. (?) Echinocrinus glabrispina M'Coy, 1844, p. 173. Archaeocidaris stellifera Daily, 1877, p. 18, text-figs, a-e. 262 ROBERT TRACY JACKSON ON ECHINI. Archaeocldaris lactis Trautschold, 1879, p. 7, Plate 2, fig. 1 u (the number of the figure is wanting on Plate). Archaeoddaris glabrispina Etheridge, 1888, p. 221; Klem, 1904, p. 62; Lambert and Thiery, 1910, pp. 124, 125. Primary spines smooth, straight, swollen about the middle, above which tapering to a point. Interambulacral plates hexagonal, about 5.2 mm. wide, and wider than high. The species stellifera and laevis may differ from glabrispina if complete material is found; but with present evidence they cannot be distinguished. The plates figured by Baily (my Plate 10, figs. 8a-8c) are so schematic as probably to be unreliable. Lower Carboniferous, the original locality given by Phillips is Northumberland; Bundaran, Ireland, in the Griffith Collection, Science and Arts Museum, Dublin (this is doubtless the material referred to by M'Coy, 1844, p. 173). The specimen figured (Plate 10, fig. 2) is from Hook Head, Ireland, and is in the Sedgwick Museum, Cambridge, England; Clitheroe, England, British Museum Collection E 10,691, this is a small slab with spines and interambulacral plates; Frome, England, a small slab with spines and interambulacral plates, British Museum Collection 38,550; Ireland, from one or more of several localities given by Baily for his A. stellifera, which is considered a synonym of glabrispina, as indeed Baily suggested as possible; Miatschkowa, Province of Moscow, Russia (Trautschold, his A. laevis). *Archaeocidaris nerei (Miinster). Plate 10, figs.*5a-5d, 6, 7. Cidarites nerei Miinster, 1839, p. 40, Plate 3, figs. 6a-6d; Koninck, 1842-'44, [description of] Plate E. Cidarites protei Miinster, 1839, p. 40. Echinocrinus nerei L. Agassiz, 1841, p. 16; d'Orbigny, 1850, p. 154. Echinocrinus protei Li. Agassiz, 1841, p. 16; d'Orbigny, 1850, p. 154. Cidaris nerei Koninck, 1842-'44, p. 34, Plate E, figs, la-li. Palaeoddaris nerei L. Agassiz and Desor, 1846-'47, p. 340. Palaeocidaris protei L. Agassiz and Desor, 1846-'47, p. 340. Archaeoddaris nerei Miiller, 1857, p. 262, Plate 4, figs. 11, 12a, 12b; Desor, 1858, p. 154, Plate 1, fig. 6; Dujardin and Hupe, 1862, p. 465; Loven, 1874, p. 43; Barrois, 1882, p. 321; Julien, 1896, p. 126, Plate 6, figs. 6, 7; Lambert and Thi<5ry, 1910, p. 124. Archaeoddaris nerii Klem, 1904, p. 52. Archaeoddaris protei Lambert and Thiery, 1910, p. 124. Known fragmentarily, interambulacral plates hexagonal, or pentagonal with rounded adradial border, primary tubercle pronounced, basal terrace marked; around the terrace on the outer portion of the scrobicular area, are numerous fine radial plications; minute secondary tubercles are outside of the scrobicular area. Primary spines cylindrical, vertically finely striate, and as Desor figures them, terminally with well developed spinules directed distally. Miiller figures an excellent pyramid (my Plate 10, figs. 6, 7) which is wide-angled, indicating an inclined lantern, with moderately deep foramen magnum, and laterally with ridges for the ARCHAEOCIDARIS. 263 attachment of interpyramidal muscles (p. 363). Miiller's figures of interambulacral plates are rather doubtfully referable to this species, but, as I show in A. rossica, plates differ enough in different parts of the test so that we must allow considerable latitude. Julien's figures are not recognizable, but his description appears to make his specimen referable to this species. Lower Carboniferous, Regnitzlosau ; Tournay, Belgium; Miinster's cotypes of both nerei and protei are in the Munich Museum; Tournay, Belgium, British Museum Collection 32,847; Museum of Comparative Zoology Collection ; La Varville and Sigaret ( Julien) ; Assise de Lena ; Villaneueva, Spain (Barrois). The references given to American localities by Desor and other European authorities are probably incorrect. *Archaeocidaris rossica (Buch). Text-figs. 208, p. 184; 239 bis, p. 264; Plate 10, fig. 10; Plate 11, figs. 1-5; Plate 12, figs. l-13k. (?) Cidaris deucalionis Eichwald, 1841, p. 88. [Description is unrecognizable so the name cannot hold. ] Cidaris rossicus Buch, 1842, p. 323. Cidariles rossicus Murchison, Verneuil and Keyserling, 1845, p. 17, Plate 1, figs. 2a-2e. Palaeocidaris rossica L. Agassiz and Desor, 1846-'47, p. 367. Echinocrinus rossica d'Orbigny, 1850, p. 154. Palaeocidaris (Echinocrinus) rossica Vogt, 1854, p. 314. Eocidaris rossica Desor, 1858, p. 156, Plate 21, figs. 3-6. Echinocrinus deucalionis Eichwald, 1860, p. 652. Eocidaris rossicus Geinitz, 1866, p. 61. Archaeocidaris rossicus Trautschold, 1868, Plate 9, figs. l-10b; 1879, p. 6, Plate 2, figs, la-lf, Ih, li, Ik, 11; Quenstedt, 1875, p. 373, Plate 75, fig. 12; Klem, 1904, p. 55. Archaeocidaris rossica Loven, 1874, p. 43; Tornquist, 1896, text-fig, p. 27, Plate 4, figs. 1-5, 7, 8. Archaeocidaris rossica var. schcllwieni Tornquist, 1897, p. 781, Plate 22, fig. 12. Cidarotropus rossica Lambert and Thiery, 1910, p. 125. This species is known from the most nearly complete material of any species of the genus ; coming from the soft yellow calcareous clay beds of Moscow, the material is not distorted and is easily cleaned. Test compressed, spheroidal, about the form of a living cidarid. Ambulacral areas are narrow, sinuous, conforming to the outline of the adambulacral plates (Plate 10, fig. 10). Ambulacral plates are low, imbricating moderately ventrally and strongly beveled under the adambulacrals (Plate 12, fig. 9). Pore-pairs are uniserial. There are four columns of plates in each interambulacral area. The plates at the mid-zone are higher than wide; ventrally they are not relatively so high, but dorsally are much higher than at the mid-zone; near the apical disc the young plates are very small, and smooth. The primary tubercles are strongly marked, scrobicular area large, basal terrace well developed at the mid-zone (Plate 11, fig. 4), and ventrally, but dorsally in the younger plates no terrace is developed. Passing dorsally to the still younger plates, it is seen (Plate 11, fig. 2) that the scrobicule is imperfectly developed, 264 ROBERT TRACY JACKSON ON ECHINI. then the tubercle is imperforate, and in the youngest plates, no primary tubercle exists. Sec- ondary and very small miliary tubercles are thickly distributed along a narrow border outside the scrobicular circle, and dorsally this border is much larger on the aboral aspect of each plate. Primary spines are stout, inflated in the lower third, tapering from there distally; the milled ring is strongly marked, above which the spine is vertically finely striate for a short distance, and above this part densely studded with short blunt knob-like spinules, set without any definite order. Secondary spines 3 to 4 mm. long are situated on secondary tubercles on the borders of the plates; they are short, flattened, spathulate, vertically finely striate. Between the secondary spines are found some miliaries (Plate 11, fig. 4) which are minute and connected with miliary tubercles. These are the only miliary spines yet seen in the Palaeozoic. The peristome is plated with ambulacral, and many rounded strongly imbricate non-ambulacral plates. The lantern is typical of the Palaeozoic as described below. Lower Carboniferous, Miatschkowa, Province of Moscow, Museum of Comparative Zoology ; British Museum; Berlin Museum fur Naturkunde, two specimens including the one described by Tornquist (1896); Strassburg Mu- seum; Munich Museum; Freiburg i. B. Museum. The var. schellwieni of Tornquist, Fusilinenkalk of the Carnic Alps; Miatschkowa and many other localities in Russia (Eichwald). A very choice and complete test of this species is in the Munich Museum (text-fig. 239 bis; Plate 10, fig. 10; Plate 11, figs. 1, 2). This is the best pre- served specimen known in the genus, o Q On the peristome there are a few am- bulacral and non-ambulacral plates all small and imbricating adorally. In the basicoronal row of the corona, in the interambulacra of areas A, I, G, the plates of columns 1 and 4 are whole and those of columns 3 and 2 are half plates, in which the ventral half has been re- sorbed. On the other hand, in areas C and E, in the basicoronal row, the plates of columns 1 and 3 are half plates, of which the ventral half has been resorbed and the plates of columns 4 and 2 are whole. This, it is believed, as in A. wortheni (Plate 9, figs. 6-8) is associated with the introduction of columns in development. If, as in the figures cited, column 4 originates E 239 bis TEXT-FIG. 239 Ms. — Archaeocidaris rossica (Buch). X 4. Ven- tral border of corona and peristome, same specimen as Plate 11, fig. 1. ARCHAEOCIDARIS. 26,5 to the right of the center, then in the adjustment of parts we find the arrangement of areas as in A, I and G in text-fig. 239 bis. Or if column 4 originates to the left of the center, we then have the arrangement as in areas C and E of text-fig. 239 bis. There are no gill slits (p. 223). Passing dorsally up to the mid-zone, the hexagonal plates progressively increase in height relatively to their width and above the mid-zone this is still more marked. In the drawings of the Munich specimen the basal terrace is not brought out. My attention was not called to this feature when the drawings were made, but other specimens show it clearly on all plates up to the mid-zone, as in Plate 11, fig. 4. Above the mid-zone, however, in younger, though still large plates, the basal terrace is wanting. This is of much interest, as if such plates occurred alone as fossils, one would assume that the species had no basal terrace, and this probably accounts for the absence of a terrace as far as known in some species. Also, it is a condition like that of Eocidaris which as a genus (most imperfectly known) has no basal terrace. Desor referred A. rossica to Eocidaris, and he was probably misled by seeing only dorsal immature plates in which the terrace had not yet developed. Still further dorsally, as we pass into the area of really young plates, the scrobicule is first small and then wanting, the tubercle is imper- fectly developed, then imperforate, and finally, in the younger plates, quite wanting, the plates close to the apical area being smooth without tubercles of any kind. This progressive develop- ment of characters of interambulacral plates as they grow older and are pushed ventrally, is exactly the same as may be traced in the development of fossil or Recent cidarids (Plate 3, figs. 1, 2) in some species of which it is especially marked (p. 106). In the A. rossica it is dis- appointing in such a perfect specimen not to have the oculars and genitals defined. There are many small plates in the center which are evidently periproctal; two of them lying above area D, and larger than the rest, may possibly be oculars or genitals (Plate 11, fig. 3). Trautschold (1868) figured nearly complete lanterns in this species, but a specimen in the Munich Museum and some fine lanterns that Dr. E. O. Hovey kindly procured for me in Russia, now in the Museum of Comparative Zoology Collections, gave the opportunity to study details and to show somewhat better figures than Trautschold's. These are seen in text-fig. 208 (p. 184), and Plate 12, figs. 1-8. The lantern is depressed, subtending an angle of about 90 degrees. The pyramids are wide-angled, with curving sides which admitted of relatively long inter- pyramidal muscles. The foramen magnum is moderately deep. The teeth in place extend just above the base of the foramen magnum. The epiphyses are narrow, capping the half- pyramids, and present a glenoid cavity for interlocking with the condyles of the brace. The brace is block-shaped, as in Recent regular Echini. In one choice specimen (Plate 12, figs. 1, 2) a compass with bifid outer end is in place resting on the brace. This is the only good compass known in the Palaeozoic, though I also show one in Pholidechinus brauni and Meeke- chinus elegans. The sides of the pyramid are corrugated for the attachment of interpyramidal muscles. This lantern, as earlier discussed (pp. 81, 82), is very much like the lantern of young cidarids, also young Strongylocentrotus. 266 ROBERT TRACY JACKSON ON ECHINI. *Archaeocidaris agassizi Hall. Plate 13, figs, la-lc, 2-A. Archacocidaris agassizi Hall, 1858, p. 698, Plate 26, figs. la-Id; Loven, 1874, p. 43; Quenstedt, 1875, p. 373, Plate 75, fig. 11; Keyes, 1894, p. 127, Plate 15, fig. 5; 1895, p. 185, Plate 18, fig. 5; Beede, 1900, p. 48, Plate 8, figs. 6-6e; Klein, 1904, p. 46; Lambert and Thiery, 1910, p. 124. Archacocidaris agassizii Jackson, 1896, p. 213. A complete test is unknown, but specimens in Mr. F. Springer's collection add a good deal of information to that previously known. The ambulacra are narrow, plates low, bev- eled strongly under the adradials, pore-pairs uniserial. Interambulacrum with four columns of plates in an area; these plates are hexagonal, the height about equal to the width, basal terrace developed; many secondary tubercles are in a narrow row about the margin of plates. Primary spines are elongate, compressed, contracted above the milled ring, swollen in the lower third, and from there tapering to the tip, smooth proximally, above which muricate with small spinulose tubercles arranged quite definitely. In Plate 13, fig. 4, are shown some ovally truncate plates which appear to be genitals. As they are not in place, nothing positive can be affirmed, but, while they do not resemble other known genitals in Echini, it is difficult to see what else they could be. The lantern is of the usual character, pyramids wide-angled, with moderately deep foramen, narrow epiphyses, and typical braces. Burlington Limestone, Lower Carboniferous, Burlington, Iowa, American Museum of Natural History; Museum of Comparative Zoology Collection 3,034-3,038 and 3,191; F. Springer Collection; University of Michigan; Munich Museum; Hannibal, Missouri (Keyes); Upper Coal Measures, Topeka, Kansas (Beede). Archaeocidaris illinoisensis Worthen and Miller. Plate 13, fig. 5. Archaeocidaris illinoisensis Worthen and Miller, 1883, p. 338, Plate 31, figs, la, Ib; Keyes, 1895, p. 187; Klem, 1904, p. 49; Lambert and Thiery, 1910, p. 124. Known fragmentarily. Primary spines stout, circular, swollen about the middle, studded with short sharp spinules that are directed outward and slightly distally. Rather close to A. agassizi, but the spines are not flattened and spinules are more pronounced as described. Beach beds of St. Louis Limestone, Lower Carboniferous, near the Illinois Furnace, Hardin County, Illinois, holotype, no. 2,475, of the Illinois State Collection. ARCHAEOCIDARIS. 267 'Archaeocidaris coloradensis nom. nov. Plate 13, fig. 6. Archacocidaris ornatus Newberry, 1861, p. 116, Plate 1, figs. 2, 3, 3a; Keyes, 1895, p. 191 ; Klem, 1904, p. 54 (non Echinocrinus [Archaeocidaris] ornatus Eichwald, 1860, p. 654, Plate 32, fig. 24; non Archaeoci- daris ornatus White, 1877, p. 104, Plate 6, fig. 7a, White's figure is here referred to A. mucronata, p. 271). Archaeocidaris ornata Loven, 1874, p. 44; Lambert and ThieVy, 1910, p. 124. Known only from fragmentary primary spines. These are 2.5 inches long by 0.36 of an inch in diameter, according to Newberry, but it may be remarked that his figured specimens are much shorter and very fragmentary. The spines are thickly studded with short spinules irregularly arranged, with points directed slightly distally. As Newberry's name ornatus is preoccupied by Eichwald 's ornatus (see p. 274), I give a new name to the species. Carboniferous (Coal Measures), Crinoidal Limestone, near junction of the two Colorados, and in same horizon, 60 miles west of that point, near Great Canon of Colorado. Cotype (Plate 13, fig. 6), Columbia University Collection, no. 6,900 G. * Archaeocidaris keokuk Hall. Plate 13, figs. 7a, 7b. Archacocidaris keokuk Hall, 1858, p. 699, Plate 26, figs. 2a, 2b; Keyes, 1894, p. 128; Klem, 1904, p. 50. Archaeocidaris wortheni Zittel, 1879, p. 485, text-fig. 343d (not 343a-343c, which are true worthrni). Archaeocidaris keokuk (Heterocidaris) Lambert and Thiery, 1910, p. 124 (their page and plate references are to true A. keokuk, but this is not Helerocidaris keokuk, see Nomina Nuda. Fragmentary known. Interambulacral plates low, wide hexagons, basal terrace marked, scrobicule wide, secondary tubercles on narrow rim around the margin. Spines circular in section, of moderate length, muricate, with elongate ridges and spiniform tubercles. Keokuk Limestone, Lower Carboniferous, Warsaw, Illinois, American Museum of Natural History; Clark County, Missouri; Boonville, Missouri (Klem). *Archaeocidaris gracilis Newberry. Plate 13, fig. 8. Archaeocidaris gracilis Newberry, 1861, p. 117, Plate 1, figs. 4, 4a; Klem, 1904, p. 49; Lambert and Thit'ry, 1910, p. 124. Fragmentarily known. Newberry says that the form of the interambulacral plates is unknown, but a fragment shows a single row of secondary tubercles around the scrobicule. Primary spines straight or curved, slender, tapering, circular in section, surface set with small spinules pointing distally. 268 ROBERT TRACY JACKSON ON ECHINI. For locality Newberry says, "Same as the last," which reads, Crinoidal Limestone [Coal Measures] near junction of the two Colorados, and in same rock, 60 miles west of that point, near the Great Canon of the Colorado. The specimen figured (Plate 13, fig. 8), which is undoubt- edly the original of Newberry's Plate 1, fig. 4, bears the locality label "Canon Diamond River." It is in Columbia University Collection from the Newberry Collection. *Archaeocidaris aculeata Shumard and Swallow. Plate 13, figs. 9a-9f. Archacocidaris verneuiliana Swallow and Hawn, 1858, p. 180 (non King, 1850, description of Plate 6, figs. 22-24, for which see this memoir, p. 245). Archacocidaris aculeatus Shumard and Swallow, 1858, p. 223; Klem, 1904, p. 45; Lambert and Thiery, 1910, p. 124. Archaeocidaris aculeata Miller, 1889, p. 225; Keyes, 1894, p. 130, Plate 15, fig. 3; 1895, p. 188, Plate 18, fig. 3. Known only from dissociated spines and plates. Interambulacral plates are rather high hexagons, basal terrace marked, secondary tubercles in a narrow border on the margin of the plates. Primary spines are stout, inflated in lower third, circular in section or multiangular, with numerous fine short spinules directed distally. Primary spine 1 to 2 inches in length. The only published figure of the species is that by Keyes, but specimens kindly sent me by Dr. Beede are apparently this species and are so figured. Upper Coal Measures, Valley of Verdigris River, on Santa Fe Road, near Rock Creek, and 25 miles west of Council Grove in valley of Cottonwood Creek; New Point, Jackson County, Missouri; Fort Belknap, Texas (Klem); Topeka, Kansas, Indiana University Collec- tion. Miller (1889) and Miss Klem (1904) ascribe this species to the Permian in part. *Archaeocidaris shumardana Hall. Plate 13, figs. lOa-lOc. Archaeotidaris shumardana Hall, 1858, p. 699, Plate 26, figs. 3a-3d; Keyes, 1894, p. 128. Archaeocidaris cf. shumardana Walcott, 1884, p. 313. Archacocidaris shumardiana Keyes, 1895, p. 186. Archaeocidaris shumardina Keyes, 1895, p. 186. Archacocidaris shumardanus Klem, 1904, p. 56. Archaeocidaris shumardi Lambert and Thiery, 1910, p. 124. Known only from plates and spines. Interambulacral plates are hexagonal, wider than high, basal terrace pronounced, secondary tubercles in a narrow row around the margins of the plates. Primary spines small, short, swollen in the lower third, smooth or finely striate proximally, above which muricate with elongate ascending spinules. ARCHAEOCIDARIS. 269 Warsaw Limestone, Lower Carboniferous, Warsaw, Illinois, American Museum of Natural History; Keokuk Limestone, LaGrange, Lewis County, Missouri. An Archaeocidaris sp. that approaches shumardana, Lower Carboniferous, Eureka District, Nevada (Walcott). *Archaeocidaris edgarensis Worthen and Miller. Plate 13, figs, lla-llc, 12-14. Archaeocidaris edgarensis Worthen and Miller, 1883, p. 337, Plate 30, figs. 15a-15c; Keyes, 1891, p. 245; Klem, 1904, p. 48; Lambert and Thiery, 1910, p. 124. Known only from dissociated plates, spines, and jaws. Interambulacral plates, as figured by Worthen and Miller, hexagonal, the height and width about equal. They do not show the basal terrace or scrobicular area clearly; this is probably due to the wear of specimens. Pri- mary spines long, tapering, slightly constricted above the milled ring, smooth proximally, above which thickly set with short spinules pointing distally. Portions of jaws associated with spines of this species are from Manhattan, Kansas. As seen in Plate 13, figs. 12-14, the pyramid is wide-angled, foramen magnum moderately deep, ridges exist laterally for the attachment of interpyramidal muscles. In an inner view (Plate 13, fig. 14) the dental slide is seen, but it does not reach the base of the foramen magnum, a general Palaeozoic character. Upper Coal Measures, Carboniferous, near Baldwinsville, Edgar County, Illinois. Type from this locality given as no. 2,447, in Illinois State Collection; Lower Coal Measures, Des Moines, Iowa; Junietta Group, Manhattan, Kansas, J. W. Beede Collection. *Archaeocidaris newberryi Hambach. Plate 8, fig. 9; Plate 13, figs. 15a, 15b. Archaeocidaris newberryi Hambach, 1884, p. 551, Plate D, fig. 1; Keyes, 1894, p. 129; 1895, p. 187; Klem, 1904, p. 53; Lambert and Thiery, 1910, p. 125. Incompletely known. Ambulacral plates wide, low, with lateral bevel which would pass under the adradials as known in other species. Interambulacral plates hexagonal, wider than high, basal terrace marked, secondary tubercles with some small secondary spines in a narrow row along margin of plates. Primary spines very long up to or exceeding 57 mm. in length, slender, tapering throughout, with numerous fine sharp spinules pointing distally, and falling in definite parallel series. Lower St. Louis Limestone, Lower Carboniferous, St. Louis, Missouri. The holotype from the Hambach Collection is now in Mr. F. Springer's collection, no. 8,119. *Archaeocidaris trudifer White. Plate 13, figs. 16a, 16b. Archaeocidaris trudifer White, 1874, p. 17; 1876, p. 89; 1877, p. 104, Plate 6, figs. 8a, 8b; Keyes, 1895, 270 ROBERT TRACY JACKSON ON ECHINI. p. 191; Beede, 1900, p. 47, Plate 8, fig. 10; (?) Girty, 1903, p. 330; Hem, 1904, p. 59; Lambert and Thiery, 1910, p. 125. Archaeocidaris trudifera Miller, 1889, p. 225. Known only fragmentarily. Interambulacral plates hexagonal, height and width about equal. Details of basal terrace, scrobicule, and secondary tubercles are not shown in the origi- nal figures. Primary spines long, fusiform, up to about 120 mm. long. Surface for a short distance above the milled ring apparently smooth, beyond which it is ornamented with numerous minute spinules arranged around the spine in imperfectly spiral lines. Red Wall, Carboniferous (Coal Measures), Camp Apache, Navajo County, Arizona, cotypes in United States National Museum 8,471. Confluence of the Grand and Green Rivers, Utah; Topeka, Kansas; Leadville district, Colorado. Upper Coal Measures, Topeka Limestone, Topeka, Kansas (Beede). *Archaeocidaris norwoodi Hall. Plate 14, figs. la-Id. Archaeocidaris norwoodi Hall, 1858, p. 701, Plate 26, figs. 5a-5e; Keyes, 1894, p. 129; 1895, p. 188; Klem, • 1904, p. 54. Cidarotropus norwoodi Lambert and Thiery, 1910, p. 125. Known only from dissociated plates and spines. Interambulacral plates are hexagonal, or pentagonal in adradial columns, wider than high, basal terrace marked. Scrobicular area sometimes shows obscure radiating plications, secondary tubercles in a narrow row on the margin of the plates. Primary spines are slender, elongate, slightly curving, longitudinally striate below and muricate above, with fine sharply elevated denticles, and at intervals marked by larger thorn-like diverging spinules; intermediate surface cancellate or granulose. Kaskaskia Group, Lower Carboniferous, Chester, Illinois, American Museum of Natural History; Kaskaskia, Illinois; near St. Louis, Missouri (Klem). Archaeocidaris paradoxa (Eichwald). Plate 14, fig. 2. Palaeoechinus paradoxus Eichwald, 1856, p. 127; 1860, p. 650, Plate 32, fig. 25 (but not fig. 26). Palaechinus paradoxus Stuckenberg, 1898, pp. 230, 343; Klem, 1904, p. 35; (?) Lambert and Thiery, 1910, p. 119. The spine, which is the only recognizable part of Eichwald's figures or description, evidently belongs to an Archaeocidaris. The shaft only is known, which is stout, tapering gradually, with frequent irregularly placed, stout, thorn-like spinules directed distally. What Eichwald figured as a test (his Plate 32, fig. 26) is an unrecognizable mass, but is entirely the wrong shape for an Archaeocidaris. It evidently has no relation to the spine. Upper Carboniferous (Coal Measures), Sterlitamak and Saraninsk, Ural, Russia. ARCHAEOCIDARIS. 271 *Archaeocidaris mucronata Meek and Worthen. Plate 14, figs. 3a, 3b, 4. Archaeoddaris mucranaius Meek and Worthen, 1800, p. 395; 1866, p. 295, Plate 23, figs. 3a-3c; Klein, 1904, p. 52. Archacocidaris ornatm White, 1877, p. 104, Plate 0, fig. 7a (non Echinocrinua [Archacocidarw] ornaliu Kiohwald, 1860, for which see p. 274; non Archaeociddfit ornntux Xrwborry, 18(11; non Archaeo- cidarix ornnta Lambert and Thii'ry, 1910, p. 124, for which see p. 267). Archaeocidnris t/nicrotiata Keyes, 1895, p. 188; Lambert and Thii'ry, 1910, p. 124. Known only from dissociated plates and spines. Interambulacral plates hexagonal, wider than high, width 0.5 of an inch, height 0.35 of an inch. Primary spines long, tapering, slightly compressed, or nearly circular in section, and apparently a little curved near the base, smooth proximally, beyond which they are armed with strong, sharp lateral spinulcs directed obliquely distally. Length of a primary spine 2.6 inches, greatest diameter of shaft 0.16 of an inch. Chester Group, Lower Carboniferous, Liberty, Randolph County, and Chester, Illinois. The spine figured by Dr. White (1877) as ornatus is apparently referable to this species and is from the Carboniferous (Coal Measures) of Ojo del Oso, near Fort Wingate, New Mexico; this speci- men is in the United States National Museum Collection 8,472. *Archaeocidaris dininnii White. Plate 14, figs. 5a-5b. Archaeocidarui dininnii White, 1880, p. 260, Plate 1, figs. 13-15; 1880a, p. 131, Plate 35, figs. 6a-6c; Keyes, 1894, p. 130, Plate 15, figs. 6a-6c; 1895, p. 190, Plate 18, figs. 6a-6c. Archaeocidaris dininni Klem, 1904, p. 48; Lambert and Thiery, 1910, p. 125. Known only from primary spines which are fusiform, 50 to 60 mm. long, with a greatest diameter of about 5 mm. Above the short plain neck the whole spine is studded with many irregularly disposed spinules, 1 to 2 mm. long, which stand out nearly at right angles to the shaft, except near its apex, where they are directed distally. The spinules are usually more numerous and stronger upon the lower portion of the spines, and upon the middle portion of some of them the spinules are obsolete. The smaller spines are usually more slender or less fusiform than the larger. A striking feature of this species is that the spinules are directed at right angles to the shaft. Upper Coal Measures, near Tecumseh, Nebraska, cotype in United States National Museum Collection 8,031. Upper Coal Measures, Kansas City, Missouri; Red Oak, Iowa (Klem). 272 ROBERT TRACY JACKSON ON ECHINI. *Archaeocidaris cratis White. Plate 14, fig. 6. Archacocidaris cratis White, 1876, p. 109; 1880, p. 130, Plate 33, fig. 2a; Keyes, 1895, p. 188; Girty, 1903, p. 331; 1908, p. 110; Klem, 1904, p. 47; Lambert and Thiery, 1910, p. 125. Archacocidaris sp. a, Girty, 1908, p. 110. Known only from primary spines, which are slender, tapering, terete, shaft with sharp, distinct, distant spinules, each about 1.5 mm. long and pointing distally. Length of spine about 60 mm., diameter just above milled ring about 4 mm. Differs from mucronata in that the spine is more slender, terete, and spinules more widely and irregularly distributed. Girty's (1908) species "a" may well be considered an immature spine of an adult, or the spine of a young individual of cratis. Carboniferous (Coal Measures) at confluence of the Grand and Green Rivers, Utah, holo- type from this locality in United States National Museum Collection 8,235 ; Nebraska. Crested Butte district; Leadville district and Ouray, Colorado (Girty). Guadaloupe Point, Guada- loupe Mountains, Texas (Girty). Archaeocidaris acanthifera Trautschold. Plate 14, figs. 7, 8a, 8b. Archacocidaris acanthifera Trautschold, 1879, p. 7, Plate 2, fig. lu [no number on figure on the Plate]. Archaeocidaris sp. Hind, 1905, p. 529, Plate 25, figs. 1, la. Known only from primary spines, which are slender, tapering, with long irregularly placed spinules pointing moderately distally. The specimens figured by Hind appear referable to this species, although the spinules are not so long as in the type. These specimens are from the Coal Measures of Staffordshire, England, and are apparently the only Palaeozoic Echini yet recorded in Europe from the Coal Measures. Lower Carboniferous, Miatschkowa, Province of Moscow, Russia (Trautschold). Coal Measures, Nettlebank, Staffordshire, England. Archaeocidaris pizzulana Gortani. Plate 10, figs. 12a-12d. Archaeocidaris pizzulana Gortani, 1905, p. 586, Plate 15, figs. 29-33, 36f. Cidarotropus pizzulana Lambert and Thiery, 1910, p. 125. Known from dissociated interambulacral plates and spines. Interambulacral plates are hexagonal, wider than high, with a double ring of secondary tubercles on the margin. Primary spines smooth, cylindrical, with from three to six pairs of opposite spinules. The spinules are stout, thorn-like, and directed distally. This species is the only Palaeozoic echinoid so far known from Italy. Frequent in the calcareous schists, Carboniferous, Forca Pizzul, Carnic Alps. ARCHAEOCIDARIS. 273 *Archaeocidaris megastyla Shumard and Swallow. Plate 14, fig. 13. Archaeocidaris mcgastylus Shumard and Swallow, 1858, p. 225; Keyes, 1894, p. 129, Plate 15, figs. 2a, 2b; 1895, p. 189, Plate 18, figs. 2a, 2b; Beede, 1900, p. 49, Plate 8, fig. 7; Klem, 1904, p. 51. Archaeocidaris mcgastylis Loven, 1874, p. 44. Cidarotropus megastylus Lambert and ThieYy, 1910, p. 125. Known incompletely from plates and spines. Interambulacral plates are large, hexagonal, wider than high, rather thick; scrobicular area very broad, nearly circular; primary tubercle very large, and relatively large secondaries are in a narrow row on margin of plates. Primary spines long, robust, circular in section, length about 3 inches. In the original description Shumard and Swallow say the spine is studded with rather distant granules, or minute short spines. Keyes's interpretation of the species is spines with rather large spinules of which he gives a good figure. As Shumard and Swallow published no figure and their specimens may have been worn, I accept Keyes's version and consider the spinules as relatively large. This char- acter is shown well in a specimen in the United States National Museum which I figure and which in other respects appears referable to this species. Upper Coal Measures, near headwaters of Verdigris River, and in the Valley of Cotton- wood Creek, Kansas; Independence, Jackson County, Missouri; St. Louis Group, St. Louis, Missouri, United States National Museum Collection 43,009, from E. O. Ulrich Collection (Plate 14, fig. 13); Kansas City (Beede). *Archaeocidaris biangulata Shumard and Swallow. Plate 14, figs. 9a-9d. Archaeocidaris biangulatus Shumard and Swallow, 1858, p. 224; Klem, 1904, p. 47. Archaeocidaris biangulata Loven, 1874, p. 44; Keyes, 1894, p. 130, Plate 15, figs, la-lc; 1895, p. 189, Plate 18, figs, la-lc. Cidarotropus biangulata Lambert and Thiery, 1910, p. 125. Known from dissociated plates and spines. Interambulacral plates hexagonal, wider than high, basal terrace marked, secondary tubercles in a narrow row on the margin of the plates. Shumard and Swallow say areolar surface with radial striae ; but such are not visible in speci- mens I have seen. Primary spines are very striking in character. They are smooth for a slight distance above the milled ring; the shaft is terete throughout, but is ornamented with two strongly marked, opposite, wing-like expansions which are in part at least nearly entire in outline, or serrately spinose. Distally the flanges pass into the general spinulose character of the shaft. Aside from the flanges, the shaft is nearly smooth at least proximally, but distally the whole of the shaft is thickly set with relatively long, pointed spinules closely resembling 274 ROBERT TRACY JACKSON ON ECHINI. those of the whole spine in mucronata. Shumard and Swallow say the length of primary spines is about 2.5 inches, diameter including spinules 0.1 of an inch. Middle Coal Measures, Lexington, Missouri; Kansas City, Missouri. Huerco Formation, Diablo Mountains, western Texas, United States National Museum Collection. Archaeocidaris ornata (Eichwalcl). Plate 14, fig. 10. Echinocrinus ornatus Eichwalcl, 1860, p. 654, Plate 32, fig. 24 (non Archaeocidaris ornatus Newberry, 1861, for which see A. coloraden»is, p. 267; non White, 1877, for which see A. mucronata, p. 271; non Klem, 1904, p. 54; non Lambert and Thiery, 1910, p. 124, for which see p. 267). Known only from primary spines. Milled ring well developed, above which the shaft tapers to the distal end; the spine is smooth proximally, but distally thickly set with long spinules directed distally at an acute angle. Lower Carboniferous, Miatschkowa, near Moscow, Russia. *Archaeocidaris ourayensis Girty. Plate 14, fig. 11. Archaeocidaris ourayensis Girty, 1903, p. 329, Plate 1, fig. 14; Klem, 1904, p. 63; Lambert and Thiery, 1910, p. 125. Known only from a primary spine, which has a slender axis slightly over 1 mm. in diameter, densely clothed with relatively large and stout spinules directed distally. Base and tip of spine unknown. Hermosa Formation, Carboniferous (Coal Measures), Ouray, Colorado, holotype, United States National Museum Collection 35,369. *Archaeocidaris triplex White. Plate 14, figs. 12a-12c. Archofocidaris triplex White, 1881, p. xxii, Plate 4, figs. 3a-3c; (?) Girty, 1903, p. 330; Klem, 1904, p. 57; Lambert and Thie"ry, 1910, p. 125. Practically known only from interambulacral plates and primary spines. Interambulacral plates described by Dr. White as imperfect, small, thin, only probably belonging to the same species as the spines. Primary spines large, strong, subtriangular in cross section; spinules are strong, short, but prominent and rather distant, in three rows, each upon one of the three obtuse angles of the spine. The rows of spinules extend from a little way above the milled ring to the end of the spine; the rest of the surface is smooth. Carboniferous (Coal Measures), near Taos, New Mexico, cotypes, United States National Museum 9,449; (?) San Juan region, Needle Mountains, Colorado. ARCHAEOCIDARIS. 275 *Archaeocidaris triserialis (M'Coy). Plate 8, fig. 10; Plate 14, fig. 14. Echinocrinus triserialis M'Coy, 1844, p. 173, Plate 26, fig. 1 (on the legend of Plate 26, fig. 1, the printed generic name has been erased and Echinocrinus written in pencil; see footnotes, pp. 275, 277, 280). Archaeocidaris triserialis Desor, 1858, p. 155; M'Coy, 1862 (on legend of Plate 26, fig. I)1; Klem, 1904, p. 58; Lambert and ThieVy, 1910, p. 125. Known only from primary spines, which are triangular in section, each of the three angular ridges armed with a row of strong tooth-like spinules; intervening space smooth; the sides between the angles are flat and almost equal. Length of specimen that M 'Coy figured is one inch eight lines, diameter one and a half lines; but it was incomplete at each end. Arenaceous Limestone, Lower Carboniferous, Killycloghy, Lisbellow, County Tyrone, Ireland. Holotype and only recorded specimen in the Science and Arts Museum, Dublin. Dr. Scharff kindly sent me the photograph of this specimen which is here reproduced. 'Archaeocidaris triserrata Meek. Plate 14, figs. 15a-15c. Archaeocidaris (?) triserrata Meek, 1872, p. 151, Plate 1, figs. 6a-6c. Archaeocidaris triserrata Miller, 1889, p. 225. Archaeocidaris triserata Keyes, 1895, p. 190. Archaeocidaris triserratus Klem, 1904, p. 58; Lambert and Thiery, 1910, p. 125. Known only from primary spines, which are moderately long, rather slender and usually a little arched near the base, where they are nearly or quite circular in section. Farther up they are compressed, rhombic in section, the lateral margins being sharp and regularly serrated, the little tooth-like projections inclined outward, and toward the apex of the spine. There are probably from 25 to 30 serrations on each side of the spine and from 9 to 12 of them may be counted in the space of half an inch. On the middle of one face of the spine there is a third serrated carina extending about two thirds the length of the spine; on the other face three or four rows of smaller granules or elongate nodes extend from the shank of the spine, but become obsolete near the middle. Length about 2.30 inches. No entire specimens were found. Upper Coal Measures, near Omaha, Nebraska, cotypes in United States National Museum Collection 6,599; Platte River, Nebraska; Vermilion County, Illinois; Kansas City, Missouri. 1 While Archieocidaris triserialis is printed on the Plate as stated, Dr. Kitchin writes me that M'Coy (1862, p. 274) in the list of errata says " Plate 26, fig. 1, read Echinocrinus instead of Archaeocidaris. (See footnotes pp. 277, 280.) 276 ROBERT TRACY JACKSON ON ECHINI. Archaeociclaris rankini Young. Archaeocidaris rankini Young, 1882, p. 108. Known only from primary spines which bear four rows of spinules or denticles; these are long, thorn-like, and stand out from the shaft at nearly a right angle. This is the only species in which there are four rows of spinules described. No figure has been published. Lower Carboniferous shales, Gillfoot, Carluke, Scotland. Archaeocidaris prisca (Miinster). Cidarites priscus Miinster, 1839, p. 41. Echinocrinus priscus L. Agassiz, 1841, p. 16. Palaeocidaris prisca L. Agassiz and Desor, 1846-'47, p. 340. Echinocrinus prisca d'Orbigny, 1850, p. 154. Archaeocidaris prisca Desor, 1858, p. 154. Archaeocidaris priscus Klem, 1904, p. 63; Lambert and Thiery, 1910, pp. 124, 125. Known only from individual plates and spines. Tubercles sensibly larger than in A. nerei. Primary spines with six granular ridges. No figure has been published. Carboniferous, Regnitzlosau, Belgium. Archaeocidaris wervekei Tornquist. Plate 14, figs. 17a-17f. Archaeocidaris wervekei Tornquist, 1897, p. 778, Plate 21, fig. 4; Plate 22, figs. 1, 2, 3, 9, 10; (?) Fraipont, 1904, p. 11, Plate 1, figs. 6, 7. Archaeocidaris werwekei Lambert and Thiery, 1910, p. 125. Interambulacral plates are hexagonal, or pentagonal in adradial columns, very high, the height equaling or exceeding the width, basal terrace marked, strong radial plications extending from margins of plates inward. Primary tubercles exceptionally high. Primary spines are incomplete, vertically plicate and finely striate. Nodose eminences are on the ridges between plications. Dr. Tornquist gives a striking and very satisfactory restoration, representing a complete test in side view. In it he shows narrow ambulacral areas, and four columns of plates in the interambulacral areas. The whole test is represented as depressed spheroidal, and I believe is quite correct in form. Fusilina Limestone, Lower Carboniferous, Hunsriicken, Alsace, Germany; Lower Car- boniferous, Marbre Noir de Dinant, Belgium (Fraipont). * Archaeocidaris urii (Fleming). Plate 14, figs. 16, 18, 19a-19c, 20a-20c; Plate 15, figs. 1, 2a-2c, 3. Echinus - -Ure, 1793, p. 318, Plate 16, figs. 7, 8. Cidaris urii Fleming, 1828, p. 478; M'Coy, 1862, (in legend of) Plate 27, fig. 1 (see footnote p. 277). ARCHAEOCIDARIS. 277 Cidaris vctusta Phillips, 1836, p. 208; Portlock, 1843, pp. xxvi, 353, Plate 16, fig. 11. Echinocrinus urii L. Agassiz, 1841, p. 16; M'Coy, 1844, p. 174, Plate 27, fig. 1 (the generic name on legend of plate in pencil).1 Cidaris bcnburbcnsis Portlock, 1843, pp. xxvi, 352, Plate 16, figs. lOa-lOcl. Echinocrinus vctustus M'Coy, 1844, p. 174. Archaeocidaris urii Roemer, 1852-'54, p. 288, Plate 4, fig. 2; Dcsor, 1858, p. 154, Plate 21, figs. 11, 12; Daily, 1875, p. Ixviii, Plate 36, figs. 12a, 12l>; Keeping, 1876, p. 39, Plate 3, figs. 14-18; Julien, 1896, p. 123, Plate 16, figs. 8-10; Tornquist, 1897, p. 775, Plate 22, figs. 4-7, 11; Fraipont, 1904, p. 11, Plate 1, fig. 5; Lambert and Thiery, 1910, p. 124. Archaeotidant vctusta Dujardin and Hupe, 1862, p. 466; Lambert and Thiery, 1910, p. 124. Archacocidaris [urii] Young, 1873; 187(i. Archaeocidaris urn Loven, 1874, p. 43; Neilson, 1895, p. 77, text-fig. 3; Klem, 1904, p. 59. Archaeocidaris bcnburbensis Etheridge, 1888, p. 221. Archaeocidaris gruneri Julien, 1896, p. 125, Plate 16, figs. 11, 12; Klein, 1904, p. 62; Lambert and Thie"ry, 1910, p. 124. Archaeocidaris rcgimontana Parkinson, 1903, p. 365, Plate 15, fig. 13; I>ambert and Thiery, 1910, p. 124. Archacocidaris vctustus Klem, 1904, p. 61. This species is widely distributed and represented by some very good material. The most complete portion of a test known to me is from Knock Hill Quarry, Fife, Scotland, and is in the Museum of Practical Geology, London. In this specimen (Plate 15, fig. 1) the ambu- lacrum is narrow, 5.5 mm. in width. The ambulacral plates are low with pore-pairs uniserial. In one area of this specimen it is seen that there are four columns of interambulacral plates, the same number that is found in all other species of the genus where a complete area is known. The interambulacral plates of median columns are low, wide hexagons, and those of adradial columns are pentagonal with a strongly rounded line on the adradial suture. This specimen shows that there are four plates in the basicoronal row of the interambulacrum and also traces of ambulacral and non-ambulacral plates on the peristome (compare Plate 9, figs. 6, 7). The largest interambulacral plate measured is 12 mm. in width by 6.5 mm. in height. The surface characters of the plates are not shown well in this specimen, though they are in others from the same locality. In another specimen from this locality in the Jermyn St. Museum, an interam- bulacral plate measures 13 mm. in width by 9 mm. in height. It also shows primary spines of the usual size and character in the species. 1 In a copy of M'Coy's Carboniferous Limestone Fossils of Ireland, of the 1862 edition, seen at the Jermyn St. Museum, London, the name Cidaris urii is printed on the plate as stated (p. 276). In two copies of the 1844 edition, which was privately issued by Sir Richard Griffith, one at the British Museum, and one at the Museum of Comparative Zoology, the generic name is erased on the plate and changed in pencil to read Echinocrinus urii. Dr. Bather (1907, p. 453, footnote) says of M'Coy's publication, "In the legend to the lithographed plates the name Archaeocidaris, which had been printed, was erased, and the name Echinocrinus inserted by hand." According to the evidence Dr. Bather is mistaken, and the name erased was doubtless Cidaris, not Archaeocidaris. (See footnotes, pp. 275, 280.) 278 ROBERT TRACY JACKSON ON ECHINI. The imbrication of plates in this species was described by Professor Young, who, I believe was the first to show that this character occurred in Archaeocidaris. A specimen from Fermanagh, North Ireland, in the Jermyn St. Museum, no. 7,659 (Plate 14, figs. 20a-c), shows interambulacral plates with prominent tubercle, basal terrace, secondary tubercles, and strong radial plications which extend inward from the margins of the plate ; also a characteristic primary spine with its strong spinules extending distally from elevated ridges. The longest spine measures 64 mm. in length, is longitudinally finely striate and thickly set with spinules. This specimen is of importance as it is the original holotype of Portlock's Cidaris benburbensif from whose figures mine are taken. Portlock (1843, p. 353) gives the locality as Benburb, boundary of Armagh and Tyrone. This may be the correct locality of this type ; but Fermanagh is the locality given on the old original label in the Jermyn St. Museum. Dr. Kitchin tells me that the matter of the locality for this specimen is open to question. Port- lock may have been mistaken, or some error may have crept into the label before the day of catalogues. A fine specimen from Millstone Neuk, Dunbar, Scotland, in the Jermyn St. Museum, is of interest from the very perfect condition of preservation of the spines. The longest of these, which is not quite complete distally, measures 61 mm. in length. The spinules are beautifully preserved, measure about 1.5 mm. in length, and are set at an angle of about 45° from the axis of the shaft, pointing distally. A specimen from Corwen, Wales, in the Sedgwick Museum, Cambridge, England, shows the surface characters of interambulacral plates very clearly, as figured by Keeping, from whom my figures (Plate 14, figs. 19 a-c) are taken. Of these plates, several show the basal terrace and radial plications extending inward from the margins. A peculiar elongate plate occurs in this specimen (Plate 14, fig. 19c), the nature of which is doubtful. As it has a perforation near one end, it is possibly a genital plate, but genitals are so far not definitely known in the genus (pp. 265, 266, 414). The species Cidaris vetusta Phillips, as suggested by M'Coy (1844), may be reasonably referred to urii as a synonym. Phillips described the spines as rudely muricate, and Portlock described them as having four or more rows of strong prickles. A specimen from the Portlock Collection, from Fermanagh, Ireland, in the Jermyn St. Museum, no. 16,321, bears the old manuscript label Cidaris vetusta. It is doubtless the specimen referred to by Portlock (1843, p. 353) from this locality, but is not the original of his Plate 16, fig. 11. The spines and plates of this specimen are not distinguishable from urii, though in the plates the radial plications are only faintly preserved. Another specimen from the Portlock Collection, from Clogher, County Tyrone, Ireland, in the Jermyn St. Museum, no. 7,768, consists of two interambulacral plates on a slab with other fossils. This specimen is probably the one referred to by Portlock (1843, p. 353) from this locality, and one of the plates corresponds so closely with that figured by ARCHAEOCIDARIS. 279 Portlock in his Plate 16, fig. 11 (here reproduced as. Plate 14, fig. 16) that it is probably the original of this figure. This plate is hexagonal, measures 11 mm. in width by 10 mm. in height; has a prominent primary tubercle, basal terrace, and on the border a row of secondary tubercles as figured by Portlock. This is the only published figure ascribed to the species vetusta. Julien's A. gruneri is in all probability simply based on small and probably young speci- mens. It presents no specific differences. A . regimontana Parkinson is also doubtless a synonym. Lower Carboniferous, Fermanagh, North Ireland, Museum of Practical Geology, no. 7,659 (the holotype of Portlock's Cidaris benburbensis. See note above in regard to the locality of this specimen) ; Benburb, Ireland, Trinity College, Dublin ; Knock Hill Quarry, Fife, Scot- land, Museum of Practical Geology, nos. 16,316 to 16,319; Millstone Neuk, Dunbar, Scotland, Museum of Practical Geology 25,507, 25,508; Fermanagh, Ireland, no. 16,321, and Clogher, County Tyrone, Ireland, no. 7,768, Museum of Practical Geology; Hayfod-y-Calch, Corwen, Wales, Sedgwick Museum, Cambridge; Yorkshire, Museum of Comparative Zoology Collec- tion 3,062; near Glasgow, Museum of Comparative Zoology Collection; Bristol, British Museum Collection 75,724; Bunderan; Ballantillich, Rahan's Bay, Ireland, and Derbyshire, England, Sedgwick Museum, Cambridge, England; Craigenglen, Campsie, Scotland (Young); Calderwood Limestone, in neighborhood of East Kilbride, Scotland (Neilson); Ardisiere, France (Julien) ; Hunsriicken, Alsace, Germany (Tornquist) ; Culm, Konigsberg (Parkinson's A. regimontana); Marbre Noir, Dinant, Belgium (Fraipont); Phillips (1836) gives as locali- ties for his Cidaris vetusta, here considered a synonym, Ravenstonedale ; Whitewell, North- umberland; Coalbrookdale and Florence Court. Archaeociclaris halliana (Geinitz). Plate 15, figs. 4a-4c. Eocidaris hdlianus Geinitz, 1866, p. 61, Plate 5, figs, la, lb, 2a, 2b; Meek, 1872, p. 152, Plate 7, figs. 9a-9d; Klem, 1904, p. 68. Eocidaris hallanus Miller, 1889, p. 242. Arrhat'ocularis hdlianus Keyes, 1894, p. 129; 1895, p. 190. (?) Eocidaris halliana Girty, 1903, p. 332. Cidarotropus hallianus Lambert and Thiery, 1910, p. 125. Known only from isolated in terambulacral plates and primary spines. Plates hexagonal, wider than high, with basal terrace, as figured by Geinitz, large secondary tubercles in a single row well in from the margin of the plate, and numerous minute granules on the marginal area. Plates small, up to 3 mm., as given by Geinitz. Primary spine slender, terete, tapering from the milled ring to the tip. Vertically finely striate, the elevated ridges being minutely and regularly set with granules. Spines about 7 mm. long. Upper Coal Measures, Nebraska City, Nebraska; Kansas City, Missouri; (?) Leadville district and Crested Butte district, Colorado. 280 ROBERT TRACY JACKSON ON ECHINI. *Archaeocidaris muensteriana (Koninck). Plate 15, figs. 5a-5c. Cidaris muensterianus Koninck, 1842-'44, p. 35, Plate E, figs. 2a-2d. Cidarites munsterianus Koninck, 1842-'44, [description of] Plate E. Echinocrinus munsterianus (?) M'Coy, 1844, p. 173, Plate 27, fig. 2 (name on legend of plate in pencil).1 Cidaris munsteriana L. Agassiz and Desor, 1846-'47, p. 367. Eocidaris munsterianus Desor, 1858, p. 156. Cidaris elegans M'Coy, 1862, [on legend of] Plate 27.1 Lepidocentrus munsterianus Koninck, 1869, p. 546; 1870, p. 260; (non Julien, 1874, p. 76, for which see Pholidocidarw gaudryi). Archaeocidaris munsteriana Loven, 1874, p. 43; Young, 1876, p. 230. Archaeocidaris elegans Etheridge, 1888, p. 221. Archaeoddaris munsterianus Etheridge, 1888, p. 221. Eocidaris munsterianus Mem, 1904, p. 69. Eocidaris munsteri Lambert and Thiery, 1910, p. 126. Known only from primary spines and incomplete interambulacral plates. Interambulacral plates of doubtful outline, probably hexagonal, primary tubercle with large scrobicular area; a basal terrace is not figured, but it is quite likely worn off. Primary spines spindle-shaped, with numerous vertical denticulate ribs, arranged regularly in parallel series. Lower Carboniferous, Vise", Belgium ; Ireland ; Beith district, Ayrshire in Scotland (Young) ; Vise", and Tournai, Belgium, British Museum Collection 32,846 and 56,991. Archaeocidaris forbesiana (Koninck). Plate 15, figs. 6a-6e. Cidaris forbesiana Koninck, 1863, p. 574, Plate 4, figs. 1, 2; 1863a, p. 4, Plate 4, figs. l-2a. Eoddaris forbesiana Waagen, 1879-'87, p. 819, Plate 95, figs. 5-16. Permocidaris forbesiana Lambert, 1899a, pp. 39, 47. Eocidaris forbesianus Klem, 1904, p. 67. Permocidaris forbesi Lambert and Thiery, 1910, p. 127. This species is known from isolated interambulacral plates and spines. The plates are most imperfectly known, and the figures given by Waagen seem to be of quite impossible shapes as regards outline, also the primary tubercle is so peculiar that it differs from that of any known type. With the meager knowledge and doubtful character of the material, it seems to me best to place it in Archaeocidaris rather than make it the basis of a distinct generic type, as does Lambert. The primary spines on which the species was based by de Koninck, are large, 1 In a copy of M'Coy's Carboniferous Fossils of Ireland of the 1862 edition, seen at the Jermyn St. Museum, the name Cidaris elegans is printed on the plate as stated. In two copies of the 1844 edition, one at the British Museum, and one at the Museum of Comparative Zoology, the name on the plate is erased and changed in pencil to read Echinocrinus munster- anus (see footnotes pp. 275, 277). ARCHAEOCIDARIS. 281 stout, and strongly swollen in the middle. The milled ring is weakly defined, shaft smooth for about the lower third, above which it is ornamented with numerous elevated nodose spinules arranged in quite definite parallel series, of which, judging from the figures, there must be about 14 vertical series on a spine. Productus Limestone, Permian, Katta, Golawali, Chidru, and Bazarwan, India. Archaeocidaris spinoclavata Worthen and Miller. Plate 15, figs. 7a-7h. Archaeocidaris (?) sp. undet. Meek and Worthen, 1873, Plate 24, figs. 13a-13c. Archaeocidaris spinoclavatus Worthen and Miller, 1883, p. 327, Plate 30, figs. 14a-14e; Keyes, 1895, p. 190; Klem, 1904, p. 57. Archaeocidaris spinoclavata Miller, 1889, p. 225; Lambert and ThieYy, 1910, p. 124. Known only from dissociated interambulacral plates and primary spines. Interambulacral plates hexagonal, wider than high, with a nodose rim around the margin, the expression of secondary tubercles. The basal terrace is not shown, and the details of the surface are doubtful in Worthen and Miller's figures, but, as they say, the specimens are highly silicified and external markings thereby obscured. Primary spines long, or short, circular in section, contracted above the milled ring, beyond which very soon, or at a considerable distance, the spine expands to a marked degree. If it expands quickly, the spine appears highly swollen, as in Plate 15, figs. 7g, 7h, or this may be much less marked, as in fig. 7f, or the greatest expansion may be near the tip of the spine, as in fig. 7e. Proximally the spine is smooth for a short distance, above which it is thickly clothed with nodose spinules. This species is more variable in the form of the spines than other species of the genus yet known. Middle and Lower Coal Measures, St. Clair and Marshall Counties, Illinois. Cotypes are stated as in the Illinois State Collection 2,404. Archaeocidaris sp. b. Girty. Archaeocidaris sp. b. Girty, 1908, p. 110, Plate 27, figs. 18, 18a. Archaeocidaris sp. b. var. The same, p. 111. Archaeocidaris sp. c. The same, p. 111. Archaeocidaris sp. d. The same, p. 111. Most fragmentary, based on two pieces of spines which Girty thinks resemble A. spino- clavata, and yet are different, so I insert the record at this place pending further knowledge, should such be attained. The piece representing the distal end expands rapidly into an almost knob-like tip, which, with the shaft, Girty says, appears to be ornamented with short spinules. The shaft is about 0.75 mm., and the expanded distal tip about 2 mm. in diameter. To recog- nize a varietal form of a species which itself is so shadowy that Girty gives it no name, does seem 282 ROBERT TRACY JACKSON ON ECHINI. beyond all reason in splitting. Certainly, without injustice to Girty, his variety of b and his species c and d may reasonably be left under his species b, until better material turns up. Delaware Mountain Formation, Carboniferous (Coal Measures) , southern Delaware Moun- tains, Texas; and Dark Limestone, Pine Spring, Guadalupe Mountains, Texas. Archaeocidaris clavata (Eichwald). Plate 15, fig. 8. Echinocrinus davatus Eichwald, 1860, p. 653, Plate 23, fig. 16. Known only from primary spines,r which are club-shaped, above the milled ring expanding to the thickest part, which is near the distal apex, tapering to a blunt end; with marked, sinu- ous, fluted ridges unlike other known species. Carboniferous, Yegor jefsk, in the Province of Kalonga, Russia. LEPIDOCIDARIS Meek and Worthen. Lepidoddaris Meek and Worthen, 1873, p. 482; Loven, 1874, p. 44; Duncan, 1889a, p. 12; Lambert and Thiery, 1910, p. 126. This genus differs very markedly from Archaeocidaris, and instead of having many species, as in that genus, there is at present only one species known. The test is high, spheroidal, or perhaps spherical. Ambulacral areas narrow, with two columns of low plates. Ambulacral plates not all alike, but at the mid-zone every third plate is higher and wider than the two inter- mediate and more or less completely abutting against the two smaller plates of the opposite half -area (Plate 17, figs. 2, 3, 12). Interambulacra are wide, with from six to eight columns of large hexagonal plates, or pentagonal in adradial columns. The plates are high, rounded, imbricating moderately aborally, and from the center laterally, and over the ambulacrals. Each interambulacral plate has a large perforate primary tubercle with a deep sunken, rather small scrobicular area but no basal terrace. On the high rounded area beyond the scrobicular circle, the surface bears many small secondary tubercles. Spines are long, cylindrical ; primary spines are associated with the primary tubercles and minute secondary spines with the secondary tubercles. Oculars and genitals unknown. A typical Palaeozoic inclined lantern exists. Type and only known species L. squamosa of the Lower Carboniferous. "Lepidocidaris squamosa Meek and Worthen. Plate 16, figs. 1-3; Plate 17, figs. 1-14. Eocidaris (?) squamosa Meek and W7orthen, 1869, p. 79. Eocidaris (?) squamosus Meek and Worthen, 1873, p. 478, Plate 9, figs. 15a-15g. Lepidocidaris squamosus Meek and Worthen, 1873, p. 478; Jackson, 1896, p. 220, Plate 7, fig. 41; Klem, 1904, p. 72. Lepidechinus squamosus Keyes, 1895, p. 193. Lepidocidaris squammosus Lambert and Thiery, 1910, p. 126. LEPIDOCIDARIS 283 This striking species is one of the most distinctive of Palaeozoic Echini. Test high, spher- oidal, perhaps nearly or quite spherical. In the type (Plate 16, fig. 1) at the upper part of the specimen, which I take to be about on the line of the mid-zone, the ambulacrum measures 8 mm. in width; the interambulacrum 52 mm. in width. From these measurements the cir- cumference must have been in the neighborhood of 300 mm. and the diameter about 100 mm., a very large sea-urchin, but no complete specimen is known. In the ambulacrum, every third plate is wider and higher than the intermediate, so that in this character the structure is very different from that of Archaeocidaris. In the type specimen at the mid-zone (Plate 17, figs. 1, 3) the ambulacral plates are rather irregular in form ; while usually all plates cross the half-area, occasional smaller plates may be excluded from the interambulacrum, or the center of the ambu- lacrum, thus making them occluded or demi-plates. Ventrally in the type, and at the mid- zone in younger specimens (Plate 17, figs. 1, 8, 12), all the plates cross the half-area and the large plate of the triplet abuts distinctly against the two smaller plates of the opposite half-area. The ambulacral plates imbricate moderately adorally, and bevel under the adradials. The interambulacrum is very wide, and in the type has eight columns of plates at the mid-zone, but in two smaller specimens (Plate 17, figs. 9, 11) there are only six columns of plates in an area. The interambulacral plates imbricate moderately dorsally and laterally. The character of the tubercles is as described for the genus. The primary spines are cylindrical, with scarcely any perceptible tapering; the largest seen, yet not quite complete, measures 35 mm. in length. The spines are longitudinally finely striate. Small secondary spines occur associated with the secondary tubercles (Plate 17, fig. 10). The pyramids are wide-angled, foramen magnum moderately deep, lateral wings with ridges for the attachment of interpyramidal muscles, all practically the same as in Archaeocidaris. This species is known only from the Lower Burlington Limestone, Lower Carboniferous, Burlington, Iowa. The holotype is in the Museum of Comparative Zoology Collection 3, 026; also a number of other specimens are in the same collection. A fine series of twelve specimens is in Mr. Frank Springer's collection. In the type and in part in other specimens, the introduction of the interambulacral columns is shown. As seen in Plate 17, fig. 9, there are four columns of plates in an interambulacral area ventrally, and apparently four in the basicoronal row, as in Archaeocidaris. Passing dorsally, new columns are introduced with a pentagonal plate, and a heptagonal plate lies ventral to the same. On the basis of introduction of columns and also on the direction of imbrication, I have oriented the type as shown in Plate 16, fig. 1, and Plate 17, fig. 1. This is reversed from the position given by Meek and Worthen. 284 ROBERT TRACY JACKSON ON ECHINI. Family LEPIDOCENTRIDAE Loven. Li-pidocentridae (pars) Loven, 1874, p. 39; (pars) Zittel, 1879, p. 482; (pars) Jackson, 1896, p. 241. Archacocidaridae (pars) Loven, 1874, p. 39; (pars) Duncan, 1889a, p. 8; (pars) Jackson, 1896, p. 241. Rhoechinidae (pars) Lambert and Thiery, 1910, p. 121. Test spheroidal or flattened horizontally, in the plane of the ambitus circular, pentagonal, or elongate through the axis III, 5. Two columns of plates in an ambulacral area, all primaries, or, in one species, occasional alternate plates slightly occluded. Pore-pairs uniserial, or in one species slightly biserial. Ambulacral plates imbricating adorally and beveled strongly under the adradials. Interambulacra with numerous, 5 to 14, columns of plates in an area, moder- ately thin to very thin. Primordial interambulacral plates are in the basicoronal row; the interambulacra usually have a very accelerated development, additional columns coming in early and rapidly. Interambulacral plates imbricate strongly aborally and from the center outward and over ambulacrals. The peristome is plated with many rows of ambulacral plates only. Oculars are small, insert; genitals wide, low, with many pores as far as known. Peri- proct with many small angular plates. Apical disc small. Lantern inclined, composed of forty pieces. There are five genera, including two new ones. KONINCKOCIDARIS Dollo and Buisseret. Koninckocidaris Dollo and Buisseret, 1888, p. 959; Duncan, 1889a, p. 9. Perischodomus (pars) Tornquist, 1897, p. 725. Lepidcchinus (pars) Lambert and Thiery, 1910, p. 122. Test spheroidal, ambulacra narrow, with two columns of plates in an area. The plates are rather high, and imbricate adorally and strongly bevel under the adambulacrals ; pore-pairs are uniserial. Interambulacra wide, with many (seven to eight) columns of plates in an area; the plates are nearly rhombic in outline, imbricating strongly aborally and from the center laterally and over the ambulacrals. Base of corona, peristome, and lantern unknown. Oculars small, genitals low, plates of periproct as far as known numerous, angular. This genus differs from Lepidocentrus in that the ambulacral plates are relatively high instead of low. Since for ambulacral plates to be high is a primitive character, it is considered a lower genus than Lepidocentrus and one of the two species, K. silurica, is geologically much older than any known Lepidocentrus. Type species K. cotteaui Dollo and Buisseret from the Lower Carboniferous of Belgium. Key to the Species of Koninckocidaris. Ambulacral plates high, two equaling the height of an adambulacral; seven columns of plates in an interambulacral area K. cotteaui Dollo and Buisseret, p. 285. Ambulacral plates high, three equaling the height of an adambulacral; eight columns of plates in an interambulacral area. K. silurica sp. nov., p. 285. KONINCKOCIDARIS. 285 Koninckocidaris cotteaui Dollo and Buisscret. Koninckocidaris cotteaui Dollo and Buisseret, 1888, p. 959. Perisckodom.ua [cotteaui] Tornquist, 1897, p. 725. Lepidechinus cotteaui Lambert and Thiery, 1910, p. 122. Known from a fragment of a test and isolated plates. General form unknown, but proba- bly it was spheroidal as is K. silurica. Apical disc and jaws unknown. Ambulacral plates high, two about equaling the height of an adambulacral plate; pore-pairs lie near the next adjacent interambulacrum, two pores to each plate, not on a line, but one higher than the other. Dollo and Buisseret say that the pore nearer the middle of the area is higher up. This is opposed to what I have found in all Palaeozoic species, and probably they had their fragment incorrectly oriented. If we change the orientation, then it would read, pore nearer the middle of the area lower, which is in accord with what I find in Palaeozoic and most modern Echini (p. 57). Ambulacral plates bear numerous secondary tubercles, similar to those on the interambulacra. Interambulacra with seven columns of plates, the central column narrower, plates polygonal, strongly imbricating, and ornamented with secondary tubercles; the adambulacral plates bear in addition marginally a primary perforate tubercle. Described from a single specimen, which has not been figured. Lower Carboniferous, Belgium. 'Koninckocidaris silurica sp. nov. Plate 19, fig. 1; Plate 20, figs. 5, 6. It was with keen delight that I received this most interesting fossil which Professor H. L. Fairchild most kindly sent me for study. It occurs in the Niagara Limestone, Silurian, and therefore is much earlier geologically than any American echinoid previously known. It also adds much to our knowledge of this very interesting ancient genus. The specimen is an internal view and the plates are beautifully preserved, but one must bear in mind that as it is internal, therefore the direction of imbrication is opposite to what it would be if the specimen were viewed from the exterior (compare text-figs. 32-38, p. 75). Test high, spheroidal, as gathered from the dorsal portion, which alone is preserved. The lower part of the specimen is probably at or near the plane of the mid-zone. Height of specimen 52 mm., width of ambulacrum J at the lower portion 9 mm.; width of the interambulacrum on same line about 43 mm. From these figures the circumference would be about 260 mm. and the diameter in the neighborhood of 83 mm. Ambulacra rather wide, much wider than they would be on the exterior, on account of the lateral beveling of ambulacral plates under (but here over) the adradials. Pore-pairs relatively near the ventral part of each plate, and near the middle of the area, largely due to its being an internal view (compare Plate 20, figs. 9, 10). Ambulacral plates are high, about three equaling the height of an adambulacral plate; in this 286 ROBERT TRACY JACKSON ON ECHINI. respect they are somewhat lower than in K. cotteaui as described, but much higher than in species of Lepidocentrus. A general depressed area surrounds the pore-pair, extending on to the next plate in this internal view. This leaves an elevated ridge between succeeding pore-pairs, and the general superficial appearance resembles the ribs of a turtle in relation to the carapace. Ambulacral plates imbricate adorally and bevel strongly under the adambulacrals. (As this is an internal view, the exact opposite appears in the specimen; that is, ambulacral plates in this view imbricate aborally and laterally bevel over the adradials; compare text-fig. 37, p. 75.) The interambulacrum is composed of eight columns of plates, which are nearly rhombic in outline, much as in Lepidocentrus mulleri. A median column is narrower than the others and in both areas this is column 7. The plates imbricate strongly aborally and from the center laterally and over the ambulacrals. (As this is an internal view, the exact opposite appears to be the case; that is, interambulacral plates in this view imbricate adorally and under the ambulacrals; compare text-fig. 34, p. 75.) The ventral part of the test is unknown, but dorsally an ocular which is low but exceptionally wide, covers ambulacrum B and in part interambulacra A and C on either side. A very low genital is in A and a part of one in C. A small plate between genital A and ocular B may be a displaced plate, but it appears as if the periproct met the interambulacrum in this area like the condition common in Recent Echino- thuriidae (text-fig. 170, p. 149; p. 287). The apical disc in this species is evidently small in pro- portion to the diameter of the test, a progressive character. A few small angular plates lying dorsal to the ocular and genitals are apparently remnants of the periproct. As the exterior of the plates is unknown, surface characters cannot be given; but they are probably as in K. cotteaui. This choice and beautifully preserved specimen was collected in 1909 by Mr. A. W. Giles from the base of the Rochester Shale, about ten feet above the Irondequot Limestone, in the Niagara Group, Silurian. It was found in these beds in a ravine of the Genesee River in the north part of Rochester, New York. On the slab are fragments of other fossils including a faceted eye of Dalmanites limulurus Green, a typical Niagara Group trilobite. The holotype with two additional fragmentary pieces is in the collections of the University of Rochester, at Rochester, New York, and was loaned to me by my friend, Professor H. L. Fairchild of that institution. LEPIDOCENTRUS Miiller. Lepidocentrw Miiller, 1857, p. 258; Schultze, 1866, p. 123; Loven, 1874, p. 39; A. Agassiz, 1881, pp. 79, 80; Duncan, 1889a, p. 9; Jackson, 1896, p. 222; Lambert and Thiery, 1910, p. 121. Test spheroidal, ambulacral areas narrow throughout, plates low, imbricating adorally and beveled under adambulacrals; pore-pairs uniserial, situated toward the next adjacent interambulacrum, as seen externally, but near the middle of the plate as seen internally. Inter- LEPIDOCENTRUS. 287 ambulacral areas with many (5 to 11) columns of plates which are moderately thin and imbricate strongly aborally and from the center outward and over ambulacrals. Interambulacral plates are rhombic, or more or less hexagonal, and the primordial interambulacral plates are in the basicoronal row. Peristomal plates are unknown in this genus. Mr. Agassiz (1881, p. 79) says that in Lepidocentrus there is no distinct line of division separating the coronal interam- bulacral plates from those belonging to the actinal membrane. He further says that in a remarkably well preserved specimen from the Lower Burlington Limestone, the ambulacral plates are continued to the very teeth, and the same is the case with the interambulacral plates. Unfortunately Mr. Agassiz did not figure this structure, or mention in what species it occurred. The peristome is not known to me in this genus, but in two other genera of the family, only ambulacral plates exist on the peristome, and such a structure as Mr. Agassiz describes is not known "to me in any sea-urchin, fossil or Recent. The genus is not known from the Burlington Limestone excepting as implied by Mr. Agassiz's remarks, and this is the first mention of its occurrence in America. It is on this statement apparently that Duncan (1889a) records the genus from this country. Insert oculars, and genitals with many pores are known in one species, the new L. whitfieldi (Plate 21, fig. 5). The apical disc is proportionately small. Mr. Agassiz (1881, p. 80) says of .Lepidocentrus that, "the genital plates bear about the same proportion to the plates of the anal system which we find in some of the recent Echino- thuridae, and there exists at the apical extremity of the coronal plates the same difficulty in defining where the interambulacral plates terminate and the plates of the apical system begin." I do not know the basis of Mr. Agassiz's statement, but in this genus, Lepidocentrus, and in all Palaeozoic Echini that I know (excepting possibly Koninckocidaris silurica, p. 286) the geni- tal and ocular plates, when preserved, are in contact throughout, so that the interambulacra are separated from the periproct by the oculo-genital ring, not in contact with it, as may occur in the Echinothuriidae (text-fig. 170, p. 149; p. 414). Lepidocentrus occurs in the Devonian and Lower Carboniferous; the type species is L. eifelianus Miiller. Key to the Species of Lepidocentrus.1 Five columns of interambulacral plates in an area . . L. rhenanus (Beyrich), p. 288. Eight columns of interambulacral plates in an area . . . . L. drydenensis (Vanuxem), p. 288. Ten or eleven columns of interambulacral plates in an area, the plates nearly rhombic in form L. mulleri Schultze, p. 289. Eleven columns of interambulacral plates in an area, the plates small and rounded hexagonal L. u'hitfirldi sp. nov., p. 290. Number of columns of interambulacral plates in an area unknown, plates similar to those of mulleri, but thinner and more rounded in outline . . . L- eifcliantui Miiller, p. 291. 1 Three species of Lepidocentrus, namely L. desori, duponli, and gaudryi, of which no description has been published, are considered under Nomina Nuda. 288 ROBERT TRACY JACKSON ON ECHINI. "Lepidocentrus rhenanus (Beyrich). Plate 20, fig. 7. Pdaechimts rhmanus Beyrich, 1857, p. 4; Quenstedt, 1875, p. 377, Plate 75, fig. 18.1 Lepidocentna rhenanus Miiller, 1857, p. 264, Plate 4, figs. 4-6; Loven,2 1874, p. 40; Jackson, 1896, p. 244; (pars) Klem, 1904, p. 17; Lambert and Thiery, 1910, p. 122. Test spheroidal, ambulacral plates low. Interambulacrum with five columns of plates which are nearly hexagonal, as seen in area E of Plate 20, fig. 7. The primordial interambulacral plate is in the basicoronal row, and from this it is inferred that the same occurs in other species of the genus. Columns 2, 3, 4 originate in succeeding rows of plates, and column 5 appears in the sixth row. There are powerful jaws in place ventrally. The type and only known speci- men, which is in the Berlin Museum fur Naturkunde, is an internal mold, and therefore the external character of the plates is unknown. The plates also are probably more hexagonal in outline than they would be on the exterior (compare text-figs. 32-34, p. 75). Devonian, Wipperfiirth, Prussia. *Lepidocentrus drydenensis (Vanuxem). Plate 16, fig. 5; Plate 21, figs. 1-3. Echinus drydenensis Vanuxem, 1842, p. 184. Eocidaris drydenensis Hall, 1868, p. 298; 1870, p. 341; Loven, 1874, p. 43; Klem, 1904, p. 71. Archaeocidaris drydenensis Keyes, 1895, p. 184; Jackson, 1896, p. 214. This species has never been figured before, and, as indicated in its synonymy, has been variously placed generically. The type, which may be considered the best preserved individual, is on a large slab with the faint impressions of two or more other individuals. The plates them- selves are not preserved, but we have an impression only with the plates entirely dissolved away. This is true of the spines as well as the plates. The best impression is fortunately of the ambulacral areas and of the spines, while the impression of the interambulacral areas is for the most part weak and ill defined. Diameter through J, E, 70 mm., also through H, C. The view, which is ventral, shows a rather deep depression in the oral region. Diameter of the peristome 6 mm. The shape of the test was doubtless spheroidal, or spherical. Ambula- cral areas narrow, plates low, about seven or eight equaling the height of an adambulacral plate. Ambulacral pore-pairs lie near the next adjacent interambulacrum and are on an angle, the outer pore a little higher than the inner; width of an ambulacrum at the mid-zone 14 mm. 1 Non Palaeocidaris rhenanus Quenstedt, 1875, p. 377, Plate 75, figs. 30-37 (for which in this memoir see Xenocidaris clavigera). 2 Lov6n writes " L.[epidocentrus] rhenanus (Palaeocidaris) Beyrich," thus indicating that Beyrich put the species in Palaeocidaris, which is a mistake, as he put it in Palaechinus. Palaeocidaris rhenanus is Qucnatedt's name, applied to another species; here referred to Xenocidaris clavigera as a synonym, see under Incertae Sedis. LEPIDOCENTRUS. 289 The plates of the interambulacra are marked as impressions, the outlines of which are largely ill defined. There are apparently nine columns of plates in each area, as shown in Plate 21, fig. 1. The spines are marked as depressions or elevations in the shale; they are elongate and slender, acicular, and the clearest impressions are about 8 mm. long. In the shaly sandstones of the Chemung Group, Upper Devonian, Dryden, Tompkins County, New York; holotype and only known specimens (on a single slab) in the New York State Museum Collection 4,200. This species is geologically the oldest known sea-urchin from America, except the Konincko- cidaris silurica herein described. It is not strange that this species has not been figured before, as it is not easy to make out. Professor John M. Clarke kindly sent me the specimen for study, and after careful examination I feel that it should be referred to Lepidocentrus. It certainly has no relation to Archaeocidaris, and does fit in with the characters of Lepidocentrus. As regards the characters of tubercles and spines, primary and secondary, nothing can be definitely said except that the larger spines would compare well enough with the larger spines of Lepido- centrus. *Lepidocentrus mUlleri Schultze. Plate 19, figs. 2-5; Plate 20, figs. 8-13. Lepidocentrus mulleri Schultze, 1866, p. 124, Plate 13, figs. 1-lf; Loven, 1874, p. 40; Jackson, 1896, p. 223, text-fig. 2; Klem, 1904, p. 17. Lepidocentrus mulleri Lambert and Thiery, 1910, p. 122. Test spheroidal as gathered from the upper part, which alone is preserved. Ambulacra at the lower part of the type specimen about 5 mm. wide; interambulacrum about 65 mm. wide. This would give a circumference of about 350 mm. and diameter of about 111 mm. The ambula- cra are narrow, plates imbricating ventrally, and strongly beveled under the adradials. The ambulacra, on account of this bevel, are much wider on the interior of the test than on the exterior, as seen by comparing Plate 20, figs. 9, 10. The pore-pairs on the exterior lie near the adradial plates, but proximally are in about the middle of each ambulacral plate. Interambula- cra are broad, with eleven columns, as shown in Plate 20, fig. 8, area A, the only complete area known; but in area C, of the same figure, there are apparently only ten columns. In area A many columns drop out passing dorsally, namely, columns 6, 5, 11, 10, 9, and in the sequence stated. This is a very marked character, indicating reversion or senescence. In my earlier paper (1896, p. 223) this dropping out of columns was by error taken for the coming in of columns, with the result that I oriented the specimen incorrectly, and also incorrectly stated the direction of imbrication (p. 76). The interambulacral plates are thin, nearly rhombic in outline, and imbricate strongly aborally (not orally as I stated before), and from the center outward and over the ambulacra. The beveled edges are shown well in Plate 20, figs. 11, 12. 290 ROBERT TRACY JACKSON ON ECHINI. The interambulacral plates bear one or occasionally two small eccentric perforate primary tubercles with scrobicules, and scattered secondary tubercles. These are shown best in the Munich specimen (Plate 19, figs. 3, 4). The spines are small primaries and secondaries. From the swollen base they taper to the tip and are longitudinally finely striate. This species is known from two good specimens : the type from the Schultze Collection in the Museum of Com- parative Zoology, and a specimen in the Munich Museum, both figured here. The Munich specimen is especially clear in its surface characters, and the interambulacral plates lie very nearly in horizontal rows instead of alternating in adjacent columns, as usual in Echini. Besides tubercles, it shows a number of spines in place, which are also figured enlarged. Isolated in- terambulacral plates are fairly common in collections. Middle Devonian, Gerolstein, Prussia, two fine specimens, the holotype, from the Schultze Collection, Museum of Comparative Zoology 3,040; and one in the Munich Museum. Spines from the same locality, including those figured by Schultze, Museum of Comparative Zoology Collection 3,043. Isolated plates from same locality, Museum of Comparative Zoology 3,042, 3,045; British Museum E 1,201; Strassburg Museum; Freiburg i. B. Museum; Pelm, Prussia, Museum of Comparative Zoology Collection 3,103-3,105; Rommersheim, near Prum, Prussia, Museum of Comparative Zoology 3,041. *Lepidocentrus whitfieldi sp. nov. Plate 19, figs. 6, 7; Plate 21, figs. 4, 5. Lepidechinw rarispinus (pars) Hall, 1868, p. 295 (non Plate 9, fig. 10); 1870 (revised edition), p. 340 (non Plate 9, fig. 10); (pars) Jackson, 1896, p. 228; (pars) Klem, 1904, p. 22. Test spheroidal, flattened on the base, probably from pressure. Known only from an internal mold. Ambulacral areas narrow throughout, plates low. Eleven columns of small plates in an interambulacral area, the plates strongly rounded in outline. The primordial interambulacral plate is in the basicoronal row, as shown in one area. The oculars, as indicated by an impression, are small, insert; genitals high, with numerous genital pores, nine or ten in the impressions preserved. Professor Hall included this specimen in his Lepidechinus rari- spinus, here called Hyattechinus rarispinus. It differs from that species in that the ambulacra are narrow throughout, instead of broad and petaloid ventrally, as in rarispinus. This differ- ence Professor Hall was not aware of, as he had only the dorsal part of rarispinus (p. 395). I think it also differs in its spheroidal form, as rarispinus is almost certainly highly flattened, (p. 292) but this might well be only a specific, not a generic difference. This species I name in memory of the late Professor R. P. Whitfield of the American Museum of Natural History. Waverly Group, Lower Carboniferous, Licking County, Ohio. Holotype, and only known specimen, American Museum of Natural History Collection 6,391. HYATTECHINUS. 291 *Lepidocentrus eifelianus Muller. Plate 20, fig. 14. Lepidocentrus eifelianus Muller, 1857, p. 258, Plate 3, figs. 1-8; Schultze, 1866, p. 123, Plate 13, figs. 2-2c; Loven, 1874, p. 40; Quenstedt, 1875, p. 374, Plate 75, figs. 14-17; Jackson, 1896, p. 225; Klein, 1904, p. 16; Lambert and Thie"ry, 1910, p. 122. This species, the type of the genus, is known only from isolated interambulacral plates and spines. The plates are thinner and more rounded in form than those of L. mulleri, but with similar surface ornaments. The spines are similar to those of mulleri. Devonian, Nohn, and Rommersheim, from the Schultze Collection, Museum of Compara- tive Zoology 3,061, 3,068, 3,069; Berlin Museum fur Naturkunde, doubtless the types. TORNQUISTELLUS Berg. Leptechinus Tornquist, 1897, p. 785 (non Gauthier, Echinides fossiles de la Tunisie, 1869). Tornquistellus Berg, 1899, p. 77. Known only from interambulacral plates, which are small, thin, imbricating, with sparsely distributed secondary tubercles. While the material is so meager, its affinities are distinctly with Lepidocentrus, from which it differs in having secondary tubercles only. Type species T. gracilis. Tornquistellus gracilis (Tornquist). Plate 20, fig. 15. Leptechinus gracilis Tornquist, 1897, p. 785, Plate 20, fig. 5. Tornquistellus [gracilis] Berg, 1899, p. 77. Perischodomus gracilis Lambert and Thiery, 1910, p. 122. Known only from isolated interambulacral plates, which are thin, flat, wider than high, slightly angular, but very nearly rhombic in outline. The type specimen measures 8 mm. in width and 5 to 6 mm. in height. The surface is ornamented with about 20 small tubercles. This species has characters which would not fit into any other genus, so that, although so little is known of it, Tornquist was quite justified in establishing a new genus for its reception. Lower Carboniferous, rare at Hunsriicken, Germany; holotype, in the Strassburg Museum Collection. HYATTECHINUS gen. nov. Test spheroidal or flattened; through the ambitus nearly circular; pentagonal or elongate through an axis passing through an ambulacrum and opposite interambulacrum, which I take to be the axis III, 5. Ambulacra wide, petaloid ventrally, narrow dorsally. Two columns of plates in each ambulacral area, plates relatively high and wide ventrally, lower and narrower 292 ROBERT TRACY JACKSON ON ECHINI. dorsally; pore-pairs uniserial. Interambulacra with in each area numerous (11 to 14) columns of thin, small plates, imbricating aborally and from the center laterally. Primordial interam- bulacral plates are in the basicoronal row; above this zone additional columns come in rapidly in succeeding rows, showing a very accelerated development. The peristome is small, with ten columns of ambulacral plates only. Oculars small, insert, covering the ambulacra, and in part the interambulacra on either side. Genitals are large and high. The apical disc is small. Periproct, as far as known, with many small, angular plates. The lantern is strongly developed and inclined, as in other Palaeozoic species. The type species is H. beecheri sp. nov. from the Waverly Group of Warren, Pennsylvania. This genus contains one of the most distinctive groups of known fossil Echini, remarkable alike for the specialized ambulacra and interambulacra. The latter attain the largest number of columns of plates known in the class, with a very accelerated development, yet all the plates are retained, since there is no ventral resorption of the corona, and ventrally one can read stages in development marked by the coming in of columns ; dorsally stages in senescence, as marked by the dropping out of columns, without a single break. The flattened form of rarispinus, the strongly pentagonal form of pentagonus and the bilaterally symmetrical form of beecheri mark these as specialized and highly unusual sea-urchins (p. 225). I take keen pleasure in naming this genus for the late Professor Alpheus Hyatt, one of the finest minds and finest natures that has graced science in this country, to whom I owe all that a pupil can owe to a master. Key to the Species of Hyattechinus. Test flattened, nearly circular, eleven to thirteen columns of plates in each interambulacral area H. rarispinus (Hall), p. 292. Test pentagonal, fourteen columns of plates in each interambulacral area H. pentagonus sp. nov., p. 295. Test clypeastriform, flattened on the base, bilaterally symmetrical through an ambulacrum and opposite interambulacrum, eleven columns of plates in each interambulacral area . . //. beecheri sp. nov. p. 297. *Hyattechinus rarispinus (Hall). Plate 21, fig. 6; Plate 22, figs. 1-8; Plate 23, figs. 1-7. Lepidechinus rarispinus (pars) Hall, 1868, p. 295, Plate 9, fig. 10; 1870 (revised edition), p. 340, Plate 9, fig. 10; (pars) Keyes, 1895, p. 192; (pars) Jackson, 1896, p. 226, Plate 7, fig. 42; (pars) Klem, 1904, p. 21; Lambert and ThieVy, 1910, p. 122. (See p. 290 and footnote, p. 394.) Lepidocentrus rarispinus Meek, 1874, p. 375. This interesting species is known from abundant material. The specimens are all internal or external sandstone molds, very flat, without distortion or separation of plates, which indi- cates that in life the test was much flattened, probably about as in the Recent Phormosoma, or Echinarachnius. Plates are extremely thin; they are for the most part wanting, but some HYATTECHINUS. 293 fragments of plates in Yale Museum specimens are only a small fraction of a millimeter in thickness. The test was nearly circular in outline but slightly elongated through an ambula- crum and opposite interambulacrum, as in Plate 22, figs. 1, 8, indicating a tendency to the bilateral symmetry which is more marked in H. beecheri (Plate 24, figs. 5-8). The ambulacrum is broad, petaloid ventrally, at its widest part twice the width of the same area at the mid- zone. Ambulacral plates are relatively high, especially ventrally, where one and one-half about equal the height of an adradial plate; dorsally about two and one-half equal the height of an adradial. This shows that the younger ventral plates are higher, which I believe is a more primitive character than that seen in the lower, later built dorsal plates. Pore-pairs are uniserial, in well marked peripodia, and each pair ventrally is on an angle, with the outer pore distinctly higher than the inner. Ambulacral plates bear small secondary tubercles only, and ventrally on the interior (Plate 23, figs. 2, 7) each plate bears a spinose projection that extends into the interior of the test. This spinose projection lies between the inner pore and the middle of the area; it is otherwise known amongst fossils in H. beecheri only, as here described, and amongst Recent Echini can be directly compared with the internal spines that I show in Phyllacanthus and Eucidaris (Plate 3, figs. 12, 13; p. 61). The interambulacra have from 11 to 13 columns of plates at the mid-zone, this range being shown in a single specimen in its several areas (Plate 23, fig. 3). The type specimen, however, (Plate 21, fig. 6), has 11 columns in each of the three areas preserved. The primordial inter- ambulacral plates are in place in the basicoronal row (Plate 23, fig. 1), and new columns come in rapidly, one, or sometimes two columns appearing in each row as added up to the ninth, but later columns may come in more slowly. Dorsally, the adambulacral or even additional columns drop out on approaching the apical disc, indicating senescence. The interambulacral plates bear a small eccentric primary tubercle with secondary tubercles (Plate 23, figs. 5, 6), to which are attached corresponding small spines. The peristome is covered with ten columns of ambula- cral plates only (Plate 23, fig. 1), much as they are in a Recent echinothuriid (text-fig. 43, p. 80). I (1896) first showed these rather imperfectly in rarispinus, and Mortensen thought it made a connection between the two genera, but I cannot agree with this view, as elsewhere disclosed (p. 213). The ocular, genital, and periproctal plates are unknown in this species, but they were probably similar to those of pentagonus. A powerful lantern is represented by molds of the parts (Plate 23, fig. 2) in several specimens. The pyramids are wide-angled, and therefore the lantern is inclined, as in other Palaeozoic types. Waverly Group, Lower Carboniferous, Meadville, Pennsylvania; the holotype (Plate 21, fig. 6; Plate 22, fig. 7) is from this locality, and is in the American Museum of Natural Hi-iory. no. 6,392. Same horizon, Warren, Pennsylvania; a superb series of ten specimens largely col- lected by the late Professor C. E. Beecher, is in the Yale University Museum nos. 324-333; another fine series of six specimens from the same locality is in the New York State Museum no. 1,799. 294 ROBERT TRACY JACKSON ON ECHINI. On account of the exceptional quality and interest of the material, some detailed discussion of the specimens is desirable. The type (Plate 22, fig. 7; Plate 21, fig. 6) is a fine sandstone mold of the dorsal portion of the test (p. 395). It has three ambulacra and interambulacra preserved, and its periphery coincides with the mid-zone. This was the only specimen of this species known to Hall, as his second specimen is considered here as belonging to a distinct species and genus, namely Lepidocentrus whitfieldi, p. 290. In this type specimen the ambulacra are narrow and the plates are relatively narrow and low, as it is a dorsal view. In each interambula- crum there are eleven columns of plates, the eleventh originating above the mid-zone as shown. In each interambulacral area the adambulacral columns drop out in passing dorsally, as a senes- cent character. As it is an external mold, the lettering is reversed from what it would be if seen from the interior (p. 21). The Yale Museum specimen shown in Plate 22, fig. 8, Plate 23, fig. 3, is also a sandstone impression of the dorsal side, but from Warren, Pennsylvania. Being an external mold, there- fore the lettering is reversed, and it is the most nearly complete dorsal area known. The ambu- lacra are narrow and plates relatively narrow and low. Interambulacra A and G have eleven columns of plates each. In area I there are twelve, and in C and E, thirteen columns of plates, thus showing considerable radial variation. In each area the adambulacral columns 1, 2 drop out dorsally, when columns 3, 4 assume an adradial position near the apical disc. Five radial depressed pits appear, seen best in Plate 22, fig. 8, which are evidently due to a forcing up of the test at these points when, in flattening, the lantern came in contact with the dorsal area. A remarkable specimen in the Yale Museum from Warren, Pennsylvania (Plate 22, figs. 1, 2; Plate 23, figs. 1, 2, 7) is one of the most interesting Echini that I have studied. As seen, the specimen consists of counterparts which structurally supplement each other. In one of these (Plate 22, fig. 1; Plate 23, fig. 1) we have for the most part an external sandstone mold of the ventral side, showing beautifully the impressions of ambulacral, interambulacral, and peri- stomal plates, with sutures, tubercles, and peripodia. With this there is in areas B, C, and imperfectly in D, an internal impression of the dorsal side, molded on the sand which filled the interior of the test. In the reverse counterpart (Plate 22, fig. 2; Plate 23, figs. 2, 7) we have in part in areas J, A, B, and C an external mold of the dorsal side showing tubercles, etc., but for the most part the specimen shows an internal impression of the ventral side molded upon the sand which filled the interior of the test. On this part there are no tubercles or peripodia, as it represents the proximal faces of the plates, but there are impressions of suture lines, pore- pairs, the spinose projections from the interior of ambulacral plates, and the lantern. Such a condition was rendered possible only by a complete solution of the calcareous parts leaving on one side an external and on the other an internal impression of these parts. Considering the structure, it is seen (Plate 23, fig. 1) that the ambulacral plates of the peristome pass directly into those of the corona, and the plates of the corona are as given in the description of the species. HYATTECHINUS. 295 In area B the ambulacral plates of the dorsal side are brought into almost immediate contact with those of the ventral side, superposing a narrower upon a wider plate. It is a similar con- tact which I think accounts for the so called roofing plates of Sollas (1899, p. 705) in Palaeo- discus, as elsewhere discussed (p. 251). In the internal view (Plate 23, figs. 2, 7) a series of slanting pits exists between the inner pore and middle of the ambulacrum and represents molds of the spinose processes, which extend into the test as described. The interambulacral areas all show the primordial plate in place as I earlier described it (1896, p. 226). This plate is directly comparable to the similar plate seen ventrally in Bothriocidaris, in the young of all other Echini, and in the adults of types where it has not been removed by resorption in the advance of the peristome. In the second row there are two plates in each area, and in the third row three plates in each interambulacral area (Plate 23, fig. 1). In the fourth row there are four plates, but in area E the fifth column is also represented by a plate in the fourth row, a case of extreme acceleration of development. Columns 6, 7, 8, 9 come in rapidly, a new one being added in each succeeding row as built. The mold of the lantern (Plate 23, fig. 2) shows casts of the five interradial alveolar cavities, each of which was surrounded by two half-pyra- mids, and also casts of the radial spaces between the half-pyramids seen best in areas B and D, which were originally occupied by the interpyramidal muscles. Evidently the lantern was inclined with the usual structure of the Palaeozoic lantern, as in Plate 27, figs. 4-6 (p. 22). Another specimen from the Yale Museum (Plate 22, figs. 3-6) shows certain differences from that just described. The figures 3 and 5 are external molds of the ventral side, with tub- ercles, spines, and peripodia. The figures 4 and 6 are external molds of the dorsal side of the same individual specimens, and also show the surface characters of tubercles, etc. A mold of the interior of the plates is shown in a small portion only of area J. In two areas of figure 4 and in a third area of the counterpart, figure 3, there are eleven columns of plates, as in tin- type specimen. The impression of ambulacral plates on the peristome is very clear in figure 3, and the mechanical displacement caused by the thrust of the lantern during flattening is clear in figure 4. This material was collected by my friend, the late Professor Beecher, near his old home at Warren, Pennsylvania. It is a pleasure to feel that his rare skill as a collector and preparator is still contributing to the science and the principles that he loved so well. *Hyattechinus pentagonus sp. nov. Plate 19, fig. 8; Plate 24, figs. 1-4; Plate 25, figs. 1-i. The material of this species is a slab with several exquisitely preserved specimens which Professor R. S. Breed kindly loaned me, and two additional specimens that I received through the same gentleman. 296 ROBERT TRACY JACKSON ON ECHINI. The test is relatively high, though far from spheroidal, and strongly pentagonal in hori- zontal outline, the apices of the pentagon coinciding with the ambulacral areas. It is the most markedly pentagonal of any known regular sea-urchin. The diameter in different specimens varies from 45 to 60 mm. The ambulacrum is petaloid ventrally, narrow dorsally, 6 mm. wide at the widest part of the petal, which is twice that of the same area at the mid-zone. Ambula- cral plates are wide ventrally, narrower dorsally, and ventrally somewhat higher than they are dorsally. Pore-pairs are uniserial, in peripodia, with ventrally the outer pore set somewhat higher than the inner pore of each pair. Interambulacra are very wide, with fourteen columns of plates in each area, the highest number yet known in Echini. The ventral surface is known in only one specimen (Plate 24, fig. 4; Plate 25, fig. 1), but this is very well preserved. It shows that the primordial interambulacral plate is in place in the basicoronal row in each area, two plates in the second row, and three in the third. In area A the fourth column appears in the fourth row, but in areas C, G, and I both columns 4 and 5 appear in the fourth row; and in area E, apparently (partially restored) columns 4, 5, and 6 appear in the fourth row. This is a degree of acceleration of development much ahead of that known in any other type, and may be correlated with the fact that the species attains more columns than are known in any other type. Columns 6 to 11 come in with great rapidity, as shown in the figure, one or more being added in succeeding rows as built. Turning to the dorsal view (Plate 24, figs. 1-3; Plate 25, figs. 3, 4), we see that the columns 13 and 14 come in later and with considerable intervals in the point of introduction, for, as usual in Hyatt's law of acceleration of development, its effect is most marked on the earlier added parts, the later differentiated structures not yet having come within its control. Dorsally, in this remarkable type, we find the dropping out of columns marking reversionary or senescent characters; this is shown in Plate 25, figs. 3, 4. The adam- bulacral columns 1 and 2 drop out, so that 3 and 4 become in further growth adjacent to the ambulacra; also some additional columns drop out, as 10 and 13 in figure 4. The exterior of the plates is marked by numerous closely set tubercles; but I did not distinguish any division into primary and secondary; rather all seem to be of the second class. The peristome is small, and as in H. rarispinus, is plated with ten columns of ambulacral plates only, which appears to be a character of the whole family. Small insert oculars cover the ambulacral areas and laterally in part the interambulacra on either side. Genitals are relatively large and high; no genital pores were recognizable in the sandstone impression. Impressions of a few small angular plates in the periproct show that it is of the usual Palaeozoic character. The lantern and in- ternal characters of the plates are not preserved in known specimens of this species. Waverly Group, Lower Carboniferous, Meadville, Pennsylvania, slab with the holotype in Alleghany College Collection; paratypes in Museum of Comparative Zoology Collection nos. 3,107 and 3,108. HYATTECHINUS. 297 *Hyattechinus beecheri sp. nov. Plate 24, figs. 5-8; Plate 25, fig. 5; Plate 26. This very remarkable sea-urchin is known from a single specimen, which is an internal sandstone mold, and bears the impress of the proximal faces of the plates only. The test is depressed, dome-shaped, flattened on the ventral aspect, elongate and bilaterally symmetrical through an ambulacrum and opposite interambulacrum, which I take to be the axis III, 5. The specimen is so perfect in form, without distortion or separation of plates, that it may be taken as representing the original shape. Excepting as shown somewhat in Hyaltechimis rarispinus, this is the only regular echinoid known with a central periproct, that presents a bilateral symmetry. The oblong form of the Echinometridae through an oblique axis does not represent a true bilateral symmetry. The specimen measures 26 mm. in height, 80 mm. in length through the axis III, 5, and 71 mm. in width through the peristome and at right angles to the longitudinal axis. While the mold represents only the impression of the interim- of the test, it is sufficiently perfect so that I am able to represent the specimen in Plate 26 spread out on the Lov6n method in which each plate was scrutinized with utmost care. At a few points in areas 3 and 4 details could not be made out, and in these areas in part the plates are restored as indicated by dotted lines. The breaks occurring in the figure at the ambitus are due to the mechanical requirements of getting over the edge in a specimen of this shape. Only one ambulacrum is filled in in detail dorsally, and for this the best area was selected. The ambulacra are broad and petaloid ventrally, being 13 mm. in width at the widest part, 9 mm. wide at the ambitus, and 6 mm. wide at about the middle of the dorsal side of the test. The plates are relatively wide and high ventrally, narrow and much lower dorsally. The pore-pairs are uniserial, situated at about the middle of each plate. This is a general character of the interior, and on the exterior they would doubtless have been much nearer to the inter- ambulacra on either side (compare Plate 20, figs. 9, 10). The outer pore of each pair ventrally is higher than the inner pore, as in other species of the genus. Between the inner pore and center of the area a slanting gash-like pit exists in each plate ventrally; these pits, being molds, represent elevated nodose spine-like processes which extended inward from the ambulacral plates (Plate 24, fig. 6), similar to those described in H. rarispinus (p. 293), and again, similar to. though less elongate than the spinose processes from the ambulacral plates of Eucidaris and Phyllacanthus (Plate 3, figs. 12, 13). Such spinose processes from ambulacral plates of the corona are known only in the types mentioned, but Sir Wyville Thomson and Mr. Agassiz described similar internal spines as given off from ambulacral plates of the peristome in Poro- cidaris (p. 61). The interambulacra are very broad, and make up the greater part of the test, as in all 298 ROBERT TRACY JACKSON ON ECHINI. species of the family. There are eleven columns of plates at the mid-zone in each area; a similar number is seen in some areas of specimens of H. rarispinus, but a greater number exists in H. pentagonus. The primordial interambulacral plates are in place in the basicoronal row in each area, as in other species of the genus. In the second row there are two plates, in the third row three, and in the fourth row four, these being the point of origin of their several col- umns. The fifth column originates in the fifth row in areas 1, 5, and 4, but in the sixth row in areas 2 and 3. Likewise the sixth column originates in the sixth row in areas 1, 5, and 4, but in the eighth row in areas 2 and 3. It is to be noticed that a bilateral symmetry is expressed by the rate of coming in of columns five and six; in both they originate a little earlier in the three posterior interambulacra than they do in the anterior two. Too much weight should not be attached to a single observation, but it is in direct accord with what I have found in the sym- metrical bilateral development of other structures in various regular Echini. Columns 7 to 11 come in very soon after the sixth, either in succeeding rows, or very nearly so, and the eleventh column is attained at or just above the ambitus in each area. Area 4 is imperfect and column 10 apparently originates far to the left of the center, as indicated in the restoration. Senescence is strongly marked by the dropping out of columns of interambulacral plates in this specimen ; the adambulacrals 1 and 2 in all areas excepting 4 drop out early, so that above that point columns 3 and 4 assume an adradial position. In addition, in area 2, columns 7, 11, 10, and 9 drop out passing dorsally, so that near the apical disc there are only five columns remaining, a structure which is a senescent reversion to a similar character seen as a stage in development in its own youth, and doubtless to the adult condition of some adult ancestral stock from which it was evolved. A similar dropping out of interambulacral columns more or less completely occurs also in the other areas. I would not point to it other than as a representative of the family, but it is noteworthy that Lepidocentrus rhenanus of the Devonian (Plate 20, fig. 7) has a slow, not an accelerated development, and has five columns of interambulacral plates in the adult. The peristome is small as in all of the family, and is evidently plated with ambulacral plates only (as in rarispinus), although in this specimen they are only partially preserved (p. 287). The apical disc is imperfectly known (Plate 25, fig. 5), but something can be gathered from the mold. The genitals are fairly clear and are high and wide. Spaces for the oculars exist, although the impress of these plates is not marked. They are restored to fill spaces between the genitals, thus making them all insert. The outline is preserved of a few small angular peri- proctal plates, and others are restored in the figure by dotted lines. A partial mold of the lan- tern orally shows that this structure existed, and was probably as in other species of the family (Plate 27, figs. 4-6). I take pleasure in naming this species in memory of my close friend the late Professor Charles Emerson Beecher, of Yale University, thus linking his name with Hyatt's in a species that is one of the most striking of known Echini. PHOLIDECHINUS. 299 This species, which I make the type of the genus, is represented only by the specimen described, which was collected by the late Dr. F. A. Randall in the Waverly Group, Lower Carboniferous, of Warren, Pennsylvania. Then it came into the hands of the late Professor Beecher, and by him was transferred to the Yale University Museum Collection. PHOLIDECHINUS gen. nov. Test high, spheroidal; ambulacra narrow throughout, with two columns of plates in each area. Plates low primaries, all alike, or at the mid-zone alternate plates slightly narrowed at the interambulacral contact; and nearly or quite cut off from that area by the marginal enlargement of their fellows. Pore-pairs are uniserial, or at the mid-zone slightly biserial. Ambulacral plates are thin, imbricate adorally, and bevel strongly under the adradials. Inter- ambulacra wide with many (nine to ten in the species known) columns of plates in an area; the plates are polygonal with very rounded outlines and imbricate strongly dorsally and laterally and over the ambulacrals. Both ambulacral and interambulacral plates bear only secondary tubercles and spines. The primordial interambulacral plates are in the basicoronal row, and succeeding columns come in with a slow, not an accelerated development. Peristome with ambulacral plates only, oculars unknown, genitals low, each with many pores. Lantern low, inclined. The type and only known species is P. brauni of the Lower Carboniferous. This genus differs from Lepidocentrus in that interambulacral plates bear secondary spines only instead of primary and secondary; also in that ambulacral plates at the mid-zone are not all alike and pore-pairs are not strictly uniserial as they are in Lepidocentrus. From Hyatt- echinus it differs in that the ambulacra are narrow throughout, instead of broad and petaloid ventrally, and the interambulacra have fewer columns of plates, without marked acceleration of development. *Pholidechinus brauni sp. nov. Text-fig. 207, p. 184; Plate 27, figs. l-<3; Plate 28, figs. 1-10; Plate 32, fig. 6. Of this striking type there is a considerable amount of excellent material. The test is high, spheroidal. In the holotype (Plate 27, fig. 1) the ambulacra measure 5 mm. in width at the mid-zone, and the interambulacra 19 mm. in width. From these measurements the circumference would be about 120 mm. and diameter about 38 mm. The two other specimens figured are somewhat larger. The ambulacra are narrow throughout, with two columns of plates, which are low, imbricating adorally, and laterally strongly beveled under the adambula- crals. The pore-pairs have well marked peripodia. Ventrally the ambulacral plates are pri- maries, all alike, with pore-pairs uniserial. Above this area and at the mid-zone alternate plates differ somewhat, one plate being a pure primary, but enlarged on its outer margin; the 300 ROBERT TRACY JACKSON ON ECHINI. next coincidently being narrowed on its outer margin and nearly or quite cut off from contact with the interambulacrum (Plate 28, figs. 5, 6). When quite cut off it becomes thereby occluded. Concurrently with this alternating difference the pore-pairs at the mid-zone are slightly biserial instead of purely uniserial as seen ventrally. The condition is quite comparable to that shown in Maccoya burlingtonensis (Plate 33, figs. 1, 2), and is interesting as a parallel taking on of a similar character in an independent family of Echini. The interambulacra in each area have nine or ten columns of plates which imbricate strongly aborally and from the center outward and over the ambulacrals. Each plate, instead of being angular, is so rounded in outline that each bounding edge represents very nearly the segment of a circle; the longest segment lies on the left of the plate in the left half-area and on the right of the plate in the right half-area (Plate 28, fig. 1). This longest segment is formed by the free edge of the plate itself. Three shorter segments of circles of the same arc occur on each plate, formed by the overlapping of neighboring plates on the inner side. The structure is much like that shown in text-fig. 32, p. 75. The middle column that imbricates laterally in two directions presents a long sweeping curve which surrounds the plate excepting for a second short curve on the adoral border where in contact with the next succeeding ventral plate of its series. The nearest thing to which the form of these plates can be compared, perhaps, is the scale of an ordinary teleost fish. In addition, a peculiar feature known in no other sea-urchin, is a very thin, delicate flange which bounds and is limited to the longest segment of the circle on each plate (Plate 28, fig. 9) . This flange therefore exists on the long curves on the left side of the left half-area, and on the long curves on the right-hand side of the right half-area. In the median column the flange borders the long curve, which nearly surrounds the plates of this column. The flange is so thin and delicate that it is usually lost by erosion, but it is found in exceptional cases, or in others the slight depression for its reception may be found, not in the plate to which the flange belongs, but in the next contiguous plates. Separated interambula- cral plates present a strong bevel toward the center and adorally as seen from above. As surface features, ambulacral and interambulacral plates alike have many secondary tubercles which support small acicular spines. There are no tubercles on the flanges described. The peristome has ten columns of low, wide plates which alone cover the area. Ocular plates are not known, but low, wide genitals exist (Plate 28, fig. 10), each of two preserved having eight genital pores. A typical Palaeozoic lantern exists as described below. This species is named for Mr. Frederick Braun of Brooklyn, New York, an ardent and skilful collector, who helped me greatly with the loan of his choicest material. Keokuk Group, Lower Carboniferous, Crawfordsville, Indiana, Museum of Comparative Zoology Collection (five specimens, 3,109-3,114, including the holotype no. 3,109); F. Braun Collection; American Museum of Natural History; British Museum of Natural History Col- lection E 10,678 (a specimen given by me, the original of Plate 27, fig. 3; Plate 28, figs. 4-6); Yale University Museum Collection 321 and 322 (two very complete lanterns). PHOLIDECHINUS. 301 In the holotype (Plate 27, fig. 1 ; Plate 28, figs. 2, 3, 9) there are nine columns of inter- ambulacral plates in each area at the mid-zone, but a tenth appears dorsally in areaC. The beveling of plates is seen below the initial plate of column 8, some spines are in place, and the delicate flanges described as bordering the plates are well preserved. In Mr. Braun's specimen (Plate 27, fig. 2; Plate 28, fig. 1) there are nine columns of plates at the mid-zone in_ each interambulacral area. The primordial interambulacral plates are in place in the basicoronal row, two plates in the second, three in the third, and four in the fourth row, above which additional columns come in with a moderate, not an accelerated rate of development. Low, wide ambulacral plates cover the peristomal area, and the teeth are in place. The British Museum specimen (Plate 27, fig. 3; Plate 28, figs. 4-6) has ten columns of plates in each interambulacral area, in both originating at or below the mid-zone; ambula- cral detail at the mid-zone is clear. In Yale University Museum there are two lanterns in the D. A. Barrett Collection from Crawfordsville belonging to this species, which are remarkably perfect in preservation, being the best specimens of this structure so far known in any Palaeozoic echinoid. One of these specimens I mentioned in my earlier paper (1896, p. 213), but they have not been described. The two are essentially similar except that one is laterally compressed. The more perfect speci- men is shown in Plate 27, figs. 4-6, and in its relations to the lanterns of other representative Echini in text-fig. 207, p. 184. It is important in itself, also because it is typical of all lanterns known from the Palaeozoic formations, others known differing from it only in trifling details. In side view with teeth in place (Plate 27, fig. 6) it is inclined at a very wide angle of about 90 degrees, the width of the top being very nearly twice the total height from the tips of the teeth. This wide angle,' which I have described as inclined, is characteristic of all Palaeozoic lanterns, also of the lanterns of young modern regular Echini. The teeth are grooved, meet in a point ventrally, and dorsally extend to a point just above the base of the foramen magnum, so that they are seen in side view. This is evidently the dorsal limit of the calcified portion of the tooth, beyond which the uncalcified portion would doubtless extend in life as in Strongylocentrotus (Plate 5, figs. 6, 9). The pyramids are very wide-angled, with a rather shallow foramen mag- num. Hollows are on either side of the face view, in which the retractor muscles took origin ; the sides of the pyramids are curved, admitting of relatively long interpyramidal muscles. The lateral wings of the pyramid are wide, as in Oligoporus (Plate 50, fig. 11), a resultant of the inclined angle of the lantern. A narrow epiphysis caps each half-pyramid, seen in face view (Plate 27, fig. 6), and in dorsal view (Plate 27, fig. 5), it extends inward, narrowing toward the oesophageal cavity. A typical brace rests on and interlocks with the two adjacent epiphyses as shown in ventral, side, and dorsal views. The brace has the usual condyles and other out- lines of modern regular Echini. In one area, D, of figure 5, a compass exists, slightly displaced, and apparently fragments of two other compasses in areas B and J. The compass is arched M02 ROBERT TRACY JACKSON ON ECHINI. as usual, but shows no bifid distal end; probably it was worn off, but possibly no bifid tip existed, as in some Recent Echini. In the ventral view (Plate 27, fig. 4) the lantern is in part covered with the ambulacral plates of the peristome, which alone fill this area in the species and the family. It is interesting to see how near the lantern of this ancient type is to the character of the lantern in young modern regular Echini, as discussed (p. 181), the similarities being in the inclined angle, shallow foramen, and wide spaces for long interpyramidal muscles. Family PALAEECHINIDAE M'Coy. Pdaechinidae M'Coy, 1849, p. 253; Lambert and ThieVy, 1910, p. 119. Palaeechinidae (pars) Loven, 1874, p. 40. Melonitidae (pars) Zittel, 1879, p. 484; (pars) Duncan, 1889a, p. 15; Jackson, 1896, p. 239. Archaeocidaridae (pars) Duncan, 1889a, p. 8. Melonechinidae Lambert, 1899a, p. 53; Lambert and Thiery, 1910, p. 119. Melechidae Lambert and Thiery, 1910, p. 120. Test high, spheroidal, elliptical, or obovate; ambulacra narrow or wide, with from two to twelve columns of plates in each area at the mid-zone. Two pores to each plate, situated in a peripodium. Pore-pairs uniserial, biserial, or multiserial. Interambulacra wide or rarely narrow, with from three to eleven columns of plates in each area at or dorsal to the mid-zone. Plates moderately to very thick, not imbricating, but ambulacral plates bevel over the adradials on the marginal sutures. The base of the corona is resorbed so that there are two plates in the basicoronal row in each interambulacral area, instead of one plate as in the Lepidocentridae. Tubercles and spines are secondaries only, on all plates of the corona, a feature pointed out by M'Coy. Peristome (known only in Melonechinus, Plate 56, figs. 7, 8) with many rows of ambulacral and some interradially situated non-ambulacral plates. The apical disc is small, the diameter in the specimens measured being about 13 to 25 % of the diameter of the test, usually it is proportionately smaller than in most Recent regular Echini (pp. 87, 104). Ocu- lars are insert, or rarely one or more to all may be exsert without pores as seen from the exterior. Genitals large, high, with from two to five pores each; a madreporite is rarely recognizable. Periproct with many angular plates. Lantern inclined, rarely preserved, but as far as known, with the typical character of the Palaeozoic. The characters of the ambulacra at the mid-zone are the essential basis for the division of this family into genera and in part into species. The characters of the genera in brief are given in the key (p. 207), and their phylogenetic relations are set forth in the systematic table (p. 209) and in text-fig. 237, p. 231. (See pp. 82, 362, 414.) The family Palaeechinidae was formed by M'Coy (1849) to include Palaeechinus and Melonechinus, the only genera then known. He defined the group clearly, but his earlier name has largely given place to Zittel's name Melonitidae. M'Coy's genus Palaeechinus included species that have since been generically divided with some resulting confusion, and some new types are generically different from any species known to M'Coy; therefore it is necessary at this place to give the history of the subject. PALAEECHINIDAE. 303 Pomel (1869, 1883), the first reviser, included in Palaeechinus those species in which am- bulacral plates are all primaries and pore-pairs are uniserial, and listed as belonging to this genus P. quadriserialis Wright, P. elliptic™ M'Coy1, and P. elegans M'Coy. Duncan (1889a, p. 3) objected to Pomel's methods and would not accept his genera. I sympathize with his feeling, but cannot see that this is any reason for rejecting Pomel's names. Duncan (1889, p. 205) referred species with this structure (plates all primaries and pore-pairs uniserial) to the genus Rhoechinus of Keeping, which was a mistake, as Rhoechinus (here, p. 394, considered a synonym of Lepidechinus Hall) has imbricate plates, thus differing essentially from Palaeechinus.2 Pomel (1869, 1883) further proposed Maccoya as a genus to include species in which am- bulacral plates are alternately enlarged and reduced toward the exterior border, from which result two vertical series of pore-pairs in each half-area. Expressed in other words, the genus Maccoya is characterized by ambulacral plates, all of which reach the middle of the area, but which are alternately primaries and nearly or quite occluded according as they extend to the interambulacrum or not, and with pore-pairs biserial. Pomel's type of this genus is Maccoya gigas (M'Coy), and his observation (1883) was probably based on Baily's (1874, Plate 3, fig. c) figure which is here reproduced as Plate 47, fig. 2. He also and quite correctly included in his Maceoya the Palaechinus burlingtonensis Meek and Worthen and P. gracilis Meek and Worthen. Pomel's (1883) Eriechinus with Palaechinus sphaericus M'Coy as a type (?)3, and his Wrightia (1869) (or Wrightella, 1883), with Palechinus phillipsiae Forbes as a type I do not recognize as distinct from Maccoya, because in both the true sphaericus and phillipsiae the ambulacral details and other structures as known are essentially the same as in Maccoya. In brief, I include in Maccoya the species burlingtonensis Meek and Worthen, intermedia Keeping, phillipsiae Forbes, sphaerica M'Coy (but not the sphaericus of Koninck3), gigas M'Coy, and gracilis Meek and Worthen (p. 312). Duncan in his (1889) discussion included in his Palaeechinus part of the species here referred to Maccoya and two species here referred to Lovenechinus. In his Palaeechinus he included P. gigas (p. 304), P. sphaericus, P. ellipticus1, P. intermedius, P. phillipsiae, and suggested, quite correctly, that the two North American species (P. burlingtonensis and P. gracilis) belong in the same generic group. Duncan's (1889) Palaeechinus ellipticus is not the Palaeechinus ellipticus of M'Coy as stated. 1 Palaeechinus ellipticus M'Coy (p. 307, Plate 29, fig. 2; Plate 30, fig. 10) belongs in this genus, as stated by Pomel but the specimen in the Museum of Practical Geology, figured by Duncan (1889, p. 206, fig. viii) as ellipticua is not that species, but is here referred to Lovenechinus lacazei (p. 329, Plate 36, fig. 1). * Professor Duncan included in his Rhoechinus, R. irregularis Keeping (here referred to Lepidechinus, p. 396) ; R. elegans (M'Coy); R. quadriserialis (Wright); R. sp., a specimen in the Woodwardian (now called Sedgwick) Museum. Cambridge, England. See footnote p. 394. 8 Pomel's (1883) Eriechinus was evidently based not on M'Coy's sphaericus but on de Koninck's (1869, 1870) figure of what he called Palaechinus sphaericus. Pomel says of his genus that it differs by the structure of the apex, one of the genitals having only a single pore, and this structure is that shown by de Koninck. De Koninck's observations were incorrect, and his specimen was not Palaechinus sphaericus M'Coy, but is -here referred to Lovenechinus lacazei (Julien), where it is fully described (p. 330-334, text-figs. 240-243; Plate 35, fig. 7). 304 ROBERT TRACY JACKSON ON ECHINI. The Palaechinus gigas M'Coy (Plate 46, figs. 1, 2; Plate 47, fig. 2) is referable to Maccoya (p. 321); but Duncan's (1889, p. 206, fig. 1) Palaeechinus gigas is doubtless based on the specimen in the Museum of Practical Geology which is here referred to Lovenechinus anglicus sp. nov., as shown on p. 346; Plate 46, figs. 5, 6; Plate 47, figs. 3-5. The new genus Lovenechinus has four columns of plates in each ambulacral area at the mid-zone, two columns of demi-, and two of occluded in each half-area, but without isolated plates; the pore-pairs are biserial. This genus includes Palaechinus lacazei Julien, Oligoporus mutatus Keyes, 0. nobilis Meek and Worthen, 0. missouriensis Jackson, and the two new species anglicus and septies (p. 326). The genus Oligoporus Meek and Worthen is here used in a restricted sense to include species with four columns of ambulacral plates at the mid-zone, two columns of demi-, and two of occluded plates in each half-area, but with, in addition, scattered isolated plates in the middle of each half-area; pore-pairs are multiserial. This is a structural advance on Lovenechinus, and yet not an attainment to the character of Melonechinus. This genus includes Oligoporus blairi Miller and Gurley, 0. coreyi Meek and Worthen, 0. sulcatus Miller and Gurley, 0. halli sp. nov., and 0. danae Meek and Worthen (the type), (p. 351). Norwood and Owen's genus Melonites, now called Melonechinus Meek and Worthen, includes species of the family in which at the mid-zone there are from six to twelve columns of plates in each ambulacral area consisting of demi-plates, occluded plates, and one to four more or less irregular columns of isolated plates in each half-area. This genus represents the final stage of differential evolution in the family, and the species are based largely on the number of columns of ambulacral plates which they attain. There has never been any question as to what species should be included in this genus, and it is unnecessary to enumerate them (p. 364). Pomel's (1883) genus Xystria was based on Palaechinus (?) konigii, and is here considered under Incertae Sedis (p. 450). PALAEECHINUS M'Coy. Palaechinus (pars) M'Coy, 1844, p. 171; Pomel, 1883, p. 114; (pars) Lambert and Thiery, 1910, p. 119. Palaeechinus (pars) Loven, 1874, p. 40 (non Palaeechinus Duncan, 1889, p. 204; 1889a, p. 13, see above pp. 303, 304). Rhoechinus (pars) Duncan, 1889, p. 205; 1889a, p. 14 (non Rhoechinus Keeping, 1876, for which see Lepidechinus, p. 294); (pars) Jackson, 1896, pp. 200, 239; (pars) Tornquist, 1897, p. 754; (pars) Klem, 1904, p. 27; (non Rhoechinus, Lambert and Thie"ry, 1910, p. 122). Palechinus Tornquist, 1897, p. 735. Test spheroidal or elliptical, ambulacra narrow, with two columns of plates in each area. Ambulacral plates are all primaries alike throughout the area, pore-pairs uniserial. Interam- bulacral areas wide, with from four to six columns of plates in an area at or above the mid- zone, two plates in the basicoronal row in each area. Peristome unknown; oculars insert, PALAEECHINUS. 305 imperf orate, at least externally; genitals wide, high, each with from two to five genital pores; periproct plated with many small angular plates; lantern unknown, but doubtless as in other genera of the family. (See pp. 82, 191.) Type species, as selected by Lambert and ThieYy (1910, p. 119), P. elliplicua M'Coy, of the Lower Carboniferous of Ireland. This genus includes only part of the species referred to it by M'Coy, and the succeeding history is given under discussion of the family. Duncan (1889a, p. 14) referred the genus (which he called Rhoechinus) to his family Archaeocidaridae because there are two columns of ambulacral plates, but in this he showed an entire lack of appreciation of other characters, which unquestionably associate the genus with the Palaeechinidae not the Archaeocidaridae. Structurally this genus is the most primitive member of the Palaeechinidae because its ambula- crum is like that found in the young, as a developing stage, in the next three genera of tin- family; also it is comparable to the young plates seen dorsally as a localized stage in all other genera of the family as set forth diagrammatically in text-figure 237, p. 231. Key to the Species of Poloeechinus. l Four columns of plates in each interambulacral area, test elliptical . P. quadriserialis Wright, p. 305. Five columns of plates in each interambulacral area, test elliptical . . P. ellipticus M'Coy, p. 307. Five columns of plates in each interambulacral area, test spheroidal . . P. elegant M'Coy, p. 308. Five or usually six columns of plates in each interambulacral area, test nearly or quite spherical P. (?) minor sp. nov., p. 310. "Palaeechinus quadriserialis Wright. Text-fig. 217, p. 191; Plate 29, fig. 1; Plate 30, figs. 1-7. Palaechinus quadriserialis Wright, 1865, pp. 62, 63, and 88, 89, Plate 3, figs, la-lc; Pomel, 1883, p. 114; Lambert and Thiery, 1910, p. 119. Palaechinus ellipticus Daily, 1865a, p. 217; 1865c, p. 65-67, and 88, Plate 3, figs. 2a, 2b; Quenstedt, 1875, p. 380, Plate 75, fig. 42; (non Palaeechinus ellipticus Duncan, 1889, see Loventchinus lacazci this memoir, pp. 326, 329, Plate 36, figs. 1, 3). Palaeechinus ellipticus (pars) Loven, 1874, p. 41. Palaeechinus quadriserialis Loven, 1874, p. 41. Rhoechinus quadriserialis Duncan, 1889, p. 205; Tornquist, 1897, p. 755; Klem, 1904, p. 30. Rhoechinus quadrangularis (by clerical error) Jackson, 1896, table facing p. 242. 1 A number of species which have been referred to the genus Palaeechinus but not known well enough to intercalate in the systematic series, or species of which no description has been published, are taken up later. These are Palaechinus (?) • konigii M'Coy, Palaeechinus (?) regnyi nom. nov. ( = P. konincki Julien), Palaechinus robineti Julien, and Rhoechinus sp. (used in the sense of Palaeechinus), considered under Incertae Sedis, p. 450. Also Palaechinus agassiri, P. carpenleri, P. loveni, all of Dollo and Buisseret, considered under Nomina Nuda, p. 457; and Palaechinus sp. Mitchell, considered under Palaeozoic Forms Incorrectly Referred to Echini, p. 458. 306 ROBERT TRACY JACKSON ON ECHINI. The test is high .elliptical; according to Wright, the type measures 51 mm. in height and 38 mm. in diameter. The British Museum specimen measures about 42 mm. in height and about 34 mm. in diameter through the mid-zone. The ambulacra measure 4.5 mm. in width near the mid-zone, and the interambulacra 17 mm. in width. The ambulacra are narrow with two columns of low plates in each area, all of which meet the middle of the area and the interambulacrum ; about five ambulacral plates equal the height of an adambulacral; pore-pairs are uniserial. Ambulacral plates bevel over the adradials on the marginal sutures. The interambulacra are wide with four columns of plates at the mid- zone in each area. There are two plates in the basicoronal row, above which the added columns come in early, and there is no loss of parts by senescent growth dorsally. Plates of the test are moderately thick, bearing numerous secondary tubercles only; spines are not known. Oculars are all insert, imperforate, and cover the ambulacra and laterally in part the inter- ambulacra on either side. Genitals are high and wide, each known having three genital pores. This species is similar to ellipticus in form, but differs in having four instead of five columns of interambulacral plates. It is also a much smaller species. Baily (1865a, 1865c) described a specimen of this species as P. ellipticus, as he felt that the difference in the number of inter- ambulacral columns did not entitle it to specific distinction. A difference in the number of interambulacral columns is a valid differential character, and I think these two species should be maintained. Baily's use of ellipticus for quadriserialis was quoted by Loven, and his figure was copied by Quenstedt as given in the synonymy. Lower Carboniferous Limestone, Middleton, County Cork, Ireland. This is the locality of the type, but I do not know where the specimen is; the specimen figured by Baily is from Betty ville, near Crome, County Limerick, Ireland; the specimen in the British Museum Col- lection E 193 is from Rathkeale, County Limerick, Ireland; Hook Head, Ireland, Museum fur Naturkunde, Berlin, a cast of this specimen is in the Museum of Comparative Zoology Collection 3,117. The British Museum specimen of this species is well preserved, so that it is represented spread out by the Lov6n method in Plate 30, fig. 3. It agrees entirely with Wright's descrip- tion and excellent figures of the species. It is preserved without distortion and free from all matrix. In parts the plates are in place, as shown in Plate 30, figs. 1, 3, 4, and at these parts the tubercles are shown. Much of the rest is preserved as an internal mold of the plates by the filling matrix, and in the figures is represented in simple outline; again, part is restored as indicated by dotted lines. There are two plates in the basicoronal row in each interambula- crum and three plates in the second row. In all areas excepting C the initial plate of column 3 is hexagonal as usual, as it is in contact with the initial plate of column 4. But in area C the initial plate of column 3 is pentagonal, as the initial plate of column 4 is in the second row above, instead of the next row. Column 4 originates in the third row in four areas with a pentagonal PALAEECHINUS. 307 plate that impinges on the initial plate of column 3, and in virtue of its one side lacking, a com- pensating side is added to this plate making it hexagonal (p. 68). In area C, however, column 4 originates in the fourth row, with the result that the plate on its ventral border is heptag- onal (partially restored as indicated by dotted lines), and the initial plate of column 3 is pen- tagonal. A similar case is shown in area C of Lovenechinus septies (Plate 45, fig. 1) but it is of rare occurrence, as column 4 almost always originates in the next row after column 3. Column 4 originates on the right of the center in areas A, C, and I, but on the left of the center in areas E and G, with some consequent readjustment of plates (compare Archaeocidaris, Plate 9, figs. 6-8;" text-fig. 239 bis, p. 264). Above the fourth row no new columns are added, but all four columns extend to the apical disc where the youngest plates on either side are in contact with the oculars. Two oculars are in place, are widely insert, and imperforate. The three gcnitiils are high, wide, and have each three genital pores. All bear secondary tubercles as shown in Plate 30, fig. 4, in which the absent plates are restored, as indicated by dotted lines. I am under obligation to Dr. Bather for the photograph of this specimen which is repro- duced on Plate 29, fig. 1. *Palaeechinus ellipticus M'Coy. Plate 29, fig. 2; Plate 30, figs. 8-10. Palacchinus ellipticus M'Coy, 1844, p. 172, figs. 3a-3d; Desor, 1858, p. 158; (?) Tornquist, 1893, p. 103; (pars) Klem, 1904, p. 31; Lambert and Thiery, 1910, p. 119. Echinocrinus ellipticus d'Orbigny, 1849, p. 126, text-fig. 278. Palaeocidaris (Echinocrinus) ellipticus Vogt, 1854, p. 332, text-figs. 212-214. Non Palai'chinus ellipticus Baily, 1865a, p. 217; non 1865c, pp. 65-67, Plate 3, figs. 2a, 2b; non Quenstedt, 1875, p. 380, Plate 75, fig. 42.1 Palaeechinus ellipticus (pars) Loven, 1874, p. 41. l Non Palaeechinus ellipticus Duncan, 1889, p. 200, text-fig, viii; (see p. 308, and this memoir, pp. 326, 329, where Duncan's specimen is referred to Lovenechinus lacazei). Non Palechinus ellipticus Torncaiist, 1897, p. 739; non Maccoya ellipticus Lambert and ThieVy, 1910, p. 119 (both of these names are based on Duncan's 1889, p. 200, text-fig, viii, Pnlncfi-hinux ellipticus, here referred to Lovenechinus lacazei as above stated). The test is high and elliptical, 51 mm. high, 41 mm. in diameter, width of the ambulacrum at the mid-zone 4 mm., width of the interambulacrum 22.5 mm. About seven and one-half ambulacral plates equal the height of an adambulacral. The observations were made on M'Coy's type specimen in Dublin, which I studied through the kindness of Dr. Scharff, who also kindly supplied me with a cast and the photograph here reproduced. The ambulacra are narrow, composed in each area of two columns of low plates, all of which 1 These several references to Palaeechinus ellipticus as a synonym are in regard to a specimen that Baily described as that species but is here referred to P. quadriserialis (pp. 305, 306). 308 ROBERT TRACY JACKSON ON ECHINI. are primaries, meeting the middle of the area and the interambulacral areas. The pore-pairs are uniserial (Plate 30, fig. 10). M'Coy was quite correct in describing the ambulacral struc- ture as he did, and Duncan (1889, p. 200, text-fig, viii) was mistaken when he claimed for this species the structure of four columns of ambulacral plates and a biserial arrangement of pores in an area. Duncan's specimen is in the Museum of Practical Geology Collection 16,301 ; it has no connection with Palaeechinus ellipticus, and is here described as Lovenechinus lacazei (footnote p. 303; p. 329, Plate 36, figs. 1-3). The interambulacrum of ellipticus has five columns of plates at the mid-zone, as shown in two areas of the type; the adambulacral plates are pentagonal, the others hexagonal. In one area (Plate 30, fig. 8) there are two plates in the basicoronal row, three in the second, four in the third, and five in the fifth row. Ambulacral and interambulacral plates alike have numerous secondary tubercles. The holotype is the only specimen of the species known to me, and the numerous figures in text-books are taken from M'Coy's original figures, since when it has not been published from direct observations. This species is the type of the genus as selected by Lambert and Thiery (1910, p. 119). Lower Carboniferous, Millicent, County Clare, Ireland; holotype in the Griffith Col- lection, Science and Arts Museum, Dublin; a cast of this specimen is in the Museum of Comparative Zoology Collection 3,115. The specimen referred to Palaeechinus ellipticus by Baily (1865a, 1865c) and by Quenstedt who copied Baily's figure, has four columns of interambulacral plates, and is here referred to Palaeechinus quadriserialis. The specimen referred to P. ellipticus by Duncan (1889, p. 200) is here referred to Lovenechinus lacazei (p. 329) as above stated. *Palaeechinus elegans M'Coy. Text-figs. 9, p. 54; 15, p. 59; 237, p. 231; Plate 29, figs. 3, 4, 6; Plate 30, fig. 11; Plate 31, figs. 1-5. PalaecUnus elegans M'Coy, 1844, p. 172, Plate 24, figs. 2a-2d; Roemer, 1852-'54, p. 287, Plate 4, figs. la-Id; Desor, 1858, p. 158; Baily, 1865, pp. 44, 45; 1865b, pp. 63-65, and 67, Plate 4, figs. A-E; Quenstedt, 1875, p. 380, Plate 75, figs. 39, 43; Baily, 1875, p. Ixviii, Plate 36, figs. 1 la-lid; A. Agassiz, 1892, p. 73, Plate 29, fig. 2; Tornquist, 1893, p. 103; Lambert and Thiery, 1910, p. 119. Palaeechinus elegans Loven, 1874, p. 41. Palaechinus [elegans] Etheridge, 1874, p. 311, Plate 3, fig. 3. Rhoechinus elugans Duncan, 1889, p. 205; Jackson, 1896, table facing p. 242 (but not text-fig.l, p. 205, and not Plate 7, fig. 401); Tornquist, 1897, p. 757, Plate 21, figs. 6, 7; Klem, 1904, p. 28; Fraipont, 1904, p. 10, Plate 2, fig. 9. I had the opportunity to study M'Coy's type of this species and also other good specimens as described in some detail below; from all of these the species description is made up. Test 1 These figures are referable to Maccoya intermedia, see p. 314. PALAEECHINUS. 309 spheroidal, in the type somewhat crushed, but it measures about 55 mm. in width, the ambula- crum at the mid-zone is 5 mm. in width, the interambulacrum 24 mm. in width. The ambulacra are narrow with two columns of low plates in each area. The plates are all primaries, meeting the interambulacra and the middle of the ambulacra throughout the areas; pore-pairs uniserial. Five or six ambulacral plates equal the height of an adambul- acral. There are five columns of interambulacral plates at the mid-zone in each area in all specimens seen. The ventral portion of the test unknown, but it is doubtless similar to that of Palaeechinus quadriserialis, Plate 30, fig. 3. Ambulacral and interambulacral plates with numerous secondary tubercles which bear small spines, swollen at the base, tapering to the tip, all of similar size and measuring about 1.1 mm. in length. Oculars are insert, imperforate (not with two pores as described by Baily) ; genitals are wide, high, with three or more genital pores each. The periproct in the type is remarkably well preserved, with many small angular plates like those of modern cidarids. The apical disc and periproct figured by Baily (1865b, Plate 4, fig. B) were freely and in some respects incorrectly restored (p. 363). Lower Carboniferous, Hook Head, County Wexford, Ireland; slab with two specimens including the holotype in the Griffith Collection, Science and Arts Museum, Dublin; a cast of this specimen is in the Museum of Comparative Zoology Collection 3,116; same locality, Museum of Practical Geology, London, 6,580; Putig, Germany (Tornquist); Marbre Noir de Dinant, Belgium (Fraipont). The most nearly complete specimen known is M'Coy's type, which is one of two specimens of this species on a slab in the Dublin Museum. I had the pleasure of studying it there and in addition, Dr. Scharff had the great kindness to bring it with him to America in order to give me further opportunity for inspection. Besides the two specimens of Palaeechinus ekgans, this choice slab bears a specimen of Perischodomus biserialis (Plate 29, fig. 5). Baily (1865b, p. 63) in his observations says that there are three specimens of Palaeechinus ekgans, but this is a mistake, the specimens being as stated. One of the specimens of P. elegans is better than the other, and is the basis of M'Coy's and Baily's observations. Ambulacra D and J extend directly to the oculars, and F is preserved in part. The ambulacra bevel over the adambul- acrals laterally (Plate 31, fig. 3). Interambulacrum E is the most nearly complete and shows five columns of plates, but dorsally, column 5 (Plate 31, fig. 4) drops out before reaching the apical disc. The surface of the plates is in part worn, but I have shown the small secondary tubercles in the parts where such occur. Interambulacra E and I (Plate 31, fig. 4) evidently have each five columns of plates, although one of the adradial columns is partially wanting in each of these areas. Dorsally four oculars are in place, but ocular F is imperfect and not shaded in the figure. The oculars are all insert, covering the ambulacra and laterally in part the interambulacra on either side. The oculars are imperforate, and Baily's (1865b, Plate 4, fig. B) figure showing two pores in each plate was a mistake. I cannot see how it occurred. 310 ROBERT TRACY JACKSON ON ECHINI. It has proved unfortunate as Baily's figure has been extensively copied as a typical apical disc for the Palaeozoic. The genitals are high and wide; E and G have each three pores, but C apparently has four pores and A has five genital pores as seen in Plate 29, figs. 3, 6. By over- sight, in Plate 31, figs. 1 and 4, only three instead of five pores are shown in genital A. A number of periproctal plates are in place, they are polygonal in outline, and doubtless filled the area, as shown by Baily in his reconstruction (pp. 89, 173). The second specimen on this slab is much less complete, but shows two columns of ambulacral plates in an area with pore-pairs uniserial, also five columns of plates in one interambulacral area. In the specimen in the Museum of Practical Geology (Plate 30, fig. 11; Plate 31, fig. 5) there are two columns of plates in each ambulacral area with pore-pairs superposed, and five columns of plates in an interambulacral area. A number of spines are in place, as described above, and these are of interest as the only ones yet known in the genus. The specimen from Dinant, Belgium, figured by Fraipont, is of about the same size as the type, and has five columns of plates in each interambulacral area. *Palaeechinus (?) minor sp. nov. Plate 29, figs. 7, 8; Plate 31, fig. 6; Plate 32, fig. 7. The specimens of this species are all internal sandstone molds, so that surface characters are unknown. Test nearly or quite spherical. The holotype (Plate 29, fig. 7) measures 36 mm., in height, and 35 mm. in diameter, but it is somewhat distorted. The Museum of Comparative Zoology's specimen (Plate 29, fig. 8) is perfect in form and measures 37 mm. both in height and diameter through the mid-zone. It is one of the very few Echini which have been found to be actually spherical. The ambulacra are narrow with two columns of low plates in each area. About five am- bulacral plates equal the height of an adambulacral ; pore-pairs are uniserial. While this species is apparently a Palaeechinus, it must be remembered, as I have shown (p. GO), that in Maccoya the plates on the proximal side are all primary in character and pore-pairs are uniserial, while on the external or distal side of the same plates the character is primary, and occluded plates and pore-pairs are biserial (Plate 33, figs. 4, 5, 7, 8). As the views of P. minor are all molds of the interior, it may therefore later prove that the species is really referable to Maccoya, but whichever the genus, the interambulacral features entitle it to specific separation from other species of Palaeechinus and from known American forms of Maccoya. In the holotype there are six columns of interambulacral plates in an area (Plate 31, fig. 6). The figure (partially restored ventrally as shown by dotted lines) is made up from two areas. Dorsally columns 6 and 3 drop out, indicating senescence, and a full grown specimen. The oculars are all insert, and genitals are high, with three pores each. MACCOYA 311 In the Museum of Comparative Zoology's .specimen (Plate 29, fig. 8) there arc six columns of plates in four interambulacral areas, but only five columns in one area. Oculars are all insert. The apical disc measures 8 mm. in diameter equaling about 21% of the diameter of the test. This is relatively larger than in adults of most species of the family, but is tin- same proportion as in the young of Lovenechinus missouriensis (p. 342). In Mr. Kirk's speci- men (Plate 32, fig. 7) there are six columns of plates in all five interambulacral areas. This species is the only one in America at present referable to Palaeechinus proper. Base of the Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype, University of Chicago Collection 9,054; paratypes, Museum of Comparative Zoology Collec- tion 3,051; E. Kirk Collection, one specimen; F. Springer Collection, two specimens. MACCOYA Pomel. MacCoya Pomel, 1869, p. xlvi. II 'riyhtia Pomel, 1879, p. xlvi (printed by error \Vrigthia); Pomel, 1883, p. 115; non Agassi/, 1M>2, A<-;ili-|>h-. Discophora, p. 354. Maccoya Pomel, 1883, p. 115; (pars) Lambert and Thidry, 1910, p. 119. Wrightella Pomel, 1883, p. 115; Lambert and Thie'ry, 1910, p. 120. Non Ericchinus Pomel, 1883, p. 114 (see footnotes, pp. 303, 312, 326). Non Typhlcchinus Neumayr, 1889, p. 362, text-fig. 82e; 1890, p. 85 (sec footnotes, pp. 312, 32li). hilacechinus (pars) Duncan, 1889, p. 205; 1889a, p. 13; (pars) Jackson, 189(5, pp. 200, 2:5!) (*«•<• this memoir, p. 303). Palafchinvs (pars) Klem, 1904, p. 31; (pars) Lambert and Thiery, 1910, p. 119. Palcchinus (pars) Tornquist, 1897, p. 735. The test is spheroidal, ambulacra are narrow, composed of two columns of plates in each area, all plates meet the middle of the area, but at the mid-zone alternate plates are primal -u>, meeting the interambulacral areas and enlarged marginally, while the plates between are nar- rowed laterally and are nearly or quite cut off from contact with the interambulacra by the marginal enlargement of their fellows (Plate 34, fig. 2). There are two pores to each plate and the pore-pairs are biserial. All this is as seen on the exterior; on the interior at the mid- zone and throughout the area all plates cross the half-areas and pore-pairs are uniserial (Plate 33, figs. 4, 5, 7, 8). As seen from the exterior, ventrally the ambulacral plates built in youth as a stage in development, and also young plates dorsally near the apical disc, as a localized stage, are all typical primaries crossing the half-areas and with pore-pairs uniserial. This is like the condition characteristic of the mid-zone in the lower genus Palaeechinus. The interambulacra in the known species have in each area from four to eight, or excep- tionally nine columns of plates at or above the mid-zone. The peristome and lanterns are 1 Miss Klcm (1904, p. 31) .says of Palaechinus [Maccoya), four pores in c;n-h arabulacral plate. This is a character not known in the genus nor in any Palaeozoic echinoid. 312 ROBERT TRACY JACKSON ON ECHINI. unknown to me in the genus; but Duncan (1889a, p. 14) says the teeth are grooved. Oculars are all insert, or one or more to all may be exsert, being shut out from contact with the peri- proct by the contact of the associated genitals. Genitals are high and wide with several pores each. The periproct is plated with many small thick angular plates similar to those of a Recent cidarid. The type species of the genus is M . gigas (M'Coy) from the Lower Carboniferous of Europe. Maccoya as a genus occupies a place structurally intermediate as regards the ambulacrum between Palaeechinus and Lovenechinus. The youthful and dorsal localized stages of Maccoya are like Palaeechinus at the mid-zone, and also the character of the plates at the mid-zone of Maccoya is like the secondary youthful and dorsal localized stages of Lovenechinus as set forth in the diagram (text-fig. 237, p. 231). Pomel's Wrightella with Palechinus phillipsiae Forbes as the type I do not consider distinct as it has essentially the same structure of the ambulacrum as Maccoya.1 Duncan's Palaeechinus used in his restricted sense was intended to cover much the same ground as Pomel's Maccoya, but was more inclusive and embraced some structural types which I refer to Lovenechinus (see pp. 303, 304 and footnote, p. 303). He apparently made a mis- take in taking for Palaeechinus, species which were not covered by M'Coy's original descrip- tion, when there were species that did fall within those limits (Duncan's Rhoechinus). At all events Pomel had priority as first reviser of the old genus Palaechinus M'Coy. Key to the Species of Maccoya. Four columns of plates in each interambulacral area (America) M. burlingtonensis (Meek and Worthen), p. 312. Four columns of plates in each interambulacral area (Europe) . . M. intermedia (Keeping), p. 314. Five (?) columns of plates in an interambulacral area M. pMUipsiae (Forbes), p. 316. Five to six or seven columns of plates in each interambulacral area, test robust, plates of moderate size M. sphaerica (M'Coy), p. 317. Six (?) columns of plates in an interambulacral area, the plates very wide and high M. gigas (M'Coy), p. 321. Seven to eight, or exceptionally in part nine, columns of plates in each interambulacral area M. gracilis (Meek and Worthen), p. 323. * Maccoya burlingtonensis (Meek and Worthen). Text-figs. 10, p. 54; 16, p. 59; 237, p. 231; Plate 32, figs. 1-3; Plate 33, figs. 1-5. Palaechinus burlingtoneruns Meek and Worthen, 1860, p. 396; 1866, pp. 230, 231, text-fig. 23, Plate 16, figs. 3a-3c; A. Agassiz, 1874, pp. 648, 649, text-fig. 7; Keyes, 1895, p. 180. 1 Pomel's Eriechinus and Neumayr's Typhlechinus were both based on what de Koninck described as Palaechinus sphaericus, but it was a mistaken identification and is considered here under Lovenechinus lacazei (Julien), pp. 330-334, text-figs. 240-243; Plate 35, fig. 7. See footnotes pp. 303, 326. MACCOYA. 313 Palaeechinus burlingtonensw Loven, 1874, p. 41; Duncan, 1889, p. 205. Maccoya burlingtoncnsis Pomel, 1883, p. 115; Lambert and Thicry, 1910, p. 119. Rhoechinus burlingtoncnsis Jackson, 1896, p. 203, Plate 7, fig. 37; Tornquist, 1897, p. 7(12; Klnii, 1904, p. 27. The test is spheroidal. In Mr. Kirk's specimen (Plate 32, fig. 2) the ambulacrum is 5 mm. wide, interambulacrum 18 mm. wide at the mid-zone. From these measurements the circum- ference would be about 115 mm., the diameter about 37 mm., and the height as estimated is very nearly the same. A specimen in the Museum of Comparative Zoology, no. 3,011, is com- plete in form and very nearly spherical. It is about 36 mm. in diameter at the mid-zone and a trifle more than that when measured through the poles. The ambulacrum is 5.5 mm. wide and the interambulacrum about 17 mm. wide at the mid-zone. The ambulacra are narrow, with two columns of low plates in each area. All ambulacra! plates meet the middle of the area, but at the mid-zone, on the exterior, alternate plates are primaries, reaching and enlarged at their contact with the interambulacrum; or plates are oc- cluded, being narrowed and cut off from interambulacral contact. The pore-pairs at the mid- zone are biserial (Plate 33, fig. 2). While this is the character of the exterior, on the interior a dif- ferent and more primitive condition exists, for here all plates cross the half-area without marginal modification, and pore-pairs are uniserial, as seen in external and internal views of the very same plates (Plate 33, figs. 4, 5). On the exterior, the plates ventrally, built in the youth of the individual, and also dorsally the young plates, as a localized stage, are all simple primarir-, completely crossing the half-area and with pore-pairs uniserial (Plate 33, figs. 1, 2). This simplicity of plates built in youth, of young plates dorsally, and of plates at the mid-zone .-ecu from within, is directly comparable to the simplicity of all plates in the more primitive grim.- Palaeechinus (p. 60). Ambulacral plates bevel over the adambulacrals on the marginal suture. There are four columns of plates in each interambulacral area at the mid-zone, as shown in twelve specimens. Ventrally, as seen clearly in one of Mr. Springer's fine series of specimens (Plate 32, fig. 1 ; Plate 33, fig. 1), there are two plates in the basicoronal row, three in the second, and four in the third row, above which no more columns are added. The same structure is shown ventrally in a large specimen in the Museum of Comparative Zoology (3, 194), only in this individual the initial pentagon of column 4 is on the left of the center in the third row instead of on the right of the center. It is interesting to see that in this species with only four columns of interambulacral plates, as also in Palaeechinus quadriserialis (Plate 30, fig. 3), that the fourth column originates in the third row from the peristome as it does throughout the family with very rare exceptions. In burlingtonensis the adradial plates are pentagonal, all others hexag- onal, excepting ventrally where new columns are coming in. Ambulacral and interambula- cral plates alike bear numerous small secondary tubercles, shown beautifully in Mr. Kirk's choice specimen (Plate 32, fig. 2). Meek and Worthen figure a spine enlarged showing that it is swollen at the base, slender, tapering, and, judging from the figure, about 4 mm. in length, 314 ROBERT TRACY JACKSON ON ECHINI. which is about the usual size in this family. The oculars and genitals are shown well in one specimen in the Museum of Comparative Zoology (3,196). In this specimen, which is an internal view, three oculars are in place, all are insert and adorally cover the ambulacra and laterally the interambulacra in part on either side. One of the two genitals has three pores, the second genital is obscure on this point. Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa, F. Springer Collec- tion, eight specimens; Museum of Comparative Zoology Collection 3,011, 3,047-3,050 and 3,194-3,196; E. Kirk Collection. The holotype is said to be in the Worthen Collection, now in the University of Illinois, at Urbana, Illinois. *Maccoya intermedia (Keeping). Plate 33, figs. 6-12; Plate 34, figs. 1-3. Palaechinus (?) intermcdius Keeping, 1876, p. 37, Plate 3, figs. 9-11. Palaccchinus intermcdius Duncan, 1889, p. 203, text-figs, ix, x. Rhocchinus clegans (by error of identification) Jackson, 1896, text-fig. 1, pp. l9l, 205, Plate 7, fig. 10. Palechinus intermedium Tornquist, 1897, p. 739. Palaechinus intermcdius Klem, 1904, p. 33; Lambert and Thiery, 1910, p. 119. I have had the privilege of studying fine material of this species at Cambridge, England, and at Munich, Dublin, and London. Test spheroidal. Ambulacra narrow, with two columns of low plates, all of which meet the middle of the area. On the exterior of the test at the mid- zone alternate plates are primaries, enlarged on the margin, and four of these primaries equal the height of an adambulacral plate; the intermediate plates are narrowed marginally and' cut off from interambulacral contact by the enlargement of their adjacent plates on either side, and therefore are occluded. Pore-pairs are biserial, the outer pores of the occluded plates falling in line with the inner pores of the primary plates (Plate 33, figs. 6, 7). As seen from the interior all ambulacral plates cross the half-area completely and pore-pairs are uniscrial (Plate 33, figs. 8, 9; Plate 34, fig. 3), (p. 60). In the interambulacra there are four columns of hexagonal median and pentagonal adradial plates in each area, as ascertained in six specimens. Keeping was evidently mistaken in think- ing that there might be five columns, and his doubt on the point is indicated by the fact that he queried the statement. Developmental details of the interambulacra are not known, as all specimens are wanting ventrally, but they are doubtless the same as shown in burlingtonensis. Ambulacral and interambulacral plates bear numerous small secondary tubercles, but the spines are unknown. Ambulacral plates bevel over the interambulacrals on the adradial sutures as in all of this family, but the sides of the plates otherwise are as nearly parallel as is possible in a curved test, and there is no imbrication. Keeping was certainly mistaken in saying that MACCOYA. 315 the interambulacral plates overlap from below upwards [imbricate aborally] and that the am- bulacrals overlap in the opposite direction. Except for the bevel on the adrudial suture I have seen no imbrication of ambulacral or interambulacral plates in this or any other species in this family. The apical disc is relatively small. Ocular plates may be insert, or in one specimen one ocular is exsert, and in another all oculars are exsert (Plate 33, figs. 11, 12). Ijt is very rare for oculars to be exsert in the family (p. 89). The genitals are wide and high, with several up to five genital pores each. The periproctal plates are unknown. This species seems to be indistinguishable from M. burlinglonensis, but in view of the incomplete knowledge of t lie- structure and the wide geographical separation it seems best to maintain both species. Lower Carboniferous, Hook Head, County Wexford, Ireland, several specimens, including the holotype, Sedgwick Museum, Cambridge, England; four specimens, Munich Museum; two specimens, Trinity College, Dublin; Museum of Practical Geology, London, Collection 16,302; Museum of Comparative Zoology Collection 3,002. Of the Munich specimens of this species, one (Plate 33, figs. 6-9) has four columns of plates in one interambulacral area, and also shows the tubercles clearly. The ambulacral detail is clear on the surface with alternate primary and occluded plates, but in a portion showing the interior the plates at this area are all primary in character with pore-pairs uniserial. Another Munich specimen (Plate 34, fig. 1) is worn, but shows the form of the test quite well. There are four columns of plates in two interambulacral areas. In area C in the middle line dorsally there is in addition a single plate which may be considered a tendency toward an extra column as a progressive variation. The only ocular preserved is insert. In the Sedgwick Museum, Cambridge, England, there are seven specimens, including Keeping's holotype. Four of these have four columns of interambulacral plates in an area. The type specimen (Plate 33, fig. 10, after Keeping) is most interesting. It has two column* of interambulacral plates in place and displaced plates representing a third column. The left adradial column is wanting in the more nearly complete area. The ambulacrum is slightly pulled away from the adradial plates on the marginal suture, and reveals the structure graphi- cally (Plate 34, figs. 2, 3). To understand it one must remember that ambulacral plates bevel over the adradials, so that the marginal sutural face of the adradials is an inclined, not a vertical face. On the exterior or distal aspect of this face four facets appear for the reception of the primary ambulacral plates, and these facets in passing proximally become much narrower. On the proximal face of the suture, between the narrowed facets, are seen other alternating facets which receive the impact of the occluded ambulacral plates. This relation is perfectly clear, for on the exterior of the specimen (Plate 34, fig. 2) ambulacral plates are alternately primary and occluded, and pore-pairs biserial, whereas on the interior, as shown in part (Plate 34, fig. 3), ambulacral plates all cross the half-area and pore-pairs are uniserial. Because of this structure it seems that from a single adradial plate one could determine the genus. 316 ROBERT TRACY JACKSON ON ECHINI. Another of the Cambridge specimens (Plate 33, fig. 11) shows four columns of plates in three interambulacral areas; all five oculars are in place, four are insert as usual in the family, but one is excluded from the periproct by the contact of two genitals. The oculars cover the ambulacra and laterally the interambulacra in part on either side, the youngest interambulacral plates being in contact with the oculars. The genitals are high, wide, and three of them have three pores each; the others, two or no pores, but the pores were probably obliterated in fossil- ization. Still another specimen (Plate 33, fig. 12) has all the oculars in place, and they are all exsert, this as above stated being the only case seen in the family. It is a variation toward the character which is the dominant one in Mesozoic regular Echini, and the youthful (sometimes adult) character of all Recent regular Echini. The genitals are very wide and high and have three or five pores each. Of the two specimens in Trinity College, Dublin, one has four columns of interambulacral plates in an area and both show the typical character of the ambulacrum. The specimen in the Museum of Practical Geology Collection 16,302, shows the ambula- crum and part of an interambulacrum. It is the original of Duncan's (1889) text-fig, ix, p. 206. Maccoya phillipsiae (Forbes). Plate 33, figs. 13, 14. Palcchinus phillipsiae Forbes, 1848, pp. 302, 384, Plate 29, figs. 1, la; Tornquist, 1897, p. 739. Palacchinus phillipsiae Roemer, 1852-'54, p. 288; Desor, 1858, p. 159; Quenstedt, 1875, p. 379, Plate 75, fig. 41; Klem, 1904, p. 35. Wrightia phillipsiae (printed by error Wrigthia) Poinel, 1869, p. xlvi. Palaeechinus lihillipsiac Loven, 1874, p. 41; Duncan, 1889, p. 205. Wrightclla phillipsiae Pomel, 1883, p. 115; Lambert and Thiery, 1910, p. 120. Form of test unknown, but probably spheroidal. Ambulacra are narrow, with two columns of low plates, all of which meet the middle of the area, but are alternately primaries which meet the interambulacra and occluded plates which fall far short of the same. Pore-pairs biserial. The specimen is badly preserved, and in Forbes's reconstruction (my Plate 33, fig. 14) the occluded plates are probably too narrow and the pores of the same too near the middle of the area. There are three columns of interambulacral plates in place, and Forbes assumed five columns for the area as shown in the reconstruction. This may or may not be correct. Forbes says, found in conglomerate under the Worcester Beacon by Miss Phillips, and gives the horizon as Silurian. Forbes (1848, p. 302) considered the age of this conglomerate as Caradoc, which is Ordovician (Lower Silurian), but with later study it is found to be Llando- very, which is the base of the Silurian. Whether the specimen described came from this hori- zon is open to doubt. A cast of the type specimen is in the Museum of Practical Geology Collection 16,359. The location of the type I do not know. MACCOYA. 317 This species is the type of Pomel's Wrightella, but its characters fit very well into the genus Maccoya, and there seems no occasion for maintaining a separate genus for its reception. Llandovery, Silurian (?), in conglomerate under the Worcester Beacon, England. *Maccoya sphaerica (M'Coy). Plate 32, figs. 4, 5; Plate 34, figs. 4-10. Palaechinus sphacricus M'Coy, 1844, p. 172, Plate 24, figs. 5a-5c; Desor, 1858, p. 158; Dujardin and Hupe, 1862, p. 464; Baily, 1865c, p. 89; Keeping, IS76, p. 38; Smith, 1901, p. 509; I*ml>ert and Thiery, 1910, p. 119. Non Palaechinus sphacrirus Koninck, 1869, p. 546, Plate [not numbered], fig. 1; mm K'oninck, IS7(), p. 259, Plate 7, fig. 1; non Baily, 1874, p. 41; mm Zittel, 1879, p. 484; (pars) Lov£n, 1874, p. 41; non Neumayr, 1881, p. 151; non A. Agassiz, 1892, p. 73; (pars) Klein, 1904, p. 35.1 Palaeechinus sphaericut (pars) Lovdn, 1874, p. 41; Duncan, 1889, p. 196, text-figs, ii vii. Non Eriechinus sphacricus Pomel, 1883, p. 114.1 Non Typhlcchinus sphacricus Neumayr, 1889, p. 362, text-fig. 82c.' Non Palechinus sphacricus Tornquist, 1897, p. 736.1 Palaechinus sphericus (pars) Klem, 1904, pp. 34, 35. M'Coy's type of this species is in Dublin (Plate 32, fig. 5; Plate 34, fig. 7). In addition, there are three specimens in the British Museum (Plate 32, fig. 4; Plate 34, figs. 4-6), three in the Sedgwick Museum, Cambridge, England, and one in the Strassburg Museum (Plate 34, figs. 8, 9), all of which are similar and are referred to sphaerica. M'Coy's type is almost spherical, but the height has to be estimated, as the dorsal part is covered by a lump of the original matrix. Of this specimen the circumference at the mid- zone measures 203 mm.; the diameter, in the same plane, 65 mm.; height, approximately 65 mm. ; width of ambulacrum B at the mid-zone, 6 mm. ; width of an interambulacrum about 34 mm. Ambulacra are narrow, rounded up in the center, so that the greatest elevation is in line with the curvature of the interambulacra. Ambulacrum B is the only one in which the surface of the plates is shown, other areas being internal molds for the most part. The details of plate structure are difficult to ascertain, but Plate 34, fig. 7, was drawn at the point marked X in Plate 32, fig. 5. As seen here, all ambulacral plates meet the middle of the area, but against the interambulacrum alternate plates are primaries, marginally expanded, and intermediate plates are narrowed and just cut off from contact with the interambulacrum. Pore-pairs are biserial. In the British Museum and other specimens all ambulacral plates usually meet the interambulacrum, though alternate plates are narrowed, and pore-pairs are biserial. 1 These several references in the above paragraphs are all in regard to the specimen described by de Koninck as Palaechinus sphaericus from Kirkby Stephen, Westmoreland, England. The specimen has a very different structure from that of Maccoya sphaerica (M'Coy), and likewise different from that of the genera Palaeechinus and Maccoya. It is here described as Lovenechinus lacazei (Julien), footnotes, pp. 303, 312, 326, also pp. 330-334, text-figs. 240-243; Plate 35, fig. 7. 318 ROBERT TRACY JACKSON ON ECHINI. In the type there are six or seven columns of plates in an interambulacral area at the mid-zone. In area A there are six columns, and below the mid-zone the introduction of the fifth and sixth columns is seen, both originating as usual with a pentagonal plate. By this means the specimen was oriented, and it will be noticed that the orientation of my figure is the reverse of that given by M'Coy. In this area, A, the six columns extend dorsally to the covering matrix. In interambulacrum C there are seven columns at the mid-zone. The seventh column consists of four plates only, on one of which the letter C occurs in Plate 32, fig. 5. Ventrally and dorsally to the seventh there are six columns in this area. Areas E and ( i are imperfect, for the most part internal molds, and the full number of columns was not ascertained. Interambulacrum I is also an internal mold, but the impress of six columns of plates was clearly ascertained at the mid-zone. In one of the British Museum specimens (E 3,052) there are seven columns of plates in the only interambulacral area clearly preserved. Of two other British Museum specimens (E 361) on a single slab, one has five columns of plates in all five inter- ambulacral areas (Plate 32, fig. 4), whereas the other has five columns in one area, but six in two other areas. On account of the matrix covering the dorsal area, the features of this part are unknown in the type. In the British Museum specimen (Plate 34, fig. 6), the apical disc is small, the oculars are all insert, genitals wide, low (pores not visible), and the periproct has numerous small angular plates as usual in the Palaeozoic. M'Coy's type is in Trinity College Museum, Dublin, where I studied it through the kind- ness of Professor Joly. There is no locality given, but it bears the label, "Presented by Dr. A. N. Fox, Staff Assistant Surgeon, 1 Nov., 1867." For several years earlier it had been in the possession of the Rev. S. W. Fox. According to Baily (1865c, p. 89) the specimen was supposed to have come from the limestone of the County Kildare, but that was not certain. A plaster cast of this valuable specimen is in the Museum of Practical Geology in London, and another in the Museum of Comparative Zoology. Confusion has been introduced as to the structure of this species by de Koninck's (1870) description of a specimen which he referred to Palaechinus sphaericus M'Coy. Through the great kindness of my friend Dr. F. A. Bather, the specimen was borrowed from the York Museum, and it proves that the description was incorrect in several particulars. The specimen is not a Maccoya sphaerica, and does not even belong to the genus Maccoya, having a very different ambulacral structure. It is here referred to Lovenechinus lacazei (text-figs. 240-243, p. 331 ; Plate 35, fig. 7). From this it occurs that statements in regard to the absence of oculars (entirely wrong), structure of the genital plates (also incorrect), and the number of inter- ambulacral columns ascribed to sphaerica, as far as based on de Koninck's observations, are erroneous (footnote, p. 303). Lower Carboniferous, probably County Kildare, Ireland; on the authority of Baily MACCOYA. 319 (1865c, p. 89) this is the probable locality of the holotype which is in the collections of Trinity College, Dublin; County Kildare, Ireland, British Museum Collection E 3,652; Waterford, County Wexford, Ireland, British Museum Collection E 361; Clitheroe, Lancashire, British Museum Collection E 4,353; Clitheroe, Lancashire, Sedgwick Museum, Cambridge, Collection 17; Hook Head, County Wexford, Ireland, Sedgwick Museum Collect ion nos. land 5; Whatley, near Frome, Somerset, Strassburg Museum; East Hum, northeast of Stewarton, Scotland (Smith). Taking up the specimens attributed to Maccoya sphacrica, a specimen in the British Museum Collection E 3,652, is from Kildare, and is free from matrix, but not very clearly pre- served. It measures about 50 mm. in height and 52 mm. in diameter. The ambulacra are narrow, about 6 mm. in width at the mid-zone. The interambulacra are about 26 mm. in widt h. The ambulacral areas are rounded outwardly as in the type, but details of plates are obscure. Pore-pairs are alternate and plates are apparently alternately primary and occluded. In the only good interambulacral area there are seven columns of plates at the mid-zone. This speci- men in structural detail resembles M'Coy's type more closely than any other specimen I have seen. It also resembles it very closely lithologically, which lends weight to Baily's statement that the type is probably from Kildare, which is the source of this individual. In the British Museum Collection E 361, is a limestone slab from Waterford, Ireland, which bears two specimens, one of which is one of the finest of known Palaeozoic Echini. The slab measures 200 mm. long by 125 mm. in width. The more nearly perfect specimen is shown in Plate 32, fig. 4, and Plate 34, figs. 4-6. The test is spheroidal, somewhat crushed laterally. The ambulacra at the mid-zone measure about 7 mm., the interambulacra 25 mm. in width. From these measurements the circumference would be about 160 mm. and the diameter about 50 mm. Ambulacral areas are narrow, with two columns of low plates in each area. All plates meet the middle of the area, and at the mid-zone most of the plates reach the inter- ambulacra, but alternately they are widened and narrowed marginally, the narrowed plates being nearly or occasionally quite excluded from contact with the interambulacrum. A few completely occluded plates occur in each of these specimens, though none is shown in Plate 34, fig. 4, the ambulacra in which are drawn somewhat diagrammatically with certain oversights. It was this specimen on which Professor Duncan (1889, p. 200, text-figs, ii-vii) based his ob- servations of the structure of the ambulacrum in this species. In his text-figs, vi, vii, small demi-plates are shown which he letters as a. These plates, having been overlooked, are not shown in my figures, but nine such plates were counted in the best specimen (Plate 32, fig. 4). Such plates are not a character of this species or genus, and are to be considered as excep- tional progressive variants. At the mid-zone the pore-pairs are biserial, the outer pore of one plate being about in line with the inner pore of the next succeeding plate. Dorsally, near the oculars, as a localized stage, all plates are of equal height, meet the interambulacra fully, and 320 ROBERT TRACY JACKSON ON ECHINI. pore-pairs are uniserial. The structure of the ambulacrum at the mid-zone is intermediate between that of Palaeechinus and Maccoya, and the alternate plates are not usually so com- pletely cut off from the interambulacrum as was observed in M'Coy's type specimen. The inter- ambulacra are wide (Plate 34, fig. 4), with five columns of plates in each area. In the second specimen, on the same slab, there are five columns in one interambulacral area and six columns in two other areas. The plates are hexagonal, or pentagonal in the adradial columns. The hexagons are much wider than high, one at the mid-zone measuring 7 mm. in width and 5.5 mm. in height. The ventral area is unknown. Ambulacral and interambulacral plates bear numerous small secondary tubercles, and in the second specimen there are in place small, tapering spines, swollen at the base, and about 3 mm. in length. All five oculars are in place. They are all insert, cover the ambulacra and laterally the interambulacra in part on either side. The genitals are wide, apparently very low for this family, but the ventral borders seem to be pushed under the interambulacra in part, which accounts for the height, and I think also for the absence of visible genital pores. The periproct is exceptionally perfect, the most nearly complete one known in the family. It differs slightly in Plate 34, figs. 4 and 6, but the latter I drew with all care, and it is to be considered a corrected drawing. The plates are numerous, small, angular, rounded up, so that they are higher in the center of each plate than on its sutural margin. They are strikingly close to the character of the same plates in the Recent Cidaridae, and may well stand as representing the typical Palaeozoic periproct, as this is the clearest and most nearly complete specimen in regard to this structure known to me from these ancient formations. This British Museum specimen E 361, is the one from which Duncan (1889, p. 196) described the apical disc with oculars reaching the periproct and with periproctal plates in place. Duncan's second specimen which he says is the same species, and describes as having the oculars excluded from the periproct, may have been the specimen in the British Museum (which was labeled P. sphaericus) which I refer to Lovenechinus lacazei (p. 328; Plate 36, fig. 6). A specimen in the British Museum Collection E 4,353, from Clitheroe, Lancashire, is frag- mentary. The interambulacral plates are very large, 11 mm. wide by 8 mm. high, representing a very large individual. Ambulacral plates are preserved only in fragmentary clusters of connected plates, but they are typically alternately primary and nearly, or in some plates quite, occluded, with pore-pairs biserial. . The Strassburg specimen of M . sphaerica from Whatley, consists of ambulacral and more or less dissociated interambulacral plates on a limestone slab. All the ambulacral plates meet the middle of the area, and also the interambulacrum, but alternate plates are enlarged or narrowed marginally (Plate 34, fig. 8), the latter not being quite cut off from interambulacral contact, in this respect being like the British Museum specimen E 361. The pore-pairs are biserial. As seen from within (Plate 34, fig. 9), all ambulacral plates are alike, of equal height, and pore-pairs are uniserial. This is the same relation as is shown between the inner and MACCOYA. 321 outer aspect of ambulacral plates in Maccoya intermedia (Plate 33, figs. 7-9). The larger hexagonal interambulacral plates measure 7 to 7.4 mm. in width, and 5.8 to 0 mm. in height, so that they are distinctly wider than high. They have numerous secondary tubercles like those of Plate 32, fig. 4. Of the specimens in the Sedgwick Museum, Cambridge, England, that from Clitheroe, no. 17, from the Aitkin Collection, consists of portions of ambulacra and dissociated interambula- cral plates. Of the ambulacrals, all plates cross the half-areas, but alternate plates arc partially pinched off marginally, and pore-pairs are biserial, as in Plate 34, fig. 8. Another specimen, from Hook Head, Ireland, no. 1, is the original specimen referred to by Keeping (1876, p. 38). What he described as an ocular plate with two pores, lies above an interambulacruin, thmifih it is not in place. In my opinion it is not an ocular, but a genital, high, as usual, and with three pores, not two. There are some ambulacral plates in place and five columns of inter- ambulacral plates, consisting of one column of pentagonal adradial, and four columns of rather low hexagonal plates. One or more columns are evidently wanting. A third specimen from Hook Head, no. 5, from the Walton Collection, consists of a portion of an interambulacrum, with four columns of plates in place, one column of pentagonal adradial and three columns of low hexagonal plates, which measure about 7.5 mm. in width by 5 mm. in height. * Maccoya gigas (M'Coy). Plate 46, figs. 1-3; Plate 47, figs. 1, 2. Palaechinm gigas M'Coy, 1844, p. 172, Plate 24, figs. 4a-4c; Dujardin and Hupe1, 1862, p. 463; Buily, 1874, p. 41, Plate 3, figs, a-d; Quenstedt, 1875, p. 380, Plate 75, fig. 40; Keeping, 1876, p. 38, Plate 3, figs. 12, 13; Julien, 1896, p. 130; (pars) Klem, 1904, p. 32. MacCoya gigas Pomel, 1869, p. xlvi. Palaeechinus gigas Loven, 1874, p. 41 (non Duncan, 1889, p. 198, text-fig, i; non Jackson, 1896, p. 204, Plate 7, figs. 38, 39 J). Maccoya gigas Pomel, 1883, p. 115; Lambert and ThieYy, 1900, p. 119. Non Palechinus gigas Tornquist, 1897, p. 739, which is based on Duncan's Palaeechiiius gigas.1 The cotypes of this species which are in the Science and Arts Museum, Dublin, are the basis of M'Coy's and Baily's observations and also of my diagnosis. The whole test is unknown, but the parts which are known indicate that it was high, spheroidal. M'Coy's restored figure is, I think, much too low. Ambulacra are relatively narrow, about 10 mm. in width, and as shown by Baily, are composed of two columns of low plates, all of which meet the middle of the area, but marginally alternate plates are primaries, reaching the interambulacra and enlarged at 1 Duncan's and Jackson's observations were apparently both based on the specimen in the Museum of Practical Geology which has a different ambulacral structure from Maccoya, and is here referred to Loveitechinus anglicus sp. nov. (pp. 304, 346, Plate 46, figs. 5-6; Plate 47, figs. 3-5). 322 ROBERT TRACY JACKSON ON ECHINI. that point, the plates between being narrowed marginally, occluded, and cut out from interam- bulacral contact by the enlargement of their fellows; pore-pairs biserial (Plate 47, fig. 2). This is the typical generic character. On the interior of the test all ambulacral plates are of about equal height and cross the half-area completely, as shown in a specimen from Rahan's Bay, in the Sedgwick Museum, Cambridge, England, no. 3, which also shows that the ambulacral plates bevel over the adambulacrals on the marginal suture, a structure similar to that shown in Maccoya intermedia (Plate 34, figs. 2, 3). The interambulacra of the type (Plate 46, figs. 1, 2) are more nearly complete than those of any other known specimen of the species. This specimen is bent sharply on itself, as on a hinge, so that on one side (Plate 46, fig. 1) is seen an ambulacrum and three adjacent inter- ambulacral columns, and on the reverse side (Plate 46, fig. 2) is seen an adradial pentagonal column and an adjacent column of hexagonal interambulacral plates. This structure is shown clearly in Baily's (1874, Plate 3, figs, a, b) excellent figures. M'Coy in his restoration assumed six columns in an area, which is very likely correct, but there may have been fewer, or possibly more than that number. The plates are very large and relatively high in proportion to their width. The pentagonal adambulacral plates measure about 12 mm. in width by 9 mm. in height; the hexagonal plates measure about 14 mm. in width by 9 mm. in height. These plates bear numerous secondary tubercles, as shown better in M'Coy's second type (Plate 46, fig. 3). The characters of the ventral and apical areas are unknown. This species is the type of the genus. Arenaceous shale, Lower Carboniferous, Rahan's Bay, Dunkineely, County Donegal, Ireland, cotypes, two specimens, in the Griffith Collection, Science and Arts Museum, Dublin; same locality, Sedgwick Museum, Cambridge, England, Collection 3 and 266; Lower Carbonif- erous shale, Drumlug, County Donegal, Ireland, Trinity College Museum, Dublin; Re'gny, Central France (Julien). • The specimen from Drumlug in the Trinity College Museum shows an ambulacrum very clearly, in which all plates meet the middle of the area, but alternate plates are primary and occluded, meeting or being cut off from the interambulacrum ; pore-pairs are biserial, as in M'Coy's type. There is a column of large pentagonal adradial plates in place with the ambu- lacrum and in addition scattered interambulacral plates. One large adradial plate measures 16 mm. in width and 10 mm. in height. The specimen in the Sedgwick Museum Collection no. 3, is an interesting individual of this species from Rahan's Bay, the type locality. This is the original of Keeping's (1876) Plate 3, fig. 13, as stated on the old and somewhat faded label. His figure, however, is somewhat inadequate. The specimen is a slab on which there are portions of an ambulacrum and ten more or less perfect and dissociated interambulacral plates. The ambulacral plates are in three short, but continuous pieces. All plates meet the middle of the area, but alternate plates MACCOYA. 323 meet and are cut off from interambulacral contact (Plate 47, fig. 1); pore-pairs are biserial, as in M'Coy's type. The ambulacral plates bevel strongly over the adradial.s laterally. Adradial plates on the inclined marginal face show one set of facets distally for articulation with the primary ambulacral plates, but, passing proximally on the inclined face, these facets become narrower and other facets appear between them, so that proximally there are facets for each ambulacral plate of the area, as explained in detail in the case of Maccoya intermedia (p. 315, Plate 34, figs. 2, 3). The adradial plates of this specimen measure 8 mm. in width and the same in height, hexagonal plates 10 mm. in width and 8 mm. in height. Another specimen from Rahan's Bay, in the Sedgwick Museum, no. 260, consists of two large hexagonal interambu- lacral plates with good tubercles. The larger of these plates measures 12 nun. in width, 9 mm. in height. The size and locality indicate that it belongs to this species. *Maccoya gracilis (Meek and Worthen). Plate 34, figs. 11, 12; Plate 35, figs. 1-3. Palaechinw gracilis Meek and Worthen, 1869, p. 82; 1873, p. 473, Plate 10, fig. 2; Keyes, 1895, p. 180. Palaeechinus gracilis Loven, 1874, p. 41; Duncan, 1889, p. 205. Maccoya gracilis Pomel, 1883, p. 115; Lambert and Thiery, 1910, p. 120. Rhoechinw gracilis Jackson, 1896, p. 201, Plate 7, figs. 36, 37; Tornquist, 1897, p. 762; Klem, 1904, p. 29. The test is small, high, spheroidal. In the holotype (Plate 35, fig. 1), the width of the ambulacrum at the mid-zone is 5.5 mm. ; width of the interambulacrum about 19.5 mm. From these measurements the circumference would be about 130 mm. and the diameter about 41 mm. The ambulacra are narrow, composed of two columns of plates, all of which meet the middle of the area, but on the margin alternate plates are primaries, meeting and enlarged at the inter- ambulacral contact; the plates between are occluded, marginally narrowed and nearly or quite cut off from interambulacral contact by the enlargement of their fellows. Pore-pairs biserial, the outer pore of the inner pair about in line with the inner pore of the outer* pair. I nter ambulacra are wide, in the holotype (Plate 34, fig. 11) with seven columns of plates at the mid-zone in the only area that is at all complete in this specimen. The adambulacral plates are pentagonal and those of intermediate columns hexagonal. Dorsally, the seventh column is interrupted, there being one row of six plates built, above which the seventh column appears again, with a pentagonal plate having a heptagon lying on its left lower border. Am- bulacral and interambulacral plates alike bear small secondary tubercles. Another specimen from Burlington in the Museum of Comparative Zoology (3,009) is a larger individual, but fragmentary and represented by an internal impression. There are six columns of interambulacral plates at the mid-zone. This specimen was incorrectly referred to burlingtonensis by me (Jackson, 1896, p. 204), as I was misled by the original label which bore that name. 324 ROBERT TRACY JACKSON ON ECHINI. In the Kentucky specimen referred to this species (Plate 34, fig. 12) there are seven columns of interambulacral plates at the mid-zone in each area, but an eighth column originates dorsally in each area, and in area C a ninth column is represented by a few plates near the apical disc. The ventral portion is unknown in the species and the dorsal portion is unknown in the type, but in this specimen, which is an external sandstone mold, impressions of insert oculars and wide, high genitals are visible dorsally (Plate 35, fig. 3). Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype, from the Wachsmuth Collection 407, in the Museum of Comparative Zoology Collection 3,052; Lower Burlington Limestone, same locality and Museum 3,009; Waverly Group, Lower Car- boniferous, Menifee County, Kentucky, two specimens on one slab, Museum of Comparative Zoology Collection 3,062. The specimens from Menifee County, Kentucky (Plate 34, fig. 12; Plate 35, figs. 2, 3) are the only ones of this species known excepting those from Burlington as described above. The better of the two is figured. The specimen is an external sandstone mold of the dorsal side, therefore in the figures the orientation is reversed from what it would be if viewed from the exterior. The ambulacra are narrow, 5 mm. in width at the widest part, which is narrower than in the type, but the specimen is smaller, and the interambulacra at the widest part are 14 mm. across. Details of ambulacral plates cannot be ascertained, and as restored by dotted lines in Plate 34, fig. 12, are doubtless given incorrectly, but this figure was drawn in 1895 when I had not studied the type. Interambulacrum A (Plate 34, fig. 12) is the most nearly com- plete area; ventrally there are five columns of plates, above which the sixth and seventh col- umns are introduced with pentagonal plates; farther dorsally, an eighth column comes in at the left of the center with a heptagonal plate on its right ventral border (just the reverse as seen from the exterior). In the several other areas there are seven columns of plates in the most adoral portion preserved, and farther dorsally in each area, an eighth column is introduced with a pentagonal plate. In area C the eighth column appears somewhat earlier than in the other areas, and near the apical disc a ninth column is represented by three small plates. This specimen occurs in the Waverly Group, which is somewhat older than the Burlington Limestone, but I think the specimen is referable to M. gracilis. The only differences seen are the somewhat narrower ambulacra and the eighth column of interambulacral plates dor- sally. The type might have shown this additional column if it were complete to the apical disc. LOVENECHINUS gen. nov. Test spheroidal, ambulacra relatively narrow, with four columns of plates at the mid- zone, which consist of two columns of narrow demi-plates and two columns of wider occluded plates, without intercalated isolated plates. The wide occluded plates are roundly arched upward in the center, and this is the beginning of that dominating prominence of the two LOVENECHINUS. 325 occluded columns, which is a marked feature of the next genus, Oligoporus, and especially most species of Melonechinus. The pore-pairs are biserial in sunken valleys on either side of the ambulacral areas, and the pores are situated in that portion of each plate nearest the next adjacent interambulacrum. All this as seen from the exterior; on the interior (Plate 43, figs. 4, 5) demi- and occluded plates are of about equal width, and pore-pairs lie near the middle line of each half-area, also demi-plates which lie opposite horizontal interambulacral sutures are higher and fan-shaped. Ventrally, next the peristome (Plate 42, fig. 1), ambulacral plati - built in youth are all primaries, with pore-pairs uniserial (as in adult Palaeechinus). Above this zone plates are primary and occluded, with pore-pairs biserial (as in adult Maccoya), before attaining the character plates of the genus. Dorsally, a comparable condition occurs next the ocular in the placogenous zone (Plate 42, fig. 3); here ambulacral plates are primaries with pore-pairs uniserial. Passing ventrally, the older plates are alternately primary and occluded as localized stages in development, before they acquire the full characters of the genus. Ambulacral plates bevel over the adradials laterally, and bear small secondary tubercles and spines only. The interambulacra are wide, with from four to seven columns of plates in an area at the mid-zone in the known species, composed of pentagonal adradial, and hexagonal median plates. There are ventrally two plates in the basicoronal row, above which additional columns come in as usual in the family (Plate 45, fig. 1). There is no imbrication in ambulacral or inter- ambulacral plates, but the adradials bevel under the ambulacrals laterally. Interambulacral and ambulacral plates bear secondary tubercles and spines only. Peristome and jaws are unknown; but they were doubtless similar to those of Oligoporus and Melonechinus. Oculars are usually all insert but one or more may be exsert. They are imperforate as seen from the exterior, but indications of a pore on the interior have been seen in some cases (Plate 41, fig. 2; Plate 42, fig. 6). Genitals are high, wide, with from three to five genital pores each; a madreporite has apparently been observed in one specimen (p. 334; text-fig. 243, p. 331). Small angular periproctal plates, as usual in the family, have been seen in one specimen (Plate 42, fig. 6). The type species is Lovenechinus missouriensis (Jackson). This genus differs from Maccoya in that ambulacral plates are demi- and occluded instead of primary and nearly or quite occluded. It differs from Oligoporus in that there are no scattered isolated plates in the middle line of each half-area as in that genus, also as a correlated character in that pore-pairs are biserial instead of multiserial. Lovenechinus in its development passes through a stage like the adult of Maccoya, and Oligoporus in its development passes through a stage like the adult of Lovenechinus (text-fig. 237, p. 231). It is thus a type structurally and phylogenetically inter- mediate between Maccoya and Oligoporus. Lovenechinus includes certain species previously referred to either Palaeechinus or Oligoporus, with two new ones (p. 304). 326 ROBERT TRACY JACKSON ON ECHINI. I take pleasure in naming this genus in memory of the late Sven Love"n, past master in the study of the structure of Echini, and whose methods of work have been of incalculable service to me. Key to the Species of Lovcnechinus. Four columns of plates in an interambulacral area . . . L. lacazei (Julien), p. 326. Five columns of plates in an interambulacral area; occluded and demi-plates meeting in serrated suture L. mutatus (Keyes), p. 335. Five columns of plates in an interambulacral area; occluded and demi-plates meeting in interlocking tongue-like suture; test massive L. nobilis (Meek and Worthen), p. 335. Five, or in part, occasionally, six columns of plates in an interambulacral area; occluded and demi-plates meeting in tongue-like suture; test not massive as in nobilis . . . L. missouriensis (Jackson), p. 337. Six (or possibly more) columns of plates in an interambulacral area; the plates are very wide and high, but not thick; occluded and demi-plates meeting in tongue-like suture . . L. anglicus sp. nov., p. 346. Seven columns of plates in an interambulacral area; occluded and demi-plates meeting in serrate suture L. septics sp. nov., p. 348. *Lovenechinus lacazei (Julien). Text-figs. 240-243, p. 331; Plate 35, figs. 4-7; Plate 36, figs. 1-8; Plate 38, figs. 1-3. 1 Palaechinus sphaericus Koninck, 1869, p. 546, Plate [not numbered], fig. 1 ; 1870, p. 259, Plate 7, fig. 1 ; Baily, 1874, p. 41; Zittel, 1879, p. 484; Neumayr, 1881, p. 151; A. Agassiz, 1892, p. 73. 1 Palaeechinus sphaericus (pars) Loven, 1874, p. 41. 1 Eriechinus sphaericus Pomel, 1883, p. 114. 1 Typhlechinus sphaericus Neumayr, 1889, p. 362, text-fig. 82e. 2 Palaeechinus ellipticus Duncan, 1889, p. 200, text-fig, viii (non M'Coy, 1844). Pdaechinus lacazei Julien, 1890, p. 737; 1896, p. 128, Plate 16, figs. 3-5; Fraipont, 1904, p. 9, Plate 1, fig. 8; Plate 2, figs. 1-6; Klem, 1904, p. 34. 1 Palechinus sphaericus Tornquist, 1897, p. 736. 2Palechinus ellipticus Tornquist, 1897, p. 739. Palechinus lacazei Tornquist, 1897, p. 742, Plate 20, figs. 1-4; Plate 21, fig. 1. 1 Palaechinus sphericus (pars) Klem, 1904, p. 34. Pdaechinus sp. Fraipont, 1904, p. 9, Plate 2, figs. 7, 8. 2 Maccoya ellipticus Lambert and Thiery, 1910, p. 119, (this is based on Duncan's, 1889, description and figure). Maccoya lacazei Lambert and Thiery, 1910, p. 120. 1 These references are all in regard to the specimen from Kirkby Stephen (text-figs. 240-243), described by de Koninck as Palaechinus sphaericus. He stated that the oculars are wanting, a mistake which has proved unfortunate as on this character were based the two genera Eriechinus and Typhlechinus. As these two genera were based on an erroneous ob- servation, and their types are not the species supposed, they are considered out of court as generic names (see footnotes pp. 303, 312). The Palaechinus sphaericus M'Coy (1844, p. 172, Plate 24, figs. 5a-5c) is an entirely distinct species and is here considered as Maccoya sphaerica, pp. 317, 318; Plate 32, figs. 4-5; Plate 34, figs. 4-10. * These references are all in regard to the specimen from Helsington Barrows in the Jermyn St. Museum, described by Duncan (1889, p. 200, text-fig, viii) as Palaeechinus ellipticus; but here referred to Lovenechinus lacazei (footnote p. 303, p. 328, Plate 36, figs. 1-3). The Palaechinus ellipticus M'Coy (1844, p. 172, Plate 24, figs. 3a-3d) is an entirely distinct species and is here considered on p. 307, Plate 29, fig. 2, Plate 30, figs. 8-10. LOVENECHINUS. 327 This species includes specimens of various sizes and many localities, but as the structure in all is essentially the same, as far as known, I consider them a single species. The specimens from Llysfaen (Plate 35, fig. 6; Plate 36, figs. 7, 8) and from Kirkby Stephen (Plate 35, fig. 7; text-figs. 240-243, p. 331) are much larger than the other known specimens. It is possible that these two may prove to be a closely related but distinct species. As they show no structural differences, however, I consider them the same as the smaller specimens. Test spheroidal, or in one case moderately elliptical. Ambulacra narrow, composed in each area of four columns of plates, which are narrow demi- and wider occluded plates in each half-area, pore-pairs in that portion of each plate nearest the next adjacent interambula- crum. Ambulacral plates low, covered with minute tubercles. From six to eight (or in the Kirkby Stephen specimen five and a half) demi-plates equal the height of an adradial. Ven- trally ambulacral plates are primaries with pore-pairs uniserial (Plate 36, fig. 2; Plate 38, fig. 2). The interambulacra in all known specimens have four columns of plates in an area at the mid-zone, the adradials being pentagonal, the median hexagonal. These plates bear minute tubercles and corresponding spines, the latter known only in the Kirkby Stephen specimen. The oculars as far as known (Plate 36, fig. 6; text-fig. 243) are small and fully exsert, an excep- tional Palaeozoic character (p. 89). Genitals are wide, high, with from two to four genital pores each (Plate 36, figs. 4, 6, 7; text-fig. 243). This last figure apparently shows a madreporite as observed by Dr. Bather. Periproctal plates are not known. Lower Carboniferous, 1'Ardoisiere, Central France, cotypes in the possession of the family of the late Prof essor Julien ; Hunsriicken, Germany (Tornquist); Hook Head, County Wexf on 1, Ireland, Science and Arts Museum Collection, Dublin; Helsington Barrows, southwest of Kendal, Westmoreland, Museum of Practical Geology Collection 16,301; Armagh, Ireland, two specimens, British Museum Collection E 10,051, and E 10,052; Llysfaen, near Llandulas, Wales, British Museum Collection E 3,432; Kirkby Stephen, Westmoreland, England, York- shire Philosophical Society Museum Collection; Marbre Noir de Dinant, Belgium (Fraipont). I will consider now the several recorded specimens, with the principal features of each. Professor Julien's types from 1'Ardoisiere, as gathered from his figures and description, have four columns of ambulacral plates in an area, wide occluded and narrow demi-plates, which latter alone reach the interambulacra. Two pores are in each plate, situated near the marginal suture. Ambulacral plates are low, six equaling the height of an adambulacral plate. Inter- ambulacra with four columns of plates in an area, the plates being pentagonal in adradial col- ums, and hexagonal in the median columns. According to Julien, the adradial plates measure 6 mm. in width by 5 mm. in height, the hexagonal 7 mm. in width by 5 mm. in height. They do not show any imbrication. Ambulacral and interambulacral plates alike with numerous small granulations, which Julien says do not merit to be called tubercles, but I do not see that 328 ROBERT TRACY JACKSON ON ECHINI. they are at all different from the small secondary or, possibly better, miliary tubercles in other species of this family. The dorsal portion is not figured or described by Julien. Tornquist next took up this species and published a detailed description of his specimens, with excellent figures, including a good restoration of the whole test. He shows (my Plate 38, figs. 1-3) that there are four columns of ambulacral plates as the species character, wide occluded and narrower demi-plates, with pore-pairs in peripodia, biserial, situated near the interambula- crum on the exterior, but near the middle of the half-area on the interior of the test. He shows that ventrally ambulacral plates are primaries, of equal width, with pore-pairs uniserial. There are four columns of interambulacral plates in an area, and both these and the ambulacrals bear small secondary tubercles. In the British Museum there are two specimens clearly referable to this species, from Armagh, Ireland, numbers E 10,052 and E 10,053. In the larger of these (Plate 35, fig. 5; Plate 36, figs. 4, 5) the ambulacrum at the mid-zone measures 7 mm. in width, the interam- bulacrum 16.5 mm. From these measurements the circumference would be about 117.5 mm. and the diameter about 37 mm. The height is about equal to the diameter. The ambulacra are narrow and at the mid-zone have four columns of narrow demi- and wide occluded plates, the pore-pairs are biserial, lying near the next adjacent interambulacrum. Interambulacra are wide, with four columns of plates in two areas, seen dorsally only in area A. The plates are pentagonal adradials and hexagonal in the median columns. A hexagon at the mid-zone measures 5 mm. in width by 4.2 mm. in height. Dorsally, in area A, a genital plate in place is high, wide, with three genital pores. The second specimen from Armagh (Plate 35, fig. 4; Plate 36, fig. 6) presents the dorsal portion only. The ambulacrum is similar to the last, and there are four columns of plates in three interambulacral areas. The most important feature is the apical disc, unknown in the type specimen. There are three oculars in place which are small and triangular in form, and all are fully exsert. Oculars D and F are as fully excluded as is ocular B (the drawing being not quite correct in this point, as I have recently ascertained by examining the specimen). The oculars cover the ambulacra and in area E the interambulacra in part on either side as usual. They do not impinge on the interambulacra in areas A, G, and in the left side of C, but this lack is ascribed to local disturbance in fossilization, as I have found so universally that oculars do reach the interambulacra in Echini (p. 86). The genitals are high and wide, and three have three pores each, but one has only two pores. This specimen was labeled " Palaechinus sphaericus " and it is probably the one referred to by Duncan (1889, p. 196) as Palaeechinus sphaericus of which he says that the oculars are all excluded from the periproct (p. 320). A specimen from Helsington Barrows, in the Museum of Practical Geology Collection 16,301, is ascribed to this species (Plate 36, figs. 1-3). The ambulacra are narrow, with four columns of demi- and occluded plates at the mid-zone, and pore-pairs are biserial. Ventrally, near the LOVENKCHINIS. 329 peristoraal border, the plates are primaries only, with pore-pairs uniserial, a typical character of this zone in the genus. The intorambulacra are somewhat imperfect and a number of plate- are restored in area A as indicated by dotted lines. With this restoration (a space for which exists in the specimen), there are four columns of plates in the area. Moth ambulacral and interambulacral plates in part bear small secondary tubercles. This specimen is of impor- tance, as the one from which Duncan (1889, p. 200, text-fig, viii) described the structure of the ambulacrum as that of Palaeechinus ellipticus. He was perhaps misled by the original label, which reads Palaechinus ellipticus M'Coy, but since studying M'Coy's type of ellipticus in Dublin, I know that this was a mistake of identification. The structure of the ambulacrum and the interambulacrum in this specimen differs essentially from that of P. ellipticus (Plate 29, fig. 2; Plate 30, figs. 8-10; p. 308, and footnotes, pp. 303, 320). A specimen from Hook Head, Ireland, in the Science and Arts .Museum, Dublin, has the same structure as that last described, with four columns of denii- and occluded ambulacra!, and four columns of interambulacral plates. The size is about the same as that of the Hel- sington Barrows specimen. The specimen from Llysfaen in the British Museum Collection E 3,432 (Plate 35, fig. 6; Plate 36, figs. 7, 8) I ascribe to this species with much hesitation, as it differs so much in M/C and superficial appearance from those previously described. However, as it has the same structural character as typical lacazei, it is placed in this species. The test is large, rounded, and somewhat elliptical, but its actual height is apparently greater from the dorsal dislocation of plates. It is a superb specimen, finely preserved. Width of ambulacrum at the mid-zone, 10 mm., interambulacrum, 30 mm. From these measurements the circumference would be about 200 mm. and diameter about 64 mm. The height as estimated is about 72 mm. and the width, if completed on the left side, about 68 mm. The ambulacra at the mid-zone have four columns of plates which are narrow demi- and wide occluded. Pore-pairs lie near the next adjacent interambulacra. About eight demi-plates at the mid-zone equal the height of an adradial. The ambulacra are high, rounded, and laterally bevel over the ambulacrals on the adradial suture. In ambulacrum B ventrally, as shown in the specimen (not in the dra\\ ingi, within about 10 mm. of the base, the ambulacral plates are all primaries crossing the half- areas, and pore-pairs are uniserial, as in the ventral area of other species of the genus. Then- are four columns of plates in an interambulacral area at the mid-zone and throughout mo-t of the vertical extent of the area, as shown in area A. The same is true of area I, and a third area on the reverse side. In area I ventrally (not shown in the drawing), there is a single plate representing the left of the two plates of the basicoronal row, three plates in the second row, and four plates in the third row, as in text-fig. 25, p. 70. The surface of the plates is high, rounded, and covered with small secondary tubercles. A single genital plate dorsally in place is high, wide, with three genital pores. Three other genitals are more or less displaced, and 330 ROBERT TRACY JACKSON ON ECHINI. with pores showing in part only. A small triangular ocular lies next to genital A and is similar in size and appearance to the small oculars shown in text-fig. 243. The specimen from Kirkby Stephen and now in the York Museum, is the original described by de Koninck (1869, 1870) as Palaechinus sphaericus. De Koninck's description and figures have entered much into succeeding publications (footnotes, pp. 303, 317, 326). In considering these, I found discrepancies and characters which I could not account for, and at my request my friend Dr. F. A. Bather, most generously came to my aid, borrowed the specimen, devel- oped it with great pains, and sent me the accompanying photographic figure and drawings (Plate 35, fig. 7; text-figs. 240-243). I would express to him my heartiest thanks for this most friendly and important service. As seen by the figures, the specimen is not a Maccoya sphaerica (M'Coy), and does not belong to that genus, the ambulacra being quite different from those of sphaerica (Plate 34, figs. 4-10) and from M'Coy's description (p. 318). Further, oculars are present, not absent, as claimed by de Koninck, a very important point, for now one can say that they are not absent in any known regular echinoid. The following description is taken from Dr. Bather's critical and painstaking notes. This specimen in character is close to the British Museum specimen from Llysfaen, and it is possible that they may form a species distinct from lacazei, but as they agree with it structurally, they are included here. Dr. Bather writes, "The specimen was originally in the collection of Mr. Edward Wood, F. G. S., of Richmond, Yorkshire, and came as part of the Reed Collection to the Museum of the Yorkshire Philosophical Society. Thence it was kindly lent to me by Mr. Oxley Grabham. It was at once obvious that de Koninck's sketch was not merely diagrammatic, but inaccurate in several important particulars. It was not, however, clear that his statement as to the oculars was incorrect. Indeed, it took me several weeks of careful preparation before all the questions asked me by Dr. Jackson could be answered with the aid of a good lens under the most favourable conditions of illumination. The wisest course, therefore, seems to be to draw up a fresh description of this interesting specimen. "The echinoid lies at the corner of a fragment of pinkish grey limestone, weathering to a darker red of almost haematite tinge. This deep color is now, however, destroyed by the methods of preparation. The matrix can never, I think, have borne to the fossil quite the relations shown in de Koninck's figure. In that figure the upwardly directed ambulacrum is the anterior one, and the left-hand boundary of the matrix now passes upwards in continuation of its median line. From the angle where the matrix joins this ambulacrum to the limit of the posterior interradius, the length of the exposed test is 60.7 mm. The distance from the same point to the apical pole is 44 mm. The distance from the apical pole to the visible end of the right anterior ambulacrum is about 36 mm., and to the visible end of the adjacent right posterior interradius about 26 mm. It may be inferred from these measurements that the diameter of the test was about 55 mm., and that its height was rather greater. LOVENECHINUS. 331 "In the corona the general relations of the interambulacra and ambulacra arc remarkably clear owing to the depression of the adradial sutures, from which the interambulacra rise up in a flattened curve, and the ambulacra in a more prominent sharply rounded curve. 243 TEXT-FIGS. 240-243. — Lovenechinus lacazci (Julien). Lower Carboniferous Limestone, Kirkby Stephen, Westmoreland, England; Yorkshire Philosophical Society Museum Collection. Drawn by A. H. Searle under the direction of F. A. Bather. 240. View of whole specimen, oriented by the madreporic pores in genital 2. X 1.5. Four columns of plativ in each ambulacral area, pore-pairs biserial. Four columns of plates in each interambulacral area. Same specimen as photo- graphic figure, Plate 35, fig. 7. 241. Ambulacrum III enlarged Xabout4. Plates X, and XX, correspond with the similarly marked plates in text-fig. 240. 242. Ambulacral detail much enlarged. 243. Dorsal aspect enlarged X about 3.8, showing small triangular exsert oculars; genitals high, wide, with three genital pores each, excepting genital 3, which has four pores; fine madreporic pores in genital 2, a very rare character to be seen in this family (p. 172). (The lettering of the figures is mine.) 332 ROBERT TRACY JACKSON ON ECHINI. "The ambulacra are composed of four columns of plates. The inner rows meet in a zigzag radial suture. The outer end of each plate, bearing a pore-pair, interlocks with the inner ends of the two adjacent outer plates. The outer plates then expand and bear pore-pairs alternating with those of the inner series. This structure obtains in all visible parts of the ambulacra, from the apical end to the ambitus. The number of ambulacrals corresponding with an inter- ambulacral is 10 to 12, and this relation also appears fairly constant, the ambulacrals being re- duced in height in proportion to the height of the interambulacrals. The fifth interambulacral from the summit, in the left anterior interambulacrum, has a height of 4.5 mm. and a great- est width of 4.7 mm. The total width of the anterior ambulacrum at the adoral margin of this plate is 6.2 mm. ; about five and a half ambulacrals of the outer series abut against it, so that the height of each ambulacral here is about 0.8 mm. "The whole of the poriferous tract of each ambulacrum is depressed, and from it the perradial tract of the ambulacrum rises in a well marked curve. The perradial tract bears miliaries like those of the interambulacrals, from 6 to 8 being on the adradial portion of each ambulacral plate of the inner series, and a single miliary on the adradial tongue of each ambula- cral of the outer series. These miliaries are regularly arranged in diagonal rows, crossing at a constant angle. I am unable to detect on these miliaries any definite mamelon or any perfora- tion, or any suggestion of a scrobicule surrounded by a scrbiocular ring. That is why I call them miliaries and not tubercles. W. H. Baily has described and figured very precisely all those appearances in the corresponding structures of Palaechinus elegans (Journ. Roy. Geol. Soc. Ireland, vol. 1, p. 63) and P. gigas (op. cit., vol. 4, p. 41), and I should be glad to know whether anyone has ever confirmed his observations. [I have not seen such a structure in any species in this family. — R. T. J.] "The pore-pairs are surrounded by a rim [peripodium], and the interporal septum is well defined and prominent. These structures, however, have been considerably worn in the prepa- ration of the specimen. The pores are not circular. Those of the inner pair are together like the outline of a hen's egg, cut across at the septum, the broader half of the egg being adradial. In the outer pore-pair, the adradial pore is of similar shape, but the outer pore lies close to the margin of the ambulacrum and appears as though compressed thereby into an ellipse with its long axis parallel to the margin. "The adradial suture. Owing to the position of the outer pore-pairs and to the sudden uprise of the adjacent interambulacrals, the ambulacrum, when viewed superficially, seems to dip under the interambulacrum, as in the flexible suture of primitive Cidaridae. The suture was probably not flexible; the abutting plates are very thick, about 3.5 mm. near the ambitus; and the suture-face of the interambulacrum dips towards the perradius [that is, ambulacrals bevel over the adradials, a typical character in this family. — R. T. J.]. The pore-canals of the ambulacra also slant in the same direction. These facts, seen somewhat obscurely at the LOVENECHINUS. 333 broken ends of the two ambulacra on the left, are more than confirmed by a larger specimen of this species in the British Museum (E 3,432) from the Carboniferous Limestone of Llysfaen, near Llandulas [my Plate 36, fig. 6]. This specimen further shows that the adradial suture face of the interambulacrum is denticulate at its outer margin, and faintly grooved over all its surface for the reception of the outer ambulacrals. " The interambulacra are closely united to the genital plates by the proximal plates of their admedian columns. Immediately adjoining these plates the proximal plates of the outer columns make their appearance. The area in which most is preserved is the right anterior, which is visible at least as far as the ambitus and possibly further. Throughout the whole of this there is no evidence for more than four columns, although de Koninck's figure shows a fifth coming in. The plates of the outer columns are pentagonal, and about the ambitus attain a width of 7.4 mm. with a height of 5 mm. Those of the admedian columns are hexagonal and, at the same level, have a width of 6.4 mm. and a height of 5.1 mm. The total width of the interambulacrum here is about 22.5 mm. "The interambulacrals are covered with miliaries, about four to the square millimeter, showing a slight tendency to be arranged in rows. They bore small radioles of which the remains are seen in the adradial furrows. The plates seem firmly united by vertical sutures. "Remains of. minute radioles, with fine longitudinal striation, are preserved in the matrix, especially in the grooves on each side of the ambulacra. "The apical system consists of five genitals (or basals) and five oculars (or radials). "The five oculars are minute triangular plates, squeezed like wedges between the genitals. They are depressed and bear miliaries like those of the genitals. Having with much trouble removed the matrix, I can now see the outlines of all, except the suture separating the anterior ocular from the left anterior genital. The plates are about 1.4 mm. high and about 0.8 mm. wide at the base, or adoral margin. On none can I detect any trace of an ocular pore, nor are the miliaries arranged round any depression where a pore might lie. Of course these pore- are notoriously difficult to see in all fossil echinoids, so that it does not appear necessary to adopt the alternative view that the ocular tentacle may have emerged between the ocular and the ambulacrum. [I have not seen a pore on the exterior of an ocular plate in any species of this family. — R. T. J.] Each ocular lies below the level of the adjacent genitals and bends sharply down to meet the ambulacrum almost at right angles. This gives the impression that the ambulacrum passes beneath the ocular and that the union was flexible; but it is difficult to see clearly into the angle. "The genital plates form a closed circlet, with abutting sides about 1.2 mm. long. Four of the genitals are approximately equal in size and form, having a width of about 4 mm., meas- ured from the distal ends of the interbasal sutures, and a height, measured along the interradius, not exceeding 3.5 mm. The outline of these plates is much more pentagonal than heptagonal; 334 ROBERT TRACY JACKSON ON ECHINI. for, though strictly speaking all have nine sides, some of these sides are very short and almost in a line with one other of those adjoining. The fifth genital (the madreporite) has a width of 3.6 mm. measured at the same level as the other genitals; but, whereas the other genitals scarcely, if at all, increase in width distally, this plate, owing to its greater height, viz., 5.4 mm., attains ultimately a width of 5.7 mm. This plate also is pentagonal in general outline, though it abuts, not only on interambulacrals as do the other genitals, but also on the adjacent ambu- lacra for about 1.5 mm. [I have found so generally in Palaeozoic and later Echini that ocular plates cover the ambulacra and laterally in part the interambulacra on either side (pp. 62, 86) that I think the lack of this latter character in the specimen here described may be due to displacements in fossilization — R. T. J.] "Each genital plate, including the madreporite, is pierced by three rounded and well marked pores; but the left anterior has a fourth pore. In three of the four ordinary genitals, these pores follow a curved line, about 0.8 mm. from the adoral margins. In the right posterior genital the two pores next the anterior margin are close together, and one of them is distal to the other. The pores of the madreporite are placed quite differently, one being near the adapical margin, the other two at irregular distances from the adoral margins. It is probable that the normal position of the pores is presented by the two genitals furthest from the madre- porite, and that the modifications in the two abutting on the madreporite were induced by the proximity of the stone-canal, which may have checked the symmetrical development of the gonads. [I have not found such irregularity in other cases in this family (Plate 42, fig. 6).— R. T. J.] The genitals are covered entirely but irregularly by miliaries, four or five to the square millimeter. These form circlets round the gonopores. The madreporite also shows a multitude of punctae, much smaller than either the round pores or the miliaries. These may be the usual minute pores of the madreporite ; but they may be due merely to a looser texture in this plate; that is to say, a larger proportion of stroma. On the latter interpretation the pore next the adapical margin, which is larger, more transversely elongate, and in more of a depression than the others, would have been the hydropore, and probably not a gonopore, as all the round pores doubtless were. "The periproct is, in the fossil, a pentagonal opening, with a diameter of 4 mm., and almost equal sides formed by the genital plates. The side formed by the right anterior genital (the madreporite) is slightly shorter than the others." Of the specimens from Dinant, Belgium, which Fraipont refers to this species, all are moderate sized, with four columns of interambulacral plates in each area, as clearly shown by his excellent photographic figures, which are similar to my Plate 35, figs. 4, 5. He says that the details of the ambulacra could not be ascertained, but, as in every other respect the speci- mens are referable to this species, it seems that they may safely be considered as belonging to L. lacazei. The only other European species in the family which has a spheroidal test and four LOVENECHINUS. 335 columns of interambulacral plates is Maccoya intermedia, and so far this species has been re- corded from Ireland only. The two larger specimens which Fraipont doubtfully refers to lacazei have each four columns of interambulacral plates, and are quite similar in appearance to the Kirkby Stephen specimen (Plate 35, fig. 7), so that I should equally refer them to Loven- echinus lacazei. Lovenechinus mutatus (KVyrs). Plate 38, figs. 10, 11. Oligoporus mutatus Kcyes, 1894, p. 12(i, Plate 15, figs. 4a, 4b; 1895, p. 183, Plate 18, figs. 4a, 4b; Klem, 1904, p. 39; Lambert and ThieYy, 1910, p. 121. Test spheroidal, with strongly marked melon-like ribs. Ambulacra less than half the width of the interambulacra, composed of four columns of low plates at the mid-zone, two of narrow demi-, and two of wide occluded plates. Pore-pairs in peripodia lying in that portion of each plate nearest the marginal portion. Occluded plates elevated in a high, steep, median, rounded ridge. According to Keyes's figure, the occluded plates do not enter between the demi-plates in a tongue-like fashion, as in L. nobilis (Plate 38, fig. 6), but the contact is rather serrate, as in L. septies (Plate 45, fig. 3) and Oligoporus danae (Plate 50, fig. 7). According to his figures also each demi-plate bears one small secondary tubercle and each occluded plate bears three or four of the same in a nearly continuous horizontal row. The interambulacra are wide, steeply rising from the adradial suture, then roundly curved across the area. There are five columns of plates in an area at the mid-zone, the adradial plates are pentagonal, the median hexagonal, their surfaces covered with small secondary tubercles. This species is known only from Dr. Keyes's original description ; the holotype is in the private collection of Mr. L. S. Cox of Keokuk, Iowa. It is smaller than, but structurally close to L. nobilis, from which it differs in the single row of tubercles on ambulacral plates, the shape of demi- and occluded plates at their point of contact and the carinate edges on the sides of the interambulacra where they dip down to the adradial sutures. Keokuk Limestone, Lower Carboniferous, Keokuk, Iowa (Keyes). *Lovenechinus nobilis (Meek and Worthen). Plate 37, figs. 1-3; Plate 38, figs. 4-9. Oligoporus nobilis Meek and Worthen, 1868, p. 358; 1873, p. 476, Plate 11, fig. 3; Loven, 1874, p. 42; Keyes, 1895, p. 182; Jackson, 1896, p. 198, Plate 6, fig. 35; Klem, 1904, p. 39; Lambert and ThieVy, 1910, p. 121. Melonopsis nobilis Meek and Worthen, 1873, p. 478. This fine species is spheroidal in form with elevated melon-like ribs. The plates are the most massive of any known Echini. Measurements of the type as given by Meek and Worthen 336 ROBERT TRACY JACKSON ON ECHINI. (1873) are: height and breadth about 3.73 inches each, width of the ambulacra about 0.6 of an inch, width of the interambulacra about LOG inches. The height of the largest interambul- acral plates is 0.26 of an inch, width 0.40 of an inch, and thickness 0.25 of an inch. In a splendid specimen in the U. S. National Museum (Plate 37, fig. 3), the ambulacra at the mid- zone measure 17 mm. in width, interambulacra 40 mm. The height as estimated is something less than the width. Two specimens in the Museum of Comparative Zoology (Plate 37, figs. 1, 2) have about the same proportions, but one of these (fig. 2) is more massive, the inter- ambulacrum measuring 50 mm. in width. The very thick plates are seen well in these two specimens. The plates in the middle of the ambulacrum and the interambulacrum (Plate 37, fig. 1) measure 7 mm. in thickness, but at the adradial suture they are only 3 mm. thick. The type according to Meek and Worthen is an internal siliceous mold, so that as this was a unique specimen the thickness of the plates was not shown. The ambulacra are relatively broad, with four columns of plates at the mid-zone, two of narrow demi- and two of wide occluded (Plate 38, figs. 5, 6). The demi-plates bevel strongly over the adradials, the occluded medially rise into a high rounded ridge, in the center of which the plates attain a thickness of some 7 mm. The inner face of the test (Plate 38, fig. 9) presents no corresponding elevation, but rather is on one continuous curve of a practically uniform arc throughout. The occluded plates laterally intercalate in a tongue-like end between the elon- gated and narrowed corresponding tongues on the inner ends of the demi-plates. The inner end of the tongue of the demi-plates in some cases is superficially almost or entirely separated from the body of its plate by the expanded tongues of the occluded plates (Plate 38, fig. 6). Pore-pairs are situated in the outer tongues of the occluded plates and close to the marginal suture in the demi-plates. Occluded plates bear double alternating rows of small secondary tubercles, the outlines of the plates waving in correspondence with their position. The demi- plates bear usually only a single tubercle on the rounded inner end of the tongue. About five or five and a half demi-plates equal the height of an adradial. The interambulacra are roundly curved and laterally dip down to the adradial sutures where they bevel under the ambulacrals (Plate 38, fig. 9). There are five columns of plates at the mid-zone in all areas of the specimens seen. The thickest plates are in the center of the area, and the thinnest are the pentagonal adradials. All five columns extend throughout the areas as far as observed; but the ventral developmental stages are not preserved in known specimens. The surface of the plates is covered with numerous small secondary tubercles, similar to those of the ambulacral areas. According to Meek and Worthen, the apical disc in the type specimen is similar to that of Melonechinus multiporus, the ocular and genital plates being much the same. No pores were seen in the oculars, and the genitals, as far as ascertained, had four or five pores each. Two of the genitals have five pores each, one apparently five, and two apparently four pores each. The apical disc is not preserved in specimens I have seen. LOVENECHINUS. 337 The type specimen is from the Burlington Group, Lower Carboniferous, Calhoun County, Illinois. It is said to be in the Worthen Collection, now in the University of Illinois, at Urbana, Illinois; same locality and horizon, United States National Museum Collection 33,277; Webb City, Missouri, Museum of Comparative Zoology Collection 3,123 and 3,124; Keokuk Lime- stone, Keokuk, Iowa, a fragmentary specimen, American Museum of Natural History Collection 7,245; Boone Formation, Lower Carboniferous, western Arkansas, a specimen collected and loaned me by Dr. G. H. Girty. The National Museum specimen of this species is a magnificent individual, one of the finest Palaeozoic Echini seen (Plate 37, fig. 3; Plate 38, figs. 6, 7). Besides having the typical species characters as described, this specimen shows dorsally a few ambulacral plates which are pri- maries crossing the half-area (Plate 38, fig. 7). This is the same feature of dorsal simplicity seen more completely in L. missouriensis (Plate 42, fig. 3). In the Museum of Comparative Zoology specimen (Plate 37, fig. 1; Plate 38, figs. 8, 9), the test is spheroidal without compression. It shows the massive character of the plates, the lateral beveling of ambulacrals, and ventrally, as an internal mold in part, an impress of the proximal faces of plates. Another specimen in the same museum (Plate 37, fig. 2; Plate 38, figs. 4, 5) is less nearly complete, but represents a larger individual, the interambulacrum being about 50 mm. in width. It shows clearly surface characters, ambulacral detail, and the thickness of plates. Adambulacral plates are rounded in outline on the internal face of the adradial suture as in missouriensis (text-fig. 244). *Lovenechinus missouriensis (Jackson). Text-figs. 11, p. 54; 18, p. 59; 221, p. 193; 237, p. 231; 244, p. 338; Plate 39, figs.1-6; Plate 40, figs. 1-3; Plate 41, figs. 1-3; Plate 42, figs. 1-7; Plate 43, figs. 1-5; Plate 44, figs. 1-5; Plate 46, fig. 4. Oligoporus missouriensis Jackson, 1896, p. 184, Plate 9, figs. 50-52; 1899, p. 131; A. Agassiz, 1904, p. 80; Klem, 1904, p. 38; Fraipont, 1904, p. 11; Lambert and ThieYy, 1910, p. 121. This species is represented by a fine series of specimens of various ages. It is largely known from internal or external siliceous molds, but in two examples seen the plates are preserved intact. Test spheroidal, somewhat wider than high. The holotype (text-fig. 244) measures 90 mm. in height. It is somewhat flattened laterally, and measures through the mid-zone 96 mm. in greatest diameter, and 70 mm. in a plane at right angles to this but in the same zone. A very large specimen, but somewhat compressed (Plate 39, figs. 4, 5), measures about 86 mm. in height and 93 mm. in diameter through the plane J, E, also 90 to 99 mm. in other horizontal planes. If the plates were in place, it would measure several millimeters more. A smaller but quite uncompressed specimen (Plate 44, fig. 2) measures 59 mm. in height, 62 mm. in diame- 338 ROBERT TRACY JACKSON ON ECHINI. ter through the mid-zone. Another specimen with plates all in place (Plate 46, fig. 4), in Mr. F. Springer's collection, measures 91 mm. in height, and 91 mm. in diameter through the mid-zone; the ambulacra at the mid-zone are a little more than 10 mm., and the interambulacra are about 44 mm. in width. The original description was based on an internal mold, and as the external characters differ con- siderably from the internal, certain features given as specific need modi- fication, and both internal and ex- ternal aspects have to bo taken into account (p. 60). The ambulacra are relatively narrow, composed of four columns of plates at the mid-zone. As seen from the exterior, the demi-plates are narrow, the occluded wide, with pore-pairs in that portion of each plate nearest the next adjacent in- terambulacrum (Plate 42, figs. 2, 3; Plate 43, fig. 3). The occluded plates are arched up in an elevated median ridge which is formed wholly by the thickening of plates, no corresponding arch existing be- neath them. The occluded plates are produced as tongues laterally, which fit between corresponding tongues extending inward of the adjacent demi-plates. Occluded plates bear two rows of alternating small secondary tubercles, the margins of the plates curving to correspond to the positions of the same. A single tubercle exists on the inner tongue of the demi-plates. While this is the character of plates at the mid-zone and throughout the greater part of the test, ventrally the plates built in youth, and young plates dorsally near the apical disc are primaries, or otherwise simple (Plate 42, figs. 1, 3), as later described in detail. Four or five demi-plates equal the height of an adradial, and demi-plates on the marginal suture bevel over the adradials. Such is the structure on the exterior, but the interior differs markedly. The interior of the ambulacrum 244 TEXT-FIG. 244. — Lovenechinus missouriensis (Jackson). Burlington Group, Lower Carboniferous, Webb City, Missouri, Museum of Com- parative Zoology Coll., 3,078 (from R. T. J. Coll.), holotype. Natural size. Four columns of ambulacral plates, demi- and occluded, of about equal width. Demi-plates opposite horizontal interambulacral sutures fan-shaped, pore-pairs in middle of half-areas. In area A a sixth column is represented by three plates 6, 6' and the next succeeding aboral plate. Adambulacral plates rounded on the adradial suture. The smaller figure (a) shows an enlargement, X 2, of ambulacral detail. LOVENECHINUS. 339 presents a continuous curve corresponding with the rest of the test (Plate 39, figs. 4, 5), instead of being arched up in the center. Demi- and occluded plates are of about equal width (Plate 43, fig. 4) instead of the occluded being wider, and pore-pairs are close to the middle line of each half-area instead of lying near to the next adjacent interambulacrum (compare Plate 43, figs. 1, 2, and 3, 4). Demi-plates opposite horizontal interambulacral sutures are broad and fan- shaped. This is not a specific, but a generic and family character, seen also in Melonechinus (Plate 56, fig. 5, p. 360). The interambulacra are wide, and at the mid-zone consist of five columns of plates in each area (Plate 39, fig. 3; Plate 44, figs. 2-4; Plate 46, fig. 4), or occasionally a sixth column in addition may be represented by from one to three or more plates in an area, but in no specimen seen does this extra column occur in all areas (text-fig. 244; Plate 40, fig. 1, area I; Plate 41, fig. 1, areas E, G, I). The adambulacral plates are pentagonal, beveled under the ambulacrals on the adradial suture, this inclined face bearing curved facets for articulation with the demi- plates. Occluded plates on the interior do not touch the adradials, as they do in Maccoya (Plate 34, figs. 2, 3). The median columns are composed of hexagonal plates excepting where new columns come in, and also excepting local irregularities as the plates marked P, in text-fig. 244, and Plate 41, fig. 1. The interambulacral plates are thick, but not nearly so much so, or so massive as in the nearly related Lovenechinus nobilis. The surface is thickly studded with small secondary tubercles like those of the ambulacra, but spines have not been observed in this species. In the interambulacra ventrally there are two plates in the basicoronal row (Plate 43, figs. 1,2), above which there are three plates in the second row, and four in the third, the fifth column coming in later at somewhat variable intervals as shown in the figures cited and on Plate 41, fig. 1. In a relatively young specimen (Plate 39, figs. 1, 2; Plate 40, fig. 1) the fifth column in four areas originates near the mid-zone, but there are many fewer rows than in an adult (Plate 41, fig. 1), in which the same column, appearing at about the same age, is pushed adorally in virtue of the fact that many more rows have been added dorsally. The peristome is unknown. The apical disc is relatively small in the several specimen- measured. Its diameter in mature individuals proportionately is about 16 to 18 % of the diameter of the test. In the young individual (Plate 39, fig. 1) the apical disc is proportionately larger, as usual in young Echini, being about 21 % of the diameter of the test. Oculars are usually all insert and cover the ambulacra and laterally the interambulacra in part on either side (Plate 39, figs. 3, 5; Plate 41, fig. 3; Plate 42, fig. 6). As seen in several of the oculars figured, there is on these internal molds an elevated siliceous plug, near the adoral margin, which apparently represents a cast of an ocular pore. An ocular pore has not been seen on the ex- terior in any species of this family, and whether these pores would have reached the surface is doubtful (p. 89). In one case, the young specimen, two oculars are exsert, being excluded from the periproct by the contact of the two adjacent genitals (Plate 41, fig. 2). The geni- 340 ROBERT TRACY JACKSON ON ECHINI. » tals are high, wide, and cover the interambulacra in part in each area. They have from three to five genital pores each, situated below the middle in each plate, and arranged in a semi- circle. There is no trace of a madreporite in any specimen seen (Plate 39, figs. 3, 5 ; Plate 40, fig. 3; Plate 41, fig. 3; Plate 42, fig. 6). In one specimen there are siliceous molds of a few periproctal plates which are small and angular; they were doubtless numerous, as in other species in this family (Plate 42, fig. 6). Jaws are represented only by indistinct impressions in two specimens (Plate 39, fig. 4). Burlington Group, Lower Carboniferous, Webb City, Missouri, Museum of Comparative Zoology Collection, the holotype, 3,078, and seventeen other specimens 3,124 to 3,141 (all from R. T. J. Coll.); British Museum Collection E 9,554, E 10,679; Coriscana, Missouri, Yale University Museum Collection, three specimens; Carterville, Joplin, Missouri, Museum of Comparative Zoology 3,189; F. Braun Collection; Keokuk Limestone, Nauvoo, Illinois, Museum of Comparative Zoology Collection 3,197; Burlington, Iowa, F. Springer Collection 8,126. I have studied altogether some thirty specimens of this species, a richness of material much exceeding that of most known species of Palaeozoic Echini. The more important features of a few of these will now be considered. The Burlington specimen, in Mr. Springer's collection, is a most instructive and important one. It is one of only two specimens so far found outside of Missouri, and with plates all in place (the other specimen being from Nauvoo, Illinois). The Missouri specimens are siliceous molds. The Burlington specimen is excellent for showing surface characters, especially thick- ness of plates, curvature of the ambulacra, and external tubercles (Plate 46, fig. 4). These features in this species are otherwise known only from external molds, as Plate 44, figs. 4, 5. There are five columns of interambulacral plates in each area at the mid-zone, and the ventral development of these areas is well shown, there being, as usual in the family, two plates in the basicoronal row, etc. The most interesting feature of this specimen is the perfection of detail shown in the ambulacrum (Plate 42, figs. 1-4), at the mid-zone, and through- out most of the area the typical species character exists as described (Plate 42, figs. 2, 4), with four columns of plates, pore-pairs biserial. Ventrally, near the peristome (Plate 42, fig. 1), the ambulacral plates are primaries with pore-pairs uniserial, like the genus Palaeechinus. Higher up, the plates are alternately primaries, crossing the half-area and enlarged marginally, with occluded plates, which meet the center of the area, but are cut off from the interambulacra by the enlargement of their fellows. Pore-pairs are biserial, which is like the character in Mac- coya. Still higher we find that the primary plates have failed to reach the middle of the half- area and are here transformed suddenly into demi-plates, thus assuming the generic character which is maintained thence to the ambitus. We see that in the development of this type it repeats the character of the lower genera in its family in a very complete degree, as set forth also diagrammatically in text-figure 237, p. 231. Looking at the dorsal region (Plate 42, fig. 3), LOVENECHINUS. 341 we see that the younger plates in the placogenous zone close to the oculars are primaries, patt- ing across the half-areas, and pore-pairs are uniserial. This simple condition of the young, last added plates as a localized stage is directly comparable to the plates built in youth (Plate 42, fig. 1), or the plates throughout the whole area in the simpler genus Palaeechinus (Plate 31, fig. 1). Passing ventrally from the youngest plates to those somewhat older and struc- turally more advanced, although there is some irregularity, we see that at the zone marked X, X, in Plate 42, fig. 3, the plates for a short distance are alternately primaries, which are expanded at the adradial suture, and occluded plates, which are cut off from the adradial suture, but both meet the center of the area, and pore-pairs are biserial. This is like the second stage in development seen ventrally, and like the character of Maccoya, the next lower genus in which ambulacral plates are typically primary and occluded with pore-pairs biserial (Plate 33, fig. 7). Thus, from ventral developing stages and from dorsal localized stages in a single specimen can be read the relations of the type to associated genera in the family. But this is not all that is shown by this wonderful specimen. At the point marked y, in the left half-area (Plate 42, fig. 3), there are two plates, and at y in the right half-area there is one plate, which lie in the middle of the half-areas and do not reach either the adradial suture or the middle of the area. In other words, these are sporadic cases of isolated plates, and t he- only ones seen in any specimen of the genus. As a character, they represent local progressive variations toward just that addition of plates which is the character of Oligoporus, and is the beginning of the system of isolated plates which is the main feature of Melonechinus. A young specimen in the Museum of Comparative Zoology Collection 3,140, which is only 32 mm. in diameter (Plate 39, figs. 1, 2; Plate 40, figs. 1, 2; Plate 41, fig. 2), is of much interest as the youngest Palaeozoic echinoid seen. It is so nearly complete that with some restoration, indicated by dotted lines, it is drawn spread out by the Love"n method (Plate 40, figs. 1, 2). There are two plates in the basicoronal row as restored, three in the second row, observed or inferred, and four in the third row, as observed or inferred. The fifth column originates in the fifth to the eighth row in four areas, but in area E this column is apparently represented by only a single plate, which is in the thirteenth row. A sixth column is represented by a single plate dorsally in the thirteenth row in area I. As it is a young specimen, there are fewer plates than in an adult, there being only 13 or 14 plates in each adradial column in four of the arc:i>. but in area E, which is much narrower, there are 15 adradial plates on each side. This area in the drawing of the internal mold is restored ventrally, but a good deal of this portion is shown in Plate 40, fig. 2, drawn from a wax cast of the external mold, which therefore supplements for this area the less complete drawing of the interior. In a large adult (Plate 41, fig. 1) there are from 25 to 27 plates in each adradial column, about twice as many as in this young specimen. (Compare studies of the interambulacrum, Jackson, 1899, p. 129.) In a dorsal view of this young specimen (Plate 41, fig. 2) oculars B, J, and probably H, 342 ROBERT TRACY JACKSON ON ECHINI. are broadly insert, but oculars D and F are exsert. This is the only case of exsert oculars seen in the species. Ventrally, the oculars bear each a small siliceous plug, representing a cast of the ocular pore, which probably did not reach the surface, as such have not been seen on the surface in any species of this family. The oculars ventrally cover the ambulacra and laterally the interambulacra in part on either side. The apical disc measures 7 mm. in diameter and is proportionately about 21 % of the diameter of the test. This is proportionately large for the species and family, but evidently, as in Recent Echini, the apical disc is proportionately larger in young individuals (p. 87). In this dorsal view the single plate representing the sixth column is clearly seen in area I. In Mr. Braun's specimen (Plate 39, fig. 3; Plate 41, fig. 3), from Joplin, Missouri, we have an internal siliceous mold about 58 mm. in diameter and nearly spherical. It has five columns of plates in each interambulacral area, but dorsally the fifth column is strung out, and in areas A, C, and E fails to reach the apical disc (Plate 41, fig. 3). Oculars are all insert, and ventrally cover the ambulacra and laterally the interambulacra in part on either side. The genitals are wide, high, and have four or five genital pores each. Dorsally, in this internal mold, ambulacral plates are all primaries, with pore-pairs uniserial; farther ventrally they are primaries and occluded, with pore-pairs biserial (compare Plate 42, fig. 3). A magnificent specimen in the Museum of Comparative Zoology Collection 3,128, from Webb City, Missouri, is one of the finest Palaeozoic Echini seen. It is an internal siliceous mold, and is represented in ventral and dorsal views in Plate 39, figs. 4, 5. The boundary of each plate is represented by a siliceous ridge, so that, if plates have been separated, there is an inde- pendent bounding ridge for each plate, as seen well in area E (Plate 39, fig. 5). Siliceous plugs represent the ambulacral and ocular pores and delicate siliceous tubes the casts of the larger genital pores. The specimen is somewhat compressed, but averages about 95 mm. in diameter. It is not only full grown, but is an old-age individual, as indicated by the dropping out of columns dorsally, as described below. So nearly .complete is this specimen that I am able to represent it spread out by the Loven method (Plate 41, fig. 1), with the restoration of only a few plates ventrally, as indicated by dotted lines. The ambulacral plates at the mid-zone are demi- and occluded, with pore-pairs biserial, but situated on either side in the middle line of each half-area (compare Plate 42, figs. 2, 3; Plate 43, figs. 4, 5). The ambulacral plates near the peristome, which were built in youth, and the young plates dorsally, near the ocular, as a localized stage, are primaries, crossing the half-areas, and with pore-pairs uniserial (compare Plate 42, figs. 1, 3). In the interambulacra (Plate 41, fig. 1) there are two plates in the basicoronal row, in part restored, three plates in the second row, also partially restored, four plates in the third row, restored in two areas. The fourth column originates on the left of the center hi areas A and C, but apparently (in part restored) to the right of the center in E, G, and I. There are a good LOVENECHINUS. 343 many local peculiarities in this choice specimen which I will now describe. In area A tin- fifth column originates in a pentagon in the eighth row, with a heptugonal plate on its right ventral border, as usual. In the ninth row there are only four plates, one being a large octag- onal plate, O, whose two extra sides are compensated for by a pentagon above it marked 5, where the fifth column starts again, and another pentagon, P, below it. Octagonal plates are very rare. In area C the fifth column originates on the left of the center with a pentag- onal plate having a heptagon in its right ventral border. In the eighth row there is an adventitious pentagon, P, in which the side wanting is compensated for by an adjacent heptagonal plate. In areas E and G the fifth column originates in the sixth row, with a heptagon on the right ventral border, as usual, and in area I it originates in the seventh row, with a heptagon on its right ventral border. In areas A and C there are only five columns of plates, but in the other areas a sixth column is represented by one or two plates in each. In areas E and I a sixth column is represented by one pentagonal plate in the thirteenth or the eleventh row, with a heptagon on its left ventral border. In addition, as a peculiarity, in each area an adventitious pentagon, P, lies on the left of pentagon 6, and to compensate for the one side wanting, a heptagonal plate, H, lies on the dorsal border of the pentagons. In area G the sixth column is represented by two plates, a pentagon in row 11 and an overlying hexagonal plate. A heptagonal plate lies on the left ventral border of the initial pentagon. In addition, as a peculiarity, an adventitious pen- tagon, P, lies on the right side of hexagon 6, and to compensate for its one side wanting, a heptagon lies on its dorsal border, as in areas E and I. Passing dorsally, column 5 drops out before reaching the apical disc, as seen more clearly in Plate 42, fig. 6. In Plate 41, fig. 1, the plates are drawn representing the character as seen on the proximal or interior aspect of the test, and here all the adambulacral columns extend to the apical disc. As viewed super- ficially, however, a somewhat different condition occurs, as shown in Plate 39, fig. 5; Plate 42, fig. 6. Taking area I as the best example, on the left and right we see the silicified marginal walls of ambulacra J and H, beveling over interambulacrum I. The plates of the adambulacral columns 1 and 2 are existent, but do not reach the surface, being roofed over, or occluded, by the lateral borders of the plates of columns 4 and 3, which alone meet the ambulacra laterally near the surface of the test. This is explained by the diagram (Plate 42, fig. 7), in which on the interior of the test there are five interambulacral plates, but on the exterior only three, as plates of columns 3 and 4 roof over and shut out plates of columns 2 and 1, which therefore meet the ambulacra proximally, but not distally. A similar shutting out of plates quite probably occurs in such a case as Plate 53, fig. 1. A comparable shutting out of plates by occlusion occurs more or less completely in the other areas of the specimen (Plate 42, fig. 6). Dorsally all oculars are in place (Plate 39, fig. 5; Plate 42, fig. 6). The apical disc measures about 16 mm, in diameter, being about 16 % of the diameter of the test which is 344 ROBERT TRACY JACKSON ON ECHINI. relatively smaller than in the young individual (p. 342). Oculars are insert, ventrally cover the ambulacra, and laterally the interambulacra in part on either side. Two of the oculars show pores ventrally as indicated by siliceous plugs like those previously described. The genitals are high, wide, with three or four pores each. These are represented by delicate siliceous tubes which were evidently formed as post-mortem linings to the original pores and before the solution of the plates. A few molds of periproctal plates are in place (Plate 42, fig. 6) ; they are small, angular, as in other species in the family, and are the only ones yet known in this genus. Impressions of jaws are imperfectly seen ventrally (Plate 39, fig. 4). A specimen that I gave the British Museum, now no. E 10,679 of its collection, is a large individual measuring 83 mm. in diameter. It is a dark brown, silicified internal mold from near Webb City, Missouri. The ambulacral plates are demi- and occluded at the mid-zone, but primaries only close to the oculars. In three interambulacral areas, A, C, and G, there are six columns of plates. In each the sixth column is represented by a considerable number of plates, more than in any other specimen of the species seen. The exact number could not be ascertained as the point of origin of this column is not preserved in any area, but in area G a sixth column is represented by at least ten plates, above which it drops out, and there are five columns; and far dorsally, another column drops out, so that only four columns are in contact with the apical disc, as in area E of Plate 41, fig. 3. Dorsally molds of the five oculars are in place, all are insert, and ventrally cover the ambulacra and laterally the interambulacra in part on either side. The genitals are high, wide, with several pores each, but details of the pores are imperfect. A specimen from Coriscana, Missouri, in the Yale University Museum Collection, is well preserved and is practically spherical (Plate 44, fig. 2), measuring 59 mm. in height, 62 mm. in diameter through the mid-zone in the view shown, and also 59 mm. in diameter in the same plane, but at right angles to that figured. The specimen is an internal siliceous mold and shows the impression of plates clearly. There are five columns of plates in each interambulacral area at the mid-zone, and in no area is a sixth column developed. The oculars are all in place and insert; genitals are high, wide, with three pores in two of the plates, five pores in two, and in one genital the pores are indistinct. Another specimen from Coriscana in the Yale Collec- tion, no. 313, is very large and somewhat elongated by compression. It measures 114 mm. in height, 101 mm. in diameter through the mid-zone in one plane, and 76 mm. in diameter through a plane at right angles to the same. There are five columns of plates in all the interambulacral areas, though one area is obscure at the mid-zone. The genitals are high, wide, two with three genital pores, two with four, and one with five pores. A choice specimen from Webb City, Missouri, in the Museum of Comparative Zoology Collection, no. 3,125, has on one side a siliceous mold of the interior and on the other a siliceous mold of the exterior, the spaces originally occupied by the plates being hollow (Plate 44, figs. 3, LOVENECH1NUS. 4). The internal mold has impressions of the proximal faces of the plates, ridges represent inn bounding lines, and siliceous filaments which are casts of ambulacral pores. The external mold has impressions of the outer or distal faces of plates with tubercles, ridges ri-pn-ciitiiig bounding lines of plates, and siliceous filaments which are casts of ambulacral pores as in the inner mold. By studying the internal mold, and wax impressions made from the external mold, it is possible to compare the external and internal characters of the same plates as if seen in optical section (Plate 43, figs. 1-4). The ambulacrum seen from the exterior at the mid- zone (Plate 43, fig. 3) has four columns of plates, wide occluded and narrower demi-plates, with pore-pairs biserial and situated in the outer end of each plate, near the marginal suture. Two rows of tubercles are on the occluded, and a single tubercle on the inner tongue of the demi- plates. On the proximal or inner side of the very same plates (Plate 43, fig. 4), the occluded and demi-plates are of about equal width. Demi-plates opposite horizontal intorambulacral sutures are higher and fan-shaped, and pore-pairs lie near the middle of the half-area. This passage of pore-pairs from the middle to the outer margin of the area, in traversing the thick- ness of the plates, is shown graphically in a unique bit of preservation (Plate 43, fig. 5), in which we find proximally a mold of the interior, distally a mold of the exterior, and the pores represented by slender siliceous filaments which traverse the hollow space originally occupied by the plates. It is here seen that the filaments are strongly inclined laterally, being near the middle of the area proximally, but close to the outer margin of each plate distally. Ventrally, in the basicoronal row, as seen from the exterior (Plate 43, fig. 1), the ambulacral plates are all primaries, and pore-pairs uniserial, lying close to the marginal sutures. On the interior at the same zone (Plate 43, fig. 2) the ambulacral plates are also primaries, but the pore-pairs are about in the middle of the half-areas. Passing dorsally, on the exterior at the zone marked X (Plate 43, fig. 1), the plates are alternately primaries, expanded marginally, with those between narrowed and nearly or quite occluded, pore-pairs biserial, as in Maccoya. On the interior at the same zone marked X in Plate 43, fig. 2, the plates are still all primary, with pore-paiis uniserial, again like Maccoya, but as seen from the interior (Plate 33, figs. 8, 9). Again passing dorsally, on the exterior at the zone marked XX (Plate 43, fig. 1) the plates are demi- and oc- cluded, the genus character. On the interior at the same zone, marked XX (Plate 43, fig. 2), the plates are primary and occluded. They have therefore not yet taken on the character as seen on the exterior, but have lagged behind in development, and are like the more ventral plates of the exterior, and again like the typical plates on the exterior of Maccoya. This close comparison that can be drawn by stages in development, as seen in plates ventrally, built in youth, and the greater primitiveness of plates on the proximal side as compared with the distal side, with the simpler characters of lower genera in the family, is all in favor of the re- capitulation theory in evolution. Abundant similar cases are found throughout the Echini, supporting the same view in the strongest way. 346 ROBERT TRACY JACKSON ON ECHINI. In the interambulacra of this choice specimen there are five columns of plates at the mid- zone, in all five areas. Ventrally, there are two plates in the basicoronal row in all areas (Plate 43, figs. 1, 2), three plates in the second, and four plates in the third row. The fourth column originates on the right of the center in areas A, C, and E; but on the left of the center in areas G and I. In area A the fifth column originates as a pentagon in the sixth row, with a heptagon on its right ventral border. In area I the fifth column originates also in the sixth row, but by rare exception the initial plate is tetragonal, and to compensate for its two sides wanting, there is a heptagonal plate, H, on its right ventral border and another on its left border. The inter- ambulacral plates on the exterior (Plate 43, fig. 1), as usual, bear numerous small, secondary tubercles. These tubercles are shown on the external mold (Plate 44, fig. 4) , and especially clearly on another external mold (Plate 44, fig. 5). The character of primary plates ventrally, passing into four columns dorsally, as seen from the interior, is shown in Plate 39, fig. 6, and Plate 42, fig. 5. There is, however, some confusion ventrally in area B, and the series is not so complete as in the cases previously described. *Lovenechinus anglicus sp. nov. Plate 46, figs. 5, 6; Plate 47, figs. 3-5. 1 Palaeechinus gigas Duncan, 1889, p. 198, text-fig, i; Jackson, 189(3, p. 204, Plate 7, figs. 38, 39. 2Non Palaechinus gigas M'Coy, 1844; non Baily, 1874, p. 41, Plate 3, figs, a-d; non Keeping, 1870. 2Non Palaeechinus gigas Loven, 1874, p. 41. 2 Non Maccoya gigas Pomel, 1883, p. 115; non Lambert and Thiery, 1910, p. 119. 1 Palechinus gigas Tornquist, 1897, p. 739. 1 Palaechinus gigas (pars) Klem, 1904, p. 32. The specimen on which this species is based, in the Museum of Practical Geology Collec- tion 6,576, is apparently that of which Professor Duncan figured the ambulacrum as Palae- echinus gigas, and I also figured it as the same species. The structure of the ambulacrum of Palaeechinus gigas, however, is entirely different, being composed of primary and occluded plates, all of which meet the middle of the half-area (Plate 47, figs. 1, 2). The great size of the interambulacral plates, and also the original label, which reads Palaeechinus gigas, probably misled Professor Duncan when he described it. This specimen is in many respects very perfectly preserved, but is somewhat remarkable for the peculiarities by which portions of the test are shown (Plate 46, fig. 5). In interambula- crum A there are five columns of plates in place and a vacancy on the right for at least one additional column, which would be a right pentagonal adradial. Ambulacrum B is represented 1 The several references included in these paragraphs are based on the specimen here described as Lovenechinus anglicus and which Duncan erroneously referred to Palaeechinus gigas, see pp. 304, 321. * The several references included in these paragraphs refer to the true Palaechinus gigas of M'Coy, here referred to Maccoya gigas, p. 321. LOVENECHINUS. 347 by the right half-area only. The left half of ambulacrum B and the right portion of inter- ambulacrum C have been pushed under areas A, B so as to be quite hidden from view. Inter- ambulacrum C is represented by the left adradial and one adjacent median column of hex- agonal plates. Of ambulacrum D, the whole width of the area is in place, though not very clearly seen. Interambulacrum E has six columns of plates, as can be seen dorsally, although they are somewhat displaced. * A complete test is unknown; but the shape as preserved indicates that the entire specimen was probably spheroidal, and the size of the plates shows that the whole specimen must have been very large, one of the largest of known Palaeozoic Echini. The height of the specimen as it exists is 115 mm., and the width 150 mm. The half ambulacrum B measures 7.5 mm. in width, therefore the whole area would measure 15 mm. in width. Interambulacrum A measures 55 mm. in width. Adding one adambulacral column on the right (as this at least is wanting), the width on the basis of six columns would be about 65 mm. Assuming 15 mm. for the width of the ambulacrum, and 65 mm. for the interambulacrum, the circumference would be about 400 mm. and the diameter about 127 mm. The interambulacral plates are very large, the pentagonal adradials measuring up to 11 mm. in width by 8 mm. in height, and the largest hexagonals 12 to 13 mm. in width by 8 mm. in height. With this great areal size they are relatively very thin, about 2 mm. in thickness. The ambulacra are relatively narrow, with four columns of plates throughout most of the area, there being two columns of wider occluded and two of narrower demi-plates in each half- area (Plate 47, figs. 3, 5) The outer ends of the occluded plates fit between the inner tongue- like extensions of the demi-plates as in Lovenechinus missouriensis. The pore-pairs are in well marked peripodia and are biserial in arrangement, each pair situated in the outer ends of the occluded and demi-plates as usual in the genus. About four demi-plates equal the height of an adradial. The extreme ventral part of the test is unknown, but as far ventrally as preserved in area D (Plate 47, fig. 4) all ambulacral plates meet the middle of the half-area, but alternate plates are primaries expanded marginally, and occluded or cut off from interambulacral contact by enlargement of their fellows. This character is like that typical of adult Maccoya (Plate 33, fig. 7), and also like that seen as a second stage in development in Lovenechinus missou- riensis (Plate 42, fig. 1). On the reverse side of the specimen are several excellent fragments of ambulacra seen from the interior of the test. In these the demi- and occluded plates are of about equal width, and the pore-pairs lie near the middle of the half-areas, as seen in the in- ternal view of Lovenechinus missouriensis (Plate 43, fig. 4). The interambulacra are very wide, composed of probably six columns in each area. In area A (Plate 47, fig. 3) the left adambulacral column of pentagonal plates is in place, and also four columns of hexagonal plates. I have indicated by dotted lines a right adambulacral column which probably would complete the area. Six columns can be made out dorsally in 348 ROBERT TRACY JACKSON ON ECHINI. area E of the photographic figure (Plate 46, fig. 5). In area A ventrally, the initial plate of column 6 is seen as a pentagon with a heptagon on its left ventral border. Ambulacral and interambulacral plates alike bear small secondary tubercles with some minute tubercles between them. Many small, slender, tapering spines up to about 3 mm. in length are borne on both ambulacral and interambulacral plates (Plate 46, fig. 6). The dorsal part of the test is quite unknown. I am indebted to Dr. Kitchin of the Museum of Practical Geology for the excellent photograph of this species, which he kindly had taken for me by Mr. J. W. Tutcher. Lower Carboniferous, Clitheroe, Lancashire, holotype and only known specimen, Museum of Practical Geology, London, no. 6,576. *Lovenechinus septies sp. nov. Text-fig. 17, p. 59; Plate 44, figs. G, 7; Plate 45, figs. 1-6. The test is small, spheroidal, with remarkably perfect detail in the type, but crushed. Width of the ambulacra at the mid-zone 8.5 mm., of the interambulacra at the same zone 18 mm. Diameter in the neighborhood of 50 mm., but from the crushing it cannot be very closely stated. Ambulacra at the mid-zone and throughout most of the areas with four columns of plates, wide occluded and narrow demi-plates in each half-area (Plate 45, figs. 1, 3). The occluded plates laterally fit into the inner angles of the demi-plates, but with serrate, not tongue-like extensions (as in L. missouriensis, Plate 42, fig. 2). Pore-pairs are biserial, situated in the outer portion of each ambulacral plate. The ambulacral plates bevel over the adradials, and the occluded plates rise in a high arch which is formed by the median thickening of these plates (Plate 45, fig. 5). Ambulacral plates ventrally and dorsally are primaries, as later described in detail. Interambulacra at the mid-zone are wide, with six columns of plates, but a seventh appears dorsally in each area (Plate 45, fig. 1). The adambulacrals are pentagonal, others hexagonal as usual. Two interambulacral plates are in the basicoronal row in most area,1--, above which additional columns appear as usual in the family, as later described in detail. Small secondary tubercles occur alike on ambulacral and interambulacral plates, but no spines are preserved. Dorsally, the apical disc is crushed in, but can be made out in part. Oculars are insert, imperforate, and adorally cover the ambulacra and laterally in part the interambul- acra on either side. Genitals are high, wide, with two and probably more pores each. This species differs from others of the genus in having more columns of interambulacral plates ; also the contact of occluded and demi-plates differs from that of other species excepting L. mutatus, where the interlocking of these plates is closely similar. The holotype is in Mr. Frank Springer's collection and was received by him from Professor G. Hambach of St. Louis, Missouri. Warsaw Group, Lower Carboniferous, Boonville, Missouri; holotype in F. Springer's LOVENECHINUS. 349 Collection, no. 8,115; also three additional incomplete specimens from the same locality ami in the same collection. Although crushed, the type specimen is so completely preserved that I am able to repre- sent it spread out by the Loven method (Plate 45, fig. 1), and it presents interesting develop- mental characters in both ths ambulacra and the interambulacra. Ventrally, for ;i short distance, ambulaeral plates are primaries (Plate 45, fig. 2), above which follow primary and demi-plates immediately, and these again are shortly followed by the typical occluded and demi- plates characteristic of the type. No stage of primary and occluded plates (such as occurs in Lovenechinus missouriensis, Plate 42, fig. 1) was found in this species, and it has apparently been skipped by acceleration of development. This is interesting, for in other characters it is the highest species in the genus, and it is in just such a case of highest species that accel- eration is most marked, as shown by Hyatt. Dorsally, close to the oculars (Plate 45, fig. 4) high, narrow primary plates exist as a localized primitive stage, but, passing adorally, they quickly change into the characteristic four columns of demi- and occluded plate-. The interambulacra with only slight reconstruction (indicated by dotted lines) are shown throughout each area (Plate 45, figs. 1, 2). Ventrally, in each area (excepting C and G, in which they are restored) there are two plates in the basicoronal row and three plates in the second row. In four areas the initial plate of column 3 is hexagonal as usual, with the initial pentagon of column 4 in the next succeeding row. In area C, however, there are two rows of three plate- each before column 4 originates in the fourth row. As a result of this difference, the initial plate of column 3 is pentagonal and the succeeding plate is heptagonal, having one side added to compensate for the one side short in pentagon 4 (p. 68). A similar case of this rare varia- tion of a later introduction of column 4 with coincident modifications in the angles of asso- ciated plates is seen in Palaeechinus quadriserialis (p. 307; Plate 30, fig. 3, area C). In /.. septies (Plate 45, fig. 1) the fourth column originates on the right of the center in areas A and E, but on the left of the center in areas C, G, and I. The fifth column originates with a pentagon in the middle in all areas. In areas A and E it originates in the sixth row with a heptagon on the right ventral border, in G and I in the sixth row with a heptagon on the left ventral border, and in area C in the seventh row with a heptagon on the left ventral border. The sixth column originates with a pentagonal plate in the tenth or twelfth row in each area. It originates in areas A and G in the twelfth row on the right of the center with a heptagon on the right or left ventral border; also in area C it originates in the twelfth row, but on the left of the center, and with a heptagon on its right ventral border. In areas E and I the sixth column originates in the tenth row, on the left of the center with a heptagon on the right ventral border. The seventh column originates with a pentagonal plate in the middle of each area, with a heptagonal plate on the ventral border. In three cases, areas E, G, and I, the heptagon lies on the right, and in two cases, areas A and C, on the left of the initial pentagon. The 350 ROBERT TRACY JACKSON ON ECHINI. seventh column originates in the sixteenth to the nineteenth row in the several areas. In area A it appears in the eighteenth row; in C in the nineteenth row; in G in the seventeenth row ; and in areas E and I in the sixteenth row. It is worth noting that in areas E and I, in which the seventh column originates earlier than in the others, column 6 also originates earlier, showing an acceleration in both features. Also, in area C columns 4, 5, and 7 all originate later than in the other areas, showing a corresponding retardation of development in those several features (p. 50). Dorsally in part, as shown in area C, the adambulacral columns 1 and 2 drop out before reaching the apical disc, indicating senescence. OLIGOPORUS Meek and Worthen. Oligoporus Meek and Worthen, 1860a, p. 472; 1866, p. 247; (pars) Loven, 1874, p. 42; Duncan, 1889a, p. 16; (pars) Jackson, 1896, p. 239; (pars) Lambert and Thiery, 1910, p. 121. Melonopsis Meek and Worthen, 1866, p. 249. The test is spheroidal, with more or less strongly developed melon-like ribs. Ambulacra at the mid-zone with four columns of plates which consist of two columns of wide occluded and two columns of narrower demi-plates, with, in addition, scattered isolated plates in the middle line of each half-area, but not of sufficient frequency to constitute an additional column. The wide occluded plates are roundly arched upward in the center. The pore-pairs are multiserial, one series in each column of demi- and occluded plates, and, in addition, a broken series in the scattered isolated plates. The interambulacra are wide, with from four to nine columns of plates in an area in the known species. The columns are composed of pentagonal adradial and hexagonal median plates. There are ventrally two plates in the basicoronal row, above which additional columns come in as usual in the family. There is no imbrication in ambulacral or interambulacral plates, but the ambulacrals bevel over the adradials laterally. Ambulacral and interambula- cral plates bear small secondary tubercles with small tapering spines. Peristome unknown. Apical disc imperfectly known, but doubtless similar to that in Melonechinus with insert, imperforate oculars and high, wide genitals bearing several genital pores each. Lantern known partially in 0. danae, from which it is seen that the lantern was inclined, pyramids wide-angled with moderately deep foramen magnum as usual in the Perischoechinoida. The type species of the genus is Oligoporus danae (Plate 49, figs. 4, 5; Plate 47, fig. 13; Plate 50, figs. 1-12). Oligoporus differs from Lovenechinus in that it has scattered isolated plates in the ambulacra in addition to the four columns of demi- and occluded plates. Thus it is a step in advance in the evolution of this important structure. In the interambulacra it is also more advanced in that the highest species (danae) has nine columns of interambulacral plates in an area, whereas OLIGOPORUS. 351 in Lovenechinus the highest known species (septies) has only seven columns in an area. Oligo- porus differs from Melonechinus, as in that genus the isolated plates are sufficiently numerous so that they form one or more irregular columns of plates between the demi- and occluded plates in each half-area. Melonechinus is also more evolved in the interambulacrum in that the high- est species has eleven columns of interambulacral plates, whereas the highest species of Oligo- porus has but nine. In the development of the ambulacrum ventrally, Oligoporus passes through a stage in which the plates are like Lovenechinus at the mid-zone; and Melonechinu- in the development of its ambulacrum ventrally passes through stages in which the plates arc successively like Lovenechinus, then like Oligoporus at the mid-zone (text-fig. 237, p. 231). Thus both the structure in adults and the progressive stages in development unite these genera into a phylogenetic whole. Key fit the SjH'rii'.t of Interambulacra with six or seven columns of plates in an area (in one area of one specimen, as an excep- tional arrested radial variation, there are four columns only); melon-like ribs moderately developed (). hlairi Miller and Gurley, p. 351. Interambulacra with seven columns of plates in an area, or in part with six columns only; melon-like ribs strongly elevated and rounded in outline ..... 0. corryi Meek and Worthen, p. 353. Interambulacra with seven columns of plates in an area; melon-like ribs strongly elevated and sharply rounded ; interambulacra dipping steeply down to adradial sutures . 0. sulcatus Miller and Gurley, p. 354. Interambulacra with eight or seven columns of plates in an area . . . 0. halli sp. nov., p. 355. Interambulacra with nine columns of plates in an area . . 0. danae (Meek and Worthen), p. 356. *Oligoporus blairi Miller and Gurley. Plate 47, figs. G, 7; Plate 48, fig. 1; Plate 49, figs. 1-3. Oligoporm blairi Miller and Gurley, 1893, p. 6, Plate l.figs. 2,6; Plate 2, fig. 7; Lambert and Thiery, 1910, p. 121. Oligoporus bellulus Miller and Gurley, 1893, p. 7, Plate 1, fig. 3; Umbert and Thiery, 1910, p. 121. Oligoporus danae (pars) Klem, 1904, p. 37. The test is spheroidal, with moderately developed melon-like ribs. In one specimen (Plate 49, fig. 1) the ambulacra measure 12 mm., the interambulacra 21 mm. in width. In a second specimen (Plate 49, fig. 3) the ambulacra measure 12 mm. and the interambulacra 18 mm. in width. The ambulacra are relatively wide, having at the mid-zone four columns of narrow derni- and wider occluded plates, also some scattered isolated plates in or near the middle of the half- areas. Occluded plates are elevated in a low rounded median ridge; pore-pairs are near the outer border of each ambulacral plate. 1 The species described as Oligoporus (?) minutus is considered under Incertae Sedis (p. 450). 352 ROBERT TRACY JACKSON ON ECHINI. Interambulacra broad, elevated in a moderate curve from the adradial sutures, with six or seven columns of plates in each area. In one specimen (Plate 48, fig. 1) one area, A, as an exception is very narrow, and has four columns of interambulacral plates, but the next ad- jacent area, C, has seven columns. This specimen, on account of the four columns in one area, was considered a distinct species by Miller and Gurley, and described as Oligoporus bellulus. The ventral and dorsal portions are unknown. Ambulacral and interambulacral plates bear small secondary tubercles, and one specimen has numerous small tapering spines about 2.5 mm. in length. The specimen which Miller and Gurley described as the type of Oligoporus bellulus (Plate 47, fig. 6; Plate 48, fig. 1) I feel is nothing more than a very peculiar exception. The ambula- crum and interambulacrum C with seven columns are quite normal for the species. The interambulacrum A is certainly very exceptional in having only four columns; no such range in two areas of one individual has been seen in any other specimen in this family. It may, however, better be considered an extreme arrested variant in this one area rather than as a basis for a distinct species. I therefore consider bellulus a synonym of blairi. Miller and Gurley do not mention that there are seven columns in one of the areas of this specimen. It has numerous small spines as described above. One of Miller and Gurley's cotypes of blairi (Plate 47, fig. 7; Plate 49, fig. 1) represents a considerable part of the dorsal half of a test. It is perhaps the most characteristic of all the specimens. The interambulacra A and C have each seven columns of plates. Miller and Gurley give six columns as the species character, but do not mention a seventh. I do not quite understand how they overlooked this feature. This specimen shows the surface form of the areas better than any other. A second cotype (Plate 49, fig. 3) represents about the middle of the corona. In area A there are six columns of plates; ventrally the initial pentagonal plate of column five is seen in the middle line and in the second row from the base. The initial pentagon of column six is seen in the sixth row from the base, and a heptagonal plate lies on its right ventral border. In area C there are six columns of plates and indications of a seventh column as shown by the pentagon, with a heptagonal plate on its right ventral border lying 30 mm. from the base of the specimen and with three columns of interambulacral plates lying between this pentagon and ambulacrum D. The third cotype of blairi and the smallest specimen (Plate 49, fig. 2) has six columns of interambulacral plates in area A. The initial plate of the sixth column is a pentagon with a heptagon on its left ventral border and lying just below the middle of the area. In area C there are seven columns of interambulacral plates. The initial plate of column 5 lies 7 mm. above the ventral border of the specimen, and there is a heptagonal plate on its right ventral border. Three rows above appears the initial pentagon of column 6, with a heptagon on its OLIGOPORUS. 353 right ventral border. Three rows higher again appears the initial plate of the seventh column with a heptagon on its left ventral border. This species is very close to Oligoporus coreyi; but apparently differs from that species in the less pronounced and less sharply elevated ribs in the arnbulacral areas. It is very distinct from Oligoporus danae of which it was treated as a synonym by Miss Klem. Through the kindness of Professor Stuart Weller, I have been able to study all of the original material and give figures of the same. Keokuk Group, Lower Carboniferous, Boonville, Missouri, cotypes, three specimens in the University of Chicago Collection 6,470; same locality, an additional specimen (which is the holotype of Oligoporus bellulus) University of Chicago Collection 6,190; Keokuk Group, Bono, Lawrence County, Indiana, Museum of Comparative Zoology Collection 3,188. *Oligoporus coreyi Meek and Worthen. Plate 47, figs. 8, 9; Plate 48, fig. 2. Oligoporus coreyi Meek and Worthen, 1870, p. 34; Love"n, 1874, p. 42; Keyes, 1895, p. 183; Jackson, 1896, p. 189, text-fig. 1, p. 191, Plate 6, figs. 25, 28, 29; Klem, 1904, p. 38; Lambert and ThieVy, 1910, p. 121. The type specimen is silicified and beautifully preserved as regards form, although not very clear in detailed structure, as it is worn, and the test is somewhat compressed. Test spheroidal, with strong, rounded, elevated melon-like ribs in both ambulacral and interambulacral areas. Height 40 mm. ; this measurement would be greater if the specimen had not been compressed. Diameter at the mid-zone through the plane B, G, 58 mm.; through the plane D, I, 59 mm. The measurements of the diameter are somewhat exaggerated by the dorso-ventral compression of the test. The ambulacra at the mid-zone measure about 12 mm. in width and the inter- ambulacra about 20 mm. in width. The ambulacra could not be made out satisfactorily at the mid-zone, but in the mid-dor- sal region (Plate 47, fig. 9) there are four columns of demi- and occluded plates. These are of about equal width, a usual character dorsally; but at the mid-zone the occluded are probably wider than the demi-plates. In addition, there are some scattered isolated plates that do not reach either the middle of the area or the interambulacra, which is the generic character. Pore-pairs are in deep sunken furrows, lying in the outer border of each plate. The occluded plates in the middle are arched up in a high rounded melon-like curve. The interambulacra just above the mid-zone have seven columns of plates in areas A, E, and G. In area C there are only six columns, and in I there are six columns, and possibly seven, but this area is not clear dorsally. The seventh column comes in a little dorsal to the mid-zone, and at that zone, strictly speaking, there are six columns of plates in all areas. The 354 ROBERT TRACY JACKSON ON ECHINI. surface ornamentation is not preserved, but it doubtless bore small secondary tubercles as in related species. The ventral portion and apical disc could not be ascertained in the type. A specimen in the Museum of Comparative Zoology Collection 3,008, which I described previously (1896) and referred to this species, is an internal view. Ventrally, the ambulacral plates are not very well preserved, but are seen to cross the half-area. Higher up the plates are in four columns, demi- and occluded, and the pore-pairs are in the middle of the half-areas, as seen on the interior of Lovenechinus. In the interambulacrum there are two plates in the basicoronal row, three plates in the second row, and four in the third. The fifth column comes in in the sixth row, and as seen in another area, the sixth column comes in three rows above the fifth, apparently in the ninth row. This specimen is preserved as calcite plates in a clay matrix, stained yellow with iron. The locality given on the label is Indiana, and Mr. Springer informs me that material of this character occurs at Crawfordsville, so that the specimen probably came from that locality or its vicinity. This species is very close to blairi and sulcatus; the difference from blairi is its more strongly elevated melon-like ribs, and the difference from sulcatus is the sharply angular character of the interambulacral areas of that species where they dip down to the adradial sutures. These differences are slight, but they are sufficient, it seems, to maintain these as distinct species, although in the number of columns of interambulacral plates they are practically identical. The specimen which I identify as the holotype is in the University of Michigan Collection 147, from the Keokuk beds of Crawfordsville, Indiana. It bears the locality and identification in Meek's handwriting, and corresponds with the original description in essential features, so that it is undoubtedly the type; another specimen from Crawsfordsville is in the British Museum Collection E 4,273. A third specimen, in the Museum of Comparative Zoology Collection 3,008, as described above, and probably from the same locality, is the only other known specimen of the species. "Oligoporus sulcatus Miller and Gurley. Plate 47, fig. 10; Plate 48, figs. 3, 4. Oligoporus sulcatus Miller and Gurley, 1893, p. 8, Plate 1, figs. 4, 5; Lambert and Thiery, 1910, p. 121. Melonites multiporus (pars) Klem, 1904, p. 43. The specimen is silicified, test high, spheroidal, with strongly marked and quite angular melon-like ribs in ambulacral and interambulacral areas. The holotype, which is the only known specimen, measures 53 mm. in height, and 65 mm. in diameter through the mid-zone, in the plane J, E. Ambulacra measure 13.5 mm. in width, interambulacra 25 mm. in width at the mid-zone. The surface detail is corroded and gone in parts, especially ventrally, as seen in the photographic figures, but the essential specific features can be ascertained. The ambulacra at the mid-zone (Plate 47, fig. 10) consist of four columns of narrower demi- and OLIGOPORUS. 355 wider occluded plates, with scattered isolated plates in the middle line of each half-area. The occluded plates are medially rounded up in a high, steeply arcuate ridge. Pore-pairs arc in deep, sunken valleys, lying in the outer border of each ambulacral plate. The interambulacra are wide, strongly elevated in melon-like ribs, which outwardly present * a gently rounded curve, but laterally dip suddenly down to the adradial sutures. At the mid- zone in each area there are six columns of interarnbulacral plates, but just above the mid-zone, a seventh column appears in each area. As noted by Miller and Gurley, part of the columns drop out dorsally before reaching the apical disc, indicating senescence. Traces of insert ocular and genital plates appear dorsally. This species is close to blairi and coreyi, but differs from them, as discussed under coreyi. Its reference to Melonechinus multiporus as a synonym by Miss Klem is certainly wide of the mark. St. Louis Group, Lower Carboniferous, Hardin County, Kentucky, holotype in University of Chicago Collection 6,623, whence it was kindly loaned me by Professor Stuart Weller. *01igoporus halli sp. nov. Plate 47, figs. 11, 12; Plate 48, fig. 5. Oligoporus sp. Klem, 1904, Plate 1, figs. 3a, 3b. A large, massive sea-urchin, slightly elliptical in form, with moderately developed melon- like ribs. Height of type 103 mm., diameter through the mid-zone 100 mm., width of ambu- lacra at the mid-zone 18 mm., width of interambulacra 31 mm. Ambulacra near the mid-zone with four columns of demi- and occluded plates, the latter slightly the wider, and with scattered isolated plates in the middle line of each half-area. Oc- cluded plates in the middle are curved outward in a low, rounded arch. Pore-pairs in lateral depressions, are situated in the outer portions of each ambulacral plate. Interambulacra are wide, rounded up from the adradial sutures in a gentle rounded curve. In areas A, C, and I there are eight columns of interambulacral plates at or just above the mid- zone, but in areas E and G there are only seven columns. Areas G and I are not seen in the photographic figure (Plate 48, fig. 5), being on the opposite side of the specimen. In area A (Plate 47, fig. 11) the two ventral rows of plates are restored, as indicated by dotted lines; there are four plates in the third row. The fifth column appears in the sixth row and the sixth column in the eleventh row. The seventh column appears on the left of the center in the fifteenth row. In area C the seventh column appears in the center five rows above the base as far as pre- served, and the eighth column originates at or just above the ambitus. The introduction of these two columns in area C is clearly seen in the photographic figure (Plate 48, fig. 5). The apical disc and dorsal portion of the specimen are wanting. This fine species is known only from the holotype which was kindly loaned me by Mr. 356 ROBERT TRACY JACKSON ON ECHINI. Springer. It is named for the late Professor James Hall, who did such extensive and valuable work for Palaeontology in America. This species is near to Oligoporus danae, but differs from it in that it has seven or eight instead of nine columns of plates in an interambulacral area; also in that the interambulacra have a much less accelerated development than in danae. Keokuk Group, Lower Carboniferous, Boonville, Missouri, F. Springer Collection 8,114, originally in G. Hambach's collection. Oligoporus danae (Meek and Worthen). Text-figs. 12, p. 54; 237, p. 231; Plate 47, fig. 13; Plate 49, figs. 4, 5; Plate 50, figs. 1-12. Mdoniies danae Meek and Worthen, 1860, p. 397. Oligoporus danae Meek and Worthen, 1860a, p. 472; 1866, pp. 248, 249-251, text-fig. 28, Plate 17, fig. 8; Love"n, 1874, p. 42; Keyes, 1894, p. 126, Plate 17, figs. 2a, 2b; 1895, p. 182, Plate 20, figs. 2a, 2b; Jackson. 1896, p. 191, text-fig. 1, p. 193, Plate 6, figs. 30-34; (pars) Klem, 1904, p. 37; Lambert and ThieYy, 1910, p. 121. Melonopsis [danae] Meek and Worthen, 1866, p. 249. Palaechinus danae Meek and Worthen, 1866, p. 251. Test high, spheroidal, with moderately elevated melon-like ribs in ambulacral and inter- ambulacral areas. Meek and Worthen say of the type that it is too imperfect to give any exact measurements, but it indicates a height of about 4 inches and a breadth of probably from 3.5 to 4 inches. In the large specimen (Plate 49, figs. 4, 5), which is the most nearly complete one known, the ambulacra measure 21 mm. in width at the mid-zone, the interambulacra about 45 mm. in width. The specimen, if complete, would measure about 115 mm. in height, and about 120 mm. in diameter; it is therefore a very large individual. The ambulacra at the mid-zone are wide, composed of four columns of narrower demi- and wider occluded plates with scattered isolated plates in the middle line of each half-area. The occluded plates in the middle line are arched up as low, rounded, melon-like ribs. Pore- pairs are in shallow valleys on either side, and situated in the outer border of each ambulacral plate. Three or four demi-plates are equal in height to an adradial. Laterally, ambulacral plates bevel over the interambulacrals on the adradial suture. Ventrally, at the peristomal border, there are a few primary ambulacral plates that cross the half-area, and the pore-pairs are uniserial (Plate 50, fig. 8). This is like the character of Palaeechinus at the mid-zone, and like Maccoya and Lovenechinus at the ventral border. Higher up on the right side of area J are two plates which are alternately primary, expanded on the outer border, and occluded, being cut off from interambulacral contact by the enlargement of its fellow. This stage, though very abbreviated, is like the character of Maccoya at the mid-zone, and like the second stage in the development of Lovenechinus. Higher again, there are four columns of plates, demi- and occluded, but without any isolated plates in the middle of the half-areas. This OLIGOPORUS. .V>7 stage in Oligoporus is like the character of Lovenechinus at the mid-zone. Still higher up in this specimen (Plate 50, fig. 9), isolated plates appear in the middle of the half-areas, fixing the character of the type. It will be seen therefore that in Oligoporus danae the development of the ambulacrum ventrally passes through a series of stages which are successively comparable to the adult character of the three lower genera of the family as set forth diagrammatically in text-figure 237, p. 231. The interambulacra are broad, gently curving in elevated ribs, not sharply inclined laterally to the adradial sutures. There are nine columns of plates in each area at or above the mid- zone in all specimens known. Ventrally, there are in the interambulacra (Plate 50, fig. 8) two plates in the basicoronal row, three plates in the second, and four in the third row. In area A the fifth column appears in the fifth row. In a fine specimen shown in Plate 49, figs. 4, 5, there are four interambulacra for study, which is more than is known in any other specimen. In area A (Plate 50, fig. 1) there are nine columns at the mid-zone, and dorsally columns 1 and 2 drop out before reaching the apex, indicating senescence. In area C the ventral portion is restored, as indicated by dotted lines. Assuming that this is correct, the fifth column origi- nates in the sixth row, with a pentagonal plate and a heptagon on its right ventral border. The sixth column originates to the right of the center in the ninth row, with a heptagon on its left ventral border. The seventh column originates in the thirteenth row, with a heptagon on its right ventral border. The eighth column originates in the sixteenth row, with a heptagon on its right ventral border. The ninth column originates to the left of the center with a pen- tagonal plate in the twenty-first row and with a heptagonal plate on its left ventral border. This is a quite typical area, whereas the following present unusual features. In area E (Plate 50, fig. 2) the ventral portion is also restored, and the adambulacral plates on either side show the beveled sutural faces that extended under the ambulacra when in place. The fifth column originates in the sixth row, with a pentagon on its right ventral border. The sixth column originates in the ninth row, on the left of the center in a pentagonal plate, with a heptagon on its left ventral border, and the seventh column originates in a pentagon in the center, in the twelfth row. In this area two curious anomalies occur just above pentagon 6; in column 3 an aberrant pentagon, P, occurs, and, to compensate for its one side wanting, there is a heptagon on its right side, immediately dorsal to pentagon 6. On the dorsal side of the aberrant pentagon P, lies a heptagon, H. This plate compensates for the one side wanting in pentagon 7, but. in- stead of lying next to it, is two plates removed. This is a very unusual and rare variant, but emphasizes the mechanical requirements of the case, that, if a side is wanting in one plate, there must be a side added to some other plate in order that all shall be either hexagonal or the equivalent of the same. The eighth column in area E originates in the fifteenth row, on the left of the center, with a pentagon, and a heptagon lies on its right ventral border. Column nine originates in the nineteenth row, but the initial plate, instead of being pentagonal, is 358 ROBERT TRACY JACKSON ON ECHINI. tetragonal, and to compensate for the two sides wanting, there are two heptagons on its right and left ventral borders respectively. Area I (Plate 50, fig. 3; compare Plate 49, fig. 5) is viewed from the interior of the test. The ventral portion is restored. Assuming that this is correct, the fifth column originates in a pentagon in the sixth row, with a heptagon on its left (right as seen from exterior) ventral border. The sixth column originates with a pentagon in the ninth row with a heptagon on its right (left as seen from the exterior) ventral border. Column 7 originates with a pentagon in the twelfth row, and a heptagon is on its right (left as seen from the exterior) ventral border. The eighth column originates with a pentagon in the fifteenth row, with a heptagon on its left (right as seen from the exterior) ventral border. Finally, the ninth column originates in the twenty-third row, and, as in the same column in area E, the initial plate of this column is tetragonal, and to compensate for the two sides wanting, has two heptagonal plates on its right and left ventral borders (pp. 369, 391). The detailed structure of the interambulacra in the type specimen, and also in a specimen in the Museum of Comparative Zoology Collection, 2,997, is figured and discussed in my earlier paper (1896, pp. 193, 197, Plate 6, figs. 31, 34). In both there are nine columns of interambulacral plates, the ninth originating late, considerably above the mid-zone. In this species both ambulacral and interambulacral plates bear numerous small secondary tubercles, with small tapering spines about 5 mm. long. A specimen from Edwardsville, Indiana, in the Museum of Comparative Zoology, no. 3,187, shows clearly the ventral developing stages of ambulacral and interambulacral areas, also spines. A genital plate is high and wide with three genital pores (Plate 50, fig. 6). The outline of this plate presents straight lateral sides for sutural contact with the oculars, so that it may be inferred, although they are not preserved, that the oculars separated the genitals and were insert, as indicated by dotted lines in the sketch. The lantern as shown by two half-pyramids (Plate 50, figs. 11, 12) is inclined, pyramids wide-angled, with moderately deep foramen magnum. The pyramidal suture extends to the base of the foramen as usual, and the dental slides, as seen in internal view, extend to about the level of the foramen. The lateral wing of the pyramids is wide (Plate 50, fig. 11) and has the remains of plicate ridges for the attachment of inter- pyramidal muscles. Oligoporus danae is the type species of the genus. The original locality given by Meek and Worthen (1866, p. 251) is Keokuk Group, Lower Carboniferous, Jersey County, Illinois; also Warsaw, Illinois. The type is said to be in the Worthen Collection, now in the University of Illinois at Urbana, Illinois. Keokuk Group, Lower Carboniferous, Adams County, Illinois, Museum of Comparative Zoology Collection 3,142; Warsaw, Illinois, Museum of Comparative Zoology Collection 2,997; Keokuk, Iowa, Museum of Comparative Zoology Collection 2,998, figured by R. T. Jackson 1896, Plate 6, fig. 30; Salem, Indiana, Museum of Comparative Zoology Collection 3,143 MELONECHINUS. .T><) 3,144 and 3,145; Edwardsville, Floyd County, Indiana, Museum of Comparative Zoology Col- lection 3,187; Missouri, Museum of Comparative Zoology Collection 3,146; Washington County, Indiana, F. Braun Collection; Alton, Illinois, Yale University Museum Collection 315, and 316; Felton, St. Louis County, and Curryville, Pike County, Missouri (Keyes). MELONECHINUS Meek and Worthen. Mi'lnnHi-a Norwood and Owen, 1846, p. 225; Meek and Worthen, 1860, p. 39(5; LoveX 1874, p. 41; A. Agassiz, 1874, pp. (547, 648, 649; 1881, pp. 78, 80; 1904, p. 80; Duncan, 1889a, p. 15; Jackson and Jaggar, 1896; Jackson, 1896, p. 240; 1899, p. 131 (non Mclonites Lamarck, 1822, Animaux sans Vertebres, vol. 7, p. 615). Mcloncchinw Meek and Worthen, 1860, p. 396; Lambert and ThieVy, 1910, p. 120. Quenstedt, 1875, p. 381. The test is spheroidal, or exceptionally (M. obovatus) obovate, typically more or less strongly marked by elevated melon-like ribs in ambulacral and interambulacral areas, but in two Euro- pean species the melon-like ribs are wanting. These ribs are due to the thickening of plates, and in most species are slightly, if at all, recognizable in internal molds (pp. 371, 373). In the ambulacra the ribs are formed mainly by the thickening of the two wide median columns of occluded plates. Ambulacra are wide, with two columns of wider occluded plates which extend from the center outward, two columns of narrow demi-plates which extend from the interambulacral sutures inward, and, in addition, at the mid-zone, from one to four irregular columns of isolated plates situated between the demi- and occluded plates in each half-area. The demi-plates bevel over the interambulacrals on the adradial suture, and may be traced ventrally to the simpler condi- tion at the peristomal border (Plate 56, fig. 3), but otherwise, as seen from the exterior, are practically indistinguishable from isolated plates. From this structure it results that in Melon- echinus there are at the mid-zone from six to twelve somewhat irregular columns of plates in each ambulacral area, the two halves of an area being equally balanced. In the lower genera of the family the structure of the ambulacra was essentially alike in all species of each genus, but in Melonechinus there is much specific difference, and, as the ambulacrum is the most important structural and physiological part, I consider those species with the simplest ambulacra as the lower species, and those with more complex ambulacra as progressively higher species. A- stated, the melon-like ridges in the ambulacra are formed mainly by the median thickening of the two central columns of occluded plates (Plate 60, fig. 3). The pore-pairs are in two more or less deeply depressed valleys on either side. Each pore-pair is surrounded by a peripodium (Plate 61, fig. 8), which, however, is commonly worn away and the pores lie in the outer border of each ambulacral plate. This is the character as seen from the external or distal side (Plate 56, fig. 4). As seen from the proximal, or internal aspect (Plate 56, fig. 5), occluded plates 360 ROBERT TRACY JACKSON ON ECHINI. are narrower than oh the exterior, and demi-plates, opposite horizontal interambulacral sutures are higher and laterally fan-shaped (compare text-fig. 244, p. 338). The pore-pairs on the inner aspect lie near the outer border of the occluded plates as they do on the exterior, but they lie near the inner border of the demi-plates, and in all isolated plates the pore-pairs are approxi- mately in the middle of each plate, instead of near the outer margin of the plate, as they are in all plates on the exterior (Plate 61, figs. 5-9). Ambulacral plates bear small secondary tubercles and spines similar to those of the interambulacra (Plate 61, fig. 8), (pp. 54, 59). Such being the structure of the ambulacrum at the mid-zone, the ventral developmental characters are of great interest. Near the peristomal border in Melonechinus there are typi- cally four columns of ambulacral plates (Plate 56, figs. 2, 3), narrow demi- and wider occluded plates; this is the character of plates at the mid-zone in Lovenechinus (Plate 42, fig. 2), and as a third stage in the development of Oligoporus (Plate 50, fig. 8). Passing dorsally in Melon- echinus (Plate 56, fig. 3), soon scattered isolated plates appear in the middle of each half-area; this is like the character at the mid-zone in Oligoporus (Plate 50, fig. 7). Again, passing dor- sally in Melonechinus, the isolated plates become more frequent, so as to come in vertical con- tact, and thus a new column is attained and the essential generic character acquired. If the species is to have only six columns of plates at the mid-zone, the ventral development goes no further, but in others additional isolated columns appear with dorsal growth until the full complement of the species in hand is attained. From this it follows that species with many columns of isolated plates pass through stages with fewer columns, which stages are directly comparable to the condition at the mid-zone of lower species in the genus, as briefly shown in the diagram (text-fig. 237, p. 231). While this is the typical character of the development of the ambulacrum in Melonechinus, as I have traced it in several species and many specimens, in one specimen of Melonechinus multiporus a still simpler condition occurs. In this choice individual (Plate 57, figs. 1, 3; text- fig. 245, p. 382), in area B, ventrally there are a few primary plates, which pass directly across the half-areas, and, while not typical as a ventral developing character in Melonechinus, these plates express a reversionary radial variation to the character typical of adult Palaeechinus, the lowest genus of the family, and also to a condition that is typical of the ventral border as a developing stage in Maccoya, Lovenechinus, and Oligoporus. And yet some people maintain that the recapitulation theory is a myth, and stages in development do not exist ! While the ventral developing stages are the most clear, yet dorsally the ambulacrum in Melonechinus presents a series of localized stages in the young last added plates. Next to the ocular are found few, even as few as two plates (Plate 53, fig. 1; Plate 56, fig. 6), and, when there are two, the condition represents two columns as a stage, which is simpler than the usual ventral stage with four columns and is comparable to the typical condition of Palaeechinus. Passing ventrally to the next older plates, we find four columns (Plate 52, fig. 2), comparable MELONECHINUS. 361 to the typical condition of Lovcncchinus. Further ventrally, some Mattered i-nlatod plate« appear (Plate 52, fig. 2), which, as a stage, repeat the typical character of Oligopoi-n-. Then the isolated plates become more frequent so that a third column is attained, which brings it to the condition typical of the lowest species in the genus. As one p:is-es ventrally toward the mid-zone, the number of columns increases progressively until that characteristic of tin- species in hand is attained (Plate 57, fig. 1; text-fig. 245, p. 382; Plate 59, fig. 1). Thu- d>. dorsal localized stages repeat, and in a measure go farther than ventral youthful stages in recapitulating the features characteristic of lower genera in the family or lower species in tin- genus, as diagrammatically shown in text-fig. 237, p. 231. In considering the ambulacrum in the Perischoechinoida, Mr. Agassiz (1874, pp. 648, 649) makes certain statements to which it seems necessary to call attention. He says (p. 648), "In Archaeocidaris (Fig. 2) [this figure is Melonechinus multiporus] there are four plates in the ambulacra; each plate forming vertical rows, much as in Hipponoe and Holopneuste-." Archaeocidaris has two columns of simple plates in each ambulacrum (Plate 9, fig. 6), while Hipponoe [= Tripneustes] and Holopneustes both have two columns of compound plate- in an ambulacral area, each plate being composed of three elements. In treating of the ambula- crum of Melonechinus and other members of the Perischoechinoida with many columns of plates in an ambulacral area, Mr. Agassiz (1874, p. 649) compares these with the plates in Stomo- pneustes, Strongylocentrotus, and Heterocentrotus. I do not think that these are parallel cases because in the Centrechinoida there are two columns of compound ambulacral plates in an ambulacral area and the component elements of these compound plates are entirely distinct from the many columns of simple plates that occur in certain Palaeozoic types. The interambulacra in Melonechinus are somewhat wider than the ambulacra or excep- tionally (M. obovatus) are narrower. Typically, they are gently or sharply rounded up from the adradial sutures in lower or higher melon-like ribs (Plates 51, 55, 60), which are formed mainly by the thickening of the plates. In two European species the melon-like ribs are appar- ently absent in the interambulacra as they certainly are in the ambulacra. There are from three to eleven columns of plates in an interambulacral area at or above the mid-zone, three (obovatus) being the smallest," and eleven (giganteus) the greatest number known in the genus and the family. Plates of adradial columns are pentagonal and bevel under the ambulacrals as in other genera of the family, and the plates of median columns are hexagonal or the mechani- cal equivalent of the same; that is, if one plate has less than six sides, some other plate has more than six to compensate (p. 68). Dorsally, near the apical disc, young interambulacral plates are more or less rhombic (Plate 57, fig. 1; text-fig. 246, p. 382), but with growth, as they are pushed ventrally by later added plates, the ventral and dorsal borders of each plate are soon truncated, and converted into hexagons, by contact with associated plates in their own vertical series. There is no imbrication of interambulacral plates, the sutures, excepting the 362 ROBERT TRACY JACKSON ON ECHINI. adradial, being perpendicular to the surface, but on account of the thickness of the plates the sides are far from parallel, being often almost wedge-shaped in some of the thick-plated species. Interambulacral plates bear small secondary tubercles with corresponding small spines as in the ambulacra. In the lower genera of the family the species are largely based on the number of interambula- cral columns in an area; but in Melonechinus there is a large range in the number of ambulacral columns, and this is considered a more important character, taking precedence over the number of interambulacral columns, which is relegated to a secondary place as a species differential. It is worth noting that the highest species, M. giganteus, has the highest number of interambula- cral columns known in the family (Plate 60, fig. 3; Plate 61, fig. 8). The interambulacra of Melonechinus ventrally have two plates in the basicoronal row (discussion, p. 66), and three plates in the second row (Plate 56, fig. 2). With rare exception the fourth column originates in the third row, above which additional columns, if added, come in with considerable regularity and with a perfectly definite system, as first shown by Jackson and Jaggar (1896). This system is the same as in all this family, and is shown in a represen- tative species in Plate 57, fig. 1 and text-fig. 246, p. 382 (p. 70). Mr. Agassiz (1881, pp. 78, 79, 95) considers that the numerous interambulacral plates of Melonechinus and other genera of the Perischoechinoida are derived from the splitting up of primary interambulacral plates, but I cannot agree with this view (pp. 28, 64, 378). Mr. Agassiz (1881, p. 79) also considers that the large number of coronal plates in the Palaeechinidae is a feature in which they " show most unmistakably their systematic affinity to the Crinoids." In thus expressing himself he supports the view that he earlier published (1864, p. 16), in which he considered the genera of the Perischoechinoida as "only synthethic and prophetic Crinoids." These statements are in striking contrast to what Mr. Agassiz says in the Revision (1874, p. 645), where he gives structural grounds for widely separating the Perischoechinoida and the Crinoidea. I give reasons (p. 200) for rejecting any close affiliation of the Echini with the crinoids. The peristome of Melonechinus is known in only one specimen (Plate 50, figs. 7, 8), but in this there are many rows of ambulacral plates. In each radial area there are two relatively larger primordial ambulacral plates adorally, and, passing aborally, the number of plates increases to many plates in a row on the outer border of each ambulacral area of the peristome. Three non-ambulacral plates occur interradially in probably each area. This is the only case of a peristome known in the family (pp. 80, 378). The apical disc in Melonechinus is small measuring proportionately about 13 to 25 % of the diameter of the test. It is interesting to note that in Melonechinus springeri which is a primitive species in the genus, the apical disc is relatively large ; its diameter being about 23 % of the diameter of the test; whereas in M . liratus and M. multiporus which are more specialized MELONECHINUS. species in the genus, the apical disc is relatively smaller, its diameter being about 13 to 16 % of the diameter of the test (pp. 87, 104, 339). The apical disc is composed of five oculars and five genitals. The oculars separate the genitals, reaching the periproct, are imperforate, and ven- trally cover the ambulacra and laterally the interambulacra in part on either side. No excep- tions to these statements are known to me in the genus (Plate 56, fig. 6). The genitals are high and wide, presenting one face to the periproct, one to each ocular on either side, and ventrally a rounded face to the interambulacrum, without reaching the ambulacra on either side (Plate 53, fig. 1; Plate 56, fig. 1). It is often difficult to see the interambulacral plates extending quite to the oculars, but, barring something abnormal, I believe this is the character (p. 89). Genital plates in this genus have typically three or four pores each. Occasionally only two, or one, or even no pores are visible (p. 149). When one or none are visible, it is doubtless a case of obliteration of pores in fossilization. I have seen no case of madreporic pores in the genus, though such are figured by Keyes (1894) in M. multiporus. His observa- tion is further considered under that species. The plates of the periproct strangely enough are known in only one specimen, an external mold (Plate 56, fig. 1). They are small, angular, and evidently fill the area as in Palaeechinus and Maccoya. The lantern is inclined, pyramids wide-angled, with moderately deep foramen magnum, and the teeth extend a considerable distance beyond the pyramids ventrally. Mr. Agassiz (1892, pp. 72, 73) expresses the view that "the many pores found on the genital and ocular plates of the Palaechinidae " are "only perforated tubercles, or the pits left after the minute radioles have been broken off." This family does not have perforate tubercles on any part of the test, and the pores pass directly through the genital plates, as the perforations of tubercles do not. I believe no one has shown supernumerary pores in ocular plates in this family excepting Baily, and he was mistaken (p. 309). I have never seen any pores perforating ocular plates in the Palaeechinidae. Mr. Agassiz (1881, p. 12) says that many genital plates may be occupied by the madreporite in the Palaeechinidae as shown in several genera figured by Baily, Worthen, and others. I know of no case in the Palaeechinidae in which a madre- porite has been previously figured excepting by Keyes in Melonechinus, and I know of no case in this or any other family of Palaeozoic Echini in which madreporic pores have been shown in more than one genital plate (p. 172). Considering the lantern of Melonechinus multiporus as figured by Meek and Wort hen (1866), Mr. Agassiz (1874, p. 647) says that there is a furrow in the center of the teeth, resem- bling that of the teeth of Archaeocidaris as figured by Miiller (1857) (my Plate 10, figs. 6, 7). Neither Meek and Worthen nor Muller as far as I am aware figured teeth, but they did figure dental pyramids, and the "furrow" referred to by Mr. Agassiz is evidently the median suture of the pyramids. Melonechinus does not have a furrow on the exterior of the teeth though doubtless there was a groove on the inner side as in other members of the Perischoechinoida (text-figs. 207, 208, p. 184). 364 ROBERT TRACY JACKSON ON ECHINI. Melonechinus occurs in the Lower Carboniferous of America, Great Britain, and Russia. The type species is Melonechinus multiporus (Norwood and Owen). Key to the Species of Melonechinus.1 Six columns of ambulacral and four columns of interambulacral plates in each area M. dispar (Fischer von Waldheim), p. 365. Six columns of ambulacral plates, and at the mid-zone five columns of interambulacral plates, a sixth column coming in dorsally in each area M. pnreus (Hambach), p. 365. Six columns of ambulacral plates, and six columns of interambulacral plates at or just above the mid-zone, with a strong tendency to adding a seventh column dorsally in each area . M. springeri sp. nov., p. 366. Eight columns of ambulacral and six columns of interambulacral plates in each area, melon-like ribs low, gently rounded M. crassus (Hambach), p. 367. Eight columns of ambulacral and six columns of interambulacral plates; a seventh interambulcral column may appear dorsally, or exceptionally, even an eighth column in each area; melon-like ribs high, sharply elevated M. indianensis (Miller and Gurley), p. 369. Eight columns of ambulacral plates and seven (or in one area of the type, six) columns of interambulacral plates in each area. Melon-like ribs strongly and sharply elevated . . M. fttewartii (Safford), p. 371. Eight columns of ambulacral and seven columns of interambulacral plates at the mid-zone in each area; test small . M. srptcnarius (Jackson), p. 373. Ten columns of ambulacral and three columns of interambulacral plates in each area; test obovate M. obovatus sp. nov., p. 373. Ten columns of ambulacral and eight columns of interambulacral plates in each area; high, steeply rounded, melon-like ribs in ambulacral and interambulacral areas . . . M. liratus sp. nov., p. 374. Ten columns of ambulacral and dorsally eight or nine columns of interambulacral plates (rarely seven columns only in an area) in each area; low, rounded, melon-like ribs in ambulacral and interambulacral areas ........... M. multiporus (Norwood and Owen), p. 375. Twelve columns of ambulacral and six columns of interambulacral plates in each area; melon-like ribs wanting M. hce-pingi sp. nov., p. 384. Twelve columns of ambulacral and seven columns (possibly more) of interambulacral plates in each area; melon-like ribs wanting M. ethrridgi! (Keeping), p. 385. Twelve columns of ambulacral and nine columns of interambulacral plates in each area; melon-like ribs strongly developed M. mndrrhilti sp. nov., p. 388. Twelve columns of ambulacral and eleven columns of interambulacral plates in each area; melon-like ribs strongly developed M. gigantcus (Jackson), p. 389. 1 M elonites ( = Melonechinus) youngi, of which no description has been published, is considered under Nomina Nuda, p. 457. MELONECHINUS. 365 Melonechinus dispar (Fischer von Wuldlirini). Plate 51, figs. 1-3. Pdcchinus dispar Fischer von Waldheim, 1848, p. 243, Plate 3, figs. 4&-4t\ (on the plate there are only three figures; all copied here). Palechtinus dispar (by typographical error) Fischer von \Valdheim, 1S48, p. 247. Palaeoeckimu dispar Eichwald, 1860, p. 651. Melonites dispar Love'n, 1874, p. 42; Jackson, 1896, p. 240; Klt-m, 1004, p. 41. Melonechinus dispar Lambert and Thiery, 1910, p. 120. The test is spheroidal, with moderately elevated melon-like ribs. Ambulacra broad, with six columns of plates at the mid-zone; according to the figures the ambulacral plates are more regular in form and size than in other known species of the genus. In the interambulacra there are four columns of quite high hexagonal and pentagonal plates, which, as figured, bear few small widely spaced secondary tubercles. This species has as few columns of ambulacral plates as any in the genus, and also the least number possible to be included in this genus. It has the least number of interambulacral plates of any species with six columns of ambulacral plates, and therefore it is considered the most primitive species in the genus. Lower Carboniferous Limestone, Ratofka, Russia, the locality of the type; Carboniferous, " Etage moyen," Moscow, and in Lower Carboniferous of the village of Sloboda. in the ( lovcrn- ment of Toula, Russia (Eichwald). 'Melonechinus parvus (Hambuch). Plate 51, fig. 4; Plate 52, fig. 1. Oligoporus parmts Hambach, 1884, p. 550, Plate C, fig. 3; Keyes, 1894, p. 127; 1895, p. 183; Klem, 1904, p. 40; Lambert and Thie"ry, 1910, p. 121. The test is small, spheroidal, and much compressed in the type specimen. Diameter through B, G, 55 mm. This is doubtless somewhat exaggerated by the vertical compression of the test. Width of ambulacrum B, at the mid-zone, 15 mm.; width of interambulacrum A about 20 mm. Ambulacra are wide, with six columns of plates at the mid-zone, one column of wide occluded plates, one of demi-, and one quite irregular column of isolated plates in the middle line of each half-ambulacrum. This character removes the species from Oligoporus in which it was described by Hambach, and places it as one of the lowest species of Melonechinus. In the development of the ambulacrum (Plate 52, fig. 1), there are ventrally in area B four columns of plates, narrow demi- and wide occluded. Above this Lovenechinus stage, 366 ROBERT TRACY JACKSON ON ECHINI. scattered isolated plates appear, the Oligoporus stage; then the isolated plates become suffi- ciently frequent to form a column when the species character in this respect is attained. The interambulacra have five columns of plates at the mid-zone in areas A and C, the two which are most nearly complete. In area A, in addition, a sixth column is represented dorsally by a single plate, dorsal to which the test is wanting (Plate 52, fig. 1). In this area the first two rows are restored as indicated by dotted lines. The fourth column originates in the third row, the fifth column in the eighth row, and the sixth column in the sixteenth row, with a pentagon and ventrally situated heptagon as usual. Area C is only partially preserved. The fifth column comes in at about the same zone as in area A. In column 4 there is an aberrant penta- gon X, and, to compensate for its one side short, an adjacent adradial plate has taken on an additional side. Interambulacral plates bear small secondary tubercles, with small spines. Lower St. Louis Limestone, Lower Carboniferous, St. Louis, Missouri. The type speci- men is in Mr. Frank Springer's collection 8,118, and was from Professor Hambach's collec- tion. Miss Klem also gives Hardin County, Kentucky, as a locality for the species. *Melonechinus springer! sp. nov. Text-figs. 19, p. 59; 237, p. 231; Plate 51, fig. 5; Plate 52, figs. 2-6. The test is small, high, and spheroidal, with strongly developed melon-like ribs in ambula- cral and interambulacral areas. Known from a single specimen in Mr. Springer's collection. Height 28 mm., diameter through the mid-zone about 32 mm. The actual measurements in diameter are: through B, G, 30 mm. ; C, H, 32mm. ; and J, E, 35 mm. Width of an ambula- crum at the mid-zone 8 mm.; width of an interambulacrum 11 mm. Ambulacra are wide with, at the mid-zone, six columns of plates in each area, composed of wide occluded, narrow demi-, and one irregular column of isolated plates in the middle line of each half-area (Plate 52, fig. 2). The occluded plates are medially elevated in a high, arching, melon-like ridge. Ventrally in the ambulacra, as developing stages, there are two columns in each half-area (Plate 52, fig. 3) of wide occluded, and narrow demi-plates ; higher up scattered isolated plates appear, which, higher again, become more frequent and fall into a vertical columnar series, the species character. ' Dorsally, near the ocular, as localized stages (Plate 52, fig. 2), there is a single column of ambulacral plates in each half-area. Passing ventrally, next we find two columns in each half-area, then two columns with, in addition, scattered isolated plates, which soon become so frequent as to make a continuous column, the species character. It is interesting to see in this primitive species of the genus how complete the ventral developing and dorsal localized stages are, and how closely they can be compared with the lower genera in the family (text-fig. 237, p. 231). The dorsal localized stages are more complete in this than in some of the higher species of the genus, in which some stages are more or less obliterated by acceleration of development. MELONECHINUS. 367 The interambulacra are a little wider than the ambulacra, arching from the adradial sutun-s outward in relatively high melon-like curves. In each area there are six columns of plates at or a little above the mid-zone. In areas E, G, and I there are only six columns, but in A and C a seventh column is represented by a few plates dorsally in the middle line of each area (Plate 52, fig. 2). Interambulacral and ambulacral plates alike bear small secondary tubercles with corresponding small spines about 3 mm. long. Ventrally, in Plate 52, fig. 4, the first three rows of interambulacral plates are restored, as indicated by dotted lines. Assuming that these are correct, the fifth column originates in a pentagonal plate in the seventh row, with a heptagon on its left ventral border. The sixth column originates in the eleventh row with a pentagon, on the right of the center, and bearing a heptagon on its left ventral border. Dorsally, the adradial columns 1 and 2 drop out before reaching the apical disc, indicating senescence. The apical disc is imperfectly preserved, but the diameter as closely as it can be ascertained is about 7.5 mm., which is proportionately about 23% of the diameter of the test. This is proportion- ately larger than in more specialized species as M. multiporus and M. liratus in which the diameter of the apical disc is only 13 to 16 % of the diameter of the test. An ocular plate in place covers the ambulacrum and laterally in part the interambulacra on either side. Two genital plates lie against the ocular, one twisted out of place and in part covering the ocular. Genital pores are not shown. This species is one of the smallest known in the genus, yet the type represents an adult, or even old-age individual, as indicated by the dropping out of adambulacral columns dorsally. As regards the ambulacrum, it is one of the simplest species known in the genus, but in its interambulacral structure is more specialized than the two previously described species. I take pleasure in naming this species for Mr. Frank Springer, the eminent crinoid specialist, who generously loaned me his whole collection of Palaeozoic Echini, which has been an invaluable aid in my work. St. Louis Group, Lower Carboniferous, Elizabethtown, Kentucky, F. Springer Collection 8,103. *Melonechinus crassus (Hambach). Plate 51, fig. 6; Plate 52, figs. 7-11. Melonites crassus Hambach, 1884, p. 548, Plate C, fig. 1; Keyes, 1894, p. 126; 1895, p. 182; Jackson and Jaggar, 1896, p. 137; Jackson, 1896, p. 240; Klem, 1904, pp. 8, 41, Plate 1, figs. 2a-2d. Melonechinus crassus Lambert and Thiery, 1910, p. 120. The test of this fine species is high and spheroidal, with strong, rounded, melon-like ribs in ambulacral and interambulacral areas. Known only from the type specimen (Plate 51, fig. G), which is compressed and with a dorso-ventral thrust. Height of the test about 90 mm., diameter about 111 mm., but this measurement is somewhat exaggerated by lateral compres- 368 ROBERT TRACY JACKSON ON ECHINI. sion; width of the ambulacrum at the mid-zone, 24 mm.; width of the interambulacrum at the same zone, about 26 mm. Ambulacra are wide, nearly equaling the width of the interambulacra, with eight columns of plates at the mid-zone composed of a column of wide occluded, narrow demi-, and two columns of somewhat irregular isolated plates in each half -area (Plate 52, fig. 7). Hambach says that there are ten columns of ambulacral plates in this species. As I count the plates there are eight columns, but in the irregular character of the ambulacra in Melonechinus, where there are many plates, it is easy to count two more or two fewer columns in an area, according as one includes or eliminates irregularities. The pore-pairs are in peripodia and lie on the outer por- tion of each ambulacral plate. Small secondary tubercles and spines about 3 mm. long occur on the ambulacral areas (Plate 52, fig. 10). The spines of these areas are perhaps a trifle longer than spines on the interambulacral plates (Plate 52, fig. 11); but they certainly are not twice as long as stated by Hambach and also by Miss Klem. In all species of this family the spines of both areas are essentially alike, as far as known, and this species is probably no exception to the rule. The slight differences observed may well be ascribed to conditions of preservation. The ambulacrum ventrally has two columns of occluded and two of demi-plates (Plate 52, fig. 9), but scattered isolated plates soon come in in the middle line of each half-area and repre- sent the second stage in development. The interambulacra are a trifle wider than the ambulacra. At the mid-zone there are six columns of plates in areas A, C, E, and G, but area I is imperfect, so that the number dorsally could not be ascertained. Hambach says that there are five columns, but he apparently over- looked an adambulacral column which in area C, one of the best areas, is sunken deeply in the lateral furrow, and is in part wanting in this area. Interambulacral plates bear numerous small secondary tubercles and spines, which, as preserved, are not quite so long as those in the ambulacral areas (Plate 52, fig. 11). In area E the ventral portion is quite complete, but the plates of the-basicoronal row are restored (Plate 52, fig. 8). There are three plates in the second row, four in the third, and the fifth column comes in in the seventh row. In area C (Plate 52, fig. 7) the fifth column originates in a pentagon, in the middle of the area, with a heptagon on its left ventral border. Three rows higher up and well below the mid-zone the sixth column originates with a pentagonal plate on the left of the center and with a heptagon on its right ventral border. The specimen (Plate 51, fig. 6) is oriented by the introduction of columns and ventral structure, and is reversed from the orientation given by Professor Hambach. Dorsally the apical system is wanting. Lower St. Louis Limestone, Lower Carboniferous, St. Louis, Missouri. The holotype and only known specimen is in Mr. Frank Springer's collection 8,116, and was from Professor Hambach's collection. MELONECHINI'S. : ',:<, KKs. 1-4. Melonites indianensis Miller and Gurley, 1894, p. ">, Plate 1, fi^. 1 ; Jackson, I Will, p. _• ID Meloniies multiporus (pars) Klein, 1904, p. 43. Melonechinus indianensis Lambert and Thiery, 1910, p. 121. A relatively small species, the type being the largest known individual. Tr-t >phoroidal, with sharply elevated melon-like ribs in ambulacra! and interambulacral areas. The holo- type (Plate 51, fig. 7) measures 54 mm. in height, 67 mm. in diameter at the mid-zone through the axis J, E; width of the ambulacra at the mid-zone 16 mm., width of the interambulaera 21 mm. The ambulacra are wide, at the mid-zone with eight columns of plates composed of wide occluded, narrow demi-, and two irregular columns of isolated plates in each half-area I Mali- 53, fig. 3). The Occluded plates medially are arched up in a high, rounded, melon-like ridge. Pore-pairs are in deep valleys on either side of the ambulacra! areas, each pair in a well marked peripodium, situated in the lateral portion of each plate. In the developing area vent rally (Plate 53, fig. 2) there are near the peristomal border two columns of plates, narrow demi- and wide occluded in a half-area. Higher up, as shown, isolated plates appear in the middle line of the half-areas as a second stage, then isolated plates become continuous so as to form one column, repeating in this stage the character of species like springeri that typically have only one isolated column. Then a second isolated column appears, fixing the species character in this feature. Dorsally, as localized stages in development, near the apical disc (Plate 53, fig. 1) there is a single column of primary plates in each half-area. Vent rally, they pass quickly into stages of two columns, then three, and finally four in a half-area. These ventral and dorsal stages and their relations to lower genera and species are set forth diagrammatical ly in text -fig. 237, p. 231. The dorsal localized development of indianensis is more accelerated than in the lower species, springeri, as in that region the Oligoporus stage of scattered isolated plate- i- skipped in indianensis although ventrally this character is retained as a developing stage. The interambulacra of indianensis are slightly wider than the ambulacra, and are roundei 1 up in high, wide, melon-like ridges which laterally dip suddenly down to the adradial sutun In the type there are six columns of plates in four interambulacral areas, A, C, E, and G, but in area I (Plate 53, fig. 4), as an exception, there are seven columns and even an eighth is repre- sented by two plates. This is evidently a progressive variation, not common in the speci. since in two other specimens here figured all the areas have six columns only. In this unusual area (Plate 53, fig. 4) the basicoronal row and a few plates on either side are re>tored as indi- cated by dotted lines. There are three plates in the second row, and four in the third. The fifth column originates in the middle in the seventh row with a tetragonal plate, which is very 370 ROBERT TRACY JACKSON ON ECHINI. exceptional (compare tetragonal plate of ninth column in Plate 50, figs. 2, 3, and Plate 59, fig. 14; pp. 358, 391). To compensate for the two sides wanting there are two heptagonal plat o>, H, one on its left and one on its right ventral border. The sixth column originates on the left of the center in the tenth row, with a pentagonal plate which has a heptagon on its left ventral border. The seventh column originates in the fourteenth row in the middle of the area with a heptagon on its right ventral border. The eighth column, consisting of only two plates, origi- nates in the eighteenth row. Both plates of this column are pentagons, and a heptagonal plate lies on the ventral border of one and the dorsal border of the second pentagon, compensating for the one side lacking in each. Dorsally, in this specimen (Plate 53, fig. 1) the adambulacral columns 1 and 2 drop out before reaching the apical disc, so that dorsally columns 3 and 4 assume an adradial position. In addition, one other column has dropped out in several areas. In area C column 4 drops out so that column 6 assumes an adradial position adapically; in area E, column 5 drops out, and in area G, column 6 drops out, before reaching the apical disc. In the type the apical disc is in place and complete; it measures proportionately 16 % of the diameter of the test. The five oculars all reach the periproct, are imperforate, and ventrally cover the ambulacra and laterally the interambulacra in part on either side. The genitals are high and wide, bounded by the periproct dorsally, the oculars laterally, and ven- trally, in a long curving line, by the interambulacra, which laterally extend in a narrow, wedge- like fashion to their points of ocular contact. There are three pores in genital G, in other plates no pores or fewer than three ; they have doubtless been obliterated in the process of silicification (p. 363). A small specimen in Mr. Braun's collection from Greenville, Indiana (Plate 51, fig. 8) is completely silicified and preserved without distortion. There are eight columns of ambula- cral plates and six columns of interambulacral plates respectively in each area. The angles of the melon-like .ribs are exceptionally sharp and well preserved. The apical disc measures proportionately 18 % of the diameter of the test. A specimen in the Museum of Comparative Zoology Collection 3,147, from Allen County, Kentucky (Plate 51, fig. 9), is silicified, and stained a yellow amber color; much wear has rounded the outlines. It has the eight columns of ambulacral plates, and in each interambula- crum six columns of plates, the species character. Another specimen in the Museum of Com- parative Zoology Collection 3,081, from the Lower Carboniferous, Berea, Kentucky, is of much interest as a silicified internal mold, and is the best internal mold of any specimen of the genus known to me. The specimen although partially wanting is perfect in form and free from all distortion. It measures 40 mm. in height and 50 mm. in diameter. At the mid-zone the ambulacra measure 12 mm. in width, and the interambulacra 27.5 mm. in width. These proportions differ considerably from those given for external measurements in the type, but MELONECHINUS. this is in part due to the fact that ambulacral plates bevel over I he adamlmlurral< on the adradial suture so that ambulacra on the interior are nere-sarily narrower than <>n the exterior. There are eight columns of plates at the mid-zone in the ambulacral areas, but only two plate- dorsally where the ambulacra are in contact with the oculars. In the interaniliulaera there are six columns of plates at the mid-zone in the areas as far a- preserved, but in four inter- ambulacra a seventh column appears dorsally. In the ambulacrum, the demi-plates opposite horizontal interambulacral sutures are high and laterally fan-shaped, as in Plate 5(5, fig. 5, also as in that figure, the pore-pairs are on the outer portion of occluded plates, the inner portion of demi-plates, and in the middle of isolated plates. The impre— ion of the apical di-«- i- very clearly preserved and measures 11.5 mm. in diameter, which is proportionately 23 % of the diam- eter of the test. This is proportionately larger than apical discs of other specimens aS measured from the exterior of the test; but this is in part due to the fact that genital plates probably present a bevel on their adoral face as in Plate 50, fig. 6, so that a measurement taken from the interior would naturally be somewhat larger than one taken from the exterior. The peri- proctal area measures 5.5 mm. in diameter. Impressions of all the oculars and genitals arc in place. The oculars all meet the periproct and adorally cover the ambulacra and laterally the interambulacra in part on either side. Melon-like ribs are quite pronounced in this internal mold both in ambulacral and interambulacral areas. This character differs from internal molds in other species in the genus and family that I have seen. The melon-ribs are formed mainly by the thickening of the plates and internal views usually show little or nothing of thi- character, as seen in Plate 38, fig. 9, and Plate 54, figs. 2, 3 (p. 359). The holotype is from the St. Louis Group, Lower Carboniferous, Greenville, Harrison County, Indiana; it is in the Chicago University Collection 6,622, whence it was kindly loaned me by Professor Stuart Weller. Same horizon and locality, F. Braun Collection. Lower Carboniferous, Allen County, Kentucky, Museum of Comparative Zoology Collection 3,147: Lower Carboniferous, Berea, Kentucky, Museum of Comparative Zoology Collection 3,081; Lower Carboniferous, Jackson County, Missouri, Museum of Comparative Zoology Collection 3,148 (all from R. T. J. Coll.). *Melonechinus stewartii (SMtl'unl . Plate 53, figs. 6-8; Plate 54, fig. 1 ; Plate .>«, fig. 1. Melonites stewartii Safford, 1869, p. 346, Plate 6 (I), figs. la-Id. Melanitcs multipora (pars) Keyes, 1895, p. 181. Melonites multiporus (pars) Klein, 1904, p. 42. This specimen is represented by a very perfect external calcareous mold of the dorsal half of the test from about the mid-zone up. So perfect is it that not only outlines of plates, but spines, tubercles, and peripodia can be clearly made out. It is known only from SatYonl'- 372 ROBERT TRACY JACKSON ON ECHINI. original type specimen which is in the Vanderbilt University Collection, and was kindly loaned me by Professor L. C. Glenn of that institution. As gathered from the dorsal half, the test is high and spheroidal, with strongly and sharply elevated melon-like ribs in ambulacral and interambulacral areas. These are shown in the plaster cast of the type (Plate 54, fig. 1). Diameter 77 mm., width of the ambulacra near the mid-zone about 23 mm., width of the interambulacra in the same plane about 24 mm. The ambulacra are of about the same width as the interambulacra near the mid-zone, with eight columns of plates, wide occluded, narrow demi-, and two irregular columns of isolated plates in each half -area (Plate 53, fig. 6). The occluded plates medially are elevated in a high, steeply rounded, melon-like curve. Pore-pairs are in peripodia, situated in the outer portion of each ambulacra] plate. The figure of ambulacral detail is drawn directly from the original mold, therefore the orientation is reversed from what it would be if seen from the exterior. The interambulacra are elevated, in high, rounded, melon-like ribs, which laterally dip down steeply to the adradial sutures. In four areas there are seven columns of interambulacral plates at or above the mid-zone, but in area I there are only six columns. In areas E and G the seventh column originates above the lower border, as preserved, with a pentagonal plate bearing a heptagonal plate on the right ventral border (Plate 53, fig. 8). This figure is also drawn directly from the original external mold, therefore the orientation is reversed from what it would be if seen from the exterior. Ambulacral and interambulacral plates bear small secondary tubercles, and spines about 3 mm. long. Dorsally, the apical disc is in place, and it measures proportionately about 17% of the diameter of the test (Plate 56, fig. 1, was drawn from a wax cast of the original mold). There are low, small, imperforate oculars all reaching the periproct, and five wide, high genitals. Genital I has three pores situated as usual toward the ventral border of the plate. In the other genitals the impressions of pores are somewhat scattered and doubtful as to the number of pores in each plate. In this specimen impressions of periproctal plates are in place. They are small, angular, and evidently fill the area, as in Maccoya and Palaeechinus where these plates are better known. In all cases these plates are closely similar to those of a Recent Eucidaris (text-fig. 66, p. 98). This is the only specimen of the genus Melonechinus in which the periproctal plates are known. This species is close to multiporus, but differs from it in that the melon-like ribs are much higher and more sharply rounded (compare Plate 55), and the ambulacral areas are propor- tionately somewhat wider. There are eight columns of ambulacral plates in stewartii whereas there are usually ten columns in multiporus; also there are seven or six columns of interambula- cral plates in each area in stewartii, whereas in multiporus there are typically eight or nine columns, very rarely seven, and as few as six are unknown. Professor Safford says of this fossil that the precise locality is not known to him, but that MELONECHINUS. 373 it is from Middle Tennessee, and he had reason to think from the Lithostrotion hod which belongs to the St. Louis Group of the Lower Carboniferous. The holotype is in Vandcrbilt University Collection, Nashville, Tennessee, 22.3. Casts of this specimen are in I''. Bourn's collection; and in the Museum of Comparative Zoology Collection 3,150. *Melonechinus septenarius (Jackson). Plate 51, fig. 10; Plate 53, fig. 5. Melonites septenariiis Jackson, 1896, p. 182, Plate 9, fig. 49; Klem, 1904, p. 43. Mclonechinus septenariw Lambert and Thiery, 1910, p. 121. The test is small and spheroidal. The type and only known specimen is an internal sili- ceous mold, so that the external characters, including melon-like ribs, are unknown.. Width of the ambulacrum at the mid-zone about 13 mm., width of the interambulacrum 23 mm. The ambulacrum at the mid-zone has eight columns of plates. As the plates are internal impressions, the pore-pairs are near the outer border of occluded plates, the inner border of demi-plates, and about the middle of isolated plates (compare Plate 56, fig. 5). About three demi-plates equal the height of an adradial plate. There are seven columns of interambulacral plates in an area. The seventh column is peculiar in that it originates far to the right of the center, but has as usual a heptagonal plate on its left ventral border. Near the mid-zone an adventitious pentagon, P, occurs, and next to it on the right is a heptagon, A, the extra side of which compensates for the missing side of the pentagon. This species is imperfectly known. It is structurally nearest to M. indianensis, but differs in that the ambulacra are proportionately much wider and the seventh column, which is ex- ceptional and late in development in indianensis, appears very early in septenarius. Warsaw Limestone, Lower Carboniferous, Buzzard's Roost, Franklin County, Alabama. Holotype in the American Museum of Natural History Collection *"— . *Melonechinus obovatus sp. nov. Plate 53, figs. 9, 10; Plate 54, figs. 2, 3. This species is a remarkable type in its character, but is only known from one specimen, which is an internal yellowish calcite mold, so that external characters, including the melon- like ribs, are unknown. Test slightly higher than wide, obovate, and apparently in its original shape without distortion. As the specimen is an internal mold, its horizontal outline presents a continuous curve of one arc (Plate 54, fig. 3), there being no indication of the melon-like ribs which doubtless existed on the exterior. As these ribs are formed mainly by the thickening of the plates, their outline is usually not indicated on the interior of the test (compare Plate 38, fig. 9; pp. 359, 371). Height about 43 mm., diameter through the ambitus 42 mm.; this measurement exceeds the diameter through the mid-zone, as this is one of the very rare cases in which the ambitus, or greatest circumference, is dorsal to the middle of the test (p. 32). 374 ROBERT TRACY JACKSON ON ECHINI. The circumference at the ambitus is 130 mm., width of the ambulacra at the mid-zone 18 mm., width of the interambulacra 9 mm. The ambulacra are remarkable for the genus in being about twice the width of the inter- ambulacra. At the mid-zone there are ten columns of ambulacral plates in an area, composed of wide occluded, narrow demi-, and three irregular columns of isolated plates in each half- area (Plate 53, fig. 9). As the plates are an internal view, the pore-pairs lie in the inner border of the demi-plates and nea"r the middle of isolated plates; also demi-plates opposite horizontal ambulacral sutures are higher and laterally fan-shaped (compare Plate 56, fig. 5). The interambulacra at the mid-zone and throughout the areas, as far as they could be ascertained, consist of three columns of plates. This is the only species in the family that has so few columns in an area, and the only other Palaeozoic Echini with three interambulacral columns in an area are Lepidesthes wortheni Jackson and Meekechinus elegans sp. nov. (Plate 67, fig. 8; Plate 76, fig. 1). The three columns continue to the apical disc and laterally are in contact with the oculars as usual (Plate 53, fig. 10), (p. 444). The impress of the apical disc is in place dorsally (Plate 53, fig. 10). It measures 10.5 mm. in diameter, which proportionately is 25 % of the diameter of the test. This is relatively the largest apical disc seen in the genus, and is exceptionally large for the Palaeozoic (pp. 87, 104). It is to be remembered, however, that the specimen is an internal mold, and on the exterior the diameter of the apical disc would doubtless be smaller (p. 362, 371). The oculars all meet the periproct and ventrally cover the ambulacra and laterally the interambulacra in part on either side. The genitals are high and wide, as usual in the genus, but the pores could not be ascertained. This species has the same number of columns of ambulacral plates as the two following, but differs from them radically in the number of columns of interambulacral plates and in the form of the test. It is striking that this species with so highly evolved an ambulacral structure should at the same time have the least evolved interambulacra known in the family. .Lower Carboniferous, White Creek, Davidson County, Tennessee; holotype in Vanderbilt University Collection, from which it was kindly loaned me by Professor L. C. Glenn. *Melonechinus liratus sp. nov. Plate 53, fig. 11 ; Plate 54, fig. 4. Test high and spheroidal, with strongly and sharply elevated melon-like ribs in ambulacral and interambulacral areas. This species is known only from the holotype, which was kindly loaned me for study by Professor L. C. Glenn. Height about 91 mm., diameter about 116 mm., width of the ambulacra at the mid-zone about 36 mm., width of the interambulacra at the same plane 40 mm. Ambulacra are nearly as wide as the interambulacra at the mid-zone with ten columns MELONECHINl S. 375 of plates composed of wide occluded, narrow demi-, and three -mnewhat irregular column- of isolated plates in each half-area. The occluded plates medially are elevated in high, steeply rounded, melon-like ridges. Pore-pairs are in deep sunken valleys on eit her side and are situated in the outer portion of each ambulacra! plate. The interambulacra are slightly wider than the ambulacra, and are arched up in high melon- like ridges, the outer faces on a gentle curve, laterally dipping suddenly down to the adradial sutures. Each of the three interambulacral areas preserved has eight columns of plates at the mid-zone. Dorsally, the apical disc is partially preserved (Plate 44, fig. 4); it mea-un - 1.'...". mm. in diameter, which is about 13 % of the diameter of the test. Ocular D is in place, the periproct, and ventrally covers the ambulacrum and laterally the interambulacra in part on either side. Spaces exist between the genitals for oculars B and J. Four genitals are in place; they are high and wide as usual, each having Ihree genital pores. This species is close to multiporus, having the same number of columns of ambulacral and interambulacral plates as that species has. It differs in the high, steeply rounded melon-like ridges and deeply sunken poriferous areas (compare Plate 55, figs. 1-3; Plate 60, figs. 1, 2). Lower Carboniferous, detailed horizon and locality unknown, but doubtless, from the lithological character, from Kentucky or Tennessee. Holotype in Vanderbilt University Col- lection, Nashville, Tennessee, 221. *Melonechinus multiporus (Norwood and Owen). Text-figs. 13, p. 54; 20, p. 59; 25, p. 70; 48, p. 80; 163, p. 149; 237, p. 231; 245, 246, p. 382; Plate 54, fig. 5; Plate 55, figs. 1-3; Plate 56, figs. 2-13; Plate 57, figs. 1-3; Plate 60, figs. 1, 2; Plate 72, fig. 12. Melonites multipora Norwood and Owen, 184(i, p. 22.">, text-figs. 1-3; Engelmann, 1S47, p. 124; Desor, 1858, p. 159; Roemer, 1855, p. 312, Plate 12, figs. !-<><•; Meek and Worthen, ISIili, p. 227, text-fig. 21; p. 228, text-figs. 21, 22; p. 248, text-fig. 27; A. Agassi/,, 1874, pp. 047, 648, text-fig*. 1. 2, '>. f-: Quenstedt, 1875, p. 380, Plate 75, figs. 44-50; Keyes, 1894, p. 12:., Plate Hi, figs, la, Ib; Plate 17 figs, la-lc; (pars) Keyes, 1895, p. 181, Plate 19, figs, la, Ib; Plate 20, figs, la-lc; Troost in Wood, 1909, p. 107. Palaechinus multipora d'Orbigny, 1850, p. 154. Melonechinus multiporus Meek and Worthen, IS60, p. 39(>; Lambert and Thiery, 1910, p. 120. Melonites irregularis Hambach, 1884, p. 549, Plate C, fig. 2; Jackson, 1896, p. 210; Klein, 1901, p. II. Melonites multiporus Miller, 1889, p. 361, text-figs. 364-366; Jackson and Jaggar, 1896, pp. 13.V170, • fig. 1, p. 164, Plate 2, figs. 1-7; Plate 3, figs. 8-17; Plate 4, fig. 18; Plate .">, fig. 20; Jackson, 1896, p. 191, text-fig. 1, p. 240; 1899, p. 131; (pars) Klein, 1901, pp. 2-6, 42, Plate 1, figs, la-lc; Plate 2, figs. 4a-4d; Plate 3, figs. 6a-6d, 7a-7e; Plate 4, figs. Sa-Sf, 9d; Plate 5, figs. 9a, 9b, lOa, lOb, 11, 12d; Plate 6, figs. lOc, 12a-12c, 13a-13c. Melonechinus irregularis Lambert and Thiery, 1910, p. 121. This species is known from very extensive and usually well preserved material from St. Louis, Missouri. I have enjoyed the privilege of studying material in many museums, includ- 376 HOHKllT TRACY JACKSON ON ECHINI. ing the choice specimens in Mr. Frank Springer's collection recently acquired by him from Professor Hambach of St. Louis. In my earlier paper with Professor Jaggar (1896) we pub- lished a detailed description and discussion of this species, so that here I shall give only the systematic description of the species, followed by a discussion of new observations. The test is high and spheroidal, with low, rounded, melon-like ribs in ambulacral and interambulacral areas. A small but nearly perfect specimen, free from all distortion (Plate 55, figs. 1, 2), measures 54 mm. in height and 62 mm. in diameter through the mid-zone; the ambulacra at the mid-zone measure 16 mm. in width, the interambulacra 20 mm. in width. A larger specimen, also quite free from distortion (Plate 60, fig. 1), measures 65 mm. in height, 79 mm. in diameter through the mid-zone; the ambulacra at the mid-zone measure 20 mm. in width and the interambulacra 25 mm. in width. A very large specimen, the largest that I have seen (Plate 55, fig. 3), is incomplete ventrally, and the figure shows practically the whole specimen. It measures 123 mm. in diameter through the mid-zone. Comparing this with smaller specimens, the estimated height is about 101 mm.; the width of the ambulacra at the mid-zone is 34 mm., and of the interambulacra 39 mm. The ambulacra are somewhat narrower than the interambulacra, with ten columns of plates at the mid-zone (Plate 56, fig. 4). These consist of wide occluded plates, extending from the middle of the area outward, narrow demi-plates extending from the interambulacral contact inward, and three irregular columns of isolated plates in each half-area. Occasionally, only eight columns of ambulacral plates can be counted at some planes, but the character is to have ten columns. The occluded plates in the median line are elevated in low, gently rounded, melon-like ribs, and demi-plates bevel over the interambulacrals on the adradial sutures, as I showed previously (1896, p. 141, Plate 2, fig. 5). The pore-pairs are situated in shallow valleys on either side of the ambulacral areas and lie in the outer portion of each plate, the pores being surrounded by a peripodium (Plate 56, fig. 12); but this structure is usually lost in erosion. Ambulacral plates bear small secondary tubercles and spines, similar to those of the interambulacral areas. As seen from the interior (Plate 56, fig. 5), the occluded plates are narrower than on the exterior, and demi-plates opposite horizontal interambulacral sutures are higher and laterally fan-shaped (compare text-fig. 244, p. 338). The pore-pairs on the interior of the test lie near the outer border of the occluded plates, the inner border of the demi- plates, and near the center of isolated plates, instead of all near the outer border of plates as seen from the exterior of the test (Plate 56, figs. 4, 5), (p. 61). Ventrally, near the peristomal border the ambulacra have four columns of plates (Plate 56, figs. 2, 3; Plate 57, fig. 1), and the complex character of the ambulacrum is built up passing dorsally, as later described in detail. Dorsally, near the oculars in the placogenous zone (Plate 56, fig. 6) a simpler condition also exists as a localized stage, and, passing ventrally to earlier built plates, the complex character is rapidly built up, as discussed later in detail. MELONECHINUS. The interambulacra are a little wider than the ambulacra and are gently rounded up in moderate melon-like ribs, laterally sloping gradually down to (lie ;idr;itnicture of having nine columns is about as frequent as only eight columns in an area. In the specimen. Plate 54, fig. 5, there are nine columns in area A, but eight columns in all other areas. In the splendid great specimen, Plate 55, fig. 3, there are nine columns in areas C, E, and G, the only ones that can be determined with certainty. There are also nine columns shown in two areas in the speci- men figured in Plate 56, fig. 11. In the very complete specimen, Plate 60, fig. 2, there are nine columns of plates dorsally in all five areas. As worked out by Jackson and Jaggar (1896, p. 162), it was found that eight columns are a little more frequent than nine in this specie-. Rarely there are only seven columns in an area (p. 50). In a specimen figured by .lacksc m and Jag- gar (1896, Plate 4, fig. 18) there are evidently only seven columns in one area, but this area has a very retarded development, the fourth column not coming in until much later than in any other specimen known in the family; in another area in this specimen, however, the fourth column originates in the next row after the third as usual (p. 439). When seven columns only are seen in an area, it is usually due to the fact that it is imperfect dorsally, -o that that portion where the additional one or two columns appear is wanting. Miss Klein (1904, p. 43) says that in a collection of several hundred specimens one can find any number of specimens with ten, eleven, and even twelve columns in one or more interambulacral areas. I have a good many specimens, but none with more than nine columns in an area. The adradial plates are pentagonal as usual in the genus and family, and bevel under the ambulacrals on the adradial sutures. All the plates of median columns are hexagonal or the mechanical equivalent of the same. Interambulacral plates, like the ambulacrals, bear secondary tubercles, similar to those shown in M. giganteus (Plate 60, fig. 3; Plate 61, fig. 8). Spines thickly cover the plates in exceptional specimens; the spines are about 3 mm. in length (Plate 56, fig. 13), swollen at the base, and taper gradually to the tip, apparently with slight constric- tions. Such constrictions have not been noticed in spines of other Palaeozoic specie-. Ventrally, the interambulacra, when perfect, have two plates in the basicoronal row ' 1 Miss Klem (1904, p. 2) says that there are three plates ventrally when the six-ciiiien is perfect. She i> certainly mis- taken, as discussed on pages 66, 67. 378 ROBERT TRACY JACKSON ON ECHINI. and three plates in the second row; with very rare exception the fourth column originates in the third row and above this zone the additional columns come in at somewhat definite intervals until the full complement is attained, as worked out by Jackson and Jaggar (1896). Dorsally, before reaching the apical disc, the adambulacral columns 1, 2, and some additional median columns may drop out as a character of senescence (Plate 57, fig. 1, text-fig. 246). It is seen in Melonechinus multiporus that there is a perfectly definite arrangemert of plates in the interambulacral areas and the same is true of all other members of the Palaeechini- dae as I have shown. In this regard remarks made by Mr. Agassiz require consideration. Mr. Agassiz (1881, p. 78) says, "The very peculiar splitting of the vertical rows of coronal plates noticed by Quenstedt in Melonites seems to point to some structural peculiarity in the Palaeechinidae such as I have described in the breaking up of a single interambulacral plate in our recent Echinothuridae. It shows, at any rate, what some of the other genera of the Palaeechinidae plainly show, that we find it impossible to define the number of rows [columns] of coronal plates in the test just as we find it impracticable near the apical system of the regular Echinids to asceitain how many rows of interambulacral plates there are present, as they appear in that region of the test packed in as they best can find place and take up their regular and symmetrical arrangement only later, while we may observe that in the Palaeechinidae this symmetrical arrangement never takes place, the vertical rows of plates running in as best they can, thus forming another important embryonic character of the Palaeechinidae." In regard to this statement of Mr. Agassiz's, I have seen no evidence for the splitting of coronal plates in Melonechinus or other members of the Palaeechinidae (p. 415). The arrangement of rows [columns] of plates is perfectly definite in Melonechinus and other members of the Palaeechinidae as well, as I have shown (p. 383). In fact they are perfectly definite in probably all Palaeozoic Echini. I have examined a good many regular Echini living and fossil and never saw any difficulty in ascertaining near the apical disc how many columns there are. An unsymmetrical arrangement of plates such as Mr. Agassiz assumes is not a primitive character according to the evidence that I know, and would not therefore show the " embryonic character of the Palae- echinidae" even if it existed in that group, which it certainly does not. Mr. Agassiz (1881, p. 81) himself says that Bothriocidaris is "by far the most primitive of all Echinoidea," yet in that type (Plate 1, figs. 1, 2) there is surely no urisymmetrical arrangement of plates. The peristome is known in Melonechinus multiporus only, in the family of the Palaeechini- . dae, and here known only from a single specimen which is in the Princeton University Museum Collection 1,464. As a whole, the specimen is neither striking nor especially good, and I found it in exchange material. This unique structure is shown in Plate 56, fig. 7, as it occurs in the specimen, and with some restoration to make clearer the relations of parts in Plate 56, fig. 8, and text-fig. 48, p. 80. Orally in areas J and D there are two ambulacral plates somewhat larger than other plates of the peristomal area. These plates I consider as the primordial MELONECHINUS. 37fl ambulacral plates which typically occupy this position in all regular Kchini ip. sJ: text -f 40-51, p. 80). The existence of two plates in an area on the peristome adorally implies that Melonechinus in an early stage had only two columns of ambulacral plates in an area (repre- sented by this one row of two plates), as in the young, probably, of all other regular Ki-liini (Plate 3, fig. 7). Passing aborally, the ambulacral plates of the pcristome <-on-i>t of many row- in each area; also the number of plates in each row increases to the periphery nf the area, where there are more plates in a row than in the basicoronal row of the corona proper. In the inter- radial areas of the peristome there are some non-ambulacral plate-, three in area A, and two or more in areas E and I. In the reconstruction (Plate 56, fig. 8) I have assumed that three is the typical number and have shown such in the two areas figured. The number is not of apparent significance, but it is important that this peristome representing the family has both ambulacral and non-ambulacral plates, and that the ambulacral consist of two plates in a row adorally, passing to more plates in a row aborally. The Archaeocidaridae is the only other family of Perischoechinoida that has both ambulacral and non-ambulacral plates on the peri- stome, and in this feature both families make an approach to the character -ecu in the Cida- roida (text-figs. 46-48, p. 80; pp. 82, 85). The apical disc is small in Melonechinus multiporus. In six specimens quite free from matrix and with this structure in place the apical discs measured proportionately from 13 to 16% of the diameter of the tests (pp. 362, 367). The apical disc has all ten ocular and genital plates preserved, or part of them, in numerous specimens (Plate 54, fig. 5; Plate 55, figs. '_'. 3; Plate 56, fig. 6; Plate 57, fig. 2; Plate 60, figs. 1, 2; text-fig. 163, p. 149). The ocular- are small and imperforate, and separate the genitals, meeting the periproct with the whole width of each plate and ventrally cover the ambulacra and laterally the interambulacra in part on each side, as best seen in Plate 56, fig. 6. The genital plates are wide and high, and have typically three or four pores each (Plate 57, fig. 2). In one case (Plate 60, fig. 2, area G) a genital has only two pores and apparently no pores have been oblitered. Not infrequently one or more pores are obliterated so that the number existent has to be judged somewhat from the position of those found; also pittings of erosion are sometimes confusing to distingui>h from actual pores. Dr. Keyes figured a specimen with a single genital pore in a plate which also shows numerous madreporic pores. I have not seen one genital pore only, nor madreporic poreS in this species or any other species of the genus (p. 363). The periproctal plates are unknown in this species, which is peculiar, as so many excellent specimens are known. The structure, however, was doubtless similar to that of M. stewartii (Plate 56, fig. 1). The lantern for the genus is known only in this species, and only partially here (Plate '^. figs. 9, 10). I can add little to what was previously shown by Meek and Wort hen. The lantern is inclined, pyramids wide-angled, foramen magnum moderately deep, and the teeth extend ventrally a considerable distance beyond the tips of the half-pyramids (p. 363). 380 ROBERT TRACY JACKSON OX ECHINI. The specimen which Professor Hambach described as Melonites irregularis I agree with Dr. Keyes in considering referable to multiporus. Hambach described irregularis as having from six to ten columns of plates in an ambulacral area and from five to seven columns of plates in an interambulacral area. This description is ambiguous, as I earlier stated (1896, p. 240). Having studied the holotype (Plate 72, fig. 12), I find that there are ten columns of plates in an ambulacral area at the mid-zone, as in multiporus. In three interambulacral areas there are seven columns of plates at the mid-zone, as is usual at this zone in multiporus, p. 377, but two areas are preserved ventrally only, and in these there are but five columns, the ventral character of most species of the genus. The specimen is poorly preserved, and no eighth columns were seen dorsally. Very likely none existed, as it is a small and presumably young individual. There is no reasonable basis for separating it as a distinct species, but rather it may be considered a small and immature multiporus. Hambach's published figure was incorrectly oriented as gathered from the ventral introduction of columns. The location of the type of M . multiporus is unknown ; I am informed that it was proba- bly destroyed by fire, a cast is in the Museum of Comparative Zoology, 3,226. This species has been found in great abundance in the St. Louis Group, Lower Carboniferous, St. Louis, Missouri. Slabs bearing twenty or more specimens occur in several museums, also a number of choice specimens free from the matrix. Many specimens from this locality have been studied in the Museum of Comparative Zoology, where there are some 75 specimens; Yale University; Mr. Frank Springer's collection; Princeton University; Munich; Berlin; Strassburg; the British Museum, and others. Keyes in localities for multiporus, gives Clarksville and Char- lotte, Tennessee. Miss Klem gives other localities taken from species she considers synonyms, but which I treat as distinct. Troost also credits the species to Tennessee. All material I have seen is from St. Louis, which is the only assured locality for the species. In my earlier paper (1896, p. 191, etc.) I worked out in part the development of the am- bulacrum in Melonechinus multiporus and compared the same with the structure in related genera; but with more material and fuller knowledge additional facts and relations have come to light. The ventral development, which is shown by the plates built in the youth of the individual, presents a fairly complete series of stages, as shown in Plate 56, fig. 3 ; Plate 57, fig. 1, area J; text-fig. 245. Close to the peristome there are typically four columns of plates, which consist of wide occluded and narrow demi-plates in each half-area. This is like the condition characteristic of Lovenechinus at the mid-zone, and also like the third stage in the development of Oligoporus, as shown diagrammatically in text-fig. 237, p. 231. Proceeding dorsally, in multiporus (Plate 56, fig. 3) scattered isolated plates appear in the middle of each half-area. This as a stage is comparable to the adult character of Oligoporus. Again, passing dorsally, the isolated plates become frequent enough so that they form a vertical column (Plate 56, fig. 3). We have therefore in this arrangement a stage with six columns of plates which is MKI.ON Will NTS. 381 characteristic of the raid-zone in the lowest species of tin- gmu.-. a- M. springeri (text-fin. 237, p. 231). Again, proceeding dorsally, in multiporus we next find two (-..11111111-- of isolated plate- in each half-area (Plate 57, fig. 1, area J; text-fig. 245); these with the demi- and occluded plates form a stage with eight columns of plates, which is chaniet eristic of the species M. indianensis (text-fig. 237, p. 231). At the mid-zone in multiporus, and for some distance below and above the same, -the full species character of ten columns of plates exists (Plate ."><>, fig. 4; Plate :>7. fig. 1). Thus do typical stages in development repeat the characters seen as adult features in lower genera, or lower species in the genus. As a case of extreme regressive radial variation, in area B of text-fig. 245 and Plate 57, figs. 1, 3, it is seen that a few plates vent rally near the peristomal border are primaries, completely crossing the half-areas. This condition was not seen in any other specimen in the genus; as a reversionary stage, it is comparable to the typical adult character of Palaeechinus and to the youthful ventral character of Maocoya, Lovenechinus, and Oligoporus (text-fig. 237, p. 231), (p. 19). Turning to the dorsal portion of the ambulacrum in Melonechinus multiporus, we find that close to the ocular in the placogenous zone in area J (Plate 56, fig. 6; Plate 57, fig. 2; text- fig. 245) there are two ambulacral plates only. In this zone there may be three plates as shown in other areas, but my figures show that one primary plate in each half-area may be found, when as a feature this may be considered a localized stage comparable to the adult typical character of Palaeechinus, and to a similar dorsal localized stage in lower genera or other species in the genus (text-fig. 237, p. 231). Proceeding ventrally, in multiporus we find next a stage with four plates in a row (Plate 56, fig. 6), which is comparable to the typical char- acter of Lovenechinus (text-fig. 237, p. 231). Again, passing ventrally, we next find a sta^e with six plates in a row (Plate 56, fig. 6) ; this is comparable to the typical character of Melonechinus springeri (text-fig. 237, p. 231). Again, passing ventrally, we next find a stage with eight plates in a row (text-fig. 245; Plate 57, fig. 1), which is comparable to the typical character in M. indianensis. Thus do dorsal localized stages, passing ventrally in the progres- sive development of plates built late in life, present stages which are quite comparable to tho-e seen in youthful development, also to the typical adult characters of lower genera or species in the genus (p. 366). Jackson and Jaggar (1896) worked out the development of the interambulacra in this species, illustrating it by a number of figures and also by tabulations. I have nothing to add to that except to give the arrangement in an exceptionally perfect specimen, lately in Pro; Hambach's and now in Mr. Frank Springer's collection. This specimen (Plate 55, figs. 1, 2) is not very large, but is free from all matrix and distortion so that I am able to represent it spread out by the Loven method with the restoration of only a few plates in the basicoronal row (Plate 57, fig. 1). Before describing the interambulacra of this specimen, attention is called to the diagrammatic text-fig. 246. This is selected to show a typical interambulacral area in this 382 ROBERT TRACY JACKSON ON ECHINI. 245 TEXT-FIGS. 245, 246. — Melonechinus muLtiporus. X 2. Adapted from original drawing of Plate 57, fig.l. 245. Showing typical character of ambulacrum, also ventral developing and dorsal localized stages. 246. Interambulacrum showing number of rows on the left, and the introduction of columns on the right. MELONECHINUS. 383 species, but in its general characters would serve for any species of the family. Lines are drawn through succeeding rows and numbered consecutively from one upward. It i- .-.-.-M that every plate is accounted for and that the angle representing each row, as indicated by dotted lines, deepens progressively passing dorsally. The row in which a given column make- it- appearance is indicated on the right side, and the number of the rows from the ba.-e or peri- stomal border is seen in the left side of the diagram (p. 378). As column 1 is theoretically considered as arising in the primordial iiiterambulucral plate (text-figs. 22-31, p. 70), which has been resorbed, there is no number to represent the row in which it originates on the right side of text-fig. 24(>. In this choice specimen t he int roduct ion of the earlier columns as added can be readily seen in the photographic figure ( Plate 55, fig. 1), but they are all plainly seen in Plate 57, fig. 1, and text-figs. 245, 246. In the basicoronal row the two plates are in place in areas G and I, and one of the two is in place in areas A ami < . In area E these two plates are restored as indicated by dotted lines. In the second row there are three plates in all areas, the initial plate of column 3 being hexagonal as usual. In the third row there are four plates in each area, the initial plate of column 4 being a pentagon. This pentagon lies on the right of the center in areas A, E, and I, but on the left of the center in C and G. The initial plates of columns 5 to 8 (with the exception of the initial plate of column 8 in area C), are all pentagonal with a heptagonal plate cither on the left or on the right ventral border of the same. Column 5 originates in the center, in areas A and G in the sixth row with a heptagon on the right or left ; in area C it originates on the left of the center (unusual for odd-numbered columns) in the sixth row with a heptagon on the right, and in areas E and I, column 5 originates in the center, in the seventh row with a heptagon on the right. Column 6 in areas A and E originates in the tenth row on the left of the center with a heptagon on the left; but in area C it originates in the ninth row on the left of the center with a heptagon on the right. In areas G and I the sixth column originates in the tenth row with a heptagon on the right in G and on the left in I. Column 7 originates in the center in all areas, as is typical of odd-numbered columns. In areas A and C this column originates in the thirteenth row with a heptagon on the left. In area E column 7 originates in the fifteenth row with a heptagon on the right, and in areas G and I it originates in the fourteenth row with a heptagon on the left in G, and on the right in I. Column 8 originates in ar- ea the left of the center in the seventeenth row with a heptagon on the right ; in area C col- umn 8 originates on the left of the center in a tetragonal plate in the eighteenth row with a heptagon on the right, also another heptagon on the left ventral border. In area E column 8 originates on the left of the center in the twenty-first row with a heptagon on the left. In area G it originates also on the left of the center, but in the nineteenth row, with a heptagon on the left. Finally, in area I, column 8 originates in the eighteenth row on the right of the center with a heptagon on the left. 384 ROBERT TRACY JACKSON ON ECHINI. In this development of the interambulacrum it is seen that it passes through a series of stages, each of which is. represented by two or more columns of plates. A more primitive type with two columns of interambulacral plates is not known in the family of the Palaeechinidae but may be reasonably hypothecated (p. 220) ; we do know, however, types with three, four, five, six, and seven columns as a character in lower species of the genus, or in lower genera of the family. These, while not perhaps the actual ancestors of the species in hand, may be looked upon as representing phases like those which its ancestors did possess. The earliest added columns come in with great regularity in a definite zone in each area, but in later added columns there is some radial variation in the zone of appearance of columns, this variation progressively increasing in degree up to the eighth column. The radial variation may be still more marked, as in Plate 54, fig. 5, in which there are nine columns of plates in area A, but only eight in the four other areas. Here the radii in one specimen present the limit of variation usually found between different specimens of the species as in Plate 60, figs. 1, 2, where fig. 1 has eight columns of plates in all interambulacral areas and fig. 2 has nine columns in all interambulacral areas. *Melonechinus keeping! sp. nov. Text-fig. 237, p. 231; Plate 58, fig. 1; Plate 59, figs. 1-3. The test of this species is incomplete but from the fragment that is known it was doubtless spheroidal; melon-like ribs are wanting. This species is known only from the dorsal portion of a corona showing a very good ambulacrum, a fair interambulacrum, and part of a second ambulacrum. It is a light delicate specimen, beautifully preserved in surface detail. This is the second species known from Great Britain ; one species is known from Russia, but all others so far described are from North America. The ambulacrum as far ventrally as pre- served measures about 30 mm. in width, and the interambulacrum at the same zone is esti- mated to be about 33 mm. in width. The ambulacrum adorally, at a zone apparently some little distance above the mid-zone, has twelve columns of plates. These consist of rather narrow (for the genus) occluded plates, narrow demi-, and four irregular columns of isolated plates in each half-area. The occluded plates are proportionately much narrower than in the American species of the genus, and as a concurrent feature the melon-like ribs are wanting. The occluded plates, which are beautifully preserved, have the same arc of curvature as the other ambulacral plates in the area. They are only slightly wider than other ambulacral plates, instead of very much wider as in American species of the genus. This same character of relatively narrow occluded plates without melon-like ribs is also a feature of the British species, M . etheridgii, as described. The pore- pairs of keepingi are enclosed by peripodia and lie in the outer portion of each ambulacral plate. About two and one half ambulacral plates equal the height of an adambulacral. As far dor- MELONECHINUS. sally as preserved, there are only two plates in a row, one primary plate pn».-ing each half-area (Plate 59, fig. 1). This as a localized stage of young plates, is comparable to the typical adult character of Palaeechinus as shown diagrammatically in text-fig. 237, p. 231. Panning ven- trally, we come directly into a stage of two columns of plates in each half-area, oVmi- and oc- cluded, like the condition characteristic of Lovenechinus. Then we pass quickly through a series of stages marked in each half-area by consisting of three columns (like M . apringeri), then four columns (like M. indicmensis) , then five columns (like M. multiporus), finally attaining six columns in a half-area, the species character; all as set forth diagrammatically in text-fig. 237, p. 231. This species has as highly evolved a structure of the ambulacrum as any in the genu>. yet its dorsal localized stages yield a complete epitome of the phylogenesis of the type. . The interambulacrum is well preserved dorsally, but part of the plates are wanting in the adoral portion of the area. As there is no dislocation of parts, it seems, however, that the missing plates can be restored with reasonable assurance of accuracy, as indicated by dotted lines (Plate 59, fig. 1). There are only six columns of interambulacral plates: two columns of pentagonal adambulacral and four median columns of hexagonal plates. Dorsally, the plates are nearly rhombic, as is usual in that zone. The adambulacral columns 1 and 2 drop out dorsally, columns 3 and 4 assuming an adradial position, an indication that the specimen, though small, is fully grown and senescent. Ambulacral and interambulacral plates bear numerous small secondary tubercles (Plate 59, figs. 2, 3), and spines which are about 1.5 mm. in length. The spines are relatively stout and tapering from the enlarged base, as usual in the genu>. This species is known from only one specimen from the Lower Carboniferous Limestone of Gledstone, Gisburn, Yorkshire. It was collected by R. H. Tiddeman, and is in the Museum of Practical Geology Collection 6,583. The photograph was taken for me through the kindm— of Dr. Kitchin of that museum. The species is named for the late Mr. Walter Keeping who published interesting studies of Palaeozoic Echini. *Melonechinus etheridgii (Keeping). Plate 58, figs. 3, 4; Plate 59, figs. 5-11. Melonites rtheridgii Keeping, 1876, p. 398, text-figs. 1-6; Jackson, 1896, p. 240; Klem, 1904, p. 44. Hhrriilgci Lambert and Thiery, 1910, p. 1-0. This species is known from a number of specimens which are considered below in detail. The largest specimen, which was figured by Keeping and selected by him as the type, is a some- what angular slab measuring 195 by 180 mm. in its larger dimensions. It i.- covered with a jumbled mass of interambulacral plates, with some nearly complete fragment.- of ambulacra. A part of this slab is shown in Plate 58, fig. 4 and Plate 59, fig. (i. A second specimen, which is apparently the one referred to by Keeping (1876, p. 398) as being in the British Mu>eum, 386 ROBERT TRACY JACKSON ON ECHINI. is smaller, but is more complete and instructive (Plate 58, fig. 3; Plate 59, fig. 5). Besides these there are several fragmentary specimens known. The test is large and was probably spheroidal. Melon-like ribs are entirely wanting, and in this character it is like M . keepingi and equally differs from American species. The ambul- acra form a gently rounded curve, doubtless corresponding to the curvature of the whole test. Keeping thought that the ambulacra formed ten broad elevated ribs; but I see no support for this view. The width of a half-ambulacrum (Plate 58, fig. 3; Plate 59, fig. 5) is about 24 mm., which would give about 48 mm. as the width of the whole ambulacrum at or near the mid-zone. In the large slab which was figured by Keeping, the ambulacra are somewhat nar- rower, a half-ambulacrum in the widest part seen measuring 16 mm. in width. In the interambulacra as shown in one specimen there are at least seven columns of plates in an area. There are six columns in place and a left adradial column is restored (Plate 58, fig. 3; Plate 59, fig. 5). On this basis the width of the area would be about 48 mm., the same width as the ambulacrum in the same individual. Keeping assumed that there were eight or nine columns of interambulacral plates. This may be correct, but there is no proof of it. The larger "interambulacral plates measure from 8 to 8.2 mm. in width by about 6 mm. in height and 4 mm. in thickness. On the basis of the measurements from the more nearly complete specimen (Plate 58, fig. 3), with ambulacra about 48 mm. in width and interambulacra of the same width, the circumference would be about 480 mm. and the diameter about 153 mm., a very large sea-urchin, exceeding any species known in the genus. The ambulacra are very wide as shown by the above measurements, and in one specimen (Plate 58, fig. 5) a half-area is quite complete at a zone probably near the mid-zone. This has six columns in the left half-area, which shows that there were twelve columns of plates in a complete area. They are composed of relatively narrow occluded plates, narrow demi-, and four columns of isolated plates in each half- area. The occluded plates (as in M. keepingi) are relatively narrower than in American species, and are not built up into an elevated melon-like ridge as in American species. The two occluded columns are clearly distinguished because the pore-pairs are set on opposite sides of the plates (p. 27), which definitely locates the center of the area. Demi-plates bevel over the adambulacrals on the adradial sutures. In most of the specimens the interambulacral plates are dissociated, so that the number of columns is quite doubtful, but in one (Plate 58, fig. 3; Plate 59, fig. 5) there are one pentagonal adambulacral and five hexagonal median columns in place. To complete the area, at least one left adambulacral column must be added, as indicated by dotted lines. There may have been more than seven columns. With seven columns the interambulacrum has about the same width as the ambulacrum, but, if there were more than seven, then the interambulacrum would be so much the wider. Ambulacral and interambulacral plates bear numerous secondary tubercles and spines. The spines are tapering, the most nearly complete being about 2.5 mm. in length. MELONKCHINl'S This species was the first one described from Great Britain, and, differ- imm othi i pean species in its robust size and number of interamlmlacral column.-; :md it difTcrs from nil American species in which the exterior of the test is known by the absence of the melon-like ribs. Lower Carboniferous Limestone, Clitheroe, Lancashire, MuHoum of Practical Geology Collection, holotype 6,577; paratype 6,578. Keeping (1876, p. 399) says that those specimen- are from the Carboniferous Limestone of Derbyshire, lnit tliis is probably a mi-take, as tin- locality given is taken from the original label, and other specimens lithologically identical are known from the Clitheroe locality. Clitheroe, Lancashire. Sedgwick Museum, Cambridge, England, Collection 18, 19, 20; Coplaw, Clitheroe, Lancashire, Museum of Practical Geology. 16,303; between Clitheroe and Chatburn, Lancashire, H. L. Hawkins Collection; Valli>, near Frome, Somerset, British Museum Collection (two specimens) 10 1,400; Thonit<>n-in-( 'raven. Yorkshire, British Museum Collection E 9,540. The holotype, which is the original of Keeping's figures, is in the Museum of Practical Geology Collection 6,577. A photograph of this specimen taken for me through thekindne-- of Dr. Kitchin is in part reproduced as Plate 58, fig. 4. It is a large slab covered with numerous dissociated interambulacral plates and twelve more or less complete fragments of ambiilacral areas, part of which are turned over so that they are viewed from within. The hexagonal interambulacral plates measure about 8 mm. in width by b mm. in height and 4 mm. in thick- ness. The external views of the ambulacra show no indication of a melon-like ridge. Several of the fragments have six columns of plates, indicating a complete section of a half-area; pore- pairs are in peripodia in the outer portion of each plate, and some of the plates have tubercles and spines in place. In the ambulacra as seen from the interior the plates are more angular, being nearly or quite hexagonal in this view, and the pore-pairs are near the middle of each isolated plate, which is gently curved toward the interior of the test, as shown in Plate 59, fig. 8, which was, however, drawn from another specimen. The second specimen in the Museum of Practical Geology Collection 6,678, is labeled at Keeping's second type. It is evidently the specimen he referred to (1876, p. 398), although he states that it is in the British Museum. Dr. Bather, after careful >earch. found no such speci- men in the British Museum, and evidently the statement was a mistake or the specimen has since been transferred to the Museum of Practical Geology. It measures 100 mm. in height and 75 to 100 mm. in width, corresponding with Keeping's description. Structurally, it is the most nearly complete specimen known. A photographic figure, which I owe to the kindne-- of Dr. Kitchin, is given in Plate 58, fig. 3, and a drawing in Plate .V.I, fig. 5. The ambulacrum shows six columns of the left half-area and some occluded and isolated plates of the right half- area. The interambulacrum has a right adambulacral column and five columns of hexagonal plates. In the figure I have added a left adradial column, but there may have been more 388 ROBERT TRACY JACKSON ON ECHINI. hexagonal columns before this adradial was reached (Keeping assumed that there were eight or nine columns, but this is doubtful). The adambulacral plates show a beveled edge on the adradial suture, and numerous tubercles and spines are present on ambulacral and interambula- cral plates (Plate 58, fig. 3). The third specimen in the Museum of Practical Geology Collection 16,303, has dissociated interambulacral plates and a portion of an ambulacral area seen from within, showing well the central position of pores on the interior of isolated plates (Plate 59, fig. 8). The specimens in the Sedgwick Museum Collection, Cambridge, England, are from the Aitken Collection, and all consist of small slabs with dissociated interambulacral plates and parts of ambulacra seen from both the exterior and the interior. The interambulacral plates are large, as in the type, and one measured is 8.2 mm. wide by 6 mm. high. The British Museum has two specimens from Frome, as above listed. They were pre- sented by the Rev. Canon Jackson in 1877. The larger of these two shows a fragment of an ambulacral area and interambulacral plates with tubercles and spines. An adradial plate shows well the beveled adradial face (Plate 59, figs. 9-11). The British Museum specimen from Thornton-in-Craven is small, but shows a very clear portion of an ambulacrum with a few inter- ambulacral plates. There are only four columns of plates in a half-area, and the specimen doubtless came from a ventral or dorsal developing area where the full number of columns of plates characteristic of the species does not exist. Mr. Hawkins's specimen from near Clitheroe is fragmentary, but has an exceptionally good ambulacrum. There are six columns of plates in a half-area, which measures 11 mm. in width. *Melonechinus vanderbilti sp. nov. Plate 58, fig. 5; Plate 61, figs. 1-1. Test large, spheroidal, with strongly marked melon-like ribs. The type and only known specimen is silicified and spmewhat distorted; it represents largely a mold of the interior, but part of the plates are in place as siliceous pseudomorphs. The great thickness of the plates is well seen in the photographic figure (Plate 58, fig. 5). Height about 93 mm. and diameter through the mid-zone about 124 mm.; this latter measurement is somewhat exaggerated by lateral compression. Width of an ambulacrum at the mid-zone about 38 mm., width of an interambulacrum about 43 mm. The ambulacra at the mid-zone have twelve columns of plates composed of wide occluded, narrow derm'-, and four irregular columns of isolated plates in each half-area (Plate 61, fig. 1). The pore-pairs are in peripodia and lie near the outer border of each ambulacral plate. These plates bear numerous secondary tubercles like those of the interambulacra (Plate 61, figs. 1, 3). On the interior, as seen from internal molds, ambulacral plates opposite horizontal sutures are MELONECHINUS. US'.) % higher and laterally fan-shaped; also pore-pairs lie near (lie inner border of demi-plates and the middle of isolated plates (Plate 61, fig. 4) instead of near the outer border of each plate as on the exterior (compare Plate 56, fig. 5). The interambulacra are about equal in width to the ambulacra, and fur the most part are preserved as molds of the interior; a few plates, however, are in place at various parts of the test. There are eight columns of plates at the mid-zone and nine further dorsally in each of the five areas. An area drawn mostly from the internal mold is given in Plate 61, fig. 2. The basicoronal plates are restored, as indicated by dotted lines. There are three plate.- in the second row and four in the third as usual. Column 5 originates in a pentagonal plate in the middle of the area in the seventh row and bears a heptagon on its right ventral border. Column 6 originates in a pentagon on the left of the center in the tenth row and bears a heptagon on its left ventral border. Column 7 originates in a pentagon in the middle in the fourteenth row with a heptagon on its left ventral border. Column 8 originates in a pentagon in the twentieth row on the left of the center with a heptagon on its right ventral border, and column 9 originates in a pentagon in the middle in the twenty-ninth row with a heptagon on its left ventral border. This area shows aberrant variations in three adventitious pentagons, P, P, P, each of which bears a heptagonal plate on its left or right border. Dorsally, the adambulacral columns 1 and 2 drop out at the points X, X, above which columns 3 and 4 assume an adradial position. At the point P', column 5 drops out; at P", column 8 drops out, so that above this zone there are only five columns, a case of rather extreme senescence. The apical disc is not preserved. This species differs from M. multiporus as it has twelve instead of ten columns of ambula- cral plates in an area, also in that it has high instead of low melon-like ribs. It differs from M . giganteus in that it has nine instead of eleven columns of interambulacral plates in an area, also it has a much less accelerated development than that species. Lower Carboniferous, detailed horizon and locality not known, but probably, from its lithological character, from Kentucky or Tennessee. Holotype in Vanderbilt University Collection (Nashville, Tennessee), 220, from which it was kindly loaned me by Professor L. C. Glenn. *Melonechinus giganteus (Jackson). Text-fig. 237, p. 231; Plate 58, fig. 2; Plate 59, figs. 4, 12-15; Plate (50, fig. 3; Plate 61, figs. 5-9. Melmites giganieus Jackson, 1896, pp. 172, 240, Plate 4, fig. 19; Plate •>, figs. 21-24. Mdanites multiporus (pars) Klem, 1904, p. 43. Mchnitcs granulatus Troost in Wood, 1909, p. 107. Melonechinus giganteus Lambert and Thiery, 1910, p. 121. This represents structurally the highest species of the genus and family, and the type is one of the largest and finest of known Palaeozoic Echini. Tost high, spheroidal, with strongly 390 ROBERT TRACY JACKSON ON ECHINI. • elevated melon-like ribs in ambulacral and interambulacral areas. The type specimen (Plate 60, fig. 3) measures 115 mm. in height; the height through the exact center from the oral to the anal area measures 100 mm. This smaller measurement is due to the ventral and dorsal incurving of the test. The greatest diameter through the mid-zone is 155 mm. This measure- ment is somewhat affected by dorso-ventral compression, which, while reducing the height, exaggerates the horizontal diameter. Width of the ambulacra at the mid-zone 38 mm., width of interambulacra 41 mm. The plates are very thick, the interambulacral plates at the mid- zone measuring 8.5 mm. in thickness, much exceeding the surface width of the plates, which is about 7 mm. In a fine specimen in Vanderbilt University Collection 222, the ambulacrum measures about 40 mm. and the interambulacrum 45 mm. in width. Ambulacral areas are wide, with twelve columns of plates at the mid-zone composed of wide occluded, narrow demi-, and four irregular columns of isolated plates in each half-area (Plate 61, fig. 8). The occluded plates in the middle are arched up in high, rounded, melon- like ribs formed by the thickening of the plates (Plate 60, fig. 3). Demi-plates bevel over the adambulacrals on the adradial sutures. Pore-pairs are situated in sunken valleys in each half-area; they are surrounded by peripodia and lie in the outer portion of each ambulacral plate (Plate 61, fig. 8). Ambulacral plates are thickly covered with small secondary tubercles like those of the interambulacra (Plate 60, fig. 3). As seen from the interior of the test (Plate 61, figs. 6, 9), occluded plates are narrower than on the exterior, and demi-plates opposite horizontal interambulacral sutures are higher and laterally fan-shaped (compare text-fig. 244, p. 338). In this view pore-pairs, as usual in the genus, lie in the outer portion of occluded plates, the inner portion of demi-plates, and near the center of all isolated plates, instead of near the outer border of all plates, as is the character of the exterior (Plate 61, figs. 5-9), (p. 359). Ventrally, the ambulacrum of M . giganteus presents interesting stages in development. Near the peristomal border there are four columns of plates, narrower demi- and wider occluded in each half-area, as shown in Plate 59, fig. 13. This is like the adult character of the genus Lovenechinus (text-fig. 237, p. 231). A little higher up in this same figure single isolated plates appear in the middle of each half-area; this is like the character of Oligoporus. Next appear more isolated plates which, being continuous, make a single column of isolated plates in each half-area like the condition in Melonechinus springeri, the simplest ambulacral condition that is referable to the genus Melonechinus (text-fig. 237, p. 231). A four-column stage like that of Melonechinus indianensis would be the next to follow the three column stage, but, owing to local imperfections, it was not ascertained in giganteus, so that a gap occurs at this point. A little higher up, however, we find a stage in which there are five columns in a half-area (Plate 59, fig. 12); this is like the typical condition at the mid-zone in Melonechinus multiporus (text- fig. 237, p. 231). Still higher appear the six columns in a half-area, which is the species char- acter. Thus the ventral stages in development of the ambulacrum in this highest species of MELONECHINUS. 391 the genus repeat very fully the adult character of reprorntative lower species and genera in its series. Dorsal localized stages could not be ascertained in Melonechinus giganteus, but in the diagram (text-fig. 237, p. 231) such stages are supplied fnun Melonechinus keepingi, which at the mid-zone has twelve columns of ambulacra! plates, and therefore in this respect represents the same structural differentiation as yiganteus. The interambulacra of Melonechinus giganteus are slightly wider than the ambulacra, and are arched up in strong melon-like ribs which outwardly are gently curved and laterally dip steeply down to the adradial sutures (Plate GO, fig. 3). There are eleven columns of plates in an area at or above the mid-zone (Plate 59, fig. 14; Plate 61, fig. 8). This is the highest number known in the genus and family, and therefore, as giganleus has as great a number of ambulacral plates as are known, it is considered the most highly evolved species of the genus and family yet discovered. The interambulacral plates bear many secondary tubercles, tin-re being about twenty-five on the larger plates (Plate 59, fig. 15). The spines are not preserved. The structure of the interambulacra of the type was described in detail and the point of origin of columns tabulated in my earlier paper (1896, pp. 174-182). Eleven columns wen- ascertained in four of the five areas, and it was estimated that there arc about 1,550 interam- bulacral plates in the specimen. It has not only more columns of interambulacral plates than any other species of the genus, but, as a natural corollary, it has a more accelerated development than lower species of the genus. Considering here only one area, that figured (Plate 59, fig. 14), it is seen that plates of the basicoronal row are wanting, but there were doubtless two, as restored in Plate 59, fig. 13. Assuming these two as a basal row, there are three plates in the second row and four in the third as usual in the whole family. The fifth column originates in the fifth row (very early), the sixth column in the eighth row, the seventh column in the tenth, and the eighth column in the fourteenth row, all very early as compared with the zone at which these columns originate in other species of the genus (compare text-fig. 2I(>. p. 382; Plate .~>7. fig. 1). The ninth column originates in the sixteenth row in a small tetragonal plate, in which the two sides wanting are compensated for by the two heptagons, H' and H", on its left dorsal and right ventral borders. The hexagon A lies on its left ventral border. In the seventeenth row there are only eight plates, but in the eighteenth row the ninth column starts again with a pentagonal plate bearing a heptagon, H, on its right ventral border as usual. The same anomaly occurs in the origination of the ninth column in three other areas in this superb speci- men, showing a strong tendency to a parallel radial variation. The tenth column originates in the twenty-second row, just below the mid-zone, about the same zone in which the eighth column ordinarily originates in M. multiporus (Plate 57, fig. 1). The eleventh column origi- nates in this area (Plate 59, fig. 14) in the twenty-ninth row, or in other areas a trifle earlier. Dorsally, as a senescent character, it drops out before reaching the apical disc. In the speci- men in Vanderbilt University Collection 222, the eleventh interambulacral column has already 392 ROBERT TRACY JACKSON ON ECHINI. been attained at the mid-zone, somewhat earlier than in the type. A fragmentary specimen in the United States National Museum has eleven columns at a point which is probably very near to the mid-zone (Plate 61, fig. 8). Dorsally, there are obscure traces of genital and ocular plates in the type, but structural details could not be made out. As closely as it can be ascertained the apical disc measures about 22 to 25 mm. in diameter, which is 15 to 16 % of the diameter of the test. In this proportion it agrees with the measurements obtained in Melonechinus multiporus (p. 379). This species is very distinct from any previously described. It differs from multiporus in the character of the highly elevated melon-like ribs, in the number of columns of ambulacral and interambulacral plates, and the accelerated development of the interambulacral area. I think Miss Klem is entirely mistaken in considering giganteus a synonym of multiporus, but it should be noticed that she includes in the synonymy of multiporus several species that are here considered distinct. Miss Wood (1909, p. 108) thinks that the Melonites granulatus of Troost, is referable to giganteus, and studying the type, I quite agree with her, although my first impression was that it should be considered a distinct species. In this specimen (Plate 58, fig. 2; Plate 59, fig. 4), which is fragmentary, there is a half-ambulacrum with six columns of plates, indicating twelve columns in the area. In the interambulacrum there are an adambula- cral and five hexagonal columns in place, but the right part of the area is wanting, so that the total number of interambulacral columns is unknown. With present evidence it can safely be referred to giganteus. Lower Carboniferous, Bowling Green, Kentucky, holotype, Museum of Comparative Zoology Collection 2,989; St. Louis Group, Clarksville, Tennessee, United States National Museum 42,340; Mississippi Group, Lower Carboniferous, Cumberland Gap, Tennessee (the holotype of Melonites granulatus Troost) United States National Museum 39,909; no detailed horizon or locality, probably St. Louis Group, Tennessee, Vanderbilt University Collection (Nashville, Tennessee), 222. The several specimens of this species studied are sufficiently considered above, excepting the National Museum specimen from Clarksville, Tennessee. This specimen, though fragmen- tary, is very instructive. From it is gathered a very good section across an interambulacrum and half -ambulacrum (Plate 61, fig. 8). In the ambulacrum there are six columns of plates in the half-area, pore-pairs are in clear peripodia near the outer border of each plate, and numer- ous secondary tubercles exist. The interambulacrum shows the introduction of column 11 in a pentagonal plate with a heptagon on its right ventral border. A section of an ambulacrum seen from within (Plate 61, fig. 9) shows plates more angular than on the exterior and convex toward the interior. The pore-pairs lie toward the outer border of the occluded plates, the inner border of demi-plates, and near the middle of isolated plates, instead of near the outer border of all plates, as seen on the exterior. In order to compare critically the inner and outer faces, these views are shown in the same individual plates in Plate 61, figs. 5, 6, and 7. In these LEPIDESTHIDAK. :{«.»:; figures the relative size, angles, and position of pores of ambulacral plates are seen. The adam- bulacral plates on the interior are much wider than on the exterior. The other inlerambnlai -r.-il plates are narrower and lower on the interior than on the exterior, due to the smaller spar.- occupied on the interior by thick plates in a curved test. Family LEPIDI.STIIIDAE Jackson. I,<'pidoccn1ridae (pars) Loven, 1874, p. 39; (pars) Jackson, 1890, p. 241; (pars) Kl-in. I!XH, p. Iti. Palaeechinidae (pars) Loven, 1874, p. 40. Archacocidaridac (pars) Love"n, 1874, p. 42; (pars) Duncan, lXX9a, p. 8; (pars) Xittcl, 1879, p. I- Melonitidae (pars) Zittel, 1879, p. 484; (pars) Duncan, ISX'ta, p. l.V Lepidesthidae Jackson, 1896, pp. 206, 241; Tornquist, 1897, pp. 730, 734; Gregory, 1900, p. 304; Klein. 1904, p. 22; Lambert and Thiery, 1910, p. 123. Hybockinidae Tornquist, 1897, pp. 732, 734. Rhoeckinidae (pars) Lambert and Thiery, 1910, p. 121. This family is enlarged from what it was as I first published it, to include certain old genera and one new one. It presents a wide range of characters, yet is fairly homogeneous as a whole. As a family it is related to the Palaeechinidae, from which it is distinguished essentially by the fact that the plates are imbricate. Test spheroidal, elliptical, obovate, or flattened. Ambula- cra are narrow or wide, with, in each area at the mid-zone, from two to twenty columns of plates which imbricate weakly or strongly adorally, and laterally bevel under the adambulacral plate-. As in the two lowest genera of the Palaeechinidae, the Jowest genera of this family (Lepidechi- nus, Perischodomus) have only two columns of plates in an ambulacral area, but other genera have from four columns upward. Pore-pairs are in peripodia, situated nearest the next adjacent interambulacrum or exceptionally (Pholidocidaris) near the middle of each plate. The am- bulacra ventrally and dorsally (as in the Palaeechinidae) are simpler than at the mid-zone, when that area is complex. Ambulacral plates bear secondary tubercles and spines only, or (Meekechinus) small primary with secondary tubercles. In the character of the number of ambulacral columns, this family includes the most specialized of Palaeozoic Echini. The interambulacra are wide or narrow with from three to thirteen columns of plates at the mid-zone in each area. The plates are thick or thin, and imbricate aborally and from tin- center laterally and over the ambulacrals on the adradial sutures. This last is an important point, as in the Palaeechinidae, in which imbrication is lacking, interambulacral plates bevel under (not over) the ambulacrals. Ventrally, apparently always in this family (Plate 64, fig. 2), the primordial interambulacral plates are in the basicoronal row. there l>eing, as far as known, no resorption of the base of the corona. From the basicoronal row passing dorsally, there are two plates in the second row and three in the third, dorsal to which additional columns, if developed, come in as in other Palaeozoic types. Interambulacral plates hear ondary tubercles and spines only, or primary with secondary tubereles and spines. 394 ROBERT TRACY JACKSON ON ECHINI. The peristome where known has ambulacral plates only. Oculars are insert or exsert, and imperforate or exceptionally with one pore (Lepidechinus, Plate 63, fig. 8), or two pores (Lepidesthes formosa, Plate 68, fig. 5) . The oculars ventrally cover the ambulacra and laterally the interambulacra in part on either side. The genitals are high and wide with from one (Lepi- dechinus, Plate 63, fig. 8) to many pores each. A madreporite is clearly existent in some species. Plates of the periproct are numerous and angular, much as in other Palaeozoic types. The lantern is inclined, teeth grooved, pyramids wide-angled, with moderately deep foramen magnum; epiphyses are narrow, capping the half-pyramids, and braces are of the character usual in all regular Echini. LEPIDECHINUS Hall. 1 Lepidechinw Hall, 1861, p. 18; (pars) 1868, p. 295; (pars) 1870, p. 339; (pars) Loven, 1874, p. 44; A. Agassiz, 1874, p. 648; non 1892, p. 74; (pars) Duncan, 1889a, p. 12; (pars) Keyes 1895, p. 192; (pars) Jackson, 1896, pp. 226, 242; (pars) Klem, 1904, p. 20; (pars) Lambert and Thiery, 1910, p. 122. 2 Rhoechinus Keeping, 1876, p: 37; (pars) Duncan, 1889, p. 205; 1889a, p. 14; (pars) Jackson, 1896, pp. 200, 239; (pars) Tornquist, 1897, p. 18; (pars) Klem, 1904, p. 27; Lambert and Thiery, 1910, p. 122. Test spheroidal, ambulacra narrow with two columns of plates in each area throughout. Plates all primaries, pore-pairs uniserial or slightly biserial at the mid-zone. The ambulacral plates imbricate moderately adorally, and laterally bevel under the adradials. Interambula- cra are wide at the mid-zone with from four to eight columns of plates in each area in the known species. Interambulacral plates are relatively thick, rounded somewhat in outline, but pentag- onal in adambulacral and hexagonal in median columns. They imbricate aborally and from the center outward and over ambulacrals on the adradial sutures. The primordial interam- bulacral plates are in the basicoronal row (Plate 64, fig. 1). The surface of interambulacral plates bears secondary tubercles only. Peristome with ambulacral plates only. Apical disc as known in one species (Plate 63, figs. 7, 8) with oculars exsert, each with one pore, at least as seen from within, and genitals high and wide, each with one pore. As the apical disc is known only from one specimen, and that one seen from within (Plate 63, figs. 7, 8), it is quite possible that an external view or other species might show other characters. Periproctal plates are unknown. The lantern is inclined, teeth grooved, and pyramids wide-angled, with moderately deep foramen magnum. The type species is Lepidechinus imbricatus Hall, from the Lower Carboniferous of America. 1 Lepidechinus as here described includes L. imbricatus Hall, the type, but not L. rarispinus Hall, which is referred to the genus Hyattechinus, p. 292. 2 Rhoechinus as used by Duncan includes R. irregularis Keeping, here referred to Lepidechinus, and also species of Palao- echinus, p. 303. In this he was followed by Jackson (1896), Tornquist (1897), and Miss Klem (1904). Lambert and Thie'ry (1910, p. 123) point out this error in the application of the name Rhoechinus. LEPIDECHINUS. This genus is considered the lowest member of the family, and is very near to Palaeechinu-. which is also considered the lowest member of its family. Lepidechirms differs from Palac- echinus chiefly in the fact that the plates are imbricate and that adambulacral plates bevel over the ambulacrals instead of ambulacrals beveling over the adambulacrals, us in Palaeechinus. Hall in describing Lepidechinus, and Keeping in describing Rhoechinus, pointed out the <-lo-e relations of these genera to Palaeechinus. Unfortunately Professor Mull did not (inure f,epid- echinus imbricatus, the type, but did figure what he described a- /.. w/.v/;//;//*. which, how- ever, has very different characters and is here referred to Hyattcrhimis (p. 292). Naturally the understanding of Lepidechinus has been taken largely from rarispinus with the result that the genus Lepidechinus has been misinterpreted. As I have studied and here figure the type, it is hoped that the relations expressed may prove correct. Mr. Agassiz (1874, p. 648) says, "In Hall's genus Lepidechinus the ambulacra and inter- ambulacra lap in opposite directions. Interambulacra in eight rows; outer pentagonal, other- hexagonal. Hall, in his Report on the Geology of Iowa, has given us excellent figures of the tubercles, spines, and portions of the ambulacral and interambulacral plates (PI. XXVI)." This reference is quite mistaken, as in the work and Plate referred to, Professor Hall figured Archaeocidaris, not Lepidechinus. Hall never figured Lepidechinus imbricatus, which has eight columns of plates in an interambulacrum, and which is here figured for the first time (Plate 62, fig. 5; Plate 64, fig. 1). Hall, however, did give a figure of Lepidechinus [Hyatte- chinus] rarispinus, which has eleven columns of plates in each interambulacral area (pp. 292, 294; Plate 21, fig. 6; Plate 22, fig. 7). Further, Mr. Agassiz (1892, p. 74) says, "Hall's figures of Lepidechinus in the Geology of Iowa [1858], Vol. I., Part 2, Plate IX, fig. 10,' show three or four plates at the actinal edge." Hall's Lepidechinus rarispinus is here referred to Hyatle- chinus rarispinus (pp. 292, 294); his figured specimen, and the only one he did figure (my Plate 21, fig. 6; Plate 22, fig. 7), is a dorsal mold, so that Mr. Agassiz is mistaken in speaking of it as ventral. In rarispinus there is a single plate at the actinal (or peristmnal) border of the test (not "three or four plates") as I show in three species of Hyattochinus (p. 292), as well as in the true Lepidechinus (p. 400). Key to tin- N/wnV.v of I,r/i//lr<'hiiuix. Four columns of plates in an interambulacral area at the mid-zone . /.. irri-giilaris (Keeping), p. Five columns of plates in an interambulacral area at the mid-y.one /.. KHMMU sp. nov., p. 397. Six columns of plates in an interamhulacral area at the mid-y.om- . /,. tr.iscllatus sp. nov., p. 397. Eight columns of plates in an interambulacral area at the mid-zone . /-. imbricaliut Hall, p. 399. 'This reference is incorrect as Hall's figure of I.epidcrtiitms, which is /,. [lli/,illirhinu.i\ rnrw/nniw wa* not published in the Geology of Iowa, but in 1868 (and 1870, revised edition) in the Twentieth Report \. V. Stntc Cabinet N tt lit-- Plate 9, fig. 10 (see this memoir, p. 292). 396 ROBERT TRACY JACKSON ON ECHINI. *Lepidechinus irregularis (Keeping). Plate 63, figs. 1, 2. Rhoechinus irregularis Keeping, 1876, p. 37, Plate 3, figs. 6-8; Zittel, 1879, p. 484; Duncan, 1889, p. 205; Jackson, 1896, p. 200; Tornquist, 1897, p. 754; Klem, 1904, p. 30; Lambert and Thiery, 1910, p. 122. Palaechinus rutoti Julien, 1896, p. 129, Plate 6, fig. 8; Klem, 1904, p. 36; Lambert and Thiery, 1910, p. 119. Palechinus rutoti Tornquist, 1897, p. 753. ' Test small, spheroidal, imperfectly known. Ambulacra are narrow, with two columns of low primary plates which imbricate adorally and laterally bevel under adambulacrals. About four ambulacral plates equal the height of an adambulacral. Pore-pairs are uniserial, situated near the outer border of each plate. Interambulacra are broad, with four columns of plates at or about the ambitus, and in the type a trace of a fifth column, as represented by one plate, exists dorsally (Plate 63, fig. 2). These plates imbricate aborally, and from the center laterally and over the ambulacra on the adradial sutures. Externally they bear small secondary tubercles. Keeping's holotype is a small specimen which I studied at the Sedgwick Museum, Cam- bridge, England. He naturally made it the type of a new genus (Rhoechinus), as it differed so distinctly from Palaeechinus by the imbrication of its plates. Keeping says of his genus Rhoechinus that it differs from Perischodomus and Lepidechinus in the absence of primary tubercles. This is true in regard to Perischodomus, but was a mistake as regards Lepidechinus, for the type of that genus and other species here attributed to it have only secondary tubercles. It is to be remembered however that Hall's Lepidechinus [Hyallechinus] rarispinus has primary tubercles (p. 293). The species irregularis is clearly referable to Professor Hall's genus Lepid- echinus, so that Rhoechinus becomes a synonym. Professor Duncan overlooked the character of imbrication and used Rhoechinus to include species which he separated from the old genus Palaechinus M'Coy, as earlier discussed (p. 303). The specimen described as Palaechinus rutoti by Julien with present evidence cannot be distinguished structurally from L. irregularis. As Julien says, it has two columns of low narrow ambulacral plates, imbricating adorally, with pore-pairs uniserial, and four columns of interambulacral plates which imbricate aborally, and bear small secondary tubercles only. Four ambulacral plates are equal in height to a pentagonal adambulacral plate. The hex- agonal interambulacral plates have a width of 5 mm. and a height of 3 mm. Lower Carboniferous, Hook Head, County Wexford, Ireland, holotype in Sedgwick Mu- seum Collection, Cambridge, England, 12; neat Savigny-Poil-Fol, central France (this is the holotype of Palaechinus rutoti Julien, and is in the possession of the family of the late Professor Julien). LEPIDECHINUS. .!'.)7 'Lepidechinus iowensis sp. tiov. Plate 62, fig. 1 ; Plute 03, figs. 3, 4. Test spheroidal. Known only from the holotype, which measures 52 mm. in diaim -ti-r. The ambulacra at the mid-zone are 4.5 mm. in width and the interambulacra 28 mm. in width. The ambulacra are narrow, composed of two columns of low primary ambulacra! plates alike throughout the area. Pore-pairs are uniserial, situated near the outer border of each plate. Ambulacral plates imbricate slightly adorally and laterally bevel under tin- adradials d'latc 63, fig. 4). The interambulacra are broad with five columns of plates in each area. Tin- in- terambulacral plates are moderately curved outward, are pentagonal in adambulacral and hexagonal in median columns. They imbricate moderately aborally and from the center outward and over the ambulacrals, on the adradial suture line presenting a curved outline (compare Perischodomus, Plate 64, fig. 3). The ventral portion and apical disc are wanting, but the lantern is in place and partially visible, as seen from above (Plate 63, fig. 3). The lantern is inclined, so that, with the angle presented, one sees a considerable portion of the inner face of the teeth (compare Plate 27, fig. 5). The teeth are grooved, pyramids wide-angled, and foramen magnum moderately deep. Typical braces are in place. The structure of the lantern as far as gathered from the dorsal view is essentially like that of Lepidesthes (Plai figs. 9-14).. Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa. The holotype and only known specimen is in Mr. Frank Springer's collection 8,010. 'Lepidechinus tessellatus sp. nov. Plate 62, figs. 2-4; Plate 63, figs. 5-11. Lepidechinus imbricattts A. Agassiz, 1904, p. 80 (non Lepidechinus imbricatus Hall, 1861, p. 18. See p. 299). Test spheroidal. The holotype (Plate 62, fig. 2) measures 50 mm. in diameter. The width of the ambulacrum at the mid-zone is 5 mm., width of the interambulacrum 25 mm. The ambulacra are narrow, composed of two columns of low primary plates in each area. Pore-pairs are uniserial, situated near the outer end of each plate (Plate 63, fig. 6). About five to six and a half ambulacral plates equal the height of an adambulacral. The ambulacral plates imbricate adorally and laterally bevel under the adambulacrals. From this beveling it occurs that the ambulacral plates on the interior of the test (Plate 63, fig. 7) are wider than on the exterior, and also on the interior the pore-pairs are in the middle of the half-areas instead of near the outer end of each plate, as on the exterior (p. 60). The interambulacra are wide, composed of six columns of plates at the mid-zone in each area. In the paratype (Plate 63, fig. 9) the sixth column originates below the mid-zone, and 398 ROBERT TRACY JACKSON ON ECHINI. in the holotype (Plate 63, fig. 6) one column, either 5 or 6, drops out dorsally with a pentagonal plate, indicating senescence. The interambulacral plates are curved on the outer surface and bear secondary tubercles only. They are slightly rounded on the suture lines and imbricate moderately aborally and from the center laterally and over the ambulacra. Adambulacral plates are pentagonal, rounded on the adradial sutures (compare Plate 64, fig. 3). The plates of the median columns are hexagonal. On the interior of the test (Plate 62, fig. 3; Plate 63, fig. 7) the interambulacral plates are more sharply angular than on the exterior, and adambula- cral plates are not rounded on the adradial sutures (compare text-figs. 32, 34, p. 75). The ventral portion of the test is unknown. Dorsally, as seen from within (Plate 62, fig. 3; Plate 63, figs. 7, 8) the apical disc is in place; it is small, measuring 9 mm. in diameter. The whole of this specimen is not known but it corresponds nearly enough with the holotype so that it was at least fully as large. On this basis the diameter of the apical disc as seen from within would be proportionately about 18 % (or less) of the diameter of the test. Several ocular and genital plates are in place. The oculars are triangular, fully exsert, each being shut out from the periproct by the contact of the two adjacent genitals, a rare character in the Palaeozoic, but like the dominant Mesozoic and the youthful character of modern Echini (p. 89). Each ocular has one pore near the ventral border, but as this is an internal view, it is not certain that the pore reached the surface (p. 89). The oculars ventrally cover the ambulacra and laterally in part the interambulacra on either side, the young interambulacral plates being in contact with the oculars (pp. 62,86). This is the specimen to which Mr. Agassiz (1904, p. 80) referred as Lepidechinus imbricatus, and in which he noted that th.e young interambulacral plates origi- nate against the oculars. The genital plates are high and wide, and, as far as preserved, meet in a continuous ring dorsally on the periproctal border. Each genital has a single pore near the middle of the plate. This single pore in each plate is the only case with this character seen in the Palaeozoic, and also the median position is unusual; but it should be remembered that this is an internal view, and in an external view the pores may be nearer the ventral border (p. 171). Genital pores are usually near the ventral border of the plates, but they may be near the middle of the plates in external view, as seen in Dermatodiadema (text-fig. 80, p. 104) and Peltastes wrighti (Plate 4, fig. 7). The plates of the periproct and the lantern are unknown in this species. This species differs from Lepidechinus iowensis in having six instead of five columns of plates in an interambulacral area. It differs from Lepidechinus imbricatus in having six instead of eight columns of plates in an interambulacral area, and also in that the plates are rela- tively larger, heavier, and less strongly imbricating. Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype, Museum of Comparative Zoology Collection 3,053; paratype, same museum, no. 3054; second paratype, F. Springer Collection 8,011. LEPIDECHINUS. 399 In the holotype, which is in the Museum of Comparative Zoology, the dorsal half of tin- test is preserved (Plate 62, fig. 2; Plate 63, figs. 5, 6). In areas A, E, and I the sixth column drops out passing dorsally and terminates in a pentagonal plate, an apex of which points dor- sally; and in areas C and G the fifth column drops out similarly. In area E the fifth column also drops out, but two rows later than column 6. The terminal pentagons in several cases have a heptagonal plate on their dorsal border. These might easily be taken for the point of intro- duction of columns, but this is the dorsal, not the ventral portion of the test, as shown by the direction of imbrication of plates. This specimen has very clear ambulacral detail which is taken to represent the species character. In Mr. Springer's specimen (Plate 62, fig. 4; Plate 63, figs. 9-11) the plates are worn, but the imbrication is clear, as shown in Plate 63, figs. 10 and 11. Ventrally there are five columns, the sixth coming in below the mid-zone. The ambulacral plates ventrally are all typical primaries with pore-pairs uniserial, but at the" mid-zone in this specimen there is a tend- ency for alternate plates to be expanded on the lateral border and the plates between narrowed. There is nothing of this seen in the type, but otherwise the specimen has the characters of this species. The Museum of Comparative Zoology specimen, which is seen from the interior, is very interesting (Plate 62, fig. 3; Plate 63, figs. 7, 8). There are three interambulacral and four ambulacral areas. The interambulacral columns in each area are all continued nearly or quite to the apical disc instead of dropping out dorsally, as in Plate 63, fig. 5. The ambulacral plates and apical disc of this choice specimen are considered above. *Lepidechinus imbricatus Hall. Plate 62, fig. 5; Plate 64, fig. 1. Lepidechinus imbricatus Hall, 1861, p. 18; 1868, p. 296; Lovfe, 1874, p. 44; Keyes, 1895, p. 192; Jackson, 1896, pp.226, 242; non A. Agassiz, 1904, p. 80; Klein, 1904, p. 21; Lambert and Thiery, 1910, p. 122. Lepidocentrw imbricatus Meek, 1874, p. 375. Lepidechinus intricatus Pomel, 1883, p. 113. In the type specimen, which is in the Museum of Comparative Zoology, the test is sphe- roidal. The ambulacra at the mid-zone measure about 3 mm., and the interambulacra about 20 mm. in width. The ambulacra #re narrow, composed throughout each area of two columns of low pri- mary plates which imbricate strongly adorally and bevel under the adjacent adambulacrals. Pore-pairs are uniserial, situated near the outer border of each plate. Two and a half ambulacral plates equal the height of an adambulacral. The interambulacra are broad, with, at the mid-zone, eight columns of plates, which are small, curving outward, and rounded on the suture lines. They imbricate strongly aborally and from the center laterally and 400 ROBERT TRACY JACKSON ON ECHINI. over the ambulacrals. The adambulacral plates are pentagonal and rounded on the ad- radial sutures. Plates of the median columns are hexagonal, but the angles of all these plates are somewhat rounded, not sharply defined, as in the Palaeechinidae. There are secondary tubercles only on ambulacral and interambulacral plates. No spines are preserved in the type, but in a second specimen in the Museum of Comparative Zoology 3,186, there are fine tapering spines, swollen at the base, and measuring up to about 2.5 mm. in length. Ven- trally, the primordial interambulacral plates are in the basicoronal row, and, passing dorsally, new columns are progressively added until the full complement is attained below the mid-zone. Although only partially preserved, it may be safely stated that there are only ambulacral plates on the peristome. The dorsal portion of the test is unknown, and the lantern is not preserved in the type, but in another choice specimen in the Museum of Comparative Zoology no. 3,186, from the Wachsmuth Collection, there is a well preserved lantern in place. The pyramids are wide-angled, with ridges for" the attachment of interpyramidal muscles, foramen magnum moderately deep, and teeth grooved, all as usual in Palaeozoic species. Some ambul- acral plates in this specimen are evidently peristomal plates. This species, the type of the genus, differs from the other species in that it has more columns of interambulacral plates, also more strongly imbricate plates, both in the ambulacra and the interambulacra. The specimen which I identify as the type has no original label, but bears the diamond-shaped green ticket that Professor Hall used to indicate types. It agrees entirely with Hall's original description. Moreover, the late Professor Whitfield informed me that the type was in the Barris Collection, which was purchased by Professor Louis Agassiz for the Museum of Comparative Zoology. Professor Hall in his description says that the interam- bulacral plates imbricate adorally, "the lower edges of each range overlapping those below; while the plates of the ambulacral areas are imbricating in the opposite direction." The fact that he said that interambulacral plates imbricate adorally is ascribed to incorrect orienta- tion, which has led to a similar interpretation in regard to imbrication in some other cases. Indeed, Professor Hall (1868, p. 296) himself said that he had probably given the direction of imbrication incorrectly in his original description. Professor Hall pointed out that the essential difference of the genus (and species) from Palaeechinus is the fact that the plates are imbri- cate. He also considered as a difference the number of columns of interambulacral plates, but this with present understanding is not considered a generic difference. The species differs generically from what Hall described as Lepidechinus rarispinus, which species is here referred to Hyattechinus (p. 292) and figured on Plate 21, fig. 6 and Plates 22, 23. Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype, Museum of Comparative Zoology Collection 3,055; another choice specimen especially good for the ventral part of the test, lantern, and spines, Museum of Comparative Zoology Collection 3,186; also a fragmentary specimen in the same museum no. 3,056 (original no. 417). PERISCHODOMI S. 401 PERISCHODOMUS M'Coy. Perischodomus M'Coy, 1849, p. 253; 1854, p. 114; Love"n, 1874, p. 40; Keeping, 1870, p. 35; (pare) Dun- can, 1889a, p. 10; Jackson, 1896, p. 242; Tornquist, 1897, p. 783; (pars) Klem, 1904, p. 18; (pare) Lambert and Thie"ry, 1910, p. 122. Tretechinus Tornquist, 1897, p. 784. Test high, spheroidal. Ambulacra are narrow, composed in each area of two columns of low plates. Interambulacra are wide, with many columns of plates (five in the known -porir- in each area. The interambulacral plates imbricate strongly aborally and from the center laterally and over the ambulacra on the adradial sutures. The primordial interambulacral plates are in place in the basicoronal row. Adambulacral plates bear medium-sized eccentric perforate primary tubercles with secondary tubercles, and median interambulacral plates bear primary and secondary tubercles, or the latter only. Spines are medium-sized primaries and small secondaries. Plates of the peristome are imperfectly known, but apparently are ambula- cral only. Oculars are imperforate, genitals low and wide, with numerous pores. The lantern is known from pyramids which are similar to those of Lepidesthes and other Palaeozoic Echini. The characters of this genus are based on Perischodomus biserialis, the type species of the genus and the only one which is well known. This genus differs from Lepidechinus in that the interambulacral plates, in part at least, bear primary with secondary tubercles. It differs from the other genera of the family in that it has two instead of more than two columns of plates in each ambulacral area. In my earlier paper (1896, p. 242) I included Perischodomus in the Lepidocentridae, but with fuller knowledge of Lepidechinus and Perischodomus it seems that both genera belong in the Lepidesthidae as primitive representatives of the family. Key to the Species of Perischodomus.1 Five columns of plates in each interambulacral area, test large . . . P. biserialis M'Coy, p. 401. Five, or perhaps more, columns of plates in each interambulacral area, test small (imperfectly known). P. illinoisi'i>.tt.i Worthen and Miller, p. 400. *Perischodomus biserialis M'Coy. Text-fig. 30, p. 70; Plate 29, fig. 5; Plate 62, figs. 6, 7; Plate 64, figs. 2-8. Perischodomus biserialis M'Coy, 1849, p. 253, text-figs, a-c; 1854, pp. 114, 115, text-figs, a-c; Desor, 1858, p. 157; Quenstedt, 1875, p. 374, Plate 75, fig. 13; Loven, 1874, p. 40; Keeping, 1876, p. 3