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See a Se ~ : x Ss + oe ape hy YZ A a : ON aN pa es LAN : ef MESO 4 La | 4 (OC RCC er w @as mic 0 ¢ ot « Ks («ce OG qq rf mx ¢ ( q i€ $s « ( ¢ aC r eae rf : CC EMC G a « ce Gat ac iC €€ ee iq < i Colt 7 is au} i (a) d a (i) MEMOIRS OF THE CONNECTICUT ACADEMY OF ARTS AND SCIENCES VOLUME VI DECEMBER, 1919 The Sauropod Dinosaur Barosaurus , Marsh Redescription of the Type Specimens in the Peabody Museum Yale University BY RICHARD SWANN LULL, Ph.D., Sc.D. PROFESSOR OF VERTEBRATE PALEONTOLOGY IN YALE UNIVERSITY, AND ASSOCIATE ‘ CURATOR IN VERTEBRATE PALEONTOLOGY IN THE PEABODY MUSEUM NEW HAVEN,. CONNECTICUT PUBLISHED BY THE CONNECTICUT ACADEMY OF ARTS AND SCIENCES AND TO BE OBTAINED ALSO FROM THE YALE UNIVERSITY PRESS MEMOIRS OF THE CONNECTICUT ACADEMY OF ARTS AND SCIENCES VOLUME VI DECEMBER, 1919 The Sauropod Dinosaur Barosaurus : Marsh Redescription of the Type Specimens in the Peabody Museum Yale University BY RICHARD SWANN LULL, Ph.D., Sc.D. PROFESSOR OF VERTEBRATE PALEONTOLOGY IN YALE UNIVERSITY, AND ASSOCIATE CURATOR IN VERTEBRATE PALEONTOLOGY IN THE PEABODY MUSEUM VAIN 1 59 Ped formal} Dinas NEW HAVEN, CONNECTICUT PUBLISHED BY THE CONNECTICUT ACADEMY OF ARTS AND SCIENCES AND TO BE OBTAINED ALSO FROM THE YALE UNIVERSITY PRESS oes beter ‘ lid TO THE MEMORY OF CHARLES EMERSON BEECHER SKILLFUL WITH HAND, BRAIN, AND PEN; REVEALER OF THE MYSTERIES OF TRILOBITES; THIS MEMOIR IS DEDICATED aD Ny aN Penn ey Were ‘ FOREWORD. By CHARLES SCHUCHERT. Trilobites are among the most interesting of invertebrate fossils and have long attracted the attention of amateur collectors and men of science. These “three-lobed minerals’ have been mentioned or described in books at least since 1698 and now several thousand species are known to paleontologists. To this group of students they are the most characteristic animals of the seas of Palzeozoic time, and even though they are usually preserved as dis- membered parts, thousands upon thousands of “‘whole ones” are stored in the museums of the world. By “whole ones” perfect individuals are not meant, for before they became fossils the wear and tear of their time and the process of decomposition had taken away all the softer parts and even most of the harder exterior covering. What is usually preserved and revealed to us when the trilobites weather out of the embrace of their entombing rocks is the test, the hard shell of the upper or dorsal side. From time to time fragments of the under or limb-bearing side had been discovered, first by Elkanah Billings, but before 1876 there was no known place to which one could go to dig out of the ground trilobites retain- ing the parts of the ventral side. — Students of trilobites have always wanted specimens to be delivered to them weath- ered out of the rock by nature and revealing the ventral anatomy without further work than the collecting, but the wish has never been fulfilled. In the Utica black shales, near Rome, New York, there was finally discovered in 1892 a layer less than ten millimeters thick, bearing hundreds of Triarthrus becki with most of the ventral anatomy intact. The collector’s first inkling that such were present in the Utica formation came to him in a chance find in 1884, and for eight years he sought off and on for the stratum whence this specimen came. His long search was finally rewarded by the discovery of the bed, and lo! here were to be had, in golden color, prostrate specimens with the breathing and crawling legs and the long and beautifully curved feeling organs all replaced by iron pyrites. Fool’s gold in this case helped to make a palzontologic paradise. The bed con- tained not only such specimens of Triarthrus becki, but also, though more rarely, of Cryp- tolithus tessellatus and exceptionally of Acidaspis trentonensis. This important discovery, which has figured so largely in unraveling the evolution of the Crustacea and even has a bearing on that of most of the Arthropoda, was made by Mr. W. S. Valiant, then curator of the Museum of Rutgers College. There were, however, great material difficulties to overcome before the specimens revealed themselves with all of their information exposed for study. No surgeon was needed, but a worker knowing the great scientific value of what was hidden, and with end- less patience and marked skill in preparation of fossils. Much could be revealed with the hammer, because specimens were fairly abundant. A chance fracture at times showed con- siderable portions, often both antennz entire, and more rarely the limbs protruding beyond the test, but the entire ‘detail of any one limb or the variation between the limbs of the head, thorax, and tail was the problem to be solved. No man ever loved a knotty problem more than Charles E. Beecher. Any new puzzle tempted him, and this one of Triarthrus becki interested him most of all and kept him busy for years. From the summer of 1893, when he quarried out two tons of the pay stratum at Rome, until his death in 1904, his 6 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. time was devoted in the main to its solution by preparing these trilobites and learning their anatomical significance. The specimens of Tvriarthrus becki from Rome are pseudomorphs composed of iron pyrites, as has been said, and are buried in a gray-black carbonaceous shale. Ubidia hoes cominidc 0 Udo CO DOT Hoar om Galvimencese anion Comair scans trys sien enmen) s (deja seoleu shoe aa} -\ ale Cephalickan pendacesh reise res wie eens eres ester eashacishey arate ce ANMOFACIS AD PSNGRIEES 3.4 5.54 delo'clo d.0.gll clos moto e bag bom Oe ue oaieMloinlda i) E IENCAIGHEMl AO PSNIACCS a'doogsooneooeoussooereD dee oUoUeceE cp epEBIC Os 12 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Relation of hypostoma to cephalon in Calymene ..................-.--- Restoration of Calymene Calynicnensp = tidaea ey ee: Ceraurus pleurexanthemus Gr Ga Goss op ooo cOo OGD Oo OOOO DDO moO OOD oN O ODO ODO S Capac a Nanees Goeadaoouadesecoouceascegosusscovevasenucssbode Thoracic appendages ... Pygidial appendages ... Relation of hypostoma to Restoration of Ceraurus céplallomi cs. lah screenees sete keee tenemos OMAPROLONICTOUS \s'o.404dcccanedsanbeseoceecec The appendages of Acidaspis trentonensis Walcott ..................-.---- Wine appaackges Ox Crnynolninnis (See allso Ieee IW) caccaacadecsncuacdcaoses Crymolinns vesscllionis GRIN 55550005. 50uc 0.0 nono sends oncancoeouBes IRGSHOAOI OH CrWWOlMMWIS covododoesocodogoeccocevoocvsddconeeonen Smimanercy Gal de wearell ainaiouayy Or Willies .242coc0c0sconse acca navoeaee Compariconomappendaves omy dite nenty cet etcyy ei eee re Coxopoditeme ance (Cephalon srccs: iBhorasc si eine sec: IP\yBiChwHTN occa Candal@ranigeyeeic Homology of cephalic ap Functions of the appendages Anitenmules) e454 Exopoditess ene... Endopodites ..... Use of the pygidium in swimming Goxopoditessyaaaer Position of the appendages in life Part Il. Structure and habits of Internal organs and muscles Alimentary canal ...... Ceraurus plewrexanthemus Calymene senaria . Cryptolithus goldfussi Summanyaeeeniae se GastaicrolandsS ere SMM, cscsc0e> LG arbe ern eeseta ley. ee Ceraurus and Calyimene The median “ocellus” or “dorsal organ” Nervous system ....... Various glands ....... Dermal glands ... Renal excretory organs Reproductive organs pendages with those of other Crustacea.......... trilobites TABLE OF CONTENTS. 13 Pand ertanvoncamSie sir certs oye cea conceal ee a ols Westy nee waste arses go Mitts Ctrl atime Mey ait reenter ceecvere net apse nizediae ayer anals ates amar aaue ets ail Ware aia: Nita Soaley gI IPE opr) Sao AiG dinlad dain cing acer Ole eco asta me es eee Senn ET Nee 92 ESCLEM SOM AmAUSCLES yes sprang tun ac Wes pote ues) cro Ge a AUD a ta i aa ea. 92 Ely postormialimiScles; emer cta neat ome a Crpraes ats ara Steep a NA es 94 EVES beia tang tetantites Mucwa ne iAab assume te tye eeaats Lau reisivs leslie lasnuahelariyatVAle ulaley 96 SS LULTTIAT Tyee Pee earner tira, SMH ie MU ost re tree SWRI cao nulic metic taeNO RCA Aan) ANU ea aie 97 SS Kae re ates HUAI Moho rr NESE Da fring POE at ceuhUenrot tay ieitc Cavaie Nec TAWI NL ya UN at 98 TP or SH set tege atau a chil UAW eid oa Deve aia ys Vee c ae MROI Meae eeSe tlh ash SACU NNT Oa 98 Methods of life (See also under “Functions of the Appendages”) ............ 98 PlabitssOtlOocomotlomeinr cence wit te skie sa aie apne tiie: uch ulate Rs cenly SOM sags Mies 99 oodkandeteedingmethodswe tn a eacor ss nee kie eae earch iu aly 103 dBrack:cpata ditnall Siena visto inti laren nin kare nbd he C Ns Mtratliore tb MIN dpree ETL 104 Part ieeRelationshipronuthe: trilobites: to,other Anthropodaes 4.0.0 «ease ae cae 106 Erristaccame ny yee ne eee issep eh aranauer esters sat wena alert ideiudctal eitaucare a etecoeenicud 106 Branchio po cdatgne vec aty ohicd a: mut Natalee a abe comme beh Pawan are 106 IBOTAGIACSIO DANG VECO 368 GG cemonis var eo aia oaldcin LA OlnIblG oa Go bios 108 LY ODE HOC HOES NNEUCOHE dono soc cocucag Boo oudooob oe doowESen oO Owe 108 WO WOUCNT CHUIS! SNNIALC OLE yacc veers tires a sts, So ee are eee peed nd arte 109 OpabinagnegalismNVialcottie merece a ee One 109 SUNT MAT Vane tenn ie et eceage ere neta cari aien oNTMA alae Mca ce hid ben oneeaaR sates 109 Wopepodaiacnnwa unmet Vokes a trey iter. cresun pecan Gousralndby ares Chena uaepems Men cereteral 110 UNTCAICO PEP OC ae arsed an tipune nee genteh ee Wee nets ge tenuate mren su telUS calc val ae ce Aaa a III @ stra cod aieprcer mle cde verge cme ae nha cme ei treater aicrie as aman A Unbcn/ atin mm aay 112 Ginnipediaerra attunements irae: Loar wisviareusl Maly aay suaabic' ej molel Sabpe buat os padege 113 INIaIACOStia Camere ru sy aii ester Stee ase E eerste eee en er ane met ate tGaa Meryl s eA SRY. De 113 Pehy ilo carter cl ae ee Hurt clear te Ra oa y seea neta es asa ve tay mec ee Mra cRay ek tea 113 Stand aererawaseyaretenen ese cca ols ceahss ot ceteneys wath tones area Parente ena 114 TSO po cl atperser reaver celia ih SOU aun teats sears sae al amMeemegn Cee ey veoh 8m len inane I14 MiannellamsplendensaNVialcottnnrsn emg ismeie cat aetoar ene ae Eee on aie ea cio 115 Restorationvore Marrella ite schetucpii theca cts ees Meee Weeee a tae 116 deNSWREVLRU GONG A a5 pA yeep ets POR eS UC eae et esc a ad Rae ee bs eA A de 117 fibril obiteswine bee Ntra clint claler tar yeiesea se rie ters cle neas cory aseraten nu eee ee leieae at Ate 117 Mlerastomia tare sr ta mainte sry Ws eciar ies ae alielanrorra Unitus Neils erae euiin (AGn) Tran uy ON 119 Swolnesia, Cnet nacneris NANCE as dat se cee eu ab ous ooo Peierls Aaa ante ie 11g Iameralolhta, loipaclah NNENCe 2c has oo be obo Gu bib e boob do ou obo mO coder 119 MACH Ate) “NaN Ve (OLA WA bie ee LA pices Bese Lee a SEO EIE A ee as aac 120 JeNSRENTINSES yea! Mec che c/a tatealarcerS cits oti rel ck po eae Bed te oR Ves rae RS 121 IBIS) 1G We broth 6.8 Boum edo ie tec Gee scien ca Neue ir ce ge NGI a Ve RE aR en 122 Chilopodamyn me aime a watts Has Ume enna. ener uemr ant tse coe fa ut alah et 123 DD iplomod ain Wye eaten Geeta tei Vere Gd EAGT A CUR RL Aeon Gn yo ca mae eae es Ak 124 RiMitiVveEcharactenisticouOnettl ODILES Imrie rk: ia tre Aire crete ee inate 125 irilobitessthesmostyprimitive arthropods. sarc. 4 yates ake ee 125 Imm DSwO att LODitesmprmitivelmn se ae re eee Cay al ere 125 SLADE ATR aae pe RRR eee RIAU Ike cal CRN Ree UNE EN ton ot Aeron Soc aas 128 INimbergo fase cuientsuim theyintimlke jane eh Weyer lage esirt on «scope 128 T4 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. FOI OF WAS SHAPES PROWAS IS sonsnccanpeunavcoacdesooensonanonozone 132 Organ Oi Woe jonyenGbnnIn 55 c0ce0cn0eco soe cccoso co ecoee ae ens eee eee 134 Wradthvo tithe vaxtalelobert. bie xigsctie oraetansptrs peter Wen Hee cee nen ats esis a serene OY IPRESSMCS Ol AIOGOMCS Oil B Mow? odassocceacccceccvaccvacausecvoacooas 137 SeRimMeEMATOM OF Uae lala, scascesoorsecuasdscsossnsenodoscacouseus 127) SS ILETUDTAEE NRA nee tle Nae Re ae ae EME NEN Ey ais RU sk (Bie a gps acccmelncay wld) Gt micas 138 ADS! Siar olksce: rset Kolo MES oO ote ania AG Gein Aca ajo 5s Sloeldig.aihtay dimiia as as roo 138 IN@raou, Comanacra NNEC soc cccacccncossoveesceseoc0do0uan D0 0s0% 139 The ancestor of the trilobites, and the descent of the Arthropoda.............. 140 Bolton wrllnin wae (Crwsiacee! osoccc0dccccusvdcdocobs Siete sey coy a 142 Surman ary a eee aah pan od au hy ea Pacer nce ieee ene ten ge sgl ovobrs AW ae 144 Ewoluscm Or Tne IMISROMKOTEN foc cccs coco oo coed ooccbesbogo so eoonoose 146 EVvolutioniot, these Dracheatar’: ¢ eae anus cpalaie see anemia teamed ae ea aed eng 147 Summrmarny Gin Wines Oi GIESSEN ose cc aadccscussoodoasonscdacadaudaecaas 147 (Fyinnall vs tamanna a tees essen ae aahcccoe che .2cU Seneca ttle tags see eLaee es oa ceal Lane ham oe er Pear I51 Part IV. Description of the appendages of individual specimens................: 152 DIG VONEIGUS De CRUNG REC II IS eV. cqtie ecb Re ies ROH. ORNS Ce REO ea EE 152 COMORES WASSANONMS (ERESN on pesos ee ee dono oea seas poodobobeooseooeos 158 1 BATH RKO vedi Tee 0) ayy aeae rem earseen ok oy a eam Mee SA srs Sates SUC et RPA aEN INI Fat ato Gh Gigi os llth & o.6' bol e-deste 163 IES Ole WEIL WIV KON, S). 1. Triarthrus becki Green. Diagram of limb to show nomenclature employed ... 20 2. Neolenus serratus (Rominger). Two thoracic appendages .................. 24 ae Wiehe: saimes So AmMexOpodite; vik ce. seks Ake ses Oe a SER eae Rare eeene 26 A, Wine serme, A. 'so-cailled “eoinoabtie” .acodcavocccccesoadcoscsoccuounesobes 26 se. Lhe «samese Dheyso-callled excites! oe oie cnctele creas suchas it ef pte: teint means 20 6s Ehesisame: ?Aiicephalics liryc a cares peenspertey ov urea e te eae a see ey ere cent rane 29 7aamhie: samer @ INeStorabion| Ola itraMsyenSeISe Ct OIe ae oie ees sets see eee eee 30 & Wine same, INeStOrABIeM Or We wemiirall SUIIACS ..cgcccoccesbovcsnscencnade 31 On GotclusmlNestorationyofmtneaventralysuiiacemer hake Anite see ener 38 10. Driarthrus becky Green. Restoration of the ventral surface -.-5--.--+2...-.- Al ii, Une same, IMiechierm eqnynxcmaee soogcsadscounceboodvcosesnoocdosoucaaconc an 12. Ceraurus pleurexanthemus Green. Slice showing an exopodite ............. 49 13. Calymene senaria Conrad. Slice showing cephalic coxopodites ............. 53 i, “We sane, Aimounar siamilasr SMCS so occncccecdsoddsacsvcdsoenaccdosceca0% 53 15. The same. Slice showing method of articulation of the appendages .......... 53 1G, Wine SANS, INCSKORAOIN Ort Me WemiUrall SUIPIACS 5 .5500cccyoccngcgscenuasecce 55 17. Ceraurus pleurexanthemus Green. Slice showing the method of articulation of thevappendacesnccas cea cmi aM cee s cc sto eats Lotanl atane le i Use arscaeain anere rage 58 18. The same. Slice showing an exopodite above an endopdite.................. 58 HO; Winks Gara, | INESKOIAMOMN Oi A. WAMSVERNS SECHOM ooccsnccconcosconsnceuscuone ‘60 20. Cryptolithus tessellatus Green. Restoration of the ventral surface............ 63 21. Ceraurus pleurexanthemus Green. Slice showing the abdominal sheath 22. The same. Slice showing the large alimentary canal ...... PLES SBSH RAC Pg. 1a 79 TABLE OF CONTENTS. 23. Calymene senaria Green. Slice showing the large alimentary canal........... 24. Ceraurus pleurexanthemus Green. Restoration of a longitundinal section...... 25. Cryptolithus tessellatus Green. Cheek showing the genal ceca............... 2onnMenuss, Volborth:sstioureom thesheart fs... 4). 40- EUR soca eect nia Ss Ae ee lon rea Bop VALS EW AE Oe wal HONS Siar wae Algiers Di aea oes cariror ed CGM Ta eee eee oh ely EUS hepeeee eee a BS Isoualins: gngas Deke, Wie lemcGlonehn ORIG eso G6 conc a son epee meee nonod 6 29. Ceraurus pleurexanthemus Green. Restoration, showing heart, alimentary canal, andmvexte mst sel esta ssa tis qt chk sayin ceyect hare sae, cre iain Bom Whensamennn Poneitudimale section mon .ceplial omme sme lees a oaenn slayer 3x. Nileus armadillo Dalman. Moberg’s figure of the muscle-scars .............. 32. Marrella splendens Walcott. Restoration of the ventral surface .............. 33. Triarthrus becki Green. Appendage of the anterior part of the thorax ........ BUSA DUST ANppendaces romethenanterior, pant orate tnunkeepem atk Acleent ee PSS ACV ILOULITON WO DUIS (HOTU) ae ker ite: cents arse iets) uae gi dats ene idemed ns Senne 20, Nendo conmpacua: NNAMIGOUE > ob coco decso dda buocla moddaadavbobioe oo cooce aes Ios CUMHG): NNANCOUE Jy dicid oe GaSe ecb 6 as oslee Go ob 6 cleo ROEHL eV Rte Bh AGUMUWSEUS CHICO: IGA 5530 oo eons dea sodedoeentonnoooue cee deeoeedud 56 AO), PGI CUTMES POOSOMCHSIS Ishohdhine s5\, sho bee pdeen se Se osbe bude eoasew occ soe oe AUOY So SALOMON AGTH AS Oks Uo Se zeman (Pn ele e ek eS ecmerF TE EERET USER Se CR eee 41. Diagram showing possible lines of descent of the Arthropoda................ Acre lindontinusmouecro Greeny uhoracc appendages! anism sees lee rea AR, Wie Savane: Je\yearabiall’ ayoynsnGeees Gog bo blacesok ode aoeesboooe mabe oe sous ber Adi, ‘Wine, sare. -Jesgenichiall, ajoynemn@leexes -oocncdcucob pee duacceossocdsuogucte sooens 45. Cryptolithus tessellatus Green. Drawing of the best single specimen.......... 46. The same. Part of the thorax and pygidium, with appendages .............. Frontispiece. Charles Emerson Beecher, 1896. Plates 1-5. Photographs of Triarthrus becki, made by C. E. Beecher. Plate 6. Photographs of Tvriarthrus becki (figs. 1-3), dcidaspis trentonensis (fig. 6), and Cryptolithus tessellatus (fig. 7), made by C. E. Beecher. Photo- graphs of the endopodites of a probable species of Calymene (figs. 4, 5) Plates 7-8. Photographs of Cryptolithus tessellatus, made by C. E. Beecher. Plate 9. Drawings of Cryptolithus tessellatus, made by C. E. Beecher or under his direction. Plate 10. Photographs of /sotelus latus and I. maximus, made by C. E. Beecher. Plate 11. Drawing of a restoration of Ceraurus pleurexanthemus, made by Elvira Wood. HISTORICAL REVIEW. The beginning of the search for the limbs of trilobites was coeval with the beginning of scientific study of the group, knowledge of the appendages being essential to the proper systematic allocation of the animals. The early search was so barren of results that negative evidence came to be accepted as of positive value, and it was for many years generally believed that such organs as may have been present beneath the dorsal test were so soft as to be incapable of preservation. This view is best expressed by Burmeister (1846, p. 43): There is good proof that the feet of trilobites must have been soft membranous organs, for the absence of the slightest remains of these organs in the numerous specimens observed is of itself evidence of the fact, and it can indeed scarcely be supposed that hard horny extremities should be affixed to a soft membranous abdominal surface; since they would not have possessed that firm basis, which all solid organs of locomotion require, in order that they may be properly available. Very well reasoned, and were it not for the discovery of new material in American local- ities, Burmeister’s views would probably never have been proved incorrect. One can not escape the suspicion that some of the accepted hypotheses of today, founded on similar “proof,’ may yield in time to the weight of bits of positive evidence. The history of the study of appendages of trilobites may be divided into two periods. The first, in which there was a general belief that the appendages were soft organs, but during which numerous “finds” of limbs were reported, extended from the time of Linné to the year (1876) in which Walcott demonstrated the fact that the animals possessed jointed ambulatory and breathing organs. The second, much more fruitful period, began with Walcott’s publication of 1881, descriptive of the appendages of Ceraurus and Calymene, and for the purposes of this memoir, closes with his great contribution on the anatomy of Neolenus (1918). Beecher’s brilliant productions came in the middle of the second period. In the first period, there were at least two authentic discoveries of appendages, those of Eichwald (1825) and Billings (1870), but since neither of these men convinced his con- freres of the value of his finds, the work of neither can be considered as having marked an especial epoch in the history. As all the authentic finds will be treated in detail on later pages, only a brief résumé of the first period will be given here. This has already been done by Burmeister (1843, 1846) and Barrande (1852, 1872), whose works have been my primary sources of informa- tion, but I have looked up the original papers, copies of nearly all of which are to be seen in the libraries in Cambridge and Boston. Brig.-Gen. A. W. Vogdes, U. S. A. (retired), has very kindly placed at my disposal a number of references and notes. Linné (1759) was the first to report the discovery of appendages of trilobites. Torn- quist (1896) has pressed for a recognition of the contribution of the great Swedish natu- ralist to this problem, but Beecher (1896 B) doubted the validity of the find. Linné figured a specimen of Parabolina spinulosa (Wahlenberg), with what he interpreted as a pair of antenne attached. He states (translation quoted from Tornquist): “Most remarkable in this specimen are the antennz in the front, which I never saw in any other sample, and which clearly prove this fossil to belong to the insects.’’ Beecher has shown as conclusively as can be shown without access to the original specimen that the supposed antennze were really only portions of the thickened anterior border, the appearance being due to imperfect preservation. Brtinnich as early as 1781 called attention to the imperfection of this speci- 18 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. men, and it is also referred to by Wahlenberg (1821, p. 39), Brongniart (1822, p. 42), Dalman (1828, p. 73), and Angelin (1854, p. 46). Audouin (1821) seems to have been the first naturalist with sufficient knowledge of the Arthropoda to be competent to undertake the study of the trilobites. He concluded that the absence of ventral appendages was probably a necessary consequence of the skeletal conformation, and thought if any were discovered, they would prove to be of a branchial nature. Wahlenberg (1821) in the same year expressed his belief that the trilobites were nearly allied to Limulus and in particular tried to show that the trilobites could have had masti- catory appendages attached about the mouth as in that modern “insect” (p. 20). Wahlen- berg was also the first to describe an hypostoma of a trilobite (p. 37, pl. 1, fig. 6), but did not understand the nature of his specimen, which he described as a distinct species. Brongniart (1822, p. 40) devoted five pages of his monograph to a discussion of the affinities of trilobites, concluding that it was very probable that the animals lacked antennee and feet, unless it might be that they had short soft feet which would allow them to creep about and fix themselves to other bodies. Schlotheim (1823) thought that the spines 0n Agnostus pisifornus were segmented and compared them with the antennz of Acarus. Stokes (1823) was the first who, with understanding, published an illustration of the ventral side of a trilobite, having figured the hypostoma of an /sotelus. He was followed in the next year (1824) by Dekay, who also figured the hypostoma of an Jsotelus, and added some observations on the structure of trilobites. The researches of Barrande, Novak, Broegger, Lindstroem, and others have dealt so fully with the hypostoma that further refer- ences to that organ need not be included here. Dalman (1826, 1828) reviewed the opinions of his predecessors, and thought it not impossible that organs of mastication may have been present under the head shield of the trilobite as in Limulus (1828, p. 18). In this he of course followed Wahlenberg. Goldiuss (1828) figured sections of Dalmanites hausmanni, Phacops macrophthalma, and Calymene tristani, which remind one of some of Doctor Walcott’s translucent slices. So far as one can judge from the illustrations, it is probable that what he took for limbs were really fragments of other trilobites. Such is certainly the case in his figures 9 and 10, where a number of more or less broken thoracic segments are present. The section of Encrinurus punctatus shown in figure 7 may possibly exhibit the position and folds of the ventral membrane beneath the axial lobe, and also, perhaps, the appendages. His figures 4, 5 and 8 show the hypostoma in section. Pander (1830) described the hypostoma in greater detail than had been done by previ- ous authors, but otherwise added nothing to the subject. Sternberg (1830) thought he had individuals showing appendages, but judging from his poor figures, he was deceived by fragmentary specimens. Green (1839 A, B, C) described specimens of Phacops from Berkeley Springs, West Virginia, which had the hypostoma in position, and appear to have had a tubular opening under the axial lobe. While appendages were not actually present, these specimens sug- gested fairly correct igeas about the swimming and breathing organs of trilobites. They were similar to the ones which Castelnau obtained, and all were perhaps from the same locality. It is not worth while to do more than enumerate the other authors of this period: Hisinger 1837, Emmerich 1839, Milne-Edwards 1841, for they all shared the same views, and added nothing to what was already known. HISTORICAL REVIEW. 19 Castelnau (1843) described and figured a Phacops said to come from Cacapon Springs, West Virginia, which he thought possessed remains of appendages. There is nothing in the description or figuresto indicate exactly what was present, but it is very unlikely that any limbs were preserved. The broad thin “appendage” figured may have been a fragment of a thoracic segment. ‘This specimen was evidently described by Castelnau-before 1843, as is inferred from a reference in the Neues Jahrbuch, 1843, p. 504, but I have not seen the earlier publication. Burmeister (1843-1846), in his “Organization of the Trilobites,” reviewed in extenso the history of the search for appendages, and concluded that they must have been so soft as to preclude the possibility of their being preserved as fossils. ‘“Their very absence in fossils most distinctly proves their former real structure” (p. 10). In figures 7 and 8 on plate 6 he gave a restoration of the ventral surface of an Asaphus, the first restoration of the ventral anatomy to be attempted. Since he chose modern branchiopods as his model, he did not go so far wrong as he might have done. Still, there is little in the figure that would now be accepted as correct. The following quotation will serve to give the opinion of this zoologist, who from his knowledge of the Crustacea, was the most competent of the men of his time to undertake a restoration of the appendages of the trilobites: 39 in giving a certain form to the feet in the restored figure, I have done so rather intending to indicate what they might have resembled, than with any idea of assuming their actual form. I merely assert that these organs were soft, membranous, and fringed, adapted for locomotion in water, placed on the abdominal portion of the body, and extending sidewise beneath the lateral lobes of the rings, as shown in the ideal transverse section. These feet were also indented, and thus divided into several lobes at the open lower side, and each separate lobe was furnished at the margin with small bristles serving as fins. The last and external lobe was probably longer, smaller, and more movable, and reached to the termination of the projecting shell lobe, bearing a bladder-shaped gill on the inner side (1846, p. 45). McCoy (1846) observed in several trilobites a pair of pores situated in the dorsal fur- rows near the anterior end of the glabella. He showed that the pits occupy precisely the position of the antennz of insects and suggested that they indicated the former presence of antennz in these trilobites (chiefly dimpyx and “Trinucleus’). The evidence from Cryp- tolithus, set forth on a later page, indicates the correctness of McCoy’s view. Richter (1848, p. 20, pl. 2, fig. 32) described and figured what he took to be a phyl- lopod-like appendage found in a section through a Phacops. Without the specimen it is impossible to say just what the structure really was. The outline figure is so obviously modeled on an appendage of Apus that one is inclined to think it somewhat diagrammatic. In calling attention to this neglected “find,” Clarke (1888, p. 254, fig.) interprets the appendage as similar to the spiral branchize of Calymene senaria, and adds that he himself has seen evidence of spiral branchize in the American Phacops rana. Beyrich (1846) described a cast of the intestine of “Trinucleus,’ and Barrande (1852) further elaborated on this discovery. Corda (1847) made a number of claims for appendages, but all were shown by Bar- rande (1852) to be erroneous. Barrande (1852, 1872) gave a somewhat incomplete summary of the various attempts to describe the appendages of trilobites, concluding that none showed any evidence of other than soft appendages, until Billings’ discovery of 1870. Volborth (1863) described a long chambered tubular organ in I//e@nus which be believed to represent a cast of the heart of a trilobite, but which has since been likened by writers to the intestinal tract in “Trinucleus.” IPAMIR TC I THE APPENDAGES OF TRILOBITES. TERMINOLOGY. The terminology employed in the succeeding pages is essentially the same as that used by Beecher, with two new terms added. Beecher assigned to the various segments of the limbs the names suggested by Huxley, but sometimes used the name protopodite instead of coxopodite for the proximal one. It is obvious that he did not use protopodite in the cor- rect sense, as indicating a segment formed by the fusion of the coxopodite and basipodite. The usage employed here is shown in figure 1. | i Fic. 1.—Tvriarthrus becki Green. Diagram of one of the limbs of the thorax, viewed from above, with the endopodite in advance of the exo- podite. 1, coxopodite, the inner extension being the endobase (gnathobase on cephalon) ; 2, basip- odite, springing from the coxopodite, and sup- porting the exopodite, which also rests upon the coxopodite; 3, ischiopodite; 4, meropodite; 5, carpopodite; 6, propodite; 7, dactylopodite, with terminal spines. The investigation of Ceraurus showed that the appendages were supported by processes extending downward from the dorsal test, and on comparison with other trilobites it appeared that the same was true in Calymene, Cryptolithus, Neolenus, and other genera. Thin sec- tions showed that these processes were formed by invagination of the test beneath the dorsal and glabellar furrows. While these processes are entirely homologous with the entopo- physes of Limulus, I have chosen to apply the name appendifer to them in the trilobites. The only other new term employed is the substitution of endobase for gnathobase in speaking of the inner prolongation of a coxopodite of the trunk region. The term gnatho- base implies a function which can not in all cases be proved. The individual portions of which the limbs are made up are called segments, and the articulations between them, joints. Such a procedure is unusual, but promotes clearness. NEOLENUS. Zin Tur APPENDAGES OF NEOLENUS. HISTORICAL. The first mention of Neolenus with appendages preserved was in Doctor Walcott’s paper of ro1t, in which two figures were given to show the form of the exopodites in com- parison with the branchiz of the eurypterid-like Sidmeyia. In 1912, two more figures were presented, showing the antennules, exopodites, and cerci. The-specimens were found in the Burgess shale (Middle Cambrian) near Field, in British Columbia. This shale is exceedingly fine-grained, and has yielded a very large fauna of beautifully preserved fossils, either unknown or extraordinarily rare elsewhere. It was stated in this paper (1912 A) that trilobites, with the exception of Agnostus and Microdiscus, were not abundant in the shale. In discussing the origin of the tracks known as Protichnites, Walcott presented four figures of Neolenus with appendages, and described the three clawlike spines at the tip of each endopodite. Three new figures of the appendages were also contributed to the second edition of the Eastman-Zittel ‘“Text-book of Paleontology” (1913, p. 701). Later (1916, pl. 9) there was published a photograph of a wonderful slab, bearing on its surface numerous Middle Cambrian Crustacea. Several of the specimens of Neolenus showed appendages. Finally, in 1918, appeared the “Appendages of Trilobites,’ in which the limbs of Neolenus were fully described and figured (p. 126), and a restoration presented. Organs previously unknown in trilobites, epipodites and exites, attached to the coxopodites, were found. Neolenus serratus (Rominger). (Text fig. 2-8.) Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1911, p. 20, pl. 6, figs. 1, 2 (exopodites of thorax and cephalon) ;—Ibid., vol. 57, 1912, p. 191, pl. 24, figs. 1, 1a (antennules, caudal rami, and endopodites of thorax) ;—Ibid., vol. 57, 1912, p. 277, pl. 45, figs. 1-4 (antennules, endopodites of cephalon and thorax, caudal rami) ;—Text-book of Paleontology, edited by C. R. Eastman, 2d ed., vol. 1, 1913, p. 701, fig. 1343 (exopo- dites), p. 716, fig. 1376 (abdominal appendages), fig. 1377 (appendages of thorax and pygidium) ;—Ann. Rept. Smithson. Inst. for 1915, 1916, pl. 9;—Smithson. Misc. Coll., vol. 67, 1918, pp. 126-131 et al., pl. 14, fig. 1; pls. 15-20; pl. 21, fig. 6; pls. 22, 23; pl. 31 (restoration); pl. 34, fig. 3 (restored section); pl. 35, fig. 4; pl. 36, fig. 3 (hypostoma). The following description of the appendages of Neolenus is summarized from Walcott’s paper of 1918, and from a study of the eight specimens mentioned below. Cephalon. The antennules are long, slender, and flexible, and lack the formal double curvature so characteristic of those of Triarthrus. There are short fine spines on the distal rims of the segments of the proximal half of each, thus giving great sensitiveness to these organs. In the proximal portion of each, the individual segments are short and wider than long, and in the distal region they are narrow and longer than wide. There are four pairs of biramous cephalic appendages, which differ only very slightly from the appendages of the thorax. All are of course excessively flattened, and they are here described as they appear. The coxopodites, shown for the first time in Walcott’s paper of 1918, are broad, longer than wide, and truncated on the inner ends, where they bear short, stout, unequal spines 22 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. similar to those along the anterior margin. The gnathobases are but slightly modified to serve as mouth parts, much less so than in Triarthrus, but the coxopodites of the cepha- Jon are shorter and wider than those of the thorax. At the distal end of the coxopodite arise the endopodite and exopodite. The endo- podite consists of six segments, the distal ones, propodite and dactylopodite, more slender than the others, the last bearing three terminal spines. The first endopodite is shorter than the others and slightly more slender (pl. 16, fig. 1) and the anterior appendages turn forward more or less parallel to the sides of the hypostoma (pl. 22). The basipodite, - ischiopodite, meropodite, and carpopodite are, in their flattened condition, roughly rectan- gular, only a little longer than wide, taper gradually distally, each bears small spines on the outer rim, and some of the proximal ones usually have a row along the margin. The exopodites of the cephalon, as of the body of Neolenus, are very different from those of any other trilobite whose appendages were previously known. As shown in the photographs (pl. 20, fig. 2; pl. 22), each exopodite consists of a single long, broad, leaf- like blade, not with many segments as in Tviarthrus, but consisting of a large basal and small terminal lobe. It bears on its outer margin numerous relatively short, slender, flat setee. The long axes of the exopodites point forward, and the sete are directed forward and outward. They stand more nearly at right angles to the shaft on the cephalic exopo- dites than on those of the thorax. This same type of broad-bladed. exopodite is also found on the thorax and pygidium. The number of functional gnathobases on the cephalon is unknown. That four endo- podites were present on one side is shown pretty clearly by specimen 58591 (pl. 16, fig. 3) and while no more than two well preserved exopodites have been seen on a side, there probably were four. Specimen 65513 (pl. 16, fig. 1) shows gnathobases on the second and third appendages of that individual as preserved, but there is no positive evidence that these are really the second and third appendages, for they are obviously displaced. The hypos- toma of Neolenus is narrow but long, several specimens showing that it extended back to the horizon of the outer ends of the last pair of glabellar furrows. It is not as wide as the axial lobe, so that, while gnathobases attached beneath the first pair of furrows would prob- ably not reach back to the posterior end of the hypostoma, they might lie parallel to it and not extend beneath. It seems possible, then, that there were four pairs of endobases but that the second rather than the first pair served as mandibles, as seems to be the case in Ceraurus. : Thorax. The thorax of Neolenus consists of seven segments, and the appendages are well shown (pl. 17, fig. 1; pl. 18, figs. 1, 2; pl. 20, fig. 1.), The endopodites of successive segments vary but little, all are slender but compact, and consist of a long coxopodite with six short, rather broad segments beyond it. In the figures, the endopodites extend some distance in a horizontal direction beyond the edges of the dorsal test, as many as four segments being in some cases visible, but measurements show that the appendages tended to fall outward on decay of the animal. The dactylopodites are provided with terminal spines as in Triarthrus. The coxopodites are long, straight, and slender. They are well shown on only one speci- men (pl. 18), where they are seen to be as wide as the basipodite, and the endobases are set with spines on the posterior and inner margins. They are so long that those on opposite *Nota bene! All references in this section are to the plates of Doctor Walcott’s paper in 1918. NEOLENUS. 23 sides must have almost met on the median line. The segments of the endopodites are mostly but little, if any, longer than broad, and at the distal end each shows two or more spines. The propodite and dactylopodite are notably more slender than the others. The exopodites of the thorax are broad and flat, and each shaft has two distinct parts with different kinds of sete. The posterior edge of the proximal lobe is fringed with a slender, flat, overlapping hairs which are a little longer than the width of the lobe, and stand at an angle of about 60 degrees with the direction of the axis of the appendage. The outer lobe is at an angle with the main one, and has short, very fine setee on the margin. One or two specimens show some evidence of a joint between the inner and outer lobes, but in the great majority of cases they seem to be continuous; if originally in two segments, they have become firmly united. The exopodites of the thorax, like those of the cephalon, are directed diagonally forward and outward. (PI. 21, fig. 6; pl. 22. Pygidium. The pygidium of Neolenus serratus is large, and usually shows five rings on the axial lobe and four pairs of ribs on the sides. There are five pairs of biramous appendages be- longing to this shield, and behind these a pair of jointed cerci. That the number of abdomi- nal appendages should correspond to the number of divisions of the axial lobe rather than to the number of ribs on the pleural lobes is of interest, and in accord with other trilobites, as first shown by Beecher. The endopodites of the pygidium have the same form as those of the thorax, are long. and very much less modified than those of any other trilobite whose appendages are known. On some specimens, they extend out far beyond the dorsal test, so that nearly all the seg- ments are visible (pl. 17, fig. 3; pl. 18; pl. 19; pl. 20, fig. 1), but in these cases are prob- ably displaced. The segments are short and wide, the whole endopodite tapering gradually outward. The dactylopodite bears terminal spines, and the individual segments also have outward-directed spines. The cerci appear to have been long, slender, very spinose organs much like the anten- nules, but stiff rather than flexible. They are a little longer than the pygidium (pl. 17, figs. I, 2), and seem to be attached to a plate on the under surface of the posterior end and in front of the very narrow doublure. The precise form of this attachment can not be deter- mined from the published figures. They bear numerous fine spines (pl. 17, fig. 3). Epipodites and Exites. Doctor Walcott has found on several specimens of Neolenus remains of organs which he interprets as epipodites and exites attached to the coxopodites. A study of the specimens has, however, convinced me that both the large and small epipodites are really exopodites, and that the exites are badly preserved and displaced coxopodites. Detailed explanation of this interpretation is given below in the description of the several specimens involved. Description of Individual Specimens. Doctor Walcott was kind enough to send me eight of the more important specimens of Neolenus figured by him, and since my interpretation of them does not agree in all re- spects with his, I have thought it fairer to the reader to present here rather full notes explaining the position I have taken. I understand that since I communicated my interpre- tation of the epipodites and exites to him, Doctor Walcott has submitted the specimens to 24 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. several palzeontologists, who consider that epipodites are really present. Since I am not able to convince myself that their conclusion is based upon sound evidence, I give here my own interpretation. There is of course, no a priori reason why trilobites should not have had epipodites. Specimen No. 58589. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, pl. 45, fig. 2;—Zittel-Eastman Text-book of Paleontology, vol. 1, 1913, fig. 1377;—Smithson. Misc. Coll., vol. 67, 1918, pl. 18, fig. 1; pl. 20, fig. I. This is one of the most important of the specimens, as it shows the coxopodites of three thoracic limbs and the well preserved endopodites of six thoracic and five pairs of pygidial appendages. The appendages are all shifted to the left till the articular socket of the coxopodite is about 8 mm. outside of its proper position. The endopodites extend a corresponding amount beyond the edge of the dorsal test and are there so flattened that they are revealed as a Fig. 2—Neolenus serratus (Rominger). A sketch of the coxopodites and endopodites of two thoracic segments. Note notch for the reception of the lower end of the appendifer. > 3. mere impression. The coxopodites, which are beneath the test, seem to have been somewhat protected by it, and while hopelessly crushed, are not flattened, but rather conformed to the ridges and grooves of the thorax. The coxopodite of the appendage of the last thoracic segment is best preserved. It is rectangular, about one third as wide as long, with a slight notch in the posterior margin near the outer end. ‘The inner end is obliquely truncated and shows about ten sharp spines which do not appear to be articulated to the segment, but rather to be direct outgrowths from it. ‘There are similar spines along the posterior margin, but only two or three of what was probably once a continuous series are now preserved. On the opposite margin of the coxopodite from the slight depression mentioned above, there is a slight convexity in the outline, which is better shown and explained by the coxopodite just in front of this. That basal segment has the same form as the one just described, but as its posterior margin is for the greater part of its length pushed under the one behind it, the spines are not shown. On the posterior margin, two-thirds of the length from the proximal end, there is a shallow notch, and corresponding to it, a bulge on the anterior side. From analogy with Ceraurus and Calymene it becomes plain that the notch and bulge represent the position of the socket where the coxopodite articulated with the appendifer. Since these structures have not been shown in previous illustrations, a drawing giving my interpretation of them is here inserted NEOLENUS. 25 (fig. 2). It is evident from the position of the notch that the row of spines was on the dorsal (inner) side of the coxopodite and that the truncation was obliquely downward and outward. The endopodite of the last thoracic appendage is well preserved and may be described as typical of such a leg in this part. The basipodite is as wide as the coxopodite, and it and the three succeeding segments, ischiopodite, meropodite, and carpopodite, are all parallel- sided, not expanded at the joints, and decrease regularly in width. The propodite and dactylopodite are also parallel-sided, but more slender than the inner segments, and on the end of the dactylopodite there are four little spines, three of them—one large and two small —articulated at the distal end, and the fourth projecting from the posterior outer angle. Each segment has one or more spines on the outer articular end, and the ischiopodite has several directed obliquely outward on the posterior margin. All of the four proximal segments show a low ridge parallel to and near the anterior margin, and several endopodites of the py- gidium have a similar ridge and a row of spines along the posterior margin of some of the segments. These features indicate that the segments in question were not cylindrical in life, but compressed. From the almost universal location of the spines on the posterior side of the limbs as preserved, it seems probable that in the natural position the segments were held in a plane at a high angle with the horizontal, the ridge was dorsal and anterior and the row of spines ventral and posterior. Because the spines on the endobases are dorsal it does not follow that those on the endopodites were, for the position of the coxopodite in a crushed specimen does not indicate the position of the endopodite of even the same appendage. The endopodites of the pygidium are similar to the one just described, except that some of them have spines on the posterior margin of the segments, and a few on the right side have extremely fine, faintly visible spines on the anterior side. The specimen shows fragments of a few exopodites, but nothing worth describing. In the middle of the right pleural lobe there is a small organ which Walcott has interpreted as a small epipodite. It is oval in form, broken at the end toward the axial lobe, and has exceedingly minute short setze on the posterior margin. From analogy with other specimens, it appears to me to be the outer end of an exopodite. Measurements: The entire specimen is about 64 mm. long and 52 mm. wide at the genal angles. The thorax is about 41 mm. wide (disregarding the spines) at the seventh segment, and the axial lobe about 13 mm. wide at the same horizon. The measurements of the individual segments of the seventh left thoracic. limb are: Coxopodite, 9 mm. long, 3 mm. wide, the middle of the notch 8 mm. from the inner end, measured along the bottom, and 6 mm. measured along the top. Basipodite, 5 mm. long, 3 mm. wide Ischiopodite, 4 3 3 it Meropodite, Geen mH Se Ghaltne Carpopodite, 3.5 “ meh 2 2 Propodite, Bate L250 bs ~ Dactylopodite, 2 “ AAR The five distal segments of the last pygidial endopodite are together 10.5 mm. long. The whole six segments of the endopodite of the third thoracic segments are together 21 mm. long. The distance from the appendifer of the third segment to the outer end of the spine is 17 mm. From the center of the notch in the coxopodite to the outer end is 1.5 mm., 20 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. which, added to the length of the endopodite, 21 mm., makes a distance of 22.5 mm. from the appendifer to the tip of the dactylopodite, showing that if projected straight outward, the endopodites of the thorax would project 5.5 mm. beyond the test, including spines. The distance across the axial lobe from appendifer to appendifer on the seventh thoracic segment is 12.5 mm. Measured along the top of the coxopodite, it is 6 nim. from the middle of the notch to the inner end, and measured along the bottom it is 8 mm. From the trun- cated form of the ends it is evident that the coxopodites extended inward and downward from the appendifers, and with the dimensions given above, the inner toothed ends would practically meet on the median line. ; Measurements on the appendages of the pygidia show that on this specimen they extend back about twice as far beyond the edge of the pygidium as they should, all being displaced. Specimen No. 65514. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, pl. 10, figs. 1-3. This specimen is so twisted apart that it is not possible to determine to what segments the appendages belong, but it exhibits the best preserved exopodites I have seen. The Fig. 3.—Exopodite of Neo- Fig. 4.—Neolenus serratus (Rominger). lenus serratus (Rominger), to One of the so-called epipodites of specimen show form of the lobes of the 65515, showing that it has the same outline shaft, and the sete. > 4. as an exopodite (compare figure 3) and fragments of sete on the margin. XX 3. best one is just in front of the pygidium on the matrix, and shows a form more easily seen than described (our fig. 3). There is a broad, flat, leaf-like shaft, the anterior side of which follows a smooth curve, while in the curve on the posterior side, which is convex backward, there is a re-entrant, setting off a small outer lobe whose length is about one third the length of the whole. This lobe seems to be a continuation of the shaft, and the test of the whole is wrinkled and evidently very thin. The main and distal lobes of the shaft both bear numerous delicate setze, but those of the outer lobe are much shorter and finer than those on the main portion. The latter are flattened and blade-like. The anterior edge of the shaft shows a narrow stiffening ridge and the setz are but little longer than its greatest width. The second segment of the pygidium has another exopodite like this one, but shows faintly the line between the two lobes, as though there were two segments. This specimen also shows some very well preserved endopodites, but they differ in no way from those described from specimen No. 58589. Walcott mentions two large epipodites pro- jecting from beneath the exopodites. I judge that he has reference to the distal lobes of the exopodites, but as these are continuous with the main shaft, there can be no other interpretation of them than that which I have given above. NEOLENUS. 27 Measurements: The pygidium is 19 mm. long (without the spines) and about 34 mm. wide at the front. The exopodites show faintly beneath the pygidial shield, but their proxi- mal ends are too indistinct to allow accurate measurement. Apparently they were just about long enough to reach to the margin of the shield. The best preserved one, that of the second segment in the pygidium, is about 11 mm. long, 2.5 mm. wide at the widest; the distal lobe is 2.5 mm. long, and the longest setze of the main lobe 3.5 mm. long. The pleural lobe of the pygidium is just 11 mm. wide at this point. The endopodites project from 8 to 12 mm. beyond the pygidium, showing about four segments. The thoracic exopodite described above is 11 mm. long and 2.75 mm. wide at the widest part. The distal lobe is 3.5 mm. long and 2.25 mm. wide, and the longest sete on the main lobe 3 mm. long. Specimen No. 655109. Illustrated: Walcott, Zittel-Eastman Text-book of Paleontology, vol. 1, 1913, fig. 1343;—Smithson. Misc. Coll., vol. 67, 1918, pl. 21, fig. 6. This specimen is somewhat difficult to study but is very valuable as showing the natural position of the exopodites of the anterior part of the thorax. Walcott’s figures are excel- lent and show the broad leaf-like shafts, the distal lobes with the re-entrant angles in the pos- terior margin, and the long fine setze of the main lobes. None of the distal lobes retains its setee. All extend back to the dorsal furrows, but the proximal ends are not actually shown. The specimen is especially important because it shows the same distal lobes as speci- men No. 65514, and demonstrates that they are a part of the exopodite and not of any other structure. Measurements: The exopodite belonging to the fourth thoracic segment is 23 mm. long and 4 mm. wide at the widest part. The longest setze are 7 mm. in length. Specimen No. 65520. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, pl. 20, fig. 2; pl. 22, fig. 1. This is a practically entire specimen, on two blocks, one showing the interior of the shell, and the other the one figured by Walcott, a cast of the interior. The first shows the low rounded appendifers at the anterior angle of each axial tergite. They are almost entirely beneath the dorsal furrows and do not project so far into the axial lobe as those of Ceraurus and Calymene. In fact, only those at the anterior end of the thorax project inward at all. As expected, there are five pairs on the pygidium. The cephalon is unfortunately so exfol- iated that the appendifers there are not preserved. The doublure of the pygidium is ex- tremely narrow. The cast of the interior shows, rather faintly, the exopodites of the right side of the thorax and of the left side of the cephalon, and, still more faintly, the caudal rami and a few pygidial endopodites. The exopodites on the right side are in what seems to be the customary position, directed obliquely forward and outward, and the tips of their distal lobes project slightly beyond the edge of the test. These lobes were interpreted by Walcott as epipodites, but after comparing them with the terminal lobes of the exopodites of speci- mens No. 65519 and 65514 I think there can be no doubt that they represent the same structure. The pleura of the individual thoracic segments on this side of the specimen have an unusual appearance, for they are bluntly rounded or obtusely pointed, instead of being spinose. 28 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The interpretation of the appendages of the cephalon is somewhat difficult. At the left of the glabella there are two large exopodites, the anterior of which lies over and par- tially conceals the other. These show by their position that they belong to the fourth and fifth cephalic appendages. In front of these lie two appendages which may be either endop- odites or exopodites, but which I am inclined to refer to the latter. Both are narrow and shaped like endopodites, but bear on their outer edges close-set fine sete. They also show what might be considered as faint traces of segmentation. If the first of these ran under the end of the exopodite behind it, as shown in Walcott’s figure (pl. 22), then it would be necessary to interpret it as an endopodite, but it really continues down between the exop- odite and the glabella, and seems to be attached opposite the middle of the eye. The specimen does not indicate clearly whether this appendage is above or below the exopo- dite behind it, but one’s impression is that it is above, in which case it also must be an exopodite. The appendage in front, being similar, is similarly interpreted. If this be cor- rect, then the exopodites of the second and third cephalic appendages are much shorter and narrower than those of the fourth and fifth. All of these appendages are obviously out of position, for the cheek has been pushed forward away from the thorax, though still pivot- ing on its inner angle at the neck-ring, till the eye has been brought up to the dorsal fur- row. In this way the anterior exopodites have been thrust under the glabella and all the appendages have been moved to the right of their original position. ‘The anterior exopo- dite is very poorly shown, but seems to be articulated in front of the eye. The posterior exopodites are very similar to those on the thorax. The distal lobe is shown only by the seconid from the last. It has the same form as the distal lobes on the thoracic exopodites, and like them has much finer seta than the main lobe, but it does not stand at so great an angle with the axis of the main lobe, nor yet is it so straight as shown in Walcott’s figure. Measurements: YVhe specimen is about 72 mm. long and 54 mm. wide at the genal angles. The pygidium is 22 mm. long and 27 mm. wide. The doublure is 1.5 mm. wide. The exopodite of the third thoracic segment is 19.5 mm. long. ‘The pleural lobe at this point is 13 mm. wide without the spines and 18.5 mm. wide with them. ‘The third exopodite of the cephalon was apparently about 15 mm. long when complete. Specimen No. 65515. Illustrated: Walcott, Smithson, Misc. Coll., vol. 67, 1918, pl. 20, figs. 3, 4. This is a small piece of the axial portion of a badly crushed Neolenus, showing appen- dages on the left side as viewed from above. On the posterior half there are three large appendages which have the exact form of the exopodites of other specimens. There is a broad, oval, proximal lobe and a distal one at an angle with it. The proximal part of the shaft has fine setz or the bases of them, and the distal lobe faint traces of much finer ones. The form, and the setae so far as they are preserved, are exactly like those of the exopodites on the specimens previously described. (See fig. 4, page 26.) Beneath them there are slender, poorly preserved endopodites. In front of the exopodites and endopodites lie a series of structures which Walcott has called exites, but for which I can see another explanation. Walcott has shown them as four broad rounded lobes, but his figure must be looked upon as a drawing and not as a photograph, for it has been very much retouched. NEOLENUS. 209 For convenience of discussion, these lobes may be called Nos. 1, 2, 3, and 4, the last being the posterior one (fig. 5). This lobe is best shown on the matrix, where the anterior end is seen to be margined by stout spines, while the posterior end lies over the endopodite and under the exopodite behind it. No. 3 is sunk below the level of the others, and only a part of it has been uncovered. Its margin bears strong spines of different sizes. Its full shape can not be made out, but it has neither the shape nor the form of spines shown in figure 3, plate 20 (1918). Lobes 2 and 1 and another lobe in front of 1 seem to form a continuous series and to be part of a single appendage. They are all in one plane, are so continuous that the joints between them can be made out with difficulty and if they do belong together, can easily be explained. Fig. 5.—A sketch Fig. 6. — Endop- of the so-called odite of a cephalic exites of Neolenus appendage of Neo- serratus (Rom- lenus serratus inger), to show the (Rominger), show- form and the char- ing the very broad acter of the spines. coxopodite. X 2. 2! Before calling these structures new organs not previously seen on trilobites, it is of course necessary to inquire if they can be interpreted as representing any known structures. That they can not be exopodites is obvious, since they are bordered by short stout spines instead of sete. The same stout spines that negate the above possible explanation at once suggest that they are coxopodites (compare fig 6). At first sight, the so-called exites seem too wide and too rounded to be so interpreted, but if reference be had to the specimens rather than the figures, it will be noted that the only well preserved structure (No. 2) is longer than wide, has spines only on one side and one end, and does not differ greatly from the coxopodite of specimen No. 58589 (pl. 18, 1918). If structures 2, 1, and the segment ahead of 1 are really parts of one appendage, it can only be an endopodite, of which No. 2 is the coxopodite, No. 1 the basipodite, and the next segment the ischiopo- dite. If one looks carefully, there are no traces of spines on either end of No. 1, but only on the margin. The extreme width of No. 2 is against this interpretation as a coxopo- dite (see, however, fig. 6), but it may be rolled out very flat, as this is an unusually 30 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. crushed specimen. No. 2 is 10 mm. long and 6 mm. wide at the widest point. No. 1 is 5 mm. long and 3.5 mm. wide. The crucial point in this determination is whether 2 and 1 are parts of the same appen- dage. I believe they are, but others may differ. Specimen No. 65513. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, pl. 45, fig. 3;—Ibid., vol. 67, 1918, pl. 16, figs. I, 2. This is nearly all of the right half of an entire specimen, but the only appendages of any interest are those of the cephalon. Five endopodites emerge from beneath that shield, but as all are displaced it is not possible to say how many belong to the head. When held at the proper angle to the light, the second and third from the front show faintly the par- tial outlines of the coxopodites. The anterior side and end of the best preserved one shows irregular stout spines of unequal sizes, and the inner end is truncated obliquely (fig. 6). These coxopodites are like those on the thorax of specimen No. 58589, but shorter and wider. This of course suggests that the “exite’ No. 2 of specimen No. 65515 may be a cephalic coxopodite. The endopodite of this appendage, like the others on this cepha- lon, is shorter and stouter than the thoracic or pygidial endopodites of the others described. Fig. 7—A restored section across the thorax of Neolenus serratus, showing the probable form of attachment of the ap- pendages, their relation to the ventral membrane, and the jaw- like endobases of the coxopodites. Measurements: The cephalon is 24 mm. long and about 60 mm. wide. The coxopodite of the third appendage is about 10 mm. long and 5.5 mm. wide at the widest point. The corresponding endopodite is 19 mm. long and projects 11 mm. beyond the margin, which is about 5 mm. further than it would project were the appendage restored to its proper position. RESTORATION OF NEOLENUS. (Text fig. 7, 8.) This restoration is based upon the information obtained from the studies which have been detailed in the preceding pages, and differs materially from that presented by Doctor Walcott. The appendages are not shown in their natural positions, but as if flattened nearly into a horizontal plane. The metastoma is added without any evidence for its former presence. The striking features of the appendages are the broad unsegmented exopodites which point forward all along the body, and the strong endopodites, which show practically no regional modification. Although the exopodites have a form which is especially adapted for use in swimming, their position is such as to indicate that they were not so used. The stout endopodites, on the other hand, probably performed the double function of natatory and ambulatory legs. NEOLENUS. 31 ~S WA PS | Oe FDS \\ KEES SERS Aft ey | KS iss - { Lf Hy S \ Hy QYy ~ & a a 3 Ss SX c ZA daa ] = = Ce TS ag QE a (I LUT Fig. 8—Neolenus serratus (Rominger). A restoration of the ventral surface, with the endopodites omitted from one side, to permit a better exposition of the exopodites. The position and number of the appendages about the mouth are in considerable doubt. Restored by Doctor Elvira Wood under the supervision of the writer. About one-half larger than the average specimen. Nathorstia transitans Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, pl. 28, fig. 2. The badly preserved specimen on which this genus and species was based is undoubt- edly a trilobite, but for some reason it does not find a place in Walcott’s recent article on “Appendages” (1918). The preservation is different from that of the associated trilo- bites, being merely a shadowy impression, indicating a very soft test. The general outline ° 32 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES, of the body, the position of the eye, and even a trace of spines about the pygidium (in the figure) are similar to those of Neolenus, and I would venture the suggestion that Nathorstia transitans is a recently moulted Neolenus serratus, still in the “soft-shelled” con- dition. Even if not a Neolenus, it is probable, from the state of preservation, that it is an animal which had recently cast its shell. Walcott describes such fragments of appendages as remain, as follows: Head. A portion of what may be an antenna projects from beneath the right anterior margin; from near the left posterolateral angle a large four-jointed appendage extends backward. I assume that this may be the outer portion of the large posterior appendage (maxilla) of the head. Thorax. Traces of several slender-jointed thoracic legs project from beneath the anterior segments and back of these on the right side more or less of six legs have been pushed out from beneath the dorsal shield; these are composed of three or four long slender joints; fragments of the three proximal joints indicate that they are shorter and larger and that they have a fringe of fine sete. Indications of a branchial lobe (gill) are seen in two specimens where the legs are not preserved. This is often the case both among the Merostomata (pl. 20, fig. 3, Molaria) and Trilobita (pl. 24, fig. 2, Ptychoparia). Two caudal rami project a little distance beneath the posterior margin of the dorsal shield. This latter feature of course suggests Neolenus. The other appendages are too poorly preserved to allow comparison without seeing the specimen. The specific name was given “on account of its suggesting a transition between a Merostome-like form, such as Molaria spinifera, and the trilobites.” In what respect it is transitional does not appear. Formation and locality: Same as that of Neolenus serratus. One nearly complete specimen and a few fragments were found. Tue APPENDAGES OF ISOTELUS. HISTORICAL. The first specimen of /sotelus with appendages was described orally by Billings before the Natural History Society of Montreal in 1864, and in print six years later (1870, p. - 479, pls. 31, 32). The specimen is described in detail on a later page. Billings recog- nized the remains of eight pairs of legs on the thorax, a pair for each segment, and he inferred from the fact that the appendages projected forward that they were ambulatory rather than natatory organs. He was unable to make out the exact number of the seg- ments in the appendages, but thought each showed at least four or five. Having examined the individual sent to London by Billings, Woodward (1870, p. 486, fig. I) reviewed the collection from the American Trenton in the British Museum and found a specimen in the “Black Trenton limestone,” from Ottawa, Ontario, in which, along- side the hypostoma, was a jointed appendage, which he described as the “jointed palpus of one of the maxille.’’ This has always been considered an authentic ‘find,’ but I am in- formed by Doctor Bather that the specimen does not show any real appendage. For further discussion, see under /sotelus gigas. In 1871, Billings’ specimen was examined by Professors James D. Dana (1871, p. 320), A. E. Verrill, and Sydney I. Smith, who agreed that the structures identified by Billings as legs were merely semicalcified arches of the membrane of the ventral surface, which opinion seems to have been adopted by zoologists generally in spite of the fact that the most elementary consideration of the structure of the thorax of a trilobite should have shown its falsity. While the curvature of the thoracic segments was convex forward, that of the supposed ventral arches was convex backward, and the supposed arches extended ISOTELUS, 33 across so many segments as to have absolutely prevented any great amount of motion of the segments of the thorax on each other. Enrollment, a common occurrence in /sotelus, would have been absolutely impossible had any such calcified arches been present. Walcott, in his study of trilobites in thin section (1881, pp. 192, 206, pl. 2, fig. 9), obtained eleven slices of Jsotelus gigas which showed remains of appendages. He figured one of the sections, stating that it ‘‘shows the basal joint of a leg and another specimen not illustrated gives evidence that the legs extended out beneath the pygidium, as indicated by their basal joints.” The second important specimen of an Jsotelus with appendages was found by Mr. James Pugh in strata of Richmond age 2 miles north of Oxford, Ohio, and is now in the U. S. National Museum.- It was first described by Mickleborough (1883, p. 200, fig. 1-3). In two successive finds, a year apart, the specimen itself and its impression were recoy- ered. Since I am redescribing the specimen in this memoir (see p. 35), it only remains to state here that Mickleborough interpreted the structures essentially correctly, though not using the same terminology as that at present adopted. His view that the anterior appen- dages were chelate can not, however, be supported, nor can his idea that the sole appendages of the pygidium were foliaceous branchial organs. Walcott (1884, p. 279, fig. 1) studied the original specimens and presented a figure which is much more detailed and clear than those of Mickleborough. By further cleaning the specimen he made out altogether twenty-six pairs of appendages. He stated that one of these belonged to the cephalon, nine to the thorax,' and the remaining sixteen to the pygidium. He showed that the endopodites of the pygidium were of practically the same form as those on the thorax, and stated that the “leg beneath the thorax of the Ohio trilobite shows seven joints in two instances; the character of the terminal joint is unknown.” His figure shows, and he mentions, markings which are interpreted as traces of the fringes of the exopodites. In the same year Woodward (1884, p. 162, fig. 1-3) reproduced all of Micklebor- ough’s figures, and suggested that the last seven pairs of appendages on the pygidium of Calymene and Isotelus were probably “lamelliform branchiferous appendages, as in Limulus and in living Isopoda.” Professor Beecher published, in 1902, an outline taken from Mickleborough’s figure of this specimen, to call attention to certain discontinuous ridges along the axial cavity of the anterior part of the pygidium and posterior end of the thorax. These ridges are well shown in Mickleborough’s figure, though not in that of Walcott, and their presence on the speci- men was confirmed by a study by Schuchert, who contributed a diagrammatic cross-section to Beecher’s paper (1902, p. 169, pl. 5, figs. 5, 6). Beecher summarized in a paragraph his interpretation of this specimen: The club-shaped bodies lying within the axis are the gnathobases attached at the sides of the axis; the curved members extending outward from the gnathobases are the endopodites; the longitudinal ridges in the ventral membrane between the inner ends of the gnathobases are the buttresses and apodemes of the mesosternites; the slender oblique rod-like bodies shown in the right pleural region in Walcott’s figure are portions of the fringes of the exopodites. j In rg10, Mr. W. C. King of Ottawa, Ontario, found at Britannia, a few miles west of Ottawa, the impression in sandstone of the under surface of a large specimen of Jsotelus arenicola, described on a later page (p. 39). ‘The posterior one of these he believed to have been crowded forward from beneath the pygidium. 34 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Finally (1918, p. 133, pl. 24, figs. 3, 3a; pl. 25), Walcott has redescribed the speci- men from Ohio, presenting a new and partially restored figure. He refers also to the speci- men from Ottawa under the name J/sotelus covingtonensis? Foerste (not Ulrich). He advances the view, which I am unable to share, that the cylindrical appearance of the segments of the appendages of Jsotelus is due to post-mortem changes. Isotelus latus Raymond. (Al, 2©, e% i) Illustrated: Asaphus platycephalus Billings, Quart. Jour. Geol. Soc., London, vol. 26, 1870, pl. 31, figs. 1-3; pl. 32, figs. 1, 2—Woodward, Geol. Mag., vol. 8, 1871, pl. 8, figs. 1, 1a—Gerstacker, in Bronn’s “Klassen u. Ordnungen d. Thier-Reichs,” 1879, pl. 49, fig. 1—von Koenen, N. Jahrb. f. Min., etc., vol. 1, 1880, pl. 8, fig. 8—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 12, fig. 45. Tsotelus latus Raymond, Bull. Victoria Mem. Mus., Geol. Survey Canada, No. I, 1913, p. 45 (species named). : Isotelus covingtonensis? Walcott (not Foerste), Smithson. Misc. Coll., vol. 67, 1918, p. 134. Knowledge of the appendages of this species is derived from the specimen which Billings described in 1870. It was found in the Trenton, probably the Middle Trenton, near Ottawa, Ontario, and is preserved in the Victoria Memorial Museum at Ottawa. Viewed from the upper surface, it shows a large part of the, test, but is broken along the sides, so that parts of the free cheeks, considerable of the pleural lobes of the thorax, and one side of the pygidium are missing. Viewed from the lower surface, the appendages are practically confined to the cephalon and thorax. A short time before his death, Professor Beecher had this specimen and succeeded in cleaning away a part of the matrix so that the appendages show somewhat more clearly than in Billings’ time, but they are not so well preserved as on the Mickleborough speci- men, found in Ohio somewhat later. The hypostoma is in place and well preserved; the posterior points are but 3 mm. in advance of the posterior margin of the cephalon. Behind the hypostoma there are only two pairs of cephalic appendages, the first of which is represented by the coxopodite and a trace of the endopodite. The outer end of the coxopodite is close to the outer margin of one of the prongs of the hypostoma and about 3 mm. in front of its posterior end. The gnatho- base curves backward and inward, and appears to pass under the tip of the hypostoma. There were probably two appendages in front of this, whose gnathobases projected under the hypostoma, but the specimen shows nothing of them unless it be that one small frag- ment about 2 mm. back of the center is really a part of a gnathobase. The specimen retains only the coxopodite and basipodite of the posterior cephalic ap- pendage on the left side. The coxopodite is long and apparently cylindrical, the cross- section being of uniform diameter throughout the length. The inner portion is nearly straight, while the outer part is curved gently forward. It is possible to make out remains of eight pairs of appendages on the thorax, some of them represented by coxopodites only, but most with more or less poorly preserved endop- odites as well. No exopodites are visible. The coxopodites of the thorax seem to be of the same form as the last one on the cephalon, but slightly less curved. All are long and heavy, and there seems to be no decrease in size toward the pygidium. The endopodites are very imperfectly shown. They seem to be longer than those of /sotelus maximus, and the segments, while of less diameter than the coxopodites, do not show so great a contrast to ISOTELUS. 35 them as do those of that species. The direction of the endopodites is diagonally forward, and the outer portions do not appear to be curved backward as in Jsotelus maximus. It would appear also that the endopodites were nearly or quite long enough to reach the outer margin of the dorsal test. On no endopodite can more than three segments be definitely dis- tinguished, but the longest ones are the most obscurely segmented. No appendages are preserved on the pygidium, but at one side of the median groove there are two projections which may be processes to which the appendages were attached. Measurements: Total length of specimen, 109 mm. Probable length when complete, 116 mm. Length of cephalon, 40 mm.; width at genal angles, restored, about 62 mm. (Billings’ restoration). Width of doublure of front of cephalon on median line, 17 mm.; length of hypostoma, 20 mm. Length of coxopodite of last appendage on left side of cephalon, 10.5 mm.; length of basipodite of the same appendage, 5 mm. Diameter of cox- opodite, 2 mm.; diameter of basipodite, 1.5 mm. Length of coxopodite on left side o} the second segment of the thorax, 11 mm.; diameter, about 2.5 mm. Length of basipodite of the same, 5 mm.; diameter, about 1.5 mm. Length of ischiopodite, 3.5 mm.; diameter. about 1.5 mm. Length of meropodite, 2.5 mm. (this may be less than the total length as the segment is not completely exposed.) Distance between proximal ends of gnathobases of the fifth thoracic segment, about 7 mm. Distance between outer ends of the coxopo- dites of the first thoracic segment (estimated from measurements on the left side), 27 mm Distance apart of the dorsal furrows at the first thoracic segment, 27 mm. Length of the longest exopodite which can be traced, about 20 mm. Isotelus maximus Locke. GE tow tes25) Illustrated: Mickleborough, Jour. Cincinnati Soc. Nat. Hist., vol. 6, 1883, p. 200, figs. 1-3 (endopodites and coxopodites).—Walcott, Science, vol. 3, 1884, p. 2790, fig. 1 (endopodites, coxopodites, and traces of exopodites)—Woodward, Geol. Mag., dec. 3, vol. I, 1884, p. 162, figs. 1-3 (copies of Mickleborough’s figures) —Bernard, The Apodide, 1892, text fig. 49—Beecher, Amer. Jour. Sci., vol. 13, 1902, p. 169, pl. 5, figs. 5, 6 (outline from one of Mickleborough’s figures and an original figure).—Walcott, Smithson. Misc. Coll., vol. 67, 1918, p. 133, pl. 24, figs. 3, 3a; pl. 25, fig. 1. This specimen, which comes from the Richmond strata 2 miles north of Oxford, Ohio, is the best preserved of the specimens of Jsotelus with appendages which has so far been found. The individual consists of two parts, the actual specimen, and the impression of the ventral side. To describe it I am using very skillfully made plaster reproductions of both parts, presented to the Museum of Comparative Zoology by Doctor Charles D. Walcott, and pre- sumably made after he cleaned the specimen as described in Science (1884). I have also | an enlarged photograph (pl. 10, fig. 2) which seems to have been made after some later period of cleaning, probably by Professor Beecher, and I have examined the original speci- mens in Washington. Viewed from the dorsal side, it is seen that the individual is very imperfect, the greater part of the cephalon being removed by a.diagonal break which cuts off the anterior third of the left eye and extends to the front of the second thoracic segment on the right side. The ends of the pleura of both sides of the thorax are broken away, as are also the greater parts of the pleural lobes and the posterior end of the pygidium. On the ventral side, merely the posterior tips of the hypostoma remain, but the distal ends of the appendages were so far within the outer margin that the appendagiferous area is quite fully retained. 36 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The most conspicuous feature of this specimen is the presence of nine pairs of large coxopodites behind the hypostoma, and of the remains of ten pairs of endopodites, mak- ing in all ten pairs of appendages which are easily seen. The apportionment of these seg- ments to cephalon, thorax, and pygidium is not agreed upon by the people who have examined the specimens, but if one remembers that it is the outer and not the inner end of the coxopodite which articulates with the appendifer, it at once becomes evident that the first two pairs of appendages on the specimen are the last two pairs belonging to the cephalon, and that the next eight pairs are those of the thorax. The impressions of fourteen pairs of coxopodites are readily counted on the pygidium, and as Doctor Walcott noted sixteen pairs on the actual specimens, his number was prob- ably correct. Cephalon. Projecting the line of the back of the cephalon through from the dorsal side, it is found that the posterior tips of the hypostoma are 7 mm. in front of the posterior mar- gin of the cephalon, and that the points of attachment of the posterior pair of cephalic ap- pendages (the second pair shown on the specimen) are just within the posterior margin. The gnathobases of this pair of appendages extend back some distance beneath the thorax, and so give the impression that they belong to that part of the body. So far as can be determined, the cephalic appendages do not differ in any way from those of the thorax. On the mould of the ventral surface, just outside of the lateral edge of the right lobe of the hypostoma, is the somewhat imperfectly shown impression of the endopodite of the third cephalic appendage. The point of junction of the endopodite and coxopodite is about 2 mm. in front of the tip of the adjacent branch of the hypostoma, and the gnathobase is curved around just behind it. This accounts for three of the pairs of cephalic appendages. The second cephalic appendages must have thrust their gnathobases under the prongs of the hypostoma, and the endopodites were probably close to its edge. No trace of this pair ap- pears on the specimen. Thorax. The thoracic appendages are the best preserved of any, and show the large coxopodites and the more slender endopodites which do not extend to the outer margin of the test. The latter extend forward and outward for about one half their length, then turn backward in a graceful curve. Walcott’s figure in Science shows hair-like markings on the under side of the right half of the thorax. These were interpreted by both Walcott and Beecher as fringes of the exopodites, but since the sete of those organs on all other trilobites are always above the endopodites, while these are represented as below them, it would seem doubtful if this in- terpretation can be sustained. Furthermore, I find no trace of them on either cast or mould, and the actual specimen does not now show them. Pygidium. The coxopodites and endopodites of the pygidium seem to be similar to those on the thorax, but both are shorter and more slender, and the former decrease in length rapidly toward the posterior end. As mentioned above, it is not perfectly plain how many appendages are present, but I have accepted Doctor Walcott’s count of sixteen pairs. Of the endopodites only the barest traces are seen, and of exopodites nothing. ISOTELUS. B One point of considerable interest in this specimen is the thickness, as it probably gives some measure of the space occupied by the animal. In 7Tyviarthrus and other trilobites from Rome, New York, the appendages are pressed directly against the dorsal test, but in this specimen a considerable space intervenes between the plane of the appendages and the shell. Between the central furrow and the inner surface of the dorsal test at the anterior end of the thorax is a distance of 13 mm. and under the dorsal furrows the thickness is about 7 or 8 mm., no accurate measurement being possible in the present state of the specimen. Measurements: Length of specimen on median line, 121 mm.; probable original length, about 195 mm. (Walcott’s restoration). Length of thorax, 58 mm.t. Width of axial lobe at the first thoracic segment, 45 mm.; total width as preserved, 92 mm.; width as esti- mated from the mould of the ventral surface, 110 mm.; Walcott’s restoration, 105 mm. Length of coxopodite of fourth left cephalic appendage, about 18 mm.; diameter, about 2.5 mm. Length of coxopodite of last left cephalic appendage, about 18.5 mm. Dis- tance apart of inner ends of gnathobases of fourth cephalic appendages, about 4mm. _ Dis- tance apart of inner ends of endobases of first thoracic segment, about 6 mm. Distance apart of outer ends of coxopodites of first thoracic segment, about 43 mm. Length of coxopodite of seventh left thoracic appendage 16 mm., diameter about 3.5 mm.; length of basipodite of the endopodite of the same appendage 6 mm.; diameter about 2 mm.; length of ischiopodite 5 mm.; length of meropodite 4.5 mm.; length of car- popodite 4.5 mm.; length of propodite 3 mm.; length of dactylopodite 2.75 mm.; total length of endopodite 25.75 mm. Length of coxopodite of fourth left thoracic appendage 20 mm., diameter 4 mm.; length of five proximal joints of the endopodite 25 mm.; diameter of basipodite about 2 mm. RESTORATION OF ISOTELUS. (ext: feso3) The exopodites have been omitted from this restoration since nothing is known of their actual form. The chief reason for the figure is to contrast the greatly developed coxopo- dites of the posterior part of the cephalon and thorax with those of other trilobites. The antennules and first two pairs of biramous appendages of the cephalon are more or less hy- pothetical, and less is known of the appendages of the pygidium than is shown here. The restoration is based somewhat upon Walcott’s figure in Science. The outline is that of a specimen of /sotelus maximus from Toronto, Ontario. Isotelus gigas Dekay. Illustrated: Woodward, Quart. Jour. Geol. Soc., London, vol. 26, 1870, text fig. 1;—Geol. Mag., dec. 3, vol. 1, 1884, p. 78, text fig—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 12, fig. 46.— Walcott, Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pl. 2, fig. 9;—Geol. Mag., dec. 4, vol. 1, 1804, pl. 8, fig. 9;—Proc. Biol. Soc. Washington, vol. 9, 1894, pl. I, fig. 9. The specimen in the British Museum which Woodward called Asaphus platycephalus, is, in all probability, an Isotelus gigas. Woodward says of it: 1If this specimen had the same proportions as specimens of /Jso/elus maximus from Toronto, the total length would be only 174 mm. The cephalon would be about 52 mm. long, the thorax 58 mm., and the pygidium about 64 mm. long. 38 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Fig. 9.—A restored composite of Isotelus maximus and J. latus. The exopodites are left out because entirely unknown. Drawn by Doctor Elvira Wood. Natural size. I was at once attracted by a specimen of Asaphus, from the Black Trenton Limestone (Lower Silurian), which has been much eroded on its upper surface, leaving the hypostoma and what appear to be the appendages belonging to the first, second, and third somites, exposed to view, united along the median line by a longitudinal ridge. The pseudo-appendages, however, have no evidence of any articulations. But what appears to me to be of the highest importance, as a piece of additional information afforded by the Museum specimen, is the discovery of what I believe to be the jointed palpus of one of the maxillz, which has left its impression upon the side of the hypostoma—just, in fact, in that position which it must have occupied in life, judging by other Crustaceans which are furnished with an hypostoma, as Apus, Serolis, etc. The palpus is 9 lines in length, the basal joint measures 3 lines, and is 2 lines broad, and somewhat triangular in form. There appear to be about 7 articulations in the palpus itself, above the basal joint, marked by swellings upon its tubular stem, which js 1 line in diameter. ISOTELUS. 39 Desiring to know more of this individual, I wrote to Doctor Bather and was surprised to learn that the specimen which was the basis of Woodward's observations is so badly pre- served as to be of no real valué. With his permission, I append a note made by Doctor Bather some years ago when selecting fossils to be placed on exhibition: Asaphus gigas Dekay. Ordovician, Trenton Limestone. N. America, Canada. Descr. H. Woodward, 1870, Q. J. G. S., XXVI, pp. 486-488, text fig. 1, as Asaphus platycephalus. Coll. and presd. J. J. Bigsby, 1851. Regd. I 14431. This specimen is in the Brit. Mus. Geol. Dept. I 14431. The supposed hypostome is exceedingly doubt- ful; it lies dorsad of the crushed glabellar skeleton. The “appendage” is merely the edge of a part in the head-shield; the maxilla is some calcite filling, between two such lamine. 13 Sept. IQ11. (Signed) F. A. BatuHer. Walcott figured a slice of Isotelus gigas from Trenton Falls, New York, which shows a few fragments of appendages, but is of particular importance because it shows the pres- ence of well developed appendifers beneath the axial lobe. Isotelus arenicola Raymond. Illustrated: Ottawa Nat., vol. 24, 1910, p. 120, pl. 2, fig. 5. The following quotations from my paper are inserted here to complete the record of appendage-bearing specimens: A rather remarkable specimen of this species. was found by W. C. King, Esq., on the shore of Lake Deschenes at Britannia [near Ottawa, Ontario]. This specimen is an impression of the lower surface of the trilobite, and shows a longitudinal ridge corresponding to the central furrow along the axis of the ventral side of the animal, ten pairs of transverse furrows, and the impression of the hypostoma. The doublure of the pygidium has also left a wide smooth impression, but in the cephalic region the hypostoma is the only portion of which there are any traces remaining. The specimen was found on a waterworn surface of the beach, partially covered by shingle. A The transverse furrows are the impressions left by the gnathobases of the basal joints of the legs. They were evidently long and very heavy, but the specimen has been so abraded that all details are obscured. The first six pairs of impressions are longer and deeper than the four behind. The first eight pairs seem to pertain to the thoracic appendages, while the last two belong to the pygidium. From the posterior tips of the hypostoma to the first gnathobases of which traces are present there is a distance of about 22 mm. without impressions. In Jsotelus gigas the hypostoma normally extends back to the posterior margin of the cephalon, so that it seems that in this specimen the impressions of the first two pairs of gnathobases under the thorax may not have been preserved. In that case, the six pairs of strong impressions may represent the last six pairs of thoracic segments, and the pygidium might begin with the first of the fainter ones. Horizon and locality: From the sandstone near the base of the Aylmer (Upper Chazy) formation at Britannia, west of Ottawa, Ontario. Specimen in the Victoria Memorial Mu- seum, Geological Survey of Canada, Ottawa. Tuer APPENDAGES OF TRIARTHRUS. Triarthrus becki Green. (Pls. 1-5; pl. 6, figs. rae Lexie se TONE T ees ADs) (Also see Part IV.) Illustrated: Matthew, Amer. Jour. Sci., vol. 46, 1893, pl. 1, figs. 1-7;—-Trans. N. Y. Acad. Sci., vol. 12, pl. 8, figs. 1-7—Beecher, Amer. Jour. Sci., vol. 46, 1893, text figs. 1-3;—Amer. Geol., vol. 13, 1804, pl. 3;— Amer. Jour. Sci., vol. 47, pl. 7, text fig. 1;—Amer. Geol., vol. 15, 1895, pls. 4, 5;—Ibid., vol. 16, 1805, pl. 8, 40 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. figs. 12-14; pl. 10, fig. 1;—Amer. Jour. Sci., vol. 1, 1896, pl. 8;—Geol. Mag., dec. 4, vol. 3, 1806, pl. 9;— Eastman-Zittel Text-book of Paleontology, vol. 1, 1900, text figs. 1267-1269;—-2d ed., 1913, fig. 1375 ;—-Studies in Evolution, 1901, reprint of all previous figs.;—Amer. Jour. Sci., vol. 13,1902, pl. 2, figs. 1-5; pl. 3, fig. 1; pl. 4, fig. 1; pl. 5, figs. 2-4;—Geol. Mag., dec. 10, vol. 9, 1902, pls. 9-11, text figs. 1-3—Walcott, Proc. Biol. Soc. Washington, vol. 9, 1894, pl. 1, figs. 1-6;—Geol. Mag., dec. 4, vol. 1, 1894, pl. 8;—Smithson. Mise. Coll., vol. 67, 1918, pl. 20, figs. 1-11; pl. 30, figs. 17-20; pl. 32; pl. 34, figs. 4-7; pl. 35, fig. 5——Bernard, Quart. Jour. Geol. Soc., London, vol. 50, 1894, text figs. 11, 12—(Ehlert, Bull. Soc. Géol. France, ser. 3, vol. 24, 1896, text figs. 1-17, 34—Jaekel, Zeits. d. d. geol. Gesell., vol. 53, 1901, text fig. 24——Moberg, Geol. Foren. Forhandl., vol. 20, pt. 5, 1907, pl. 4, fig. 2; pl. 5, fig. 1—Handlirsch, Foss. Insekten, 1908, text fig. 6—Tothill, Amer. Jour. Sci., vol. 42, 1916, p. 380, text fig. 5——Crampton, Jour. N. Y. Entomol. Soc., vol. 24, 1917, pl. 2, fig. 20. HIIsToRICcAL. Specimens of Triarthrus retaining appendages were first obtained by Mr. W. S. Valiant from. the dark carbonaceous Utica shale near Rome, New York, in 1884, but no consid- erable amount of material was found until 1892. The first specimens were sent to Columbia University, and were described by Doctor W. D. Matthew (1893). This article was accompanied by a plate of sketches, showing for the first time the presence of antennules in trilobites and indicating something of the endopodites and exopodites of the appendages of the cephalon, thorax, and pygidium. Specimens had not yet been cleaned from the lower side, so that no great amount could then be learned of the detailed structure. Matthew con- cluded that ‘The homology with Limulus seems not to be as close in Triarthrus as in the forms studied by Mr. Walcott; but the characters seem to be of a more comprehensive type, approaching the general structure of the other Crustacea rather than any special form.” Professor Beecher’s first paper, dated October 9, 1893, merely mentioned the fact that the Yale University Museum had obtained material from Valiant’s locality, but was quickly followed by a paper read before the National Academy of Sciences on November 8, and published in December, 1893. This paper described particularly the thoracic appendages. This was followed in January (1894 A) by an article in which some information about the mode of occurrence of the specimens was added, and in April (1894 B), the limbs of the pygidium were described and figured. The determination of the structure of the appen- dages of the head evidently presented some difficulty, for the article describing this portion of the animal did not appear until the next February (1895 A). This cleared up the ven- tral anatomy of Triarthrus, and was followed by a short article (1896 A) accompanied by a restoration of the trilobite showing all the appendages. This ended Professor Beecher’s publications on Triarthrus until his final paper in 1902, although he contributed some of his results and figures to his chapter on the trilobites in the Eastman-Zittel Text-book of Paleontology in 1900. i The discovery of these excellent specimens had of course excited very great interest. Doctor Walcott also studied a number of specimens from Valiant’s locality, and published in 1894, with some original figures, the results of his comparison of the appendages of Triarthrus with those of Calymene and Ceraurus. In his article on the “Systematic Position of the Trilobites,’ Bernard (1894) used the results of Professor Beecher’s studies of 1893, and also quoted the papers by Matthew (1893) and Walcott (1894), though the article by the latter appeared too late to be used except for a note added while Bernard’s paper was in press. A final footnote quoted from Professor Beecher’s paper of April, 1894 (1894 B). (Ehlert (1896) gave an excellent summary in French of the work of Beecher and Wal- cott on Triarthrus, with reproductions of many of their figures. TRIARTHRUS. 4! Valiant (1901) in a non-technical article described his long search for trilobites with antenne. The discovery of the wonderful pyritized trilobites at Cleveland’s Glen near Rome Xe li Se FW My f ne RN Nin SA a Z Te pe ae reff - === =~ 7 eo ZZ ning... gph OSS so So : tt et oS an Lob AN Nae aN Trails AIT S zh i} 2 Gil ftir il Ml Y lee OS Ais TS Ii 4 le UN : my \ ts ie Mitre = Gf oe pene, NU sau ut Nw Yi ape i Fig. 10.—Triarthrus becki Green. A new restoration, modified from Professor Beecher’s, to incorporate the results of his later work. The inner ends of the endobases are probably too far apart, as it was not discovered until after the drawing had been made that the appendifers projected within the dorsal furrows. Drawn by Doctor Elvira Wood. > about 3.8. was not the result of a lucky accident, but the culmination of eight years of labor in a local- ity especially selected on account of the fineness of grain of the shale. After 1896, Professor Beecher turned his attention largely to the problem of the classi- fication of trilobites, and while he continued the arduous task of cleaning the matrix from om 42 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. specimens of Triarthrus and Cryptolithus he did not again publish upon the subject of appendages until forced to do so by the doubts cast by Jaekel (1901) upon the validity of his earlier conclusions. Because of certain structures which he thought he had interpreted correctly from a poorly preserved specimen of Ptychoparia, Jaekel came to the conclusion that Beecher’s material was not well preserved. Professor Beecher would have taken much more kindly to aspersions upon his opinions than to any slight upon his beloved trilobites, and his article on the “Ventral Integument of Trilobites’” of 1902 was designed not only as an answer to Jaekel, but also to show by means of photographs the unusually perfect state of preservation of the specimens of Triarthrus. This article, like so many describ- ing the appendages of trilobites, beginning with Matthew’s, was published in two places (Beecher 1902). Most of Beecher’s papers, except the last one, were reprinted in the volume entitled “Studies in Evolution,’ published by Charles Scribner's Sons at the time of the Yale Bi- centennial in 1901. The part pertaining particularly to 7viarthrus is on pages 197 to 219. Moberg (1907), in connection with a specimen of Eurycare angustatum which he thought preserved some appendages, described and illustrated some of the appendages of Triarthrus. The most recent discussion of Triarthrus, with some new figures, is by Walcott (1918, p. 135, pls. 29, 30). He gives a summary of Beecher’s work with numerous quotations. — The principal original contribution is a discussion of the form and shape of the appendages before they were flattened out in the shale. He found also what he thought might possibly be the remains of epipodites on three specimens, one of which he illustrated with a photo- graph. I have seen nothing which could be interpreted as such an organ in the many speci- mens I have studied. A point in which Walcott differs from Beecher in the interpretation of specimens is in regard to the development of the endopodites of small pygidia. Beecher (1894 B, pl. 7, fig. 3) illustrated a series of endopodites which he likened to the endites of a thoracic limb of Apus. Doctor Walcott finds that specimens in the United States National Museum show slender endopodites all the way to the back of the pygidium, and thinks that Beecher mistook a mass of terminal segments of exopodites for a series of endopodites. On care- ful examination, however, the specimen shows, as Beecher indicated, a series of endopodites in undisturbed condition (No. 222, our pl. 4, fig. 5). Restoration of Triarthrus. One of the more important points noted in the later studies of Triarthrus is that the enathites of the cephalic appendages are much less like the endobases under the thorax than Beecher earlier thought, and showed in his restored figures and in his model. The four enathites of each side are curved, flattened, not club-shaped, and so wide and so close together that they overlap one another. The metastoma is somewhat larger and more nearly cir- cular than Beecher’s earlier preparations led him to suppose. The restoration here presented is modified only slightly from the one designed by Pro- fessor Beecher, and the modifications are taken principally from figures published by him. The gnathites are drawn in form more like that shown by the specimens and his figures in the American Geologist (1895 A), and the metastoma is taken from one of the specimens. On the thorax. the chief modification is in the addition of a considerable number of spines to the endopodites. In spite of the trivial character of most of these changes, they empha- TRIARTHRUS. 43 size one of the important characteristics of Triarthrus—the regional differentiation of the appendages. It should be pointed out that although Triarthrus is usually considered to be a very primitive trilobite, its appendages are more specialized than those of any of the others known. This is shown in their great length, the double curvature of the antennules, the differentiation of four pairs of endobases on the cephalon as gnathites, and the flatten- ing of the segments of the posterior endopodites. These departures from the uniformity existing among the appendages of the other genera lead one to question whether the genus is really so primitive as has been supposed. Relation of the Cephalic Appendages to the Markings on the Dorsal Surface of the Glabella. Triarthrus becki is usually represented as having four pairs of glabellar furrows, but the two pairs at the front are exceedingly faint and the first of them is hardly ever visible, though that it does exist is proved by a number of authentic specimens. The neck furrow is narrow and sharply impressed, continuing across the glabella with a slightly backward curvature. In front of it are two pairs of linear, deeply impressed furrows which in their inward and backward sweep are bowed slightly forward, the ends of the corresponding furrows on opposite sides nearly meeting along the crest of the glabella. In front of these, near the median line, is a pair of slight indentations, having the appearance and position of the inner ends of a pair of furrows similar to those situated just behind them. In front of and just outside this pair are the exceedingly faint impressions of the anterior pair of furrows, these, as said above, being but seldom seen. They are short, slightly indented linear furrows which have their axes perpendicular to the axis of the cephalon, and do not connect with each other or with the dorsal furrows. The latter are narrow, sharply impressed, and merge into a circumglabellar furrow at the front. In front of the circumglabellar furrow is a very narrow rounded ridge, but the anterior end of the glabella is very close to the margin of the cephalon. Specimen No. 214, which was cleaned from the dorsal side, shows the posterior tip of the hypostoma, apparently in its natural position, 3.5 mm. back from the anterior margin. The entire length of the cephalon is 6 mm., so that the hypostoma reaches back slightly over one half the length (0.583). The greater part of it has been cleaned off, and one sees the proximal portions of the antennules, which are apparently attached just at the sides of the hypostoma, 2.5 mm. apart and 2.25 mm. back from the anterior edge of the cephalon. This position is distinctly within the outline of the glabella and corresponds approximately to the location of the second pair of glabellar furrows. Specimens 214, 215, 216, 217, and 219 all seem to show the same location for the bases of the antennules. Specimen 220 is the one in which the basal shafts are best preserved and the points of attachment seem to be further apart in it than in any of the others. This specimen is 38 mm. long, and the bases of the antennules are 5.5 mm. apart and’4 mm. behind the anterior margin. As. the specimen is cleaned from the ventral side, the dorsal furrows do not show distinctly, but another specimen of about the same size (No. 228, 38.5 mm. long) has the dorsal furrows 8mm. apart 4 mm. back of the anterior margin. On the same slab with specimens 209 and 210 there is an individual which, although retaining the test, has had the proximal ends of the antennules so.pressed against it that the course of the one on the left side is readily visible. It originates in a small oval mound 44 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. whose posterior margin impinges upon the third glabellar furrow near the middle of its course, and just outside the outer end of the second glabellar furrow. The cephalon of this specimen is 5 mm. long, and the point of origin of the left antennule is 2.75 mm. in front of the posterior margin and 0.75 mm. from the dorsal furrow. It is therefore evident that the antennules in this species are not attached beneath the dorsal furrows, but within them and opposite the second pair of glabellar furrows. All cephalic appendages behind the antennules are attached somewhat within the dorsal furrows, the first pair as far forward as the antennules and the last pair apparently under the anterior edge of the neck ring. They do not appear to correspond in position to the posterior glabellar furrows and neck ring, being more crowded. The last pair is attached to appendifers beneath the nuchal segment, and the first pair beneath the third glabellar fur- rows. There are no depressions on the dorsal surface corresponding to the points of at- tachment of the mandibles. Anal Plate. Professor Beecher, during his first studies of Tviarthrus, found no appendages pertain- ing to the anal segment, but later evidently came upon a spinose anal plate which he caused eS “LG Fig. 11.—Triarthrus becki Green. Anal plate of specimen 65525 in the U. S. National Museum. Drawn by Doctor Wood. X 20. to be figured. The specimen (No. 201) on which this appendage is preserved is cleaned from the dorsal side, and the anal plate is a small, bilaterally symmetrical, nearly semicir- cular structure margined with small spines. Specimen 202 also shows the same plate (pl. 5, fig. 6), but it is imperfectly preserved. It has a large, perforation in the anterior half. Both of these specimens are in the Yale University Museum. The anal plate is especially well shown by specimen 65525 in the United States National Museum (fig. 11). This specimen is from Rome, New York, and two photographs of it have been published by Walcott (1918, pl. 20, fig. 6; pl. 30, fig. 19). It is developed from the dorsal side, and the anal plate is displaced, so that it projects behind the end of the pygidium. It is semicircular in shape, with a hemispheric mound at the middle of the an- terior half. Two furrows starting from the anterior edge on either side of the mound border its sides, and, uniting back of it, continue as an axial furrow to the posterior mar- gin. The mound is perforated for the opening of the posterior end of the alimentary canal. The lateral borders of the plate bear five pairs of short, symmetrically placed spines. The plate is 1 mm. wide and 0.5 mm. long, and the entire trilobite is 11.5 mm. long. PTYCHOPARIA. 45 THE APPENDAGES OF PTYCHOPARIA. Ptychoparia striata (Emmrich). Illustrated: Jaekel, Zeits. d. d. geol. Gesell., 1901, vol. 53, part 1, pls. 4, 5. Jaekel has described a specimen of this species obtained from the Middle Cambrian near Tejrovic, Bohemia, which on development showed beneath the test of the axial lobe, cer- tain structures which he believed represented the casts of proximal segments of appendages. On the basis of this specimen he produced a new restoration of the ventral surface of the trilobite, in which he showed three short wide segments in the place occupied by the coxopo- dite of an appendage of Tvriarthrus. He also made the mouth parts considerably differ- ent from those of the latter genus. Beecher (1902) showed that the structures which Jaekel took for segments of appendages were really the fillings between stiffening plates of chitin on the ventral membrane, and demonstrated the fact that similar structures ex- isted in Triarthrus. It cannot be said, therefore, that any appendages are really known in Ptychoparia striata, but some knowledge of the internal anatomy of the species is sup- plied by the specimen. Ptychoparia cordillere (Rominger). Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 192, pl. 24, fig. 2;—Ibid., vol. 67, 1918, pl. 21, figs. 3-5 (corrected figure). Walcott has figured a single individual of this species showing appendages, the accom- panying description being as follows (1918, p. 144): Ventral appendages.—Only one specimen has been found showing the thoracic limbs. This indicates very clearly the general character of the exopodite and that it is situated above the endopodite, although there are only imperfect traces of the latter. The exopodites are unlike those of any trilobite now known. They are long, rather broad lobes extending from the line of the union of the mesosternites and the pleurosternites. At the proximal end they appear to be as wide as the axial lobe of each segment, and to increase in width and slightly overlap each other nearly out to the distal extremity. . . . They are finely crenulated along both the anterior and dorsal margins, which indicates the presence of fine sete. The specimen is quite imperfectly preserved, but seems to indicate that the exopodite of Ptychoparia had a long, rather narrow unsegmented shaft. Measurements (from Walcott’s figure): The specimen is a small one, about 9.5 mm. long, an individual exopodite is about 2 mm. long and the shaft 0.33 mm. wide. FHlorizon and locality: Middle Cambrian, Burgess shale, between Mount Field and Wapta Peak, above Field, British Columbia. Ptychoparia permulta Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, p. 145, pl. 21, figs. 1, 2. Walcott figured one individual of this species showing long slender antennules pro- jecting in front of the cephalon. It is of especial interest because one of the antennules shows almost exactly the same sigmoid curvature which is so characteristic of the related Triarthrus. The individual segments are not visible. Measurements: The specimen is 23 mm. long and the direct distance from the front of the head to the anterior end of the more perfect antennule is 9.5 mm. Measured along the curvature, the same antennule is about 11 mm. long. Horizon and locality: Same as the preceding. 46 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Tue APPENDAGES OF KOOTENIA. Kootenia dawsoni Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, pl. 14, figs. 2, 3. One specimen figured by Doctor Walcott shows the distal ends of some of the exopo- dites and endopodites of the right side. He compares the exopodites with those of Neo- lenus, stating that the shaft consists of two segments, the proximal section being long and flat, fringed with long sete, while the distal segment has short fine sete. The endopodite best shown is very slender, and the segments are of uniform width and only slightly longer than wide. Measurements (from Walcott’s figures): Length of specimen, about 41 mm. Length of five distal segments of an endopodite, 7.5 mm. Since the pleural lobe is only 7 mm. wide, the endopodites, and probably the exopodites also, must have projected a few milli- meters beyond the dorsal test when extended straight out laterally. Formation and locality: Burgess shale, Middle Cambrian, on the west slope of the ridge between Mount Field and Wapta Peak, above Field, British Columbia. Tur APPENDAGES OF CALYMENE AND CERAURUS. HISTORICAL. All of the work on these species has been done by Doctor Walcott, who summarized his results in 1881. In the first of his papers (1875, p. 159), Walcott did not describe any appendages but paved the way for further work by a detailed and accurate description of the ventral surface of the dorsal shell of Cerawrus. He demonstrated the presence in this species of strongly buttressed processes which extend directly downward from the test just within the line of the dorsal furrows. One pair of these is seen beneath each pair of the gla- — bellar furrows, each segment of the thorax has a pair, and there are four pairs on the pygidium. He pointed out also that these projections were but poorly developed on that part of the glabella which is covered by the hypostoma. He called them axial processes, the only name which appears to have been suggested thus far. The first announcement of the discovery of actual appendages in Ceraurus and Calym- ene was made by the same investigator in a pamphlet published in 1876 in advance of the 28th Report of the New York State Museum of Natural History, the publication of the whole report being delayed till 1879. The results were obtained by the process of cut- ting translucent slices of enrolled trilobites derived from the Trenton limestone at Trenton Falls, New York. Since he summarized all the results of this study in one paper at a later date, it is not necessary to follow the stages of the work. A second preliminary paper was published in pamphlet form in September, 1877, and in final form in 1879, when the first figures were presented. In his important paper of 1881, Walcott reviewed all that was known of the appen- dages of trilobites to that time, and gave the results of seven years of study of sections of enrolled specimens. Slices had been made of 2,200 individuals from Trenton Falls, which resulted in obtaining 270 which were worthy of study. Of these, 205 were from Ceraurus pleurexanthemus, 49 from Calymene senaria, 11 from Isotelus gigas, and 5 from Acidaspis trentonensis. CALYMENE AND CERAURUS. 47 Walcott’s views on certain portions of the anatomy can best be set forth in the form of a few extracts (1881, pp. 199-208) : The Ventral Membrane.—In those longitudinal sections in which the ventral membrane is most perfectly preserved, it is shown to have been a thin, delicate pellicle or membrane, strengthened in each segment by a transverse arch, to which the appendages were attached. These arches appear as flat bands separated by a thin connecting membrane, somewhat as the arches in the ventral surface of some of the Macrouran Decapods. . . In by far the greater number of sections, both transverse and longitudinal, the evidence of the former presence of an exterior membrane, protecting the contents of the visceral cavity, rests on the fact that the sections show a definite boundary line between the white calcspar, filling the space formerly occupied by the viscera, and the dark limestone matrix. Even the thickened arches are rarely seen. The mode of attachment of the leg to the ventral surface is shown [in transverse and longitudinal sections of Ceraurus and Calymene]. These illustrations are considered as showing that the point of articula- tion was a small, round process projecting from the posterior surface of the large basal joint, and articulating in the ventral arch somewhat as the legs of some of the Isopods articulate with the arches in the ventral membrane. The arches of the ventral membrane in the trilobite . . . afford a correspondingly firm basis for the attachment of the legs. Branchial appendages—The branchie have required more time and labor to determine their true structure than any of the appendages yet discovered. They were first regarded as small tubes arranged side by side, like the teeth in a rake; then as setiferous appendages, and finally as elongate ribbon-like spirals and bands attached to the side of the thoracic cavity, the epipodite being a so-called branchial arm. All of these parts are now known to belong to the respiratory system, but from their somewhat complex structure, and the various curious forms assumed by the parts when broken up and distorted, it was a long time before their relations were determined. The respiratory system is formed of two series. of appendages, as found beneath the thorax. The first is a series of branchiz attached to the basal joints of the legs, and the second, the branchial arms, or epipodites. The branchie, as found in Calymene, Ceraurus, and Acidaspis, have three forms. In the first they bifurcate a short distance from the attachment to the basal joint of the leg, and extend outward and downward as two simple, slender tubes, or ribbon-like filaments. In the second form they bifurcate in the same manner, but the two branches are spirals. These two forms occur in the same individual but, as a rule, the more simple ribbon-like branchia is found in the smaller or younger specimens, and the spiral form in the adult. . The spiral branchiz of Ceraurus are usually larger and coarser than those of Calymene. The third type of the branchiz [consists of rather long straight ribbons arranged in a digitate manner on a broad basal joint]. As far as yet known, this is confined to the anterior segments of the thorax. The epipodite or branchial arm was attached to the basal joints of the thoracic legs and formed of two or more joints. This has been called a branchial arm, not that it carried a branchia, but on account of its relation to the respiratory system. It is regarded as an arm or paddle, that, kept in constant motion, produced a current of water circulating among the branchize gathered close beneath the dorsal shell. Of the modification the respiratory apparatus underwent beneath the pygidium, we have no evidence. In his latest publication (1918, pp. 147-153, pls. 26-28, 33), Walcott has reviewed his earlier work on Calymene and Ceraurus, and presented a new restoration of the former. The coxopodites are now interpreted as being similar to those of Triarthrus and Neolenus, but the exopodites are still held to be spiral and the setiferous organs labelled as epipo- dites rather than exopodites. CoMPARISON OF THE APPENDAGES OF CALYMENE AND CERAURUS WITH THOSE OF TRIARTHRUS. As one may see by reading the above quotations from Doctor Walcott’s descriptions, he found certain branchial organs in Ceraurus and Calymene which have not been found in other trilobites but otherwise the essential features of the appendages of all are in agree- ment. 48 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Spiral Branche. It is now necessary to inquire if the thin sections can not»be interpreted on the basis of trilobites with the same organs as Triarthrus. The interpretation of the structures seen in these translucent slices is exceedingly difficult, and Doctor Walcott deserves the utmost praise for the acumen with which he drew his deductions. Even with the present knowl- edge of Triarthrus, Isotelus, and Neolenus as a guide, 1 do not think it is safe to speak dogmatically about what one sees in them. Walcott has summarized his results in his restoration of the appendages of Calymene (1918, pl. 33). The coxopodite supports a slender six-jointed endopodite as in Triarthrus, dorsal to which is a short setiferous epipodite which differs from the exopodite of Triar- thrus, in being less long, unsegmented, and in having shorter sete. Arising from the same part of the coxopodite with this epipodite is the bifurcate spiral branchia which has not been seen in this form in other trilobites. The evidence on which the existence of this organ is postulated consists of a series of sections across the thorax, the best of them figured by Wal- cott in his plates 2 and 3 (1881) and plate 27 (1918). The specimens sliced were all partially or quite enrolled, and in that position one would expect to find the appendages so displaced that it would be only rarely that a section would be cut, either by chance or design, in such a direction as to show any considerable part of any one appendage. ‘This expectation has proved true in regard to the endopodites, the sections rarely showing more than two or three consecutive segments. Sections like those shown in figures I and 2 in plate 2 (1881) seem to be unique. On the other hand, there are numerous slices showing the so-called spiral branchie. They show for the most part as a succession of rectangular to kidney-shaped spots of clear calcite.t Usually these clear spots are isolated, not confluent, but in a small number of specimens, perhaps three or four, the spots are connected in such a way as to show a zig-zag band which suggests a spiral. Such an explanation is of course entirely reasonable, but it would be surprising if so slender a spiral should be cut in such a way as to exhibit the large series of successive turns shown in many of these thin sections. Continuous sections of such organs should be no more common than continuous sections of endopodites. One of the arguments against the interpretation of these series of spots as sections across spiral arms is that of probabilities. It is known from flattened specimens that Nceo- Ienus, Kootenia, Ptychoparia, Triarthrus, and Cryptolithus all have a single type of exopo- dite, consisting of a simple setiferous shaft. All these genera have been examined in a way that permits no doubt about the structure, and no trace of spiral arms has been de- tected. On the other hand, Walcott found spiral arms in three‘unrelated genera, Calym- ene, Ceraurus, and Acidaspis, all of the trilobites in which he found exopodites by the method of sectioning. What are the probabilities that genera of three different families, studied by means of sections, should agree in having a type of exopodite different from that of the five genera about whose interpretation there can be no doubt? Another argument against the interpretation of the sections as spirals is that in any one line the individual spots are of roughly uniform size. This means of course that the spiral has been cut by a plane parallel to the tangent plane. This might happen once, just as once Doctor Walcott cut all six segments of a single endopodite, but that it should happen *In looking at Walcott’s figures of 1881, it should be remembered that the dark portions of the figures are clear calcite in the specimens, while the light part is the more or less opaque matrix. CALYMENE AND CERAURUS. 49 repeatedly is highly improbable. Moreover, there is a limit to the diameter of the section which may be made from these slender spirals. Most of the spots have one diameter about one half greater than the other, but others are from three to six times as long as wide. These last could obviously be cut only from a very large spiral, and they are therefore interpreted by Walcott as setze of epipodites. Yet all gradations are found among the sec- tions, from the long sete to the short dots. (See pl. 27, 1918.) In referring to one slice, Walcott says (1918, p. 152): In the latter figure and in figure 13, plate 27, the sete of several epipodites appear to have been cut across so as to give the effect of long rows of sete. The same condition occurs in specimens of Marrella when the sete of several exopodites are matted against each other. Fig. 12.—A slice of Ceraurus pleurexanthemus in which the exopodite happened to be cut in such a way as to show a part of the shaft and some of the sete in longitudinal section. Specimen 80. X 4. This is certainly an apt comparison, and equally true if Neolenus, Triarthrus, or Cryp- tolithus were substituted for Marrella. : Now consider the “epipodites.” They are well shown in Calymenc in the specimens illustrated on plate 27, figure 11 (1918), and plate 3, figure 3 (1881), and less clearly in one or two others. Slices 22 (pl. 27, fig. 12, 1918) and 80 (our fig. 12) show what is called the same organ in Cerawrus. It will be noted that all of these slices are cut in the same way, that is, more or less parallel to the under surface of the head, or, at any rate, on a plane parallel to a plane which would be tangent to the axial portion of the coiled shell. The sections which show the spirals best are those which are cut by a plane perpendicular to the long axis of the body. If one were to attempt to cut an enrolled Tviarthrus in such a way as to get a section showing the length of the setae, one would not cut a section per- pendicular to the axis of the animal, nor, in fact, would he cut one parallel to the ventral plane, but it is obvious that in this latter type of section he would stand a better chance of finding a part of the plane of the exopodite coincident with the plane of his section than in the former. And that seems to be what has happened in these sections of Calymene and Ceraurus. If the exopodites were preserved, transverse sections were bound to cut across many sets of fringes, and the resultant slice would show transverse sections of the setae as a series of overlapping spots. A few fortunately located sections in a more nearly hori- 50 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. zontal plane might cut the setae and occasionally the shaft of one or more exopodites in the longitudinal plane, and the resulting effect would produce the so-called “epipodites.”’ A careful study has shown that no one of these epipodites is complete, and they do not have the palmate form shown in Walcott’s figures. And the last and most important argument against the spiral appendages is that cer- tain slices, of both Calymene and Ceraurus, show definitely exopodites of exactly the type found in other trilobites. These are discussed later in the detailed description of the vari- ous slices. If these series of spots are interpreted on the basis of the known structure of Triarthrus, they are of course a series of sections through the sete of the exopodites. It will be shown in Part IV that these setee are not circular in section, but flattened, in Cryptolithus even blade-like, and that they overlap one another. A section across them would give the same general appearance as, for instance, that shown in figures 4, 6, 9, and 10 of Walcott’s plate 3 (1881). When both endopodites and the “spiral branchiz’’ are present in the same section (pl. 1, fig. 4; pl. 2, figs. 1, 2), the “spiral branchiz’’ are dorsal to the endopodites, as the setzee of the exopodites would be expected to be. The specimens which show the clear spots connected, and which suggest a spiral (pl. 3, fig. 5), may seem at first sight to bear evi- dence against this interpretation, but one has only to think of the effect of cutting a sec- tion along the edge where the sete are attached to the shaft of the exopodite of Triar- thrus to see that such a zigzag effect is entirely possible. One would expect to cut just this position only rarely, and, in fact, the zigzags are seen in only three or four sections. The bifurcation of the basal segment of the “spiral branchie” (pl. 3, fig. 10, 1881) is probably more apparent than real, if indeed these basal segments have anything to do with the succeeding one. A second peculiarity of Calymene, shown in Walcott’s restoration, is the great enlarge- ment of the coxopodites and of the distal segments of the endopodites of the fifth pair of appendages of the cephalon. This is based on the sections of plate 3, figures 6, 7, 8, 9, 10 (1881). After a study of the specimens I regret to find myself still unconvinced that the posterior cephalic appendages were any larger than those in front. Ventral Membrane. The most striking value of the thin sections of Cerawrus and Calymene, and therein they have a great superiority over all the other forms so far investigated, is that they show the extent of the body cavity and the position, though not the substance, of the ventral membrane. ‘Transverse sections through Ceraurus (Walcott’s pl. 1, figs. 1-5; pl. 2, figs. I, 3, 1881) and Calymene (pl. 3, figs. 9, 10, 1881) show that the body. cavity was almost entirely confined to the axial lobe. The longitudinal sections of Ceraurus (pl. 2, figs. 6, 8; pl. 4, fig. 8) and of Calymene (pl. 2, figs. 5, 7; pl. 5, figs. 1-4) show that the ventral membrane was exceedingly thin and was wrinkled transversely when the shell was enrolled. The specimens of figures 1-3, plate 5 (1881) show the form of the’ ventral membrane more distinctly than any of the others. The section of figure 1 was cut just inside the dorsal furrow on the right side, and figure 2, which is on the opposite side of the same slice, is almost exactly on the median line. Figure 3 shows a section just inside the left dor- sal furrow. Section 2 did not cut any of the appendages, and the ventral membrane is CALYMENE AND CERAURUS. 51 shown as a thickened, probably chitinous sheet thrown into low sharply crested folds equal in number to, and pointing in a direction just the reverse of, the crests of the segments of the thorax. Under the pygidium, where there would of course be less wrinkling, the folds are hardly noticeable. In the actual specimens one sees more plainly than in the figures the line of separation between the ventral membrane and the appendages, but the state of preservation of everything beneath the dorsal shell is so indefinite that one does not feel sure just what the connection between the appendages and the membrane was. In the origi- nal of figure 5, plate 2, which seems to have heen cut so as to cross the appendages at their line of junction with the ventral membrane, there appear to be narrow chitinous (?) plates extending from the ventral membrane to the dorsal test. Appendifers. In Ceraurus there are regular calcareous processes which extend down from the dor- sal test just inside the line of the dorsal furrow, and which undoubtedly serve as points of attachment of the appendages. These processes, which for convenience I have desig- nated as “appendifers,’ are broken off in most specimens showing the lower surface of Ceraurus pleurexanthemus, but on certain ones cleaned with potash they are well preserved. Doctor Walcott showed them well in his figures of the lower surface of this species (1875, pl. 11; 1881, pl. 4, fig. 5), while the attempt of Raymond and Barton (1913, pl. 2, fig. 7) to show them by photography was not so successful. There is one pair of appendifers on each of the thoracic segments and four pairs on the pygidium. On the cephalon there is one pair under the neck furrow, and a pair under the posterior glabellar furrows. These are not concealed by the hypostoma. Further for- ward, and completely covered by the hypostoma, are two much less strongly developed but similar ones, so that there are in all four pairs of appendifers on the cephalon, though it is extremely doubtful if the appendages were articulated directly to all of them. Ona specimen of Ceraurus pleurexanthemus 30 mm. long on the median line, the dorsal furrows are 7.5 mm. apart at the anterior end of the thorax, and the tips of the appendifers of this segment are only 4 mm. apart. Each consists of a straight slender rod with a knob- like end projecting directly downward from the dorsal test, and supported by a thin cal- careous plate which runs diagonally forward to the anterior edge of the segment directly under the dorsal furrow. On the pygidium three pairs of the appendifers have this form, while the fourth pair consist of low rounded tubercles which are concealed by the doublure. These appendifers are probably cut in many of Walcott’s sections of Ceraurus, but owing to the state of preservation it is not always possible to determine what part is appendage, what part is body cavity, and what part is appendifer. Nearly forty years ago Von Koenen (1880, p. 431, pl. 8, figs. 9, 10) described and figured the appendifers of Phacops latifrons. He found them to be calcareous pro- jections on the hinder margin of each segment, converging inward, and about 1.5 mm. long. He correctly considered them as supports (Sttitzpunkte) for the feet. Appendifers are well developed also in Pliomerops, and in well preserved specimens of Calymene senaria from Trenton Falls they are present, but instead of being rod-like processes, they are rather thick, prominent folds of the shell. They are also well shown in some of the thin sections. A specimen of Triarthrus (No. 229, our pl. 5, fig. 2) has broad processes extending downward from the lower side of the test below the dorsal furrows, much as in Calymene, and the individual of Cryptolithus shown in plate 8, figure 52 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. I, possesses slender appendifers. Two other specimens (Nos. 237 and 242) show them quite well. They were probably present in all trilobites, but seldom preserved. The appen- difers have the same origin as the entopophyses of Limulus, and like them, may have rela- tively little effect on the dorsal surface. Calymene senaria Conrad. (Text figs. 13-16, 23.) Illustrated: Walcott, Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pl. 1, figs. 6-10; pl. 2, figs. 5-7, 10; pl. 3, figs. 1, 3, 8-10; pl. 4, figs. 3, 7; pl. 5, figs. 1-6; pl. 6, figs. I (restoration), 2;—Proc. Biol. Soc. Washington, vol. 9, 1894, pl. 1, fig. 7 (restoration) ;—Geol. Mag., dec. 4, vol. 1, 1894, pl. 8, figs. 7, 8;— Smithson. Misc. Coll., vol. 67, 1918, pl. 26, figs. 1-7, 9-13; pl. 27, figs. 4, 5 (not 5a), 11 (not 12, Ceraurus), 13, 14, 15 (not Ceraurus); pl. 28, figs. 7, 8; pl. 33, fig. 1 (restoration); pl. 34, fig. 2; pl. 35, fig. 6—Dames, N. Jahrb. f. Min., etc., vol. 1, 1880, pl. 8, figs. 1-5.—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 11, figs. 19-32; pl. 12, figs. 33-41—Packard, Amer. Nat., vol. 16, 1882, p. 796, fig. 12—Bernard, The Apodide, 1892, text figs. 50, 52, 54;—Quart. Jour. Geol. Soc., London, vol. 50, 1894, text figs. 13, 15, 17.— Géhlert, Bull. Soc. Géol. France, ser. 3, vol. 24, 1896, fig. 12—Beecher, Amer. Jour. Sci. vol. 13, 1902, pl. 5, fig. 7. In both of Walcott’s accounts (1881, 1918) of the appendages of Calymene and Ceraurus, he has described them together, so that those who have not taken time to study the illustrations and disentangle the descriptions are very apt to have a confused notion in regard to them. I have therefore selected from the original specimens those slices of Calymene which are most instructive, and bearing in mind the probable appearance of the appendages of an enrolled Triarthrus, have tried to interpret them. In such a method of study, I have of course started with a pre-formed theory of what to expect, but have tried to look for differences as well as likenesses. Cephalic Appendages. Antennules.—The evidence of antennules rests on a single slice (No. 78). The appen- dage in question is exceedingly slender and arises at the side of the hypostoma near its posterior end. It shows fine, slender segments, and curves first outward and then forward. If it is in its natural position, it is not an antennule, but the endopodite of the second or third pair of cephalic appendages. It is short, only about one-third the length of the hy- postoma, but is doubtless incomplete. The two distal segments show a darker filling, indi- cating that they were hollow. Judging from analogy with other trilobites, the appendage is probably an endopodite and not an antennule. There can be no reasonable doubt, how- ever, that Calymene possessed antennules. Some idea of the form of the coxopodites of the cephalic appendages may be obtained from sections which cut in approximately the plane of the hypostoma. Such sections are shown in Walcott’s photographs (pl. 26, figs. 4, 6, 11, 1918). Specimens 50 (fig. 4, our fig. 13), 51 (fig. 6), 6 (fig. 11), and 4o (our fig. 14) agree in showing two pairs of slender coxopodites which are attached at the sides of the hypostoma and run backward parallel and close to it, and two pairs of larger coxopodites which are behind the hypostoma, although the point of attachment of the third pair is in front of its tip. The anterior pair are appar- ently under-developed and no longer function as mouth parts, while the posterior two pairs are large and armed on their inner ends with spines. Specimen 78, which has already been mentioned in connection with the antennules, shows a second very slender appendage back of the so called antennule, which is equally slender, but is directed outward instead of for- CALYMENE. 53 ward. It seems not improbable, from their position and similarity, that these two are the endopodites of the first two appendages on one side of the hypostoma.. Specimen 6 shows rather inadequately the endopodites of the second and third cephalic appendages. I have not found other slices showing endopodites of the cephalon. Walcott, in both his restora- tions, has shown enlarged, paddle-shaped dactylopodites on the distal ends of the fourth cephalic endopodites. The evidence for this rests principally on three slices, No. 38 (pl. 26, figs. 9, 10), 53 (pl. 26, fig. 12), and 43 (pl. 26, fig. 13). Of these, No. 43 may be dis- missed at once as too poorly preserved to be interpreted. No. 53 does show a section of an appendage: which seems to have an unusually wide dactylopodite, but this slice presents no evidence at all as to the appendage to which the dactylopodite appertains, nor can one even be sure that there has not been a secondary enlargement. Specimen 43 shows this Fig. 13.—Slice through Caylmene senaria in the plane of the hypostoma, showing the very slender coxopodites beside that organ, the spines on the inner end of one of the maxillule, and the anterior position of the at- tachment of all these appendages. From a photographic enlargement. Specimen 50. X 4. Fig. 14.— Slice through the hypo- stoma and _ tho- rax of Calymene senaria Conrad, showing the small size of the coxop- odites nearest the hypostoma. Shell in black, append- ages and filling of abdominal cavity dotted. From a photographic en- largement. Speci- men 40. X 3.8. Fig. 15.—Transverse section of Calymene, showing method of articulation with the ap- pendifer. The shell is in solid black, the filling of the append- age and appendifer stippled. Traced from a photographic enlargement of the slice. Specimen 63. XX 7. feature much less definitely than is indicated by the published photograph and drawing. The segment in question is strongly curved, with a constriction possibly dividing it into two. If it is in its natural position in this section, it obviously belongs to one of the thoracic segments and not to the cephalon. With evidence of difference so unsatisfactory, ‘I prefer to reconstruct the posterior cephalic endopodites on the same plan as those of the thorax. Exopodites—Walcott admits that there is no direct evidence of spiral exopodites in the cephalon of Calymene. No one of the sections cutting through the plane of the hypos- toma shows any trace of appendages which could be interpreted as exopodites. Thoracic Appendages. The large coxopodites of the anterior thoracic appendages are well shown in many speci- mens cut longitudinally, of which Nos. 23, 50, and 55 may be mentioned, since photographs of them have been published by Walcott (pl. 26, figs. 1-4, 1918). The endobases of all taper toward the proximal ends. Transverse slices show sections of the coxopodites which 54 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. are no wider than those in longitudinal sections, indicating that they were not compressed but probably cylindrical. This is borne out by an individual (pl. 28, fig. 7, 1918) which is not a slice but an actual specimen, the body cavity of which was hollow, and, opened from above, shows the impressions of the last two coxopodites of the cephalon, and the first four of the thorax. One transverse section (No. 63, see our fig. 15) is especially valuable, as it shows the method of articulation of the coxopodites with the dorsal skeleton. Another specimen (No. 73) shows that appendifers are present in Calymene, and while the appendifer does not retain its original form in slice No. 63, the section does show clearly that there was a notch in the inner (upper) side of the coxopodite into which the lower end of the appen- difer fitted, thus giving a firm, articulated support for the appendage. This notch appears to be slightly nearer the outer than the inner end of the coxopodite, and since it must have made a kind of ball-and-socket joint, considerable freedom of movement was allowed. The appendage must have been held in place by muscles within the coxopodite and attached to the appendifer. No slice which I have seen shows a continuous section through all the segments of an endopodite, but.many, both longitudinal and transverse, show one, two, or as many as three segments. Such sections as No. 120 show that the endopodites of the thorax were slender and composed of segments of rather uniform diameter. Other sections, notably No. 83, 154, and 111, show that they tapered distally, and bore small spines at the outer end of each segment. The exopodites of course furnish the chief difficulty in interpretation. Doctor Wal- cott finds two sets of structures attached to the coxopodite, a long, slender, spiral exopo- dite, and a short, broad epipodite with a fringe of long sete. Since he has given the same interpretation for Calymene, Ceraurus, and Acidaspis, I have considered the question of all three together on a preceding page (p. 48),and given my reasons for regarding both struc- tures as due to sections in different directions across setiferous exopodites. : Sections like those shown in figures 11, 13, and 14 of plate 27 (1918) happen to be cut in or near the plane of the setee of an exopodite, and so show hairs of considerable length. Such sections are, as would be expected, very few in number, while sections like those shown on figures 4, 5, 7, and 9 of plate 27, which cut the setze more nearly at right angles, are very common. Slices which give any definite idea of the form of the shaft of the exopodite are exceedingly rare. Perhaps the most satisfactory one is, No. 23 (pl. 3, fig. 3, 1881), which shows the proximal part of a long, slender, unsegmented shaft, with the bases of a number of slender sete. The organ is not complete, as would be inferred from the pub- lished figure, but the section cuts diagonally across it, and the total length is unknown. It is directed forward, like the exopodites of Neolenus, but whether or not this is a natural position is yet to be learned. The proximal, non-setiferous portion of the exopodite is evidently at an angle with the setiferous part. Another similar exopodite is apparently shown by specimen 29 (pl. 3, fig. 9, 1881, which has a similar angulated shaft and just a trace of the bases of the sete. Pygidial Appendages. That appendages were present under the pygidium is shown by longitudinal sections, but nothing is known of the detail of structure. CALYMENE. 55 Relation of Hypostoma to Cephalon in Calymene. In Calymene the shape of the hypostoma bears little relation to the shape of the gla- bella, and it is relatively smaller, both shorter and narrower, than in Ceraurus. In shape, neglecting the side lappets at the front, it is somewhat rectangular, but rounded at the back, where it is bifurcated by a shallow notch. The anterior edge has a narrow flange all across, which is turned at almost right angles to the plane of the appendage, and which LZR Sa Se IN SSN SARA Gy, Fig. 16.—Restoration of Calymene senaria Con- rad, based upon data obtained from the study of the translucent sections made by Doctor Walcott. Prepared by Doctor Elvira Wood, under the su- pervision of the author. About twice natural size. fits against the doublure of the free cheeks at the sides and against the epistoma in the middle. The side lappets show on their inner (upper) surface shallow pits, one on each lappet, which fit over projections that on the dorsal surface show as deep pits in the bottom of the dorsal furrows in front of the anterior glabellar furrows. The appendifers on the head in Calymene take the form of curving projections of shell underneath the gla- bellar and neck furrows, and owing to the narrowness of the hypostoma, all these are visi- ble from the ventral side, even with it in position. This shield extends back about 0.6 of 56 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. the length of the cephalon, and to a point a little behind the second glabellar furrow from the back of the head. In Doctor Walcott’s restoration of Calymene he has represented all four pairs of bira- mous appendages as articulating back of the posterior end of the hypostoma. I think his sections indicate that the gnathobases of two pairs of these appendages rested alongside or beneath it, and in particular, the longitudinal sections (1881, pl. 5) would appear to show that the mouth was some distance in advance of its posterior end. Restoration of Calymene. @RextaiioiriGs)) From what has been said above, it is evident that for a restoration of the appendages of Calymene considerable dependence must be placed upon analogy with other trilobites. Nothing is positively known of the antennules, the exopodites of the cephalon, or any ap- pendages, other than coxopodites, of the pygidium, but all were probably. present. It is inferred from the slices that the first two pairs of cephalic appendages were poorly devel- oped, the endopodites short and very slender, the coxopodites lying parallel to the sides of the hypostoma and nearly or quite functionless. The gnathites of the last two pairs of cephalic appendages are large, closely approximated at their inner ends, and bear small tooth-like spines. The endopodites are probably somewhat better developed than the an- terior ones and more like those on the thorax. ’ The coxopodites of the thorax appear to have had nearly cylindrical endobases which tapered inward. The endopodites were slender, tapering gradually outward, and probably did not extend beyond the dorsal test. Small spines were present on the distal end of each segment. Each exopodite had a long, slender, unsegmented shaft, to which were at- tached numerous long, overlapping, flattened sete. The shaft may have been angulated near the proximal end, and may have been directed somewhat forward and outward as in Neolenus, but the evidence on this point is unsatisfactory. The number of pairs of ap- pendages is that determined by Walcott from longitudinal sections, namely, four pairs on the cephalon beside the antennules, thirteen pairs in the thorax, and nine pairs on the pygidium. Calymene sp. ind. (Pl. 6, figs. 4, 5.) Illustrated: Walcott, Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pl. 6, figs. 5a, b;—Proc. Biol. Soc. Washington, vol. 9, 1894, pl. 1, fig. 10;—Geol. Mag., dec. 4, vol. 1, 1894, pl. 8, fig. 10;—Smithson. Misc. Coll., vol. 67, 1918, pl. 36, figs. 1, 2, 2a-d—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 12, figs. 44a, b. In the United States National Museum there is a thin piece of limestone, about 3 inches square, which has on its surface eight jointed objects that have been called legs of trilobites. Two of these were figured by Walcott (1881, pl. 6, fig. 5). The slab contains specimens of Dalmanella and Cryptolithus, in addition to the appendages of trilobites, and is said by Doctor Ulrich to have come from the upper part of the Point Pleasant formation (Trenton) on the bank of the Ohio River below Covington, Kentucky. The specimens are all endopodites of long slender form, similar to those of Triarthrus, but since that genus does not occur in the Point Pleasant, it is necessary to look upon some other trilobite as the former possessor of these organs. Both /sotelus and Calymene occur CERAURUS. 57 at this horizon, and as the specimens obviously do not belong to [sotelus or Cryptolithus, it is probable that they were formerly part of a Calymene. All the endopodites are of chitinous material, and the various specimens show, accord- ing to the perfection of their preservation, from four to six segments. The endopodite as a whole tapers but slightly outward, and the individual segments are of nearly equal length. They appear to be but little crushed, and are oval in section, with a crimped anterior and posterior margin. One or two show a median longitudinal ridge, such as is seen in some appendages of Triarthrus. Each segment is parallel-sided, with a slight expansion at the distal end, where the next segment fits into it. Under the heading ‘Ordovician Crustacean Leg,” Walcott (1918, p. 154, pl. 36, figs. I, 2) has recently redescribed these specimens, and thinks that they do not belong to Calym- ene, nor, indeed, to any trilobite. He concludes that they were more like what one would expect in an isopod. Passing over the fact that the oldest isopod now known is Devonian, the fossils in question seem to me quite trilobite-like. Walcott says: ” The legs are associated with fragments of Calymene mecki but it is not probable that they belong to that species; if they did, they are unlike any trilobite leg known to me. The very short coxopodite and basopodite are unknown in the trilobites of which we have the legs, as they are fused into one joint forming the long protopodite in the trilobite. The distal joint is also unlike that of the trilobite legs known to us. A great deal of Doctor Walcott’s difficulty probably arises from his homology of the coxopodite of the trilobite with the protopodite of the higher Crustacea. The coxopodite of the trilobite is not fused with the basipodite, this latter segment always remaining free. Indeed, Walcott himself says of Neolenus (1918, p. 128): Each thoracic leg (endopodite) is formed of a large elongate proximal joint (protopodite), four strong joints each about 1.5 times as long as wide (basopodite, ischiopodite, meropodite and carpopodite); two slender elongate joints (propodite and dactylopodite) and a claw-like, more or less tripartite termination. Walcott’s drawing (pl. 36, fig. 1) is a composite one, and while it shows eight seg- ments, I was not able to count more than seven on any of the specimens themselves. In regard to the terminal segment, the dactylopodite of the limb shown in his plate 36, figure 2, is unusually long, and a comparison with other photographs published on the same plate shows that such long segments are unusual. Proof that these are appendages of a Calymene is of course wanting, but there is no particular reason so far to say that they are not. Measurements: Two of the more complete specimens, each showing six segments, are each 8 mm. long. Somewhat similar to the specimens from Covington are the ones described by Eich- wald (1825, p. 39, 1860, pl. 21), the specimens being from the Silurian of Gotland. The figure copied by Walcott (1881, pl. 6, fig. 4) has never been looked upon as entirely satisfactory evidence of the nature of the specimen, and so far as I know, the fossil has not been seen by any modern investigator. Ceraurus pleurexanthemus Green. @Erustext figs ie. 17-19)/21, 225 247 20; 20!) Illustrated: Walcott, Ann. Lyc. Nat. Hist. New York, vol. 11, 1875, pl. 11;—31st Ann. Rept. New York State Mus. Nat. Hist., 1870, pl. 1, fig. 3;—Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pl. 1, figs. 1-5; pl. 2, figs. 1-4, 6-8; pl. 3, figs. 2, 4-7; pl. 4, figs. 1, 2, 4-6, 8; pl. 6, fig. 3;—-Smithson. Misc. Coll., vol. 67, 58 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 1918, pl. 26, figs. 8, 14, 15; pl. 27, figs. 1-3, 5a, 6-9, 12 (not Calymene), (not 15, Calymene); pl. 28, figs. 1-5; pl. 34, fig. 1; pl. 35, fig. 7—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 10, figs. 1-18.— Bernard, The Apodide, 1892, text figs. 46, 51. Cephalic Appendages. No trace of antennules has yet been found. I find only three sections cut through the plane of the hypostoma of Cerawrus which show anything of the cephalic appendages, and no one of them is very satisfactory. The best is No. 22, the one figured by Walcott (pl. 3, fig. 2, 1881; pl. 27, fig. 12, 1918), but one should remember that this section is not actually cut in the plane of the hypostoma but is a slice diagonally through the head, cutting through one eye and the posterior end of the hypostoma. It shows what seem to be the coxopodites of the second, third, and fourth pairs of cephalic appendages, the exopodites of the third and fourth pairs, and the metas- toma. If this interpretation is correct, the first pair of gnathites lay alongside the hypos- Fig. 17.—Transverse section of Ceraurus Fig. 18.—Slice of Ceraurus pleurex- pleurexanthemus, showing the relation of anthemus, showing a nearly continu- the coxopodite to the appendifer. Traced ous section of an endopodite and an from a photographic enlargement of the exopodite above it. The latter is so cut as to show only the edge of the shaft and the bases of a few sete. Traced from a photographic enlarge- ment. Specimen I1I. X 4. slice. Specimen 128. X 4.5. toma or under its edge, and were feebly developed, the second pair were attached in front of the tip of the hypostoma, curved back close to it, and their inner ends reached the sides of the metastoma. The third and fourth pairs were back of the metastoma, the third pair was stronger than the second, and the fourth probably like the third. Specimen 92 shows traces of the slender endopodites belonging to the cephalon, but no details. Specimen 22 shows on one side exopodites (epipodites of Walcott) belonging to the third and fourth cephalic appendages. That belonging to the third shows some long setee and a trace of the shaft, while the one on the fourth appendage (third coxopodite) has a portion of a broad shaft and a number of long sete. Jt should again be remembered that the slice does not cut through the plane of the exopodite, but across it at a low angle, so that a part but not all of the shaft is shown. On the other side of this slice there is a fairly good section of one of the thoracic exopodites. It is, however, turned around in the opposite direction from the others, as would be expected in an enrolled specimen. Specimens 4 and 5 (pl. 1, figs. 4, 5, 1881) are slices cut diagonally through the head of Ceraurus, in front of the posterior tip of the hypostoma. They show fragments of endopodites and exopodites which may be interpreted as practically identical in form with those oi the thorax. Due to the diagonal plane in which the section is cut, slice 5 shows CERAURUS. 59 the coxopodites of two pairs of appendages, one lying nearer the median cavity than the other. It is extremely difficult to visualize the interpretation of such sections. Thoracic Appendages. A transverse section through a thoracic segment (No. 128, our fig. 17) shows the re- lation of coxopodite to appendifer to be the same as in Calymene, the upper side of the coxopodite having a notch a little outward from the middle. After seeing that specimen, it is possible to understand slice No. 168, which shows longitudinal sections through a num- ber of coxopodites of the thorax, with fragments of both exopodites and endopodites artic- ulated at the distal ends. These and longitudinal vertical sections like No. 18 (pl. 2, fig. 8, 1881) show that the endobases taper inward, and the general uniformity in width in sections taken at various angles indicates that the coxopodites were not greatly flattened. A unique slice (No. 111, pl. 2, fig. 2, 1881; pl. 27, fig. 1, 1918; our fig. 18) shows a nearly complete thoracic endopodite, and above it a part of the proximal end of the exopo- dite of the same segment. When one considers that out of over two thousand sections only this one shows the six successive segments of an endopodite, one realizes how futile it is to expect that dozens of the equally slender “‘spirals’ should be cut so as to show prac- tically all their turns. This endopodite is slender, all the segments have nearly the same length and diameter, though there is a slight taper outward, each segment is expanded distally for the articula- tion of the next, and there are small spines on the distal ends of some of them. There is probably a terminal Spine present, though it is neither so long nor so plainly visible as in Walcott’s photograph. The exopodite on this same specimen was evidently cut diagonally across near the setif- erous edge, showing a section through the shaft and the bases of seven sete (fig. 18). This section is so exactly what would be obtained by cutting similarly an exopodite of either Neolenus or Triarthrus that it should in itself dispose of the “‘spiral-exopodite’ theory. Several sections have already been illustrated showing sections across the setze of the exopodites (pl. 3, figs. 4-6, 1881; pl. 27, figs. 3, 4, 9, 1918), and similar sections are not uncommon. Only a very few, however, show sections in the plane of the exopodite. If only No. 111, described above, were known, it would be inferred that the exopodite had a slender shaft as in Calymene, but another good slice, No. 80 (fig. 12, ante) shows that the blade was rather broad, though not so broad as in Neolenus. The other specimen is No. 22, which has already been discussed. The thoracic exopodite of this specimen has been very incorrectly figured by Walcott, as it shows no such palmate shaft as he has indicated, but a long blade-like one is outlined, though its entire width is not actually shown. Pygidial Appendages. Sections 14 and 18 (pl. 2, figs. 4, 8, 1881) prove the presence under the pygidium of three pairs of appendages, the coxopodites and fragments of endopodites of which are shown. Nothing is known of the exopodites. Relation of Hypostoma to Cephalon. In Ceraurus the body portion and posterior end of the hypostoma are roughly oval, about as wide as the glabella at its broadest part, and the posterior edge extends back to 60 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. within 0.5 to 1 mm. of the neck furrow. The posterior pair of appendifers are behind the hypostoma, while the second pair are in front of its posterior end but escape being covered by it on account of its oval shape. At the anterior end the hypostoma is widened by the presence of two side lappets which extend beyond the boundaries of the glabella. In both Ceraurus and Cheirurus the anterior edge of the hypostoma fits against the doublure at the anterior margin of the head and the epistoma is either entirely absent or is so narrow as not to be seen in specimens in the ordinary state of preservation. A section across the cephalon of Ceraurus pleurexanthemus at the horizon of the eyes shows the sides of the hypostoma fitting closely against the sides of the glabella (Walcott’s pl. 1, fig. 1). Further back on the head it is not in contact with the dorsal test, and the gnathobases extend beneath it. Restoration of Ceraurus pleurexanthemus. (PI. 11; text fig. 19.) The restoration of the appendages of Ceraurus pleurexanthemus is a tentative one, based upon a careful study of the translucent sections prepared by Doctor Walcott. In no case Fig. 19.—Restoration of a transverse section of the thorax of Ceraurus pleurexanthemus Green, showing the relation of the appendages to the appendifers and the ventral membrane. The probable positions of the heart and alimentary canal are indicated. among these sections is the actual test of any appendage preserved, and the real form of each part is generally obscured by the crystallization of the calcite which fills the spaces formerly occupied by animal matter. No section shows anything which can be identified as any part of the antennules, so that these organs have been supplied from analogy with Tviarthrus. There are undoubtedly four pairs of biramous cephalic appendages, but their points of attachment are not so obvious. There are two pairs of conspicuous appendifers on the posterior part of the cephalon and another pair almost concealed by the hypostoma. It is probable that the appendages of the cephalon were not attached directly beneath them, as the four pairs have to be placed within the space occupied by the three pairs of appendifers. As the mouth is in front of the posterior end of the hypostoma, the gnathites of the first pair of biramous appendages may have extended beneath that organ, or they may have lain beside it, and only become functional when the hypostoma was dropped down in the feed- ing position. The second pair of gnathites reached just to the tip of the hypostoma, and the other two pairs seemingly curved backward behind it. The points of attachment on the thorax, as shown clearly in sections, were directly be- neath the lower ends of the appendifers. The endopodites were long enough to reach to or a little beyond the outer extremities of the pleural spines, while the exopodites were apparently somewhat shorter. Each endopodite consisted of six short, fairly stout seg- ments, each with at least two spines on the somewhat expanded distal ends. The exact CERAURUS. 61 form of the exopodites could not be made out. The shaft was apparently rather short, unseg- mented, and fairly broad. The setee appear from the sections to have been more or less blade-shaped and to have overlapped, as do those of the exopodites of Cryptolithus. Judg- ing from their position in the sections, the setee not only bordered the posterior side of the shaft, but radiated out from the end as well. The pygidium shows three pairs of functional appendifers, hence three pairs of appen- dages have been supplied. There is a fourth pair of rudimentary appendifers, but as they are beneath the doublure they could not have borne ambulatory appendages. Tur APPENDAGES OF ACIDASPIS TRENTONENSIS WALCOTT. (GAB Oy anter,: (6),)) A single individual of Acidaspis trentonensis, obtained from the same locality and hori- zon as the specimens of Triarthrus and Cryptolithus, when cleaned from the ventral side shows a number of poorly preserved endopodites which seem very similar in shape and position to those of Triarthrus. One endopodite on the right side of the head and the first five on the right side of the thorax are the best shown. All are slender, are directed first forward at an angle of about 45° with the axis, then, except in the case of the cephalic appendage, turn backward on a gentle curve and extend a little distance beyond the margin of the test, but not as far as the tips of the lateral spines of the thoracic segments. The individual segments of the endopodites can not be seen clearly enough to make any measurements. On the fourth and fifth endopodites of the thorax, some of the seg- ments seem to be broad and triangular as in Tviarthrus. All that can be seen indicates that Acidaspis had appendages entirely similar to those of Tviarthrus, but perhaps not quite so long, as they seem not to have projected beyond the limits of the lateral spines. There are no traces of antennules nor, unfortunately, of exopodites. Measurements: Length 8 mm. Walcott (1881, p. 206) stated that his sections had shown the presence in this species of legs “both cephalic and thoracic” and also the “spiral branchize.’’ His specimens were from the Trenton at Trenton Falls, New York. THE APPENDAGES OF CRYPTOLITHUS. Cryptolithus tessellatus Green. (Pl. 6, fig. 7; pls. 7-9; text figs. 20, 25, 45, 46.) (See also Part IV.) Illustrated: Beecher, Amer. Jour. Sci., vol. 49, 1895, pl. 3. When Professor Beecher wrote his short article on the ‘‘Structure and Appendages of Trinucleus” (1895), he had only three specimens showing appendages. In his later work he cleaned several more, so that there are now thirteen specimens of Trinucleus = Cryp- tolithus available for study, though some of these do not show much detail. In his last and unpublished study, Beecher devoted the major part of his attention to this genus, and summarized his findings in the drawings which he himself made of the best individuals (text figs. 45, 46). Valiant (1901) stated that he had found a Trinuwcleus with antennze in the Frankfort shale south of Rome, New York. The specimen has not been figured. 62 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. None of the specimens shows much more of the appendages of the cephalon than the hypostoma and the antennules, so that we are still in ignorance about the mouth parts. The most striking characteristics of the appendages are as follows: the antennules are long, and turn backward instead of forward; none of the limbs projects beyond the margin of the dorsal test; the exopodites extend beyond the endopodites, reaching very nearly to the margin of the test; the endopodites are not stretched out at right angles to the axis, but the first three segments have a forward and outward direction as in Triarthrus, while the last four turn back abruptly so that they are parallel to the axis; the limbs at the anterior end of the thorax are much more powerful than the others; the dactylopodites of the endop- odites show a fringe of sete instead of three spines as in Triarthrus and Neolenus. All these would, as Beecher has already suggested, seem to be adaptations to a burrowing habit of life, the antennules being turned backward and the other appendages kept within the shelter of the dorsal test in order to protect them, and the anterior endopodites enlarged and equipped with extra spines to make them more efficient digging and pushing organs. Restoration of Cryptolithus. (Text fig. 20.) It should be definitely understood that the present figure is a restoration and not a drawing of a specimen, and that there are many points in the morphology of Cryptolithus about which no information is available, especially about the appendages under the central portion of the cephalon. The information afforded by all the figures published in this memoir is combined here. As gnathites are preserved on none of the specimens, those rep- resented in the figure are purely conventional. A person who is acquainted only with Crypiolithus preserved in shale, or with figures, usually has a very erroneous idea of the fringe It is not a flat border spread out around the front of the head, but stands at an angle about 45° in uncrushed specimens of most species. When viewed from the lower side, there is a single outer, concentric row of the cup-shaped depressions, bounded within by a prominent girder. This row is in an approxi- mately horizontal plane, while the remainder of the doublure of the fringe rises steeply into the hollow of the cephalon. Since the front of the hypostoma is attached to this doublure, it stands high up within the vault and under the glabella. Two specimens, Nos. 231 and 233, show something of the hypostoma, and they are the only ones known of any Ameri- can trinucleid. That of specimen 233, the better preserved, is very small, straight across the front, and oval behind. It seems that it is abnormally small in this specimen and | should not be surprised if in other specimens it should be found to be larger. In the Bohemian Trinucleoides reussi (Barrande), the oldest of the trinucleids, the hy- postoma is very commonly present, and is of the proper size to just cover the cavity of the glabella, seen from the lower side, and has, toward the anterior end, side flaps which reach out under the prominent glabellar lobes. This large size of the hypostoma would cause the antennules to be attached outside the dorsal furrows, and the position in which they are at- tached in the American species of Cryptolithus may be explained as an inherited one, since with the small hypostoma they might have been within the glabella, as in Triarthrus. The antennules are seen in three specimens, and in all cases are directed backward. The particular course in which they are drawn in the restoration is purely arbitrary. . The sec- ond pair of cephalic appendages are represented as directed downward and forward, since CRYPTOLITHUS. 63 ' in one or two specimens fragments of forward-pointing endopodites were seen near the front of the cephalon, and because in other trilobites the second pair of appendages is always directed forward. The remaining three pairs have a more solid basis in observed fact, for the two or three specimens retaining fragmentary remains of them indicate that they turn backward like those on the thorax, and that the individual segments are longer and more BO COS SCG65 eases @) C6e @) S JO fo) 2G © O X Ny IXgo060 Mi (@) "969200 AVES SD we ES hy oo NR Ay \ i Pe eS —aa, Sg Seen Le ZR yi SS ( Fig. 20—Cryptolithus tessellatus Green. A restoration of the appendages drawn by Doctor Elvira Wood from the original specimens and from the photographs made by Professor Beecher. X09. nearly parallel-sided than those of the more posterior appendages. The gnathites of all the cephalic appendages are admittedly purely hypothetical. None of the specimens shows them. As drawn, they are singularly inefficient as jaws, but if, as is suggested by the casts of the intestines of trinucleids found in Bohemia, these trilobites were mud-feeders, ineffi- cient mouth-parts would be quite in order. The appendages of the thorax and pygidium can fortunately be taken quite directly from the photographs of the dorsal and ventral sides of well preserved specimens. There 64 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. is of course a question as to the number and the exact form of those on the pygidium, but I think the present restoration is fairly well justified by the specimens. As would be ex- pected from the narrow axial lobe, the gnathobases of the coxopodites are short and small. SUMMARY ON THE VENTRAL ANATOMY OF TRILOBITES. COMPARISON OF APPENDAGES OF DIFFERENT GENERA, Since the appendages of Triarthrus, Cryptolithus, Neolenus, Calymene, and Ceraurus are now known with some degree of completeness, those of Jsotelus somewhat less fully, and something at least of those of Piychoparia, Kootema, and Acidaspis, these forms being representatives of all three orders and of seven different families of trilobites, it is of some interest to compare the homologous organs of each. All in which the various appendages are preserved prove to have a pair of antennules, four pairs of biramous limbs on the cephalon, as many pairs of biramous limbs as there are segments in the thorax, and a variable number of pairs on the pygidium, with, in the case of Neolenus alone, a pair of tactile organs at the posterior end. Each limb, whether of cephalon, thorax, or pygidium, consists of a coxopodite, which is attached on its dorsal side to the ventral integument and supported by an appendifer, an exopodite, and an endopo- dite. The exopodite is setiferous, and the shaft is of variable form, consisting of one, two, or numerous segments. The endopodite always has six segments, the distal one armed with short movable spines. Coxopodite. The coxopodite does not correspond to the protopodite of higher Crustacea, the basip- odite remaining as a separate entity. The inner end of the coxopodite is prolonged into a flattened or cylindrical process, which on the cephalon is more or less modified to assist in feeding, and so becomes a gnathobase or gnathite. The inner ends of the coxopodites of the thorax and pygidium are also prolonged in a similar fashion, but are generally some- _ what less modified. These organs also undoubtedly assisted in carrying food forward to the mouth, but since they probably had other functions as well, I prefer to give them the more non-committal name of endobases. In Triarthrus and Neolenus the endobases are flattened and taper somewhat toward the inward end. In Jsotelus, Calymene and Ceraurus, they appear to have been cylindrical. In other genera they are not yet well known. In all cases, particularly about the mouth, they appear to have been directed somewhat backward from the point of attachment. As it is supposed that these organs moved freely forward and backward, the position in which they occur in the best preserved fossils should indicate something of their natural position when muscles were relaxed. Cephalon. Antennules—Antennules are known in Triarthrus, Cryptolithus, Neolenus, and Ptycho- paria. In all they are long, slender, and composed of numerous segments, which are spinif- erous in Neolenus, and very probably so in the other genera. In Triarthrus, Neolenus, and Ptychoparia they project ahead of the cephalon, emerg- ing quite close together under the front of the glabella, one on either side of the median line. In Cryptolithus they turn backward beneath the body, but since only three or four specimens are known which retain them, it is possible that other specimens would show COMPARISON OF APPENDAGES. 65 that these organs were capable of being turned forward as well as backward. The proxi- mal ends of the antennules being ball-like, it is probable, as Doctor Faxon has suggested to me, that these “feelers’’ had considerable freedom of motion. The antennules of Triarthrus are apparently somewhat less flexible than those of the other genera, and have a double cur- vature that is seen among the others only in Ptychoparia. The proximal end of an an- tennule in Triarthrus is a short cylindrical shaft, apparently articulating in a sort of ball- and-socket joint. The proximal end in the other genera is still unknown. The points of attachment in Triarthrus seem to be under the inner part of the second pair of glabellar fur- rows. InCryptolithus they appear to be beside the anterior lobe of the glabella under what have long been known as the antennal pits. In the other genera the location is not definitely _ known, but in Neolenus it seems to be under the dorsal furrows near the anterior end of the glabella. Viewed from the under side, the point of attachment is probably always beside the middle or anterior part of the hypostoma, just behind the side wings. Paired biramous appendages.—Behind the antennules all the appendages except those on the anal segment are biramous, consisting of a coxopodite with an inward-directed endo- base and an outward-directed pair of branches, the exopodite above, and the six-jointed en- dopodite beneath. The basipodite really bears the exopodite, but the latter also touches the coxopodite. This structure has been seen in Triarthrus, Cryptolithus, Neolenus, Koo- tenia, Calymene, Ceraurus, and Ptychoparia. In Triarthrus, Neolenus, Acidaspis, Ptycho- paria, and Kootenia, the appendages extend beyond the margins of the dorsal test. In “Cryptolithus and Isotelus none (other than antennules) does so. In Jsotelus and Acidaspis only the endopodites have been seen. In Tvriarthrus, Calymene, Ceraurus, and Neolenus there are four pairs of appendages behind the antennules. The other genera probably had the same number, but the full structure of the under part of their cephala is not known. In Triarthrus the endopodites of the cephalon are slender, the individual segments parallel-sided, the inner ones flattened, the outer ones cylindrical in section. They project slightly beyond the edge of the cephalon when fully extended, and each terminates in three small spines. In Cryptolithus the endopodites of the cephalon are longer than those of the thorax, but with the possible exception of the first pair, are bent backward at the carpopodite, and do not ordinarily project beyond the brim of the test. In Neolenus the endopodites of the cephalon are rather thick and wide, but are long, project for- ward, and extend beyond the brim. The individual segments are flattened, probably com- pressed oval in section. The terminal segment of each is furnished with three strong spines at its distal end. In Calymene and Ceraurus the endopodites appear to consist of slender segments which are oval or circular in section. In Calymene Walcott believed the three distal segments of the last endopodites of the head to be greatly enlarged, giving these ap- pendages a paddle-like- form similar to some of the ‘appendages of eurypterids. The evi- dence for this does not seem to me to be good. The cephalic endopodites of Jsotelus are entirely similar to those of the thorax, and are rather short, consisting of a series of short cylindrical segments which do not taper greatly toward the distal end. The endopodites of the cephalon of Acidaspis, Kootenia, and Ptychoparia are still unknown. The exopodites of the cephalon seem in all known cases (Triarthrus, Cryptolithus, Neo- lenus, and Ceraurus) to be like those of the thorax. They point more directly forward in most cases, project beyond the margin of the head normally only in Triarthrus, and usually occupy the region under the cheeks (fixed and free). The endobases of the coxopodites of the appendages of the cephalon probably in all cases 66 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. function as mouth-parts (gnathites), and are especially modified for this purpose in Triar- thrus, being flattened, shoe-shaped in outline, and so arranged that they work over one an- other in a shearing fashion. While the more anterior of the coxopodites are attached in front of the posterior tip of the hypostoma, the gnathites of Triarthrus bend backward so that all are behind the hypostoma. In Calymene and Ceraurus, two or three pairs of the enathites are back of the hypostoma, and one or more pairs may be beside or under the hypostoma. In these genera the mouth is probably in front of the tip of the upper lip. In Jsotelus, the mouth seems to have been situated in the notch between the two branches of the hypostoma, and the gnathites of two or three pairs of the appendages probably worked under its forks. Since the length of the hypostoma differs in the various species of Jsotelus, there would be a variable number of gnathites projecting under its forks, according to the species. In this genus the gnathites are of the same long form, cylindrical in cross-section, as the endobases of the thoracic segments, but each is bowed back consider- ably from the point of attachment. The gnathites of Neolenus are like the endobases of the thorax, but broader. ‘The great length of the hypostoma makes it probable that the mouth was far back and that some of the gnathites were in front of it. The gnathites of Cryptolthus are unknown. Professor Beecher in his drawing shows some fragmients with toothed ends near the hypostoma, and it may be that they are inner ends of gnathites, but I see nothing to substantiate such an in- terpretation. Ii, as some suppose, Cryptolithus was a mud feeder, the gnathites were prob- ably poorly developed. Of ithe gnathites of Kootenia, Ptychoparia, and -lcidaspis also nothing is known. Thorax. In each genus there is a pair of appendages for each segment of the thorax. When the axial lobe is narrow, the enlobases of the coxopodites are small and short (Cryptolithus, Ceraurus, Calymene). When the axial lobe is wide, the endobases are long and stout (/sot- elus, Triarthrus). The exopodites always lie above and in front of the corresponding endop- odites. In Tviarthrus the two branches are of practically equal length. In Cryptolithus the exopodites are much the longer. In Neolenus, Calymene, Ceraurus, Kootenia, and Pty- choparia, the exopodites are shorter than the endopodites. The exopodites in Triarthrus consist of a proximal shaft, succeeded by numerous short segments, and ending distally in a long, grooved, somewhat spatula-shaped segment. Along the anterior margin of the shaft there are many small spines. Along the posterior margin there are numerous flattened seta: which all lie in one plane and which seem to be more or less united to one another like the barbs of a feather. The sete are short, not much longer than the width of one of the thoracic segments, and point backward and outward. In Cryp- tolithus the shaft does not seem to be made up of small segments, and is narrow, with a decided backward curve. The sete are considerably longer and much more flattened than in Triarthrus. In Calymene the state of preservation does not allow a very full knowledge of the exopodites, but they appear to have a slender, unjointed shaft and short and delicate setee. The coiled branches of the exopodites as described by Walcott seem to me to be only ordinary Triarthrus-like organs, and this, as I understand from Schuchert, was also the view of Beecher. In Ceraurus the exopodite seems to have been somewhat paddle-shaped, expanded at the distal end, and to have had rather thick, blade-like sete. The exopodite of Neolenus is decidedly leaf-like, and reminds one somewhat of the exites COMPARISON OF APPENDAGES. 67 of some of the phyllopods. The shaft is a broad unsegmented blade. The sete are slender, delicate, flattened, and a little longer than the width of the shaft. The exopodites of this genus point forward all along the body. In Kootenia the exopodites are like those of Neolenus, but with a narrower shaft. The exopodites of Ptychoparia appear to be very much like those of Triarthrus, but the shaft is probably not segmented. The endopodites of the thorax of Triarthrus, Cryptolithus, and Acidaspis show pro- gressive modification from front to back in the broadening of the individual segments and the assumption by them of a triangular form. Not only do the individual segments become more triangular from front to back, but more of the segments of each endopodite become tri- angular. This modification has so far been seen in these three genera only. The individ- ual segments, except the distal ones, seem to be flattened in all these genera. The distal end of the terminal segment of each endopodite of Triarthrus bears three small movable spines, and each of the segments usually bears three or more spines, located in sockets along the dorsal surface and at the anterior distal angle of each segment. The endopodite of Cryptolithus is bent backward at the carpopodite and this segment is always thickened. At the distal end of the dactylopodite there is a tuft of spines, the triangular segments have tufts of spines on their posterior corners, and there are groups of spines also in the neigh- borhood of the articulations. The endopodites of Ceraurus, Calymene, and Isotelus are all relatively slender, the seg- ments are parallel-sided, and there seems to be no particular modification from front to back of the thorax. The endopodites of /sotelus -are short, the entire six segments of one being but little longer than the coxopodite of the same appendage. The segments of the endopo- dites of Neolenus are mostly short and wide, and at the distal end of the terminal segment there are three stout spines. In Kootenia the endopodites are long and very slender. The endopodites of Ptychoparia are too poorly preserved to show details, and those of the thorax of Acidaspis likewise reveal little structure, but they seem to have the triangular modifica- tion, and to turn back somewhat sharply at about the position of the carpopodite. Pygidium. Beecher showed that in Triarthrus there was a pair of appendages on the pygidium for every segment of which it is composed except the !ast or anal segment (protopygidium). Walcott has since shown that in Neolenus this segment bears a pair of cerci, and Beecher’s drawings show that in his later studies he recognized a spinous plate, the possible bearer of cerci, on the anal segment of Triarthrus. The appendages of the anal segment have not yet been seen on other species of trilobites. The appendages of the pygidium do not show any special modifications, but seem in all cases to be similar to those of the posterior part of the thorax. In Cryptolithus all the pygidial appendages are short and remain beneath the cover of the dorsal test, while in Triarthrus and Neolenus they extend behind it. In the latter genus the endopodites of the pygidial appendages appear to be practi- cally identical in form with those of the thorax, the individual segments being perhaps a little more nearly square in outline. Like those of the thorax, the segments of the pygidial endopodites bear numerous short spines. The caudal cerci are richly segmented, slightly flexible, spinous tactile organs. They are symmetrically placed, nearly straight when in their natural position, and make an angle of about 75° with one another. They appear to be 68 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. attached to a narrow rim-like plate which seems to fit in just ahead of the doublure of the pygidium, or perhaps over it. In Ceraurus, Calymene, and Isotelus, the endopodites of the pygidium are similar to those of the thorax, but seemingly more slender, with less well developed coxopodites, and with, in the last-named genus, slender cylindrical segments. Exopodites are not known on the pygidia of any of these genera, but since they are present and like those of the thorax in Triarthrus, Cryptolithus, Neolenus, and Ptychoparia, there is little reason to think that they were absent in Cerawrus or Calymene, though there is some question about /sotelus. The limbs are largest and longest on the anterior part of the thorax of a trilobite, and diminish regularly in length and strength to the posterior end of the pygidium. This reg- ular gradation shows, as Beecher was the first to point out, that the growing point of the trilobites is, as in other arthropods, in front of the anal segment. New free segments are introduced into the thorax at the anterior end of the pygidium, and this has led to some confusion between the growing point and the place of introduction of free segments. If a new segment were introduced at a moult in front of the pygidium, that segment would probably have less fully developed appendages than those adjacent to it, and so make a break in the regular succession. The condition of the appendages corroborates the evi- dence derived from the ontogeny of the pygidium, and proves that the new segments are introduced at the same growing point as in other Arthropoda. Caudal Rami. Bernard, who believed that the Crustacea had been derived through an Apus-like an- cestor (1892, pp. 20, 85, 274), pointed out that four or less than four anal cirri were to be expected. Two well developed cirri and two rudimentary ones are present in Apus, and they are also to be found in other phyllopods and some isopods. It is, however, character- istic of the Crustacea as a whole to lack appendages on the anal segment. Caudal cirri (cerci) are much more freely developed in the hexapods than in the Crustacea, particularly in the more primitive orders, Paleeodictyoptera, Apterygota, Archiptera, and Neuroptera. They are supposed, in this case, to be modified limbs, and therefore not homologous with the bristles on the anal segment of an annelid. Doctor W. M. Wheeler of the Bussey In- stitution has kindly allowed me to quote the following excerpt from a letter to me, as expressing the opinion of one who has made an extensive study of the embryology of insects: I would say that I have no doubt that the cerci of insects are directly inherited from the insect ancestors. They are always highly developed in the lower insects, and only absent or vestigial in a few of the most highly specialized orders such as the Hemiptera, Diptera, and Hymenoptera. I have further no doubt concerning their being originally ambulatory in function. They are certainly not developed independently in insects. Embryologically they arise precisely like the legs, and each cercus contains a diverticulum of the mesoblastic somite precisely as is the case with the ambulatory legs and mouth parts. The “pygidial antennz’’ seem to be as fully developed in Neolenus as in any of the other arthropods, and may suggest a common ancestry of the phyllopods, isopods, and hexapods, in the trilobites. They were doubtless tactile organs, and while the evidence is chiefly negative, it would seem that they proved useless, and were lost early in the phylog- eny of this group. Possibly the use of the pygidium as a swimming organ proved de- structive to them. COMPARISON OF APPENDAGES. 69 HOMOLOGY OF THE CEPHALIC APPENDAGES WITH THOSE OF OTHER CRUSTACEA. The head of the typical crustacean bears five pairs of appendages, namely, the antennules, antennz, mandibles, and first and second maxillz, or, as they are more properly called, the maxillulz and maxille. As Beecher has pointed out, the “antennz”’ of the trilobites, on account of their pre- oral position and invariably uniramous character, are quite certainly to be correlated with the antennules. The second pair of appendages, the first pair of biramous ones, Beecher homologized with the antenne of other crustaceans, and that homology has been generally accepted, though Kingsley (1897) suggested that it was possible that no representatives of the true antenne were present. In preparing the restorations in the present study, the greatest difficulty has been to adjust the organs about the mouth. In Tyiarthrus, numerous specimens show that without question there are four pairs of gnathites back of the hypostoma, and that all four belong to the cephalon. In forms with a long hypostoma, however, there was no room on the cephalon for the attachment of four pairs of gnathites, neither were there enough appen- difers to supply the requisite fulera. At first I supposed I had solved the difficulty by assuming the mouth to be in front of the posterior tip of the hypostoma, as it really is in Ceraurus and Calymene, and allowing the gnathites to play under the hypostoma as Wal- cott (1912) has shown that they do in Marrella. Finaliy, when I came to study in greater detail the slices of Calymene and Ceraurus, they seemed to show that the anterior one or two pairs of appendages became degenerate and under-developed. This was probably a special- ization due to the great development of the hypostoma in trilobites, that organ being much more prominent in this than in any other group. As the hypostoma lengthened to accom- modate the increasing size of sub-glabellar organs (stomach, heart, etc.), the mouth mi- grated backward, leaving the anterior appendages ahead of it, with their gnathobases, at least, functionless. That such migration has taken place, even in Tvriarthrus, is shown by the fact that the points of articulation of the first biramous appendages are pre-oral, and it is more obviously true of Cerawrus. Correlated with the weakening of the appendages on the lower surface is the loss of glabellar furrows on the upper surface. The glabellar furrows mark lines of infolding of the test to form the appendifers and other rugosities for the attachment of tendons and muscles. It is conceivable that this migration backward of the mouth began very early in the history of the race, and that even before Cambrian times, the antennze, probably originally biramous appendages like those on the remainder of the body, had dwindled away and become lost. If this is the case, then the first pair of bira- mous appendages of Triarthrus would be mandibles, the second pair maxillulce, and the third pair maxillz. There remain the last pair of cephalic appendages, and they bring up the whole head problem of the trilobites. Beecher has stated (1897 A, p. 96) his conviction that the head of the trilobite is made up of five segments, representing the third, fourth, fifth, sixth, and seventh neuromeres of the theoretical crustacean. As a matter of fact, he really made up the head of seven segments, since he stated that the first neuromere was represented by the hypostoma and the second by the epistoma and free cheeks. Jaekel (1901, p. 157) nearly agreed with Beecher, but made eight segments, as he saw 79 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. five segments in the glabella of certain trilobites. In his table (p. 165) he has listed the segments with their appendages as follows: 1. Acron, with hypostoma; 2, rostrum (epis- toma), with free cheeks; 3, first frontal lobe, with (?) antennules; 4, second frontal lobe, with antenne; 5, mandibles; 6, first, or pre-maxille; 7, second maxille; 8, occipital seg- ment with maxillipeds. Jaekel refused to believe that the antenne of trilobites were really entirely simple, and so homologized them with the antennz and not the antennules of other Crustacea. In this he was obviously incorrect, but it accounts for his homology of the remainder of the cephalic appendages. It is, at present, impossible to demonstrate the actual number of somites in the cephalon of the trilobite, but I believe that Beecher was correct in holding that the glabella was composed of four segments. There are, it is true, a number of trilobites (Mesonacide, Para- doxide, Cheiruride, etc.) which show distinctly four pairs of glabellar furrows, indicat- ing five segments in the glabella. This is, however, probably due to a secondary division of the first lobe. The correspondence of the five segments on the dorsal side with the five pairs of appen- dages makes it unlikely that any pair of limbs has been lost. The condition in Marrella, where a trilobitelike cephalon bears five pairs of appendages, the second pair of which are tactile antennze, is favorable to the above interpretation. In spite of the apparent degener- ation of the first two pairs of appendages in Calymene, no limbs are actually missing, and if some are dropped out in the later trilobites it would not affect the homology of those now known. I therefore agree with Beecher in homologizing the appendages, pair for pair, with those of the higher Crustacea. FUNCTIONS OF THE APPENDAGES. Antennules. The antennules were obviously tactile organs, probably freely movable in most trilo-— bites, but in the case of Triarthrus perhaps rather rigid, judging from the great numbers of specimens which show the characteristic sigmoid curve made familiar by Professor Beecher’s restoration. The proximal end of the shaft of each antennule of Triarthrus is hemispheric and doubtless fitted into a socket, thus suggesting great mobility of the whole organ. In spite of this, I have seen no specimens in which they did not turn in toward each other and cross the anterior margin very near the median line. In front of the margin, various specimens show evidence of flexibility, but from the proximal end to the margin the position is the same in all specimens. In all the few specimens of Cryptolithus retaining the antennules, these organs are turned directly backward, but it is entirely within the range of probabilities that while its burrowing habits made this the more usual position, the animal had the power of turning them around to the front when they could be used to advantage in that direction. Exopodites. It has. been the opinion of most observers that the exopodites of trilobites were swim- ming organs, while others have thought that they functioned also in aérating the blood. To the present writer it seems probable that the chief function was that of acting as gills, for which the numerous thin, flattened or blade-like sete are particularly adapted. That FUNCTION OF APPENDAGES. 71 they were also used in swimming is of course possible, but that was not their chief function. It should be remembered that the exopodites are always found dorsal to or above the endopo- dites, and in a horizontal plane. For use in swimming it would have been necessary to rotate each exopodite into a plane approximately perpendicular to or at least making a con- siderable angle with the dorsal test. In this position, the exopodites would have been thrust down between the endopodites, and one would expect to find some specimens in which a part at least of the exopodites were ventral to the endopodites. Specimens in this condi- tion have not yet been seen among the fossils. To avoid having the exopodites and endopo- dites intermingled in this way, the animal would have to bring all the endopodites together along the axial line in a plane approximately perpendicular to the dorsal test, in which case the exopodites would be free to act as swimming organs. The fact that the sete of an exopodite stay together like the barbs on a feather would of course tend to strengthen the idea that the exopodites could be used in swimming, hut that is not the only possible ex- planation of this condition. The union of the basipodite and exopodite shows that the two branches of the appendage acted together. Every movement of one affected the other, and the motion of the endopodites in either swimming or crawling produced a movement of the exopodites which helped to keep up a circulation of water, thus insuring a constant supply of oxygen. Although Neolenus is usually accounted a less primitive form than Ptychoparia or Triarthrus, it has much the most primitive type of exopodite yet known. It would appear that the exopodites were originally broad, thin, simple lamellz, which became broken up, on the posterior side, into fine cylindrical setae. As development progressed, more and more of the original lamella was broken up until there remained only the anterior margin, which became thickened and strengthened to support the delicate filaments. The sete in turn be- came modified from their original simple cylindrical shape to form the wide, thin, blade-like filaments of Cryptolithus and Ceraurus. Another possible use of the exopodites is suggested by the action of some of the bar- nacles, which use similar organs as nets in gathering food and the endopodites as rakes which take off the particles and convey them to the mouth. The exopodites of the trilo- bite might well set up currents which would direct food into the median groove, where it could be carried forward to the mouth. Endopodites. The endopodites were undoubtedly used for crawling; in some trilobites, probably most of them, for swimming; in the case of Cryptolithus, and probably others, for burrowing; and probably in all for gathering food, in which function the numerous spines with which they are arrayed doubtless assisted. Various trails have been ascribed to the action of trilobites, and many of them doubtless were made by those animals (see especially Walcott, 1918). Some of these trails seem to indicate that in crawling the animal rested on the greater part of each endopodite, while others, notably the Protichnites recently interpreted by Walcott (1912 B, p. 275, pl. 47), seem to have touched only the spinous tips of the dactylopodites to the substratum. The question of the tracks, trails, and burrows which have been ascribed to trilobites is dis- cussed briefly on a later page, but can not be taken up fully, as it would require another monograph to treat of them satisfactorily. The flattened, more or less triangular segments of the endopodites of the posterior part 72 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. of the thorax and pygidium in Triarthrus, Cryptolithus, and Acidaspis probably show an adaptation of the endopodites of the posterior part of the body both as more efficient push- ing organs and as better swimming legs. The fact that these segments are pointed below enabled them to get a better grip on whatever they were crawling over, and the flatten- ing allowed a much greater surface to be opposed to the water in swimming. In this con- nection it might be stated that it seems very probable that the trilobites with large pygidia at least, perhaps all trilobites, had longitudinal muscles which allowed them to swim by an up and down motion of the fin-like posterior shield, the pygidium acting like the caudal fin of a squid. Such a use would explain the function of the large, nearly flat pygidia seen in so many of the trilobites beginning with the Middle Cambrian, and of those with wide concave borders. It should be noted here that it is in trilobites like /sotelus, with pygidia particularly adapted to this method of swimming, that the endopodites are most feebly de- veloped, and show no flattening or modification as swimming organs. The relatively strong, curved, bristle-studded endopodites of Cryptolithus, combined with its shovel-shaped cephalon, indicate Limlus-like burrowing habits for the animal, and the mud-filled casts of its intestine corroborate this view. That it was not, however, en- tirely a mud groveller is indicated by its widespread distribution in middle Ordovician times. Use of the Pygidium in Swimming. The idea that the use of the pygidium as a swimming organ is a possible explanation of that caudalization which is so characteristic of trilobites has not been developed so far as its merits seem to deserve. Two principal uses for a large pygidium of course occur to one: either it might form a sort of operculum to complete the protection when the trilo- bite was enrolled, or it might serve as a swimming organ. ‘That the former was one of its important functions is shown by the nicety with which the cephalon and pygidium are adapted to one another in such families as the Agnostidze, Asaphidz, Phacopidz, and others. That a large pygidium is not essential to perfect protection on enrollment is shown by an equally perfect adjustment of the two shields in some families with small pygidia, notably the Harpedidz and Cheiruride. That the large pygidial shields are not for protective pur- poses only is also shown by those forms with large pygidia which are not adjusted to the conformation of the cephalon, as in the Goldiidz and Lichadidz. It is evident that a large pygidium, while useful to complete protection on enrollment, is not essential. It would probably be impossible to demonstrate that the trilobites used the pygidium in swimming. The following facts may, however, be brought forward as indicating that they probably did so use them. 1. The appendages, both exopodites and endopodites, are relatively feebly developed as swimming organs. ‘This has been discussed above, and need not be repeated. It must in fairness be observed, however, that many modern Crustacea get about very well with limbs no better adapted for swimming than those of the trilobites. 2. The articulations of the thoracic segments with each other and with the two shields are such as to allow the pygidium to swing through an arc of at least 270°, that is, from a position above the body and at right angles to it, around to the plane of the bottom of the cephalon. Specimens are occasionally found in which the thorax and pygidium are so flexed that the latter shield stands straight above the body. A well preserved Dipleura in this position is on exhibition in the Museum of Comparative Zoology, and Mr. Narraway and I have figured a Bumastus muilleri in the same attitude (Ann. Carnegie Mus., vol. 4, 1908, pl. 62, fig. 3). FUNCTION OF APPENDAGES. 73 3. What little can be learned of the musculature (see under musculature, seq.) indi- cates that the trilobites had powerful extensor and flexor muscles, such as would be required for this method of swimming. It may be objected that the longitudinal muscles were too small to permit the use of a caudal fin. In the lobster, where this method of progression is most highly developed, there is a large mass of muscular tissue which nearly fills the pos- terior segments. ‘Trilobites have not usually been thought of as powerfully muscled, but it may be noted that in many cases broad axial lobes accompany large pygidia. As the chief digestive region appears to have been at the anterior end, and other organs are not largely developed, it seems probable that the great enlargment of the axial lobe was to accommo- date the increased muscles necessary to properly operate the pygidium. It may be noted that in all these genera the axial lobe of the pygidium is either short or narrow. 4. The geological history of the rise of caudalization favors this view. With the ex- ception of the Agnostidze and Eodiscidze, all Lower Cambrian trilobites had small pygidia, and the same is true of those of the Middle Cambrian of the Atlantic realm (except for the Dorypyge of Bornholm). In Pacific seas, however, large-tailed trilobites of the families Oryctocephalidze, Bathyuridze, and Asaphide then began to bé fairly common, though mak- ing up but a small part of the total fauna of trilobites. In the Upper Cambrian of the Atlantic province the Agnostidz were the sole representatives of the isopygous trilobites, while in the Pacific still another family, the Dikelocephalidz, was added to those previously existing. With the Ordovician, caudalization reached its climax and the fashion swept all over the world. It is shown not so much in the proportion of families with large pygidia, as in the very great development of the particular trilobites so equipped. Asaphide and Illzenidze were then dominant, and the Proétidz, Cyclopygidz, Goldiide, and Lichadide had begun their existence. A similar story is told by the Silurian record, except that the burden of the Asaphidz has been transferred to the Lichadide and Goldiide. All the really old (Cam- brian) families of trilobites with small pygidia had now disappeared. In the general dwin- dling of the subclass through the Devonian and later Palzeozoic, the few surviving species with small pygidia were the first to go, and the proétids with large abdominal shields the last. The explanation of this history is probably to be found in the rise of the predatory cephalopods and fishes, the natural enemies of the trilobites, against whom they could have no other protection than their agility in escaping. While the records at present known carry the fishes back only so far as the Ordovician (fishes may have arisen in fresh waters and have gone to sea in a limited way in the Ordovician and more so in Silurian time) and the cephalopods to the Upper Cambrian, the rise of the latter must have begun at an earlier date, and it is probably no more than fair to conjecture that the attempt to escape swim- ming enemies caused an increase in the swimming powers of the trilobites themselves. At any rate, the time of the great development of the straight cephalopods coincided with the time of greatest development of caudalization; both were initiated in the Pacific realm, and both spread throughout the marine world during the middle Ordovician. And since, in the asaphids, a decrease in swimming power of the appendages accompanied the increase in the size of the pygidium, it seems probable that the swimming function of the one had been transferred to the other. A high-speed, erratic motion which could be produced by the sudden flap of a pygidium would be of more service in escape than any amount of steady swiftness produced by the oar-like appendages of an animal of the shape of a trilobite. 74 : THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Coxopodites. The primary function of the endobases of the coxopodites was doubtless the gathering, preparation, and carrying of food to the mouth. Although the endobases of opposite sides could not in all cases meet one another, they were probably spinose or, setiferous and could readily pass food from any part of the axial groove forward to the mouth, and also send it in currents of water. The endobases of the cephalic coxopodites were probably modified as gnathites in all cases, but little is known of them except in Tvriarthrus, where they were flattened and worked over one another so as to make excellent shears for slicing up food, either animal or vegetable. In some cases the proximal ends of opposed gnathites were toothed so as to act as jaws, but a great deal still remains to be learned about the oral organs of all species. The writer has suggested (1910, p. 131) that a secondary function of the endobases of the thorax of Jsotelus and probably other trilobites with wide axial lobes was that of loco- motion. In Isotclus the endobases of the thorax are greatly over-developed, each being much stouter and nearly as long as the corresponding endopodite, and the explanation seemed to me to lie in the locomotor or crawling use of these organs instead of the endopodites. Cer- tain trails which I figured seemed to support this view. POSITION OF THE APPENDAGES IN LIFE. In almost all the specimens so far recovered the appendages are either flattened by pressure or lie with their flat surfaces in or very near the plane of stratification of the sedi- ment. This flattening is extreme in Neolenus, Ptychoparia, and Kootemia, moderate in Triar- thrus and Cryptolithus, and apparently slight or not effective in Jsotelus, Ceraurus, and Calymene. These last are, however, from the conditions of preservation, least available for study. In Part IV, attention is called to a specimen of Tviarthrus (No. 222) in which some of the endopodites are imbedded nearly at right angles to the stratification of the shale. This specimen is especially valuable because it shows that the appendages in the average specimen of Triarthrus have suffered very little compression, and it also suggests the prob- able position of the endopodites when used for crawling. In considering the position of the appendages in life, one must always remember one great outstanding feature of trilobites, the thinness and flexibility of the ventral membrane. The appendages were not inserted in any rigid test but were held only by muscular and con- nective tissue. Hence we must premise for them great freedom of motion, and also rela- tively little power. ‘The rigid appendifers, and the supporting apodemes discovered by Beecher, supplied fulcra against which they could push, but their attachment to these was rather loose. Considering, first, the position of the appendages in crawling, it appears that different trilobites used their appendages in different ways. Neolenus had compact stocky legs, which allowed little play of one segment on another, as is shown by the wide joints at right angles to the axis of the segment. Such limbs were stiff enough to support the body when the animal was crawling beneath the water, where of course it weighed but little. That such a crawling attitude was adopted by trilobites has been shown by Walcott in his explanation of the trails known as Protichnites (1912 B, p. 278). Many trilobites probably crawled in POSITION OF APPENDAGES. 75 this way, on the tips of the toes, so to speak. In such the limbs would probably extend downward and outward, with the flattened sides vertical. The limb of Triarthrus, however, is of another type. The endopodites are long, slender, flexibly jointed, the whole endopodite probably too flexible to be used as a unit as a leg must be in walking on the “toes.” The proximal segments of the thoracic and pygidial endopodites are, however, triangular instead of straight-sided, and, the spine-bearing apex of the triangle being ventral, it enabled the endopodites to get a grip on the bottom and thus push the animal forward. This method of progression was more clumsy and less rapid than that of Neolenus, but it sufficed. The natural position of the endopodite when used in this way would seem to be with the flattened sides of the segments standing at an angle of 30° to 45° with the vertical, thus allowing a good purchase on the bottom and at the same time offering the minimum resistance to the water when moving the appendages forward. Isotelus has endopodites different from those of either Neolenus or Triarthrus. They are composed of cylindrical segments, the joints indicating a certain amount of flexibility. Since there is no method by which the segments may get a purchase on the bottom other than by pushing with the distal ends, it would seem at first thought that Jsotelus, like Neo- lenus, crawled on its “toes.” The endopodites of Jsotelus are however, short and feeble when compared with the size of the test, while the endobases of the coxopodites are ex- traordinarily developed. These facts, together with certain trails, strongly suggest the use of the coxopodites as the primary ambulatory organs, the endopodites probably assisting. In this event, the position of the endopodites and coxopodites would be downward, both outward and inward from the point of attachment, and the motion both backward and forward. ‘The fact that in the specimens as preserved the coxopodites point backward and the endopodites forward indicates that the limb as a whole swung on a pivot at the appen-* difer. It is of course natural to suggest that the coxopodites and endopodites of all the trilobites with wide axial lobes, Nileus, Bumastus, Homalonotus, etc., were developed in this same way. Cryptolithus presents still another and very peculiar development of the endopodites where ability to get purchase on the sea floor is obtained by a stout limb of slight flexibility, bowed and turned backward in the middle, where an enlarged segment insures stiffness. The segments are flattened, and since the greatest strength when used in pushing and crawl- ing is in the long axis of the oval section of the flattened limb, it seems probable that these limbs did not hang directly down, with their sides vertical, but that their position in life was very much the same as that in which they are preserved as fossils. By moving these bowed legs forward and backward in a plane at a small angle to the surface of the body, a powerful pushing impetus could be obtained. They may, however, have occupied much the same position as do those of Limulus. In the case of the endopodites, therefore, it is necessary to study the structure and prob- able method of their use in each individual genus before suggesting what was the probable position in life. In the act of swimming, the position was probably more uniform. When the endopodites were used in swimming, as they undoubtedly could be with more or less effect in all the trilobites now known, those with flattened surfaces probably had them at such an angle as to give the best push against the water on the back stroke, while on the forward stroke the appendage would be turned so that the thin edge opposed the water. The great flexibility of attachment would certainly permit this, though unfortunately nothing 76 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. is as yet known of the musculature. The coxopodites of course had less freedom of move- ment in this respect, and probably could not turn their faces. For this reason, it seems to me likely that those coxopodites which are compressed did not stand with their flattened faces vertical, but in a position which was nearly horizontal or at least not more than 45° from the horizontal. If the flattened faces were vertical, they would be in constant oppo- sition to the water during forward movements and would be of no use in setting up cur- rents of water toward the mouth, as every back stroke would reverse the motion. The position of the exopodites in life seems. to have been rather uniform in all the genera now known. I have set forth on a previous page my reasons for thinking that they took little part in swimming, and I look upon them as being, in effect, leaf-gills. It seems probable that in all genera the exopodites were held rather close to the test, the shaft more or less rigid, the filamentous sete gracefully pendent, but pendent as a sheet and not individ- ually, there having been some method by which adjoining sete were connected laterally. Free contact with the water was thus obtained without the mingling of endopodites and ex- opodites which would have been so disastrous to progression. Levee IGE STRUCTURE AND HABITS OF TRILOBITES. INTERNAL ORGANS AND MUSCLES. Granting that the trilobite is a simple, generalized, ancient crustacean, it appears justifi- able to attribute to it such internal organs as seem, from a study of comparative anatomy, to be primitive. The alimentary canal would be expected to be straight and simple, curving downward to the mouth, and should be composed of three portions, stomodzum, mesenteron, and proc- todzeum, the first and last with chitinous lining. In modern Crustacea, muscle-bands run from the gut to part of the adjacent body wall, so that scars of attachment of these muscles _ may be sought. At the anterior end of the stomodzum, they are usually especially strong. From the mesenteron there might be pouch-like or tubular outgrowths. The heart would probably be long and tubular, with a pair of ostia for each somite. In modern Crustacea, the chief organs of renal excretion are two pairs of glands in the head, one lying at the base of the antennz and one at the base of the maxille. Only one pair is functional at a time, but these are supposed to be survivors of a series of segmen- tally arranged organs, so that there might be a pair to each somite of a trilobite. The nervous system might be expected to consist of a supracesophageal “brain,” com- prising at least two pairs of ganglionic centers, and a double ventral chain of ganglia with a ladder-like arrangement. Besides these organs, a variety of glands of special function might be predicted. Reproductive organs probably should occur in pairs, and more than one pair is to be expected. There is little to indicate the probable location of the genital openings, but they may have been located all along the body back of the cephalon. It may be profitable to summarize present knowledge of such traces of these organs as have been found in the fossils, if only to point out what should be sought. ALIMENTARY CANAL. ' Beyrich (1846, p. 30) first called attention to the alimentary canal of a trilobite, (Cryp- tolithus goldfussi,) and Barrande (1852, p. 229) confirmed his observations. A number of specimens of this species have been found which show a straight cylindrical tube or its filling, extending from the glabella back nearly to the posterior end of the pygidium. It lies directly under the median line of the axial lobe, and less than its own diameter beneath the dorsal test. At the anterior end it apparently enlarges to occupy the greater part of the space between the glabella and the hypostoma, but was said by the early observers to extend only a little over halfway to the front. Beyrich thought the position of the median tubercle indicated the location of the anterior end. Walcott (1881, p. 200) stated that in his experience in cutting sections of trilobites it was a very rare occurrence to find traces of the alimentary canal. The visceral cavity was usually filled with crystalline calcite and all vestiges of organs obliterated. There were, however, some slices which showed a dark spot under the axial lobe, which probably rep- resented the canal. In his restoration he showed it as of practically uniform diameter throughout, and extending but slightly in front of the mouth. 78 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Jaekel (1901, p. 168, fig. 28) has produced a very different restoration. His discus- sion of this point seems so good, and has been so completely overlooked, that I will append a slightly abridged version of a translation made some years ago for Professor Beecher. The idea was, however, not original with Jaekel, as it was suggested by Bernard (1894, p 417), but not worked out in detail. While considering the problem as to what organ could have lain beneath the glabella of the trilobite, and while studying the organization of living Crustacea for the purpose of comparison, I found in the collections of the Geological Institute preparations of Limulus which seemed to me to directly solve the entire question. From the mouth, which lies at about the middle of the head shield, the cesophagus bends forward, swells out at the frontal margin of the animal at a sharp upward bend in order to take a straight course backward after the formation of an enlarged stomach. Still within the head shield there branch out from each side of the canal two small vessels which pass over into the richly branched mass of liver lying under the broad lateral parts of the head shield. After seeing this specimen, I no longer had the least doubt that the head shield of the trilobites is to be interpreted in a similar manner. The position of the hypostoma and gnathopods makes it necessary to assume that the position of the mouth of the trilobite lay pretty far back. If, therefore, this depends upon the secondary ventral deflection of the oral region, as seems to be the case, then it is a@ priori probable that the anterior part of the canal has also shared in this ventral inflection. The posterior part of the canal in the region of the segmented thorax and pygidium is comparatively narrow, as shown long ago by Beyrich; he represents only a thin tube which shows no swellings whatever, and such are usually missing in Arthropoda. As the glabella of most trilobites is regularly convex, there must lie beneath it an organ running from front to back, which presses the bases of the cephalic legs away from each other and down from the dorsal test, An organ so extensive and unpaired, running thus from front to back, can, among the Arthropoda, be regarded only as an alimentary canal, for the swellings of the cephalic ganglia and the heart are by far too small to produce such striking elevations on the front and upper surface of the glabella. The canal might then have consisted of a gizzard belonging to the cesophagus, and a stomach proper or main digestive canal. 5 Among the trilobites there are two pairs of vessels on both sides of the glabella which have precisely the same position with reference to the supposed course of the alimentary canal as the ducts of the hepatic lobes in Limulus. One observes in numerous trilobites, although in different degrees of clearness and under various modifications, a dendritic marking of the inner surface of the cheeks which takes its rise at the lateral margins of the glabella and spreads thence like a bush over the entire surface of the cheeks. Exactly the same position is taken by the richly branched hepatic lobes of Limulus on the lower surface of the head shield; a fact of special weight in favor of the homology and similar significance of the two phenomena, is that in the trilobites also, the anterior of the two main ducts is the larger, the posterior the smaller. The striking similarity of the two structures is shown by a comparison of the head shield of Eurycare {Elyx] from the Cambrian of Sweden, in which the course of the canals is shown with remarkable clearness [with those of Limulus]. I have been able to convince myself that the existence of the two canals on each side is also the rule in other genera, even though the posterior pair is frequently but feebly developed or completely obscured by the anterior pair. In Dionide formosa,.for example, I find only the anterior pair, which is very large and divided into two principal branches. From all these considerations it seems to me no ionger doubtful that the median elevation was caused by the stomach and gizzard, and that Jaks cheeks have principally served to cover the hepatic appendages of the alimentary canal. The cause of the incomplete development of the glabellar lobes lies, hence, in the intrusion of the alimentary canal, and it makes naturally the most effect where the gizzard spreads out and bends into the stomach. This spot lies behind the frontal lobe, which is hence increased in size according as the stomach increases in size; in this way not only the foremost segments of the glabella become enlarged, but also the following ones more or less pressed aside. This process is easily followed phylogenetically and ontogenetically. From the latter point of view, the development of Paradowxides is very instructive. In a head shield 2.5 mm. long the whole anterior part of the glabella is broadened, but the five pairs of lateral impressions are clearly marked and the six segments of the head bounded by them are all of about the same size, In a head shield about 13 mm. long, the foremost segment is very much increased in size, the jaw lobes pressed still further apart; in adult forms both anterior segments are combined into the frontal swellings of the glabella. In other groups this process proceeds phylogenetically still further, so that among the Phacopide and in Trinucleus, behind the frontal swelling of the glabella only the last cephalic segment retains a certain independence. The frontal lobe is thus no definite part, although it is as a rule composed of the mesotergites of the first two cranidial segments. ALIMENTARY CANAL. 79 This idea of an enlarged mesenteron certainly has much to commend it, and such actual evidence as exists seems in favor of rather than against it. The strongest, firmest, best- protected place in the whole body of the trilobite is the cavity between the vaulted glabella and the hypostoma. As Jaekel has said, it is far too large a cavity for the brain, larger than would seem to be required for a heart, and what else could be there but a stomach? As has already been pointed out, Beyrich and Barrande found a pear-shaped enlargement of the alimentary canal under the glabella of Crjptolithus. Longitudinal sections through the glabella of Calymene and Ceraurus practically always show the cavity there filled with clear crystalline calcite. One actual specimen of Ceraurus (Walcott 1881, pl. 4, fig. 1) shows the cavity between the glabella and hypostoma entirely empty. The vacant spaces in these two classes of specimens do not, however, necessarily mean anything more than im- perfect preservation. Fig. 21.—Transverse slice through Ceraurus pleurexanthemus, to show the dorsal sheath above the abdomi- nal cavity. Specimen 118. Traced Fig. 22.—Transverse section through the cephalon of Ceraurus pleurexan- themus, showing the abdominal sheath and the large mud-filled alimentary Fig. 23.—Trans- verse section of the thorax of Ca- lymene senaria, showing the large from a photographic enlargement. canal (clear white). Traced from a X 4. photographic enlargement. Specimen 07. X 3-3. size of the mud- filled alimentary canal (clear white). Traced from a photographic en- largement. One appendifer (also clear white) is ‘ shown. Specimen Hise SREY Ceraurus pleurexanthemus. This species is taken up first, as it is the one shown in Walcott’s often-copied figure (1881, pl. 4, fig. 6). It is to be feared that too many have looked at this figure without reading the accompanying explanation, and have taken it for a copy of an actual specimen and not a mere diagram, which it admittedly is. The evidence on which it is based is com- prised in eight transverse slices, one through the glabella and seven through the thorax. Three of these have been figured by Walcott: No. 27, 1881, pl. 3, fig. 7; No. 13, 1881, pl. 2, fig. 3, 1918, pl. 26, fig. 14; No. 202, 1918, pl. 27, fig. 8. In all, as can be seen by reference to the figures, the canal is partially collapsed, and is much larger than is indicated in Walcott’s restoration. The other sections bear out the testimony of those figured. One of these figured specimens (No. 27) and another figured herewith (No. 118, see fig. 21) show an exceedingly interesting structure which has previously escaped notice. The body cavity seems to have had, in this region at least, a chitinous sheath on the dorsal side. As shown especially in figure 21, this sheath impinges dorsally and laterally against the axial lobe and thus fur- nishes a special protection for the soft organs beneath, probably protecting them from the strain of the dorsal muscles. 80 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. While there is no way in which the location of these sections in the thorax can be posi- tively determined, it is probable that they came from the anterior end. In sections further back, supposed to be in the posterior region of the mesenteron, no sheath is shown, but the canal is nearly if not quite as large in relation to the size of the axial lobe. The single section through the glabella (specimen 97) is of course important and for- tunately well preserved (fig. 22). It shows the dorsal sheath pressed against the inner sur- face of the axial lobe along its middle portion, but diverging from it at the sides. The section of the canal is oval, nearly twice as wide as high, but it is obviously somewhat de- pressed. The original canal evidently filled nearly the whole of the dorsal part of the glabella in this particular region. Unfortunately, the connection with the mouth is not shown, and the form of the hypostoma indicates that the section cut the glabella diagonally, either in the anterior or posterior part, probably the latter. In all these cases it should be remem- bered that the specimens were found lying on their backs, and the canal has fallen in (dor- sally) since death. The sections show that in Ceraurus pleurexanthemus the anterior part of the alimentary canal was large, filling the part of the glabella below the heart; that the body cavity was provided with a chitinous dorsal sheath extending back into the thorax; and that the pos- terior portion of the mesenteron was likewise large and oval in section. Since the alimen- tary canal must be connected with the mouth and anus, some such restoration as that of Jaekel is indicated. No chitinous lining of the stomodeeum or proctodeum was found, but it is not certain that any of the sections cut either of those regions. Calymene senaria. Ten transverse sections and one longitudinal slice show the form of the alimentary canal in Calymene. One of these has been figured by Walcott (1881, pl. 1, fig. 9) but without showing the organ in question. = The only section cutting the cephalon which shows any trace of the canal is a longi- tudinal one (No. 141), which is not very satisfactory. It has a large, nearly circular, opaque spot under the anterior part of the glabella which may or may not represent a sec- tion across the anterior end of the mesenteron. Three sections (No. 9, 115, 143) show the dorsal sheath, the latter having the mud-filled canal beneath it. The sheath arches across the axial lobe as in Cerawrus, leaving room for the dorsal muscles at the sides and above it. In this region the canal is large and oval in section. Six slices cut the mesen- teron behind the abdominal sheath (Nos. 39, 117, 148, 153, 62, 65) (see fig. 23). In the first four of these it is oval in section and large, but not so large as in No. 143. In the last two, it is small and circular in section, from which it is inferred that the canal tapers posteriorly. Cryptolithus goldfussi (Barrande). Tlustrated: Beyrich, Untersuch. tiber Trilobiten, Berlin, 1846, pl. 4, fig. 1c—Barrande, Syst. Sil. Bohéme, vol. 1, 1852, pl. 30, figs. 38, 39. Both Beyrich and Barrande have shown that from the posterior end of the axial lobe to the neck-ring on the cephalon, the alimentary canal in Cryptolithus has a nearly uniform diameter of less than half the width of the axial lobe. In front of the neck-ring, it enlarges, and while its original describers state that it extends only about halfway to the front of ALIMENTARY CANAL. 81 the glabella, Barrande’s figure 39 shows it extending quite to the front, and his figure 38 shows it fully two thirds of the distance to the anterior end, as does Beyrich’s figure of 1846. The Museum of Comparative Zoology contains a single specimen of this species from Wesela, Bohemia, which shows the course of the canal from the middle of the pygidium to the anterior part of the glabella. The enlargement appears to begin about halfway to the front of the glabella and to be greatest at the anterior end. At the anterior end of the glabella, the anterior end of the thorax, and the posterior end of the pygidium, the canal is still packed full of a material somewhat darker in appearance than the matrix, while the re- mainder of it is open. A well defined constriction is present under the middle of the next to the last thoracic segment, but whether this is accidental or whether it indicates the point where the mesenteron discharges into the proctodeeum can not be determined. The inside of the canal has somewhat of a lustre and there are three conical projections into it on the median ventral line, a very small one in front of the neck furrow, a larger one under the anterior part of the second segment, and a third between the fourth and fifth segments. . Summary. The specimens of Cryptolithus from Bohemia and of Ccraurus and Calymene from New York seem to substantiate the claim of Bernard and Jaelkel that at the anterior end Fig. 24.—Longitudinal section of Ceraurus pleurexanthemus, show- ing the probable outline of the alimentary canal and the heart above it. A restoration based on the slices described above. of the canal there was an enlarged organ which occupied the greater part of the cavity of the glabella. It appears that it extended into the thorax, and that above it and the heart was a chitinous dorsal sheath. Behind the enlarged portion, the mesenteron appears to have been of practically uniform diameter in Cryptolithus, but to have tapered posteriorly in Ceraurus and Calymene. The proctodeum can not yet be differentiated from the mesen- teron, and only in Cryptolithus has the posterior portion of the alimentary canal been seen. It is, there, merely a continuation of the mesenteron. The stomodzeum likewise has not been identified, but was probably a short gullet leading up from the mouth into the enlarged digestive cavity. The principle of the enlargement of the latter and its influence on the dorsal shell once established, the significance of different types of glabella becomes apparent. It will be re- membered that the glabella of the protaspis of most trilobites is narrow, and that the same is true of the glabellze of most ancient and all primitive trilobites. The free-swimming larvee and the free-swimming ancestors of the trilobites were probably strictly carnivorous, lived on concentrated food, and needed but a small digestive tract. As the animals “discovered the ocean bottom’? and began to be omnivorous or herbivorous, larger stomachs were re- quired, and so in the later and more specialized trilobites the glabella became expanded lat- terally or dorsally, or both, to meet the requirement for more space, until, in such Devonian genera as Phacops, the cephalon was nearly all glabella. 82 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. GASTRIC GLANDS. Jaekel’s suggestion, quoted above, that the so called “nervures” seen on the under sur- faces of the heads of some trilobites are really glands for the secretion of digestive juices, is at least worthy of consideration. Moberg, however (1902, p. 299), suggested that these markings probably had something to do with the eyes rather than the stomach. He says in part (translation) : In general we can now say that such features are common to all the eyeless Conocoryphide. With the conocoryphs I include Ely and consider Harpides as at least closely related. Similar impressions are also found in forms with eyes, as, for instance, in the Olenide, but here such radiate partly from the border of the eye, partly from the front end of the glabella, partly from the [visual surface of the] eye, and some- times from the angle between the occipital ring and the glabella. They therefore go out from such different points that they can not possibly be branches of the liver. It would also be very remarkable if such an important organ should have been developed in a few eyeless forms, but have failed to leave the least trace in the rest of the trilobites. Lindstroem (1901, pp. 18, 19, 33; pl. 5, figs. 29, 31; pl. 6, figs. 43-45) has discussed these markings and given beautiful figures showing their appearance in Olenus, Parabolina, Elyx, Conocoryphe, and Solenopleura. He decided that they were to be explained as branches of the circulatory system, comparing them with the veins and arteries of Limulus. He pointed out that there was a coincidence between these markings and the position of the eyes, and suggested a causal connection with the latter. Beecher (1895 B, p. 309), also from a comparison with Limulus, suggested that the eye-lines of Cryptolithus, Harpes, Conocoryphe, Olenus, Ptychoparia, Arethusina, etc., prob- ably represented the optic nerves, and since the eye-lines are usually the main trunks of the dendritic markings, it is fair to assume that he considered the whole as due to branches of nerves. Reed has recently (1916, pp. 122, 173) discussed these lines as developed in the Tri- nucleidee, and seems to accept Beecher’s explanation. Three explanations of the “nervures” are thus current, and the authors of all of them refer us to Limulus as proving their claims! So far as general appearance goes, the mark- ings on the trilobites more closely resemble the veins of a Limulus than either the nerves or ‘liver’ of that animal. The veins, however, are not in contact with the dorsal shell, but are buried in the liver and muscles, while the arrangment of the arteries, which are dorsal in position, is quite unlike what is seen in the trilobites. The term nervures, as applied to these markings, is not only misleading, but an incor- rect use of one of Barrande’s words, for by nervures he meant delicate surface markings. Until the real function of the organs which made these markings is definitely established, it may be well to call them genal ceca, for they obviously were open tunnels ending blindly, whatever they contained. The question of the function of the genal ceca can not, in any case, be settled by an appeal to Limulus, and it is doubtful if it can be settled at all at the present time. Cer- tain things tend to show that Jaekel’s explanation is the most plausible, and these may be briefly set forth. Walcott (1912 A, pp. 176, 179, pls. 27, 28) has described specimens of Naraoia and Burgessia in which similar markings are well shown, and where they are obviously con- nected with the alimentary canal just at the anterior end of the mesenteron. In Burgessia, which seems to be a notostracan branchiopod, the trunk sinuses are very wide, and the ap- GASTRIC GLANDS. 83 pearance is on the whole unlike that of any known trilobite. In Naraoia, however, the markings are much finer and directly comparable with those of Elyx. If my contention that Naraoia is a trilobite should be sustained, it might almost settle the question of the “ner- vures.”” In Burgessia these lateral trunks enter the main canal behind the fifth pair of ap- pendages. In the trilobites they debouch much further forward. The principal argument in favor of the interpretation of these markings as nerves lies in their connection with the eyes. There is considerable evidence to indicate that the eye- lines and the genal ceca are two distinct structures, but because both originate from the sides of the anterior lobe of the glabella, and both extend outward at nearly right angles to the axis, or obliquely backward, they are, when both present, coincident. Genal czeca occur on blind trilobites, on trilobites with simple eyes, and on trilobites with compound eyes. Eye-lines occur on trilobites with both simple and compound eyes, and genal ceca may or may not be present in both cases. The morphology of the ridge forming the eye-line in trilobites with compound eyes is well known. It is abundantly proved by ontogeny that it is the continuation of the palpebral lobe, and a development of the pleura of the first dor- sal segment of the cephalon. Lake, Swinnerton, and Reed have tried to show that the eye- lines of the Harpedidz and Trinucleidz are homologous with the eye-lines of the trilobites with compound eyes, and that the ocelli on the cheeks are therefore degenerate compound eyes. The simplest form of the genal caecum is seen in the blind Elya (Lindstroem toot, pl. 6, fig. 43). The main trunk is at nearly right angles to the axis, the increase in its width is gradual in approaching the glabella, and an equal number of branches diverge from both sides. Ptychoparia striata (Barrande 1852, pl. 14, figs. 1, 3) is an excellent example of a trilo- bite with compound eyes and genal ceca. It will be noted that the main trunk and the eye- line are coincident, and that both on the free and fixed cheeks the branches are all on the anterior side of the eye-line. Compare this with the condition in Conocoryphe (Barrande, pl. 14, fig. 8; Lindstroem, pl. 6, fig. 44), and one sees there a main branch having the same direction as in Ptychoparia and likewise with all the branches on the anterior side. At first sight this would seem to support the contention that these lines do lead out to the eyes, since Conocoryphe is blind, and the main trunk leads practically to the margin. But although Conocoryphe is blind, it has free cheeks, and the main trunk does not lead to the point on those free cheeks where eyes are to be expected, but back into the genal angles. And this direction holds in such diverse genera (as to eyes and free cheeks) as Harpes, Crypto- lithus, Dionide, and Endynuonia. In all these the genal czeca fade out in the genal angles, and in none of them would compound eyes be expected in that region. The coincidence of the eye-lines with the trunks of the genal czeca in Ptychoparia seems to be merely a coincidence. That the markings which radiate from the eyes of Ptychoparia and Solenopleura are not im- pressions made by nerves is obvious. That they are of the same nature as the similar mark- ings in the eyeless trilobites is equally obvious. Ergo, they can not be nerves in either case, and that they have anything to do with the eyes is highly improbable. The eye was merely superimposed upon these structures. The relation of the genal czeca to the ocelli on the cheeks is best shown in the Trinu- cleide. In all species of Tretaspis simple eyes are present, and in most of them there are very narrow eye-lines. The latter are occasionally continued beyond the ocular tubercle back to the genal angle. A similar course is seen in Harpes. If the simple eye is the homologue 84 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. of the compound eye, and the eye-line here the homologue of the eye-line in Ptychoparia, why does it continue beyond the eye? In any case, it can not be interpreted as a nerve. Cryptolithus tessellatus, when the cephalon is 0.45 mm. to 0.65 mm. long, shows short eye- lines and a small simple eye on each cheek. In some hali-grown specimens, traces of the ocelli can be seen, but the eye-lines are absent. In the adult, both the eye-lines and the ocelli are entirely wanting. Reed states that ‘“‘nervures’ are also absent, and so they are from most specimens, but well preserved casts of the interior from the Upper Trenton opposite Cincin- nati show them, and one cheek is here figured (fig. 25). As apparent from the figure, the main trunk is very short and gives rise to two principal branches, the first of which in its turn sends off lines from the anterior side. It was a specimen showing these lines which Ruedemann (1916, p. 147) figured as showing facial sutures. The interest lies in the fact that while the ocelli and eye-lines were lost in. development, the genal ceca are present in the adult, showing that they are different structures. Fig. 25.— Cryptolithus tessellatus Green. Side view of the cheek of a specimen from the top of the Trenton opposite Cin- cinnati, Ohio, to show the branching genal ceca. These are the “facial sutures” of Ruedemann. Harpides is another genus in which genal ceca are strikingly shown, and in this case they completely cover the huge cheeks, radiating from two main trunks to the front and sides. I have seen no good specimens, but it would appear from Angelin’s figure (1854, pl. 41, fig. 7) that the rather large, simple eyes are not situated exactly on the vascular trunks. In the Harpides from Bohemia, the main trunks extend out with many branches beyond the simple eyes. It should be stated that the courses of the genal czeca are not correctly figured by Barrande (Supplement, 1872, pl. 1, fig. 11), as shown by casts of the original specimen in the Museum of Comparative Zoology. From Barrande’s figure, one would suppose that the eve-lines and their continuation beyond the “ocelli’’ were superimposed upon the genal ceca without having any definite connection with them, but as a matter of fact the radial markings really diverge from the main trunks as in Elyx and similar forms. Summary. ‘As Reed has said, these lines are not mere ornamentation, but rather represent traces of structures of some functional importance. They probably can not be explained as traces 4 . . . . of nerves and more likely represent either traces of the gastric czeca or of the circulatory HEART. 85 system. While they are known chiefly in Cambrian and Lower Ordovician trilobites, there is no evidence that the organs represented were not present in later forms, even if the shell may not have been affected by them. While they indicate very fine, thread-like canals, the present evidence seems to be in favor of assigning to them the function of lodging the glands which secreted the principal digestive fluids. HEART. Tllenus. Volborth (1863, pl. 1, fig. 12== our fig. 26) has described the only organ in a trilobite which suggests a heart. A Russian specimen of J/lenus with the shell removed shows a somewhat flattened, tubular, chambered organ extending from under the posterior end of the cephalon to the anterior end of the pygidium. The posterior nine chambers were each 1.5 mm. long and 1.5 mm. wide, while the two anterior chambers were respectively 2.5 mm. BED pie) Fig. 26.—Copy of Vol- Fig. 27. — Heart _borth’s f.gure of the heart of Apus. Copied of Illenus. from Gerstacker. and 3 mm. wide. These were all under the thorax, and at least two more chambers are shown under the cephalon, but rather obscurely. The species of the J/lenus is not stated, but since no J/Jenus has more than ten segments in the thorax, and this tube has at least thirteen chambers, it is evident that its constrictions are inherent in it, and are not due to the segmentation of the thorax. Beecher has made a passing allusion to this organ as an alimentary canal. This was the original opinion of Volborth. Pander, however, suggested to him that it might be a heart. The alimentary canal of Cryptolithus does not show any constrictions, while the heart of Apus (see fig. 27) and other branchiopods does show them. It should be noted, further, that while this heart enlarges toward the front, it is everywhere very small as compared with the width of the axial lobe, and much narrower than sections of Ceraurus and Calymene would lead one to expect the alimentary canal of Jllenus to be. Where the heart is 1.5 mm. to 3 mm. wide, the axial lobe is 11 mm. wide. While this may be merely a cast of the alimentary canal it is sufficiently like a heart to deserve consideration as such an organ. Ceraurus and Calymene. Nothing suggesting a heart has been seen in the sections of Ceraurus and Calymene. The mesenteron and its sheath crowd so closely against the dorsal test in the anterior part 86 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. of the thorax that there seems to be no room for the heart, but it must have been located beneath the sheath and above the alimentary canal. If the latter were filled with mud, and the animals lay on their backs, as most of them did at death, the canal would drop down into the axial lobe and the soft heart would naturally disappear and leave no trace of its presence in the fossils. The Median “Ocellus’ or “Dorsal Organ.” - Many trilobites, otherwise smooth, bear on the glabella a median pustule which is usually referred to as a simple eye or median ocellus, but whose function can not be said to have been certainly demonstrated. Ruedemann (1916, p. 127), who has recently made a careful study of this problem, lists about thirty genera, members of ten families, Agnostidze, Eodi- scide, Trinucleide, Harpedide, Remopleuride, Asaphide, Ilzenidze, Goldiide, Cheiruride, and Phacopidz, in which this tubercle is present, and had he wished he might have cited more, for it is of almost universal occurrence in Ordovician trilobites. I have not especially searched the literature for references to this median tubercle. It is often mentioned by writers in descriptions of species, but apparently few have tried to explain it. Beyrich (1846, p. 30) suggested that it indicated the beginning of the alimentary canal. Barrande mentioned it, but if he gave any explanation, it has escaped me. McCoy (Syn. Pal. Foss. 1856, p. 146) called it an ocular (?) tubercle, and that seems to have been the interpretation which most writers on trilobites have assigned to it, if they suggested any function at all. Beecher (1895 B, p. 309) concurred in this opinion. Bernard (1894, p. 422) ascribed to this tubercle, as well as to the median tubercle on the nuchal segment, an excretory function, comparing it with the “dorsal organ” in Apus. Reed (1916, p. 174) states that it may be either the representative of the “dorsal” organ of the branchiopods, or a median unpaired ocellus. Ruedemann (1916) has made the only real investigation of the subject. He came to the conclusion that it was a parietal eye, without a crystalline lens, but corresponding to the “parietal eye of other crustaceans, and especially of the phyllopods, which is a lens-shaped or pear-shaped sac, usually filled with sea water.” He found that above the “ocellus’ the test was usually thin or even absent, and in a few cases a dark line beneath seemed to out- line the original form of the sac. His summary follows: It is claimed that most, if not all, trilobites possessed a median or parietal eye on the glabella. [In proof of this assertion the following facts are stated:] 1. A great number of species, belonging to more than thirty genera, possess a distinct tubercle on the glabella. This tubercle occurs alone in many genera, otherwise smooth, as in the Asaphide, and is hence of functional importance. é 2. In certain cases, as in Cryptolithus tessellatus, distinct lenticular bodies [not lenses] were recognized; in others, as in Asaphus expansus, only a thinner, probably transparent test. Many other species show a distinct pit in interior casts of the tubercle, indicating a lens-like thickening of the top of the tubercle. The median eye therefore probably possessed all the different stages of development seen in other crustaceans. 3. As in the parietal eyes of the crustaceans and the eurypterids, the tubercles are most prominent and distinct in the earlier growth-stages, notably so in Jsotelus gigas. 4. The tubercle is especially well developed in the so called blind forms where the lateral eyes are abortive, as in Cryptolithus (Trinucleus), Dionide, Ampy-x. 5. The tubercles always appear on the apex on the highest part of the glabella, where their visual function would be most useful. 6. The tubercle is generally situated between the lateral eyes, like ise parietal eye in crustaceans and eurypterids, on account of its close connection with the brain. 7. Frequently it forms the posterior termination of a short crest, also as in certain eurypterids (Sty- lonurus), indicating the direction of the nerve. HEART. 87 8. The median eye is borne on a tubercle or mound in the Ordovician and Silurian trilobites, while the tubercle is rarely noticed in the Devonian and in few Cambrian forms. In the Devonian forms, similarly as in many crustaceans and in later growth-stages of some asaphids, the strong development of the lateral eyes may have led to a loss of the parietal eyes. In the Cambrian genera evidence is present to suggest that the parietal eyes consisted only of transparent spots or lens-like thickenings of the exoskeleton, hardly noticeable from the outside. 9. It is a priori to be inferred that the trilobites should, as primitive crustaceans, have possessed median or parietal eyes. As a student, I accepted Professor Beecher’s dictum that this tubercle represented a median ocellus, but more recently a number of things have led me to the view that it is the point of attachment of the ligament by which the heart is supported. The chief arguments against its interpretation as a parietal eye seem to be that its structure is not absolute proof, being capable of other explanation; its position is variable, in front, between, or back of the eyes; it is exactly like other tubercles on the median line, especially the nuchal spine or tubercle, and the similar ones along the axial lobe of the thorax; and it is not present in the protaspis or very young trilobites. 1. The structure disclosed by Ruedemann’s sections, a sort of sac-like cavity beneath a thinned test, can be explained as a gland, a ligamentary attachment, or a vestigial spine, as well as aneye. Ina section of Asaphus expansus, which I made some years ago when try- ing to get some light on this problem, there is a similar cavity under the pustule, but a secondary layer of shell lay beneath it and apparently cut it off from the glabellar region, thus indicating that it had lost its function in the adult of this animal. Sections through the tubercles of the glabella of Cerawrus show all of them hollow, with very thin upper covering or none at all, and their structure is not unlike that of the tubercle of Cryptolithus. In fact, sections can be seen in Doctor Walcott’s slices which are practically identical with the one Ruedemann obtained from Cryptolithus. Since it is obvious that not all of the pustules of a Ceraurus could have been eyes, the evidence from structure is rather against than for the interpretation of the median pustule as such an organ. 2. The position of the tubercle varies greatly in different genera. Where furthest for- ward (Tretaspis, Goldius), it is just back of the frontal lobe, while in some species of asa- phids it is in the neck furrow. In species with compound eyes it is frequently between the eyes, but more often back of them. If its history be traced in a single family, it is gen- erally found farthest forward in the more ancient species and moves backward in the more recent ones. The eyes do this same thing, but the median tubercle goes back further than the eyes. This can be seen, for example, in the American Asaphidz, where the pustule is up between the eyes of Hemigyraspis and Symphysurus of the Beekmantown and back of the eyes of the Jsotelus of the Trenton. Turning now to the under side of the head, it appears that the tubercle bears a rather definite relation to the hypostoma. If the hypostoma is short, the tubercle is well forward. If long, it is far back on the head. It seems in many cases to be just back of the posterior tip of the hypostoma, or just behind the position of the mouth, while in others it is not as far back as the tip of the hypostoma. The median tubercle is in many cases developed into a long spine. This is usually in an ancient member of a tubercle-bearing family, and suggests that in most cases the tubercle is a vestigial organ. An example of this occurs in Trinucleoides, the most ancient of the Trinucleidee. Tvrinucleoides reussi (Barrande) (Supplement, 1872, pl. 5, figs. 17, 18) has a very long slender spine in this position. It could be explained as an elevated median eye, but it also very strongly suggests the zozeal spine of modern brachyuran Crustacea. 88 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Gurney (Quart. Jour. Mic. Sci., vol. 46, 1902, p. 462) supports Weldon in the conclusion that the long spines of the zozea are directive, and states that the animal swims in the direction of the long axis of the spine. He also suggests that, since the period of their presence cor- responds to the period before the development of the “auditory” organs, the spines may perform the functions of balancing and orientation. It is generally admitted that the spine of the zozea is also protective, and the obvious function, first pointed out by Spence Bate in 1859, is that it contains a ligament which helps suspend the heart, which lies beneath the spine. This latter function may have been that of the median tubercle in the trilobite. Such an explanation would account for the backward migration mentioned above, for as the stomach enlarged and the mouth moved backward on the ventral side, the heart may have been pushed backward on the upper side. There is also a curious parallelism between the ontogenetic history of the zozeal spine and the phylogenetic history of the Trinucleidz or Cheiruridze (Nieszkowskia is the ancient member of this family in which the spine replaces the tubercle). When first hatched, the larval crab shows no trace of the spine, but very quickly it evaginates, lying dorsally on the median line, pointing forward (Faxon, Bull. Mus. Comp. Zool., vol. 6, 1880, pl. 2). With the splitting of the original envelope, the spine becomes erect, but persists only a short time, and is reduced to a vestigial tubercle toward the end of the zozeal stages, its disappearance be- ing, as pointed out by Gurney, coincident with the development of the balancing organs. This manner of suspension of the heart by a long tendon certainly does suggest that Gurney is right in his interpretation of the function. Briefly, the zozeal spine served for a. short time a function later taken over by other organs. It was not present in the youngest stages, it became prominent at a very early stage, was soon vestigial, and then lost. Take now the trilobites. There is no trace of the median pustule in the protaspis of any form, and in many primitive trilobites it is absent. It appears first as a long spine in certain families, and later becomes vestigial and disappears. Very few trilobites of Silurian and later times show it at all. In the particular case of the Trinucleidze, which were burrowers, the spine is present - on only the oldest and most primitive of the group, a form which has only a most rudimen- tary fringe. It is obvious from the large size of the pygidium in the larval trinucleid that this family is derived from a group of free swimmers. Tvimucleoides reussi was perhaps in the transitional stage, just leaving the swimming mode of life, and belonged to a group which had not developed any other “statocyst’ than the median spine. Among the later Trinucleidz the spine became a vestigial tubercle, and in some cases entirely disappeared. A similar history can be traced in the Cheiruride, starting from some such forms as the Ameri- can Lower Ordovician Nieszkowskia (N. perforator p. ex.). Another example of a median spine instead of a tubercle is in Goldius rhinoceros (Bar- rande). Since this species is not from the oldest Goldius-bearing rocks, but from the Lower Devonian, it does not follow what seems to be the general rule, but makes an interesting ex- ception. Goldius rhinoceros (Barrande) (Supplement, 1872, pl. 9, figs. 12, 13) has the median tubercle elevated into a stubby, recurved spine very suggestive of the horn of a rhinoceros. Since the eyes of this species are very well developed, there seems no especial reason for the elevation of a parietal eye, and the example certainly does not support that interpretation. 3. This tubercle is essentially similar to other tubercles on the median line of cephalon, thorax, and even pygidium. This has been discussed sufficiently under section 1 above, but VARIOUS GLANDS. 89 it may perhaps be justifiable to point out that in some of the Agnostidz there is a median tubercle on both shields, and since it has not yet been demonstrated beyond question which shield is the cephalon, to say which one is a parietal eye and which one is a tubercle is im- possible. In other words, the parietal eye can not be differentiated from any other tubercle except by its position. 4. One of the as yet unexplained features of the protaspis of trilobites is the absence of the “‘nauplius eye.’ Beecher (1897 B, p. 40) explained this on the ground of the extremely small size of the protaspis and the imperfection of the preservation. If the me- dian tubercle were really a median eye, it should be present in the protaspis and the earlier stages of the ontogeny, even if not in the adult, and should certainly appear before the com- pound eyes. (In Limulus, however, the compound eyes appear first.) The median eye has not so far been seen in any young trilobite in any stage previous to that in which compound eyes are present. The full ontogeny is not known of any species with compound eyes in which the median tubercle is present in the adult, but theoretically the median eye should be most prominent in the young of just those primitive trilobites about whose development most is known. NERVOUS SYSTEM. There has been a rather general impression among students of trilobites that the eye- lines, which should be differentiated from the genal caca, denote the course of the optic nerves, but no other evidence of the nervous system has been found, save the so called nervures which have been discussed above. In Apus the nerves leading to the eyes come off from the anterior ganglion or “brain” and run directly to the eyes. If conditions were similar in the trilobites, the “brain’’? was beneath the anterior glabellar lobe, provided, of course, that the eye-lines do indicate the course of the optic nerve. The ontogenetic history of the eye-lines of trilobites with compound eyes is instructive, and has already been discussed by Lindstroem (1901, pp. 12-25), but he did not cite the case of Ptychoparia, which is particularly interesting, because in this genus both eye-lines and “nervures” are present. Beecher (1895 C, p. 171, pl. 8, figs. 5-7) has shown that in Ptychoparia kingi the eye-lines of a specimen in the metaprotaspis stage run forward at a low angle with the glabella, while in the adult their course is nearly at right angles to it. They have therefore swung through an arc of at least 60° and in so doing haye had ample oppor- tunity to become coincident with the primary trunks of the genal ceca. Once that was ac- complished, it is quite likely that the one fold in the shell would continue to house both structures. In other trilobites, there is a similar backward progression of the eye-lines. As would be expected, the ventral ganglia and the longitudinal cords left no trace in the test. Since each segment has appendages, there was probably a continuous chain of ganglia back to the posterior end of the pygidium. VARIOUS GLANDS. Dermal glands.—The surface of many trilobites is ‘‘ornamented” with pustules and spines which on sectioning are nearly always found to be hollow, and in many cases have a fine opening at the tip. While it is generally believed that the purpose of these spines was protective, yet it is possible that many of them were merely outgrowths which increased the area through which the respiratory function could be carried on. It will be recalled foje) THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. that most of the smooth trilobites are punctate, some of them very conspicuously so, and the spines and pustules of ornamented trilobites may merely subserve the same function as the pores of smooth ones. If the spines were protective, it would not be surprising if some of them, hollow and open at the top, were poisonous also, and had glands at the base. ‘These are, however, purely matters of speculation so far. Renal excretory organs.—Nothing has been seen of any such organs, unless the genal ceca may possibly be of that nature. The main trunks of these always lead to the sides of the anterior glabellar lobe, which is not the point of attachment of either antennze or biramous limbs, so that there seems little chance that they will bear this interpretation. Reproductive organs.—Nothing is yet positively known about the reproductive organs or the position of their external openings. If the “exites” of Neolenus could be interpreted as brood-pouches, which does not seem probable, then the genital openings were located near the base of some pair of anterior thoracic appendages. The Panderian Organs: Internal Gills or Poison Glands? At a meeting of the Mineralogical Society at St. Petersburg, Volborth (1857) announced that Doctor Pander had two years before discovered certain organs on the lower side of the doublure of the pleural lobes of the thorax of a specimen of Asaphus expansus. These organs were oval openings in the doublure, one near the posterior margin of the cephalon, and one on each thoracic segment of the half-specimen figured by Volborth in 1863. They were explained by Volborth and by Eichwald (1860, 1863) as the points of attachment of appendages. Billings (1870) described and figured the “Panderian organs” of “Asaphus platycephalus’ and stated that he had seen them in Asaphus [Ogygites| canadensis and A. megistos [Isotelus maximus| as well. He thought some sort of organ was attached to them, but could not suggest its function. Woodward (1870) thought that the openings were “only the fulcral points on which the pleuree move.” Their position outside the fulcra shows that this explanation is impossible. So far as I am aware, the Panderian organs have been seen only in the Asaphidz. Barrande figured them in “Ogygia’ [Hemigyraspis| desiderata (1872) and Schmidt in two species of Pseudasaphus. They seem to occupy the same position in Bohemian, Russian, and American specimens. There is always one pair of openings on each thoracic segment, and one pair in line with them on the posterior margin of the cephalon. They occur near the anterior margin of the segment, and near the inner end of the doublure. In some cases they are surrounded by a ventrally projecting rim, while in others they have a thin edge. There seem to be no markings on the interior of the shell which are connected with them. While thinking over the trilobites in connection with the origin of insects, it occurred to me that these hitherto unexplained Panderian organs might possibly be openings to internal gills and that the Asaphide might have been tending toward an amphibious existence. On mentioning this to Doctor R. V. Chamberlin of the Museum of Comparative Zoology, he called my attention to the possibility that they might be openings similar to those of the repugnatorial glands of Diplopoda. While no definite decision as to the function can be made, the explanation offered by Doctor Chamberlain seems more plausible than my own, and has suggested still a third, namely, that they might be the openings of poison glands. If one were to argue that these apertures are really connected with respiration, it might be pointed out that they are ventral in position, while the foramina repugnatoria are always MUSCULATURE. gI dorsal or lateral, even in diplopods with broad lateral expansions. If offensive secretions were poured out beneath a concave shell like that of a trilobite, they would be so confined as to be but slightly effective against an enemy. This would indicate that if these open- ings were the outlets of glands, the substance secreted might be a poison used to render prey helpless. On the other hand, openings to gills are normally ventral in position, and if the _ pleural lobes were folded down against the body, they would be brought very close to the bases of the legs. A further curious circumstance is that so far no traces of exopodites have been found on Isotelus. The endopodites of both Isotelus latus and I. maximus are fairly well pre- served in the single known specimen of each, yet no authentic traces of exopodites have been found with them. Moreover, Walcott sliced specimens of Jsotelus from Trenton Falls and found only endopodites. It may also be recalled that the finding of the specimen of Isotelus arenicola at Britannia and the tracks which I attributed to it, suggested to me that it was a shore-loving animal (1910). It offers a field for further inquiry, whether the Fig. 28—Side view of a specimen of Isotelus gigas Dekay, from which the test of the pleural lobes has been broken to show the position of the Panderian organs. Natural size. Specimen in the Museum of Comparative Zoology. Asaphidz may not have had internal gills, and whether some primitive member of the family may not have given rise to tracheate arthropods. The explanation of the Panderian organs as openings of poison glands is less radical than the one just set forth, and so possibly lies nearer the truth. One would expect poison glands to lie at the bases of fangs, and so they do in specialized animals like chilopods and scorpions, but the trilobites may have had the less effective method of pouring out the poison from numerous glands. The purpose may have been merely to paralyze the brachiopod or pelecypod which was incautious enough to open its shell in proximity to the asaphid. MUSCULATURE. This is a field which is rather one for investigation than for exposition. Very little has been done, though probably much could be. The chief obstacle to a clearer understand- ing of the muscular system lies in the difficulty of getting at the inner surface of the test without obscuring the faint impressions in the process. There exist in the literature a number of references to scars of attachment of muscles, and any study of the subject should of course begin by the collection of such data. I shall at this time refer to only a few observations on the subject. The structure and known habits of trilobites make it obvious that strong flexor and extensor muscles must have been present, and some trace of them and of their points of attachment should be found. It is likely that their proximal ends were tough tendons. The muscles holding up the heart and alimentary canal would be less likely to reveal their pres- 92 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. ence by scars, but there must have been at least one pair of strong muscles extending from the under side of the head across to the hypostoma. Judging from the method of attach- ment, the muscles moving the limbs were short ones, chiefly within the segments of the legs themselves. Flexor Muscles. Since the majority of trilobites had the power of enrollment, and seem also to have used the pygidia in swimming, the flexors must have been important muscles. Beecher (1902, p- 170) appears to have been the only writer to point out any tangible evidence of their former presence. Walcott (1881, p. 199) had shown that the ventral membrane was reinforced in each segment by a slightly thickened transverse arch. Beecher showed that on this thickened arch in Triarthrus, Isotelus, Ptychoparia, and Calymene, there are low lon- gitudinal internal ridges or folds. One of these is central, and there is a pair of diagonal ridges on either side. Beecher interpreted these ridges as separating the strands of the flexor muscles, and believed that a line of median ridges divided a pair of longitudinal muscles, while the outer ridges showed the place of attachment of the pair of strands which was set off to each segment. He did not discuss the question as to where the anterior and posterior ends were attached. In trilobites with short pygidia, the attachment would prob- ably have been near the posterior end, and it is possible that the two scars beneath the dou- blure and back of the last appendifers in Ceraurus may indicate the point of attachment in that genus. There is as yet no satisfactory evidence as to where the anterior ends of the flexors were attached. In Apus these muscles unite in an entosternal sinewy mass above the mouth, but no evidence of any similar mass has been found in the trilobites and it is likely that the muscles were anchored somewhere on the test of the head. Extensor Muscles. The exact position of these muscles has not been previously discussed. The interior of the dorsal test shows no such apodemes as are found on the mesosternites, but, as I have shown in the discussion of the alimentary canal of Calymene and Ceraurus, there is an opening on either side of the axial lobe between the dorsal test and the abdominal sheath, and it is entirely probable that an extensor muscle passed through each of these. The ab- dominal sheath extends only along the posterior region of the glabella and the anterior part of the thorax, and probably served to protect the soft organs from the strain of the heavy muscles. The extensors (see fig. 29) probably lay along the top of the axial lobe on either side of the median line of the thorax to the pygidium, where they appear to have been attached chiefly on the under side of the anterior ring of the axial lobe, although strands probably continued further back. This is above and slightly in front of the fulcral points on the pleura, and meets the mechanical requirements. Ceraurus (Walcott, 1875, and 1881, p. 222, pl. 4, fig. 5) shows a pair of very distinct scars on the under side of the first ring of the pygidium, and in many other trilobites (///lenus, Goldius, etc.) distinct traces of muscular attachment can be seen in this region, even from the exterior. The anterior ends were probably attached by numerous small strands to the top of the glabella, and, principally, to the neck-ring. On enrolling, the sternites of all segments are pulled forward and the tergites backward. In straightening out, the reverse process takes place. The areas available for muscular at- MUSCULATURE. 93 tachment are so disposed as to indicate longitudinal flexor and extensor muscles rather than short muscles extending from segment to segment. Indeed, the tenuity of the ventral mem- brane is such as to preclude the possibility of enrollment by the use of muscles of that sort, while powerful longitudinal flexors could have been anchored to cephalon and pygidium. The strongly marked character of the neck-ring of trilobites is probably to be explained as due Fig. 29.—Restoration of a part of the internal organs of Ceraurus pleurexanthemus as seen from above. At the sides are the extensor muscles, and in the middle, the heart overlying the alimentary canal. Drawn by Doctor Elvira Wood, under the supervision of the author. to the attachment of the extensor muscles, rather than to its recent incorporation in the cephalon. The same is true of the anterior ring on the pygidium. Possible preservations of extensors and flexors in Ceraurus—Among Doctor Walcott’s sections are four slices which I should not like to use in proving the presence of longitudinal muscles, but which may be admitted as corroborative evidence. Two of these transverse sections (Nos. 114 and 199) show a dorsal and a ventral pair of dark spots in positions which suggest that they represent the location of the dorsal and ventral muscles, while two others (Nos. 131 and 140) show only the upper pair of spots. The chief objection to this 94 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. interpretation is that it is difficult to imagine how the muscles could be so replaced that they happen to show in the section. Both the sections showing all four spots are evidently from the anterior part of the thorax, as they show traces of the abdominal sheath, which seems to be squeezed against the inside of the axial lobe, with the muscles (?) forced out to the sides. The ventral pair lie just inside the appendifers, but even if they are sections of muscles, all four are probably somewhat out of place. Hypostonial Muscles. The hypostoma fits tightly against the epistoma, or the doublure when the epistoma is absent, but in no trilobite has it ever been seen ankylosed to the dorsal test, and its rather frail connection therewith is evidenced by the relative rarity of specimens found with it in position. That the hypostoma was movable seems very probable, and that it was held in place by muscles, certain. The macule were always believed to be muscle scars until Lind- stroem (1901, p. 8) announced the discovery by Liljevall of small granules on those of Goldius polyactin (Angelin). These were interpreted as lenses of eyes by Lindstroem, who tried to show that the maculz of all trilobites were functional or degenerate eyes. Most pa- leontologists have not accepted this explanation, and since the so called eyes cover only a part of the surface of the maculee, it is still possible to consider the latter as chiefly muscle- scars. In Lindstroem’s summary (1901, pp. 71, 72) it is admitted that the globular lenses are found only in Bronteus (Goldius) (three Swedish species only) and Cheirurus spinu- losus Nieszkowski, while the prismatic structure supposed to represent degenerate eyes was found in eleven genera (Asaphidee, [lzenidze, Lichadide). All of these are forms with well developed eyes, and Lindstroem himself points out that the appearance of actual lenses in the hypostoma was a late development, long after the necessity for them would appear to have passed. The use of the hypostoma has been discussed by Bernard (1892, p. 240) and extracts from his remarks are quoted: The earliest crustacean-annelids possessed large labra or prostomia projecting backward, still retained in the Apodide and trilobites. This labrum almost necessitated a very deliberate manner of browsing,, The animal would creep along, and would have to run some way over its food before it could get it into its mouth, the whole process, it seems to us, necessitating a number of small movements backwards and forwards. Small living prey would very often escape, owing to the fact that the animal’s mouth and jaws were not ready in position for them when first perceived. The labrum necessitates the animal passing forwards over its prey, then darting backward to follow it with its jaws. We here see how useful the gnathobases of Apus must be in catching and holding prey which had been thus passed over. Indeed the whole arrangement of the limbs of Apus with the sensory endites forms an excellent trap to catch prey over which the labrum has passed. In alcoholic specimens of Apus the labrum is not in a horizontal plane, as it is in most well preserved trilobites, but is tipped down at an angle of from 30° to 45°, and the big mandibles lie under it. It has considerable freedom of motion and is held in place by muscles which run forward and join the under side of the head near its posterior margin. It seems entirely possible that the hypostoma of the trilobite had as much mobility as the labrum of Apus, and that by opening downward it brought the mouth lower and nearer the food. It will be recalled that the hypostomata of practically all trilobites are pointed at the posterior margin, there being either a central point or a pair of prongs. By dropping down the hypos- toma until the point or prongs rested on or in the substratum, and sending food forward MUSCULATURE. 95 to the mouth by means of the appendages, a trilobite could make of itself a most excellent trap, and if the animal could dart backward as well as forward, the hypostoma would be still more useful. There is no reason to suppose that they could not move backward, and the “pygidial antenn’’ of Neolenus indicate that animals of that genus at least did so. This habit of dropping down the hypostoma would also permit the use of those anterior gnatho- bases which seem too far ahead of the mouth in the trilobites with a long hypostoma. For actual evidence on this point, it is necessary to have recourse once more to Doctor Walcott’s exceedingly valuable slices. From such sections of Ceraurus as his Nos. 100, 106, 108, 170, and 173, it is evident that the hypostoma of that form could be dropped con- siderably without disrupting the ventral membrane (fig. 30). Sections of Calymene already published (Walcott 1881, pl. 5, figs. 1, 2) show the hypostoma turned somewhat downward, and the slices themselves show sections of the anterior pair of gnathobases beneath the TITTIES A TM OTR S s. TN : Vu Sis 2 by Hyp OI, My yt, a Fig. 30.— Longitudinal section of cephalon of Ceraurus pleurexanthe- mus, to show position of the mouth and folds of the ventral membrane between the glabella and the hypostoma. The test MOSUL yin ceed rne pana is in solid black and the Fig. 31—A copy of Doctor Moberg’s figure of part within the ventral Nileus armadillo, showing the position of the membrane. dotted. muscle scars. From a photographic enlargement. Specimen 169. X 3.9. hypostoma. When the hypostoma was horizontal, these gnathobases were crowded out at the sides. If the hypostoma were used in the manner indicated, the muscles must have been more efficient than those of the labrum of Apus, and it is probable that they crossed to the dorsal test. Just where they were attached is an unsolved problem. Barrande (1852, pl. 1, fig. 1) has indicated an anterior pair of scars and a single median one on the frontal lobe of Dalmanites that may be considered in this connection, and also three pairs of scars on the last two lobes of the glabella of Proétus (1852, pl. 1, fig. 7). Moberg (1902, p. 295, pl. 3, figs. 2, 3, text fig. 1) has described in some detail the muscle-scars of a rather remarkable specimen of Nilews armadillo Dalman. While, as I shall point out, I do not agree wholly with Professor Moberg’s interpretation, I give here a translation (made for Professor Beecher) of his description, with a copy of his text figure: The well preserved surface of the shell permits one to note not only the tubercle (t) but a number of symmetrically arranged glabellar impressions. And because of their resemblance to the muscular insertions of recent crustaceans, I must interpret them as such. They appear partly as rounded hollows (k and 1), also as elongate straight or curved areas (a, b, c, e, g, h) made up of shallow impressions or furrows about 1 mm. long, sub-parallel, and standing at an angle to the trend of the areas. Impression e is especially well 96 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES, marked, inasmuch as the perpendicular furrows are arranged in a shallow crescentic depression; and impres- sion d shows besides the obscure furrows a number of irregularly rounded depressions. Larger similar ones occur at f, and in part extend over toward g. The meaning of these impressions, or their myologic significance, could be discussed, although such discussion might rather be termed guessing. Inner organs, such as the heart and stomach, might have been attached to the shell along impressions a and b. Also along or behind c and h, which both continue into the free cheeks, ligaments or muscular fibers may have been inserted. From d, e, f, and g, muscles have very likely gone out to the cephalic appendages. Against this it may be urged that impression d is too far forward to have belonged to the first pair of feet. Again, the impression h may in reality represent two confluent muscular insertions, from the first of which, in that case, arose the muscles of the fourth pair of cephalic feet. Were this the case, the muscles of the first pair of cheek feet should be attached at e. And d in turn may be explained as the attachment of the muscles of the antenne, k those of the hypostoma, and from i possibly those of the epistoma. That k is here named as the starting point of the hypostomial muscles and not those of the antennz, depends partly on the analogous position of i and partly on the fact that the hypostoma of Nilews armadillo (text figure, in which the outline of the hypostoma is dotted), by reason of its wing-like border, could not have permitted the antenne to reach forward, but rather only outward or backward. My own explanation would be that impressions e, f, and g correspond to the glabellar furrows, h the neck furrow, and all four show the places of attachment of the appendifers. Those at d may possibly be connected with the antenne, although I should expect those organs to be attached under the dorsal furrows at the sides of the hypostoma. It will be noted that either b, k, or i correspond well with the maculze of the hypostoma and some or all of them may be the points of attachment of hypostomial muscles. They correspond also with the anterior scars of Dalmanites. EYEs. While I have nothing to add to what has been written about the eyes of trilobites, this sketch of the anatomy would be incomplete without some reference to the little which has been done on the structure of these organs. Quenstedt (1837, p. 339) appears to have been the first to compare the eyes of trilo- bites with those of other Crustacea. Johannes Muller had pointed out in 1829 (Meckel’s Archiv) that two kinds of eyes were found in the latter group, compound eyes with a smooth cornea, and compound eyes with a facetted coat. Quenstedt cited Trilobites esmarkw Schlo- theim (= /llenus crassicauda Dalman) as an example of the first group, and Calymene ma- crophthalma Brongniart (= Phacops latifrons Bronn) for the second. Misreading the some- what careless style of Quenstedt, Barrande (1852, p. 133) reverses these, one of the few slips to be found in the voluminous writings of that remarkable savant. Burmeister (1843; 1846, p. 19) considered the two kinds of eyes as essentially the same, and accounted for the conspicuous lenses of Phacops on the supposition that the cornea was thinner in that genus than in the trilobites with smooth eyes. Barrande (1852, p. 135) recognized three types of eyes in trilobites, adding to Quen- stedt’s smooth and facetted compound eyes the groups of simple eyes found in Harpes. In his sections of 1852, pl. 3, figs. 15-25, which are evidently diagrammatic, he shows sepa- rated biconvex lenses in both types of compound eyes, Phacops and Dalmanites on one hand, and Asaphus, Goldius, Acidaspis, and Cyclopyge on the other. Clarke (1888), Exner (1891) and especially Lindstroem (1901) have since published much more accurate figures and descriptions. The first person to study the eye in thin section seems to have been Packard (1880), who published some very sketchy figures of specimens loaned him by Walcott. He EYES. 97 studied the eyes of Jsotelus gigas, Bathyurus longispinus, Calymene, and Phacops, and decided that the two types of eyes were fundamentally the same. He also compared them with the eyes of Limulus. Clarke (1888), in a careful study of the eye of Phacops rana, found that the lenses were unequally biconvex, the curvature greater on the inner surface. The lens had a cir- cular opening on the inner side, leading into a small pear-shaped cavity. The individual lenses were quite distinct from one another, and separated by a continuation of the test of the cheek. Exner (1891, p. 34), in a comparison of the eyes of Phacops and Limulus, came to the opinion that they were very unlike, and that the former were really aggregates of simple eyes. Lindstroem (1901, pp. 27-31) came to the conclusion that besides the blind trilobites there were trilobites with two kinds of compound eyes, trilobites with aggregate eyes, and trilobites with stemmata and ocelli. His views may be briefly summarized. I. Compound eyes. I. Eyes with prismatic, plano-convex lenses. “A pellucid, smooth and glossy integument, a direct continuation of the common test of the body, covers the corneal lenses, quite as is the case in so many of the recent Crustacea. The lenses are closely packed, minute, usually hexagonal in outline, flat on the outer and convex on the inner surface. Such eyes are best developed in Asaphus, Illenus, Nileus, Bumastus, Proétus, etc.” 2. Eyes with biconvex lenses. The surface of the eye is a mass of contiguous lenses, covered by a thin membrane which is frequently absent from the specimens, due to poor preservation. ‘The lenses are biconvex, and being in contact with one another, are usually hexagonal, although in some cases they nearly retain their globular shape. Such eyes are found in Euwrycare, Peltura, Spheropthalmus, Ctenopyge, Goldius, Cheirurus, and probably others. II. Aggregate eyes. The individual lenses are comparatively large, distinct from one another, each lying in its own socket. There is, however, a thin membrane, which covers all those in any one aggregate, and is a continuation of the general integument of the body. This membrane is continued as a thickened infolding which forms the sockets of the lenses. Such eyes are known in the Phacopide only. III. Stemmata and ocelli. The stemmata are present only in Harpes, where there may be on the summit of the cheek two or three ocelli lying near one another. Each, viewed from above, is nearly circular in outline, almost hemispheric, glossy and shining. In section they prove to be convex above and flat or slightly concave beneath. The test covers and separates them, as in the case of the aggregate eyes. The ocelli of the Trinucleidee and Eoharpes are smaller, and the detailed structure not yet investigated. Lindstroem concludes that so far as its facets or lenses are concerned, the eye of the trilobite shows the greatest analogy with the Isopoda, and the least with Limulus. SUMMARY. The simplest eyes found among the Trilobita are the ocelli. These consist of a simple thickening of the test to form a convex surface capable of concentrating light. The simi- larity in position of the paired ocelli of trilobites and the simple eyes of copepods has per- haps a significance. The schizochroal eyes may well be compared with the aggregate eyes of the chilopods and scorpions. The mere presence of a common external covering is not sufficient to prove this a true compound eye, especially as the covering is merely a continuation of the general test. 98 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The holochroal eyes are of two kinds, one with plano-convex and one with biconvex lenses. The latter would seem to be mechanically the more perfect of the two, and it is worthy of note that the trilobites possessing the biconvex lenses have, in general, much smaller eyes than those with the other type. If, as some investigators claim, the parietal eye of Crustacea originates by the fusion of two lateral ocelli, trilobites show a primitive condition in lacking this eye, which may have originated through the migration toward the median line of ocelli like those of the Trinu- cleidie. SEX. That the sexes were separate in the Trilobita there can be very little doubt, but the study of the appendages has as yet revealed nothing in the way of sexual differences. One of the most important points still to be determined is the location of the genital openings. In many modern Crustacea, the antenne or antennules are modified as claspers, and it is barely possible that the curious double curvature of the antennules of Tviarthrus indi- cates a function of this sort. The antennules of many specimens have the rather formal double curvature, turning inward at the outer ends, and retain this position of the frontal appendages, no matter what may be the condition of those on the body. Other specimens have the antennules variously displaced, indicating that they are quite flexible. It is conceiv- able that the individuals with rigid antennules are males, the others females. It is interesting to note that the antennules of Ptychoparia permulta Walcott (1918, pl. 21, fig. 1) have the same recurved form. All the specimens of Neolenus, however, show very flexible antenne. Barrande and Salter laid great stress upon the “forme longue’ and “forme large” as indicating male and female. This was based upon the supposition that the female of any animal would probably have a broader test than the male, a hypothesis which seems to be very little supported by fact. In practical application it was found that the apparent dif- ference was so often due to the state of preservation or the confusion of two or more species, that for many years little reference has been made to this supposed sex difference. EGGs. In his classic work on the trilobites of Bohemia, Barrande described three kinds of spheri- cal and one of capsule-shaped bodies which he considered to be the eggs of trilobites. After a review of the literature and a study of specimens in the collections of the Museum of Comparative Zoology, it can be said that none of these fossils has proved to be a trilobite egg, but that they may be plants. A full account of them will be published elsewhere. Walcott (1881) and Billings (1870) have described similar bodies within the tests of Calymene and Ceraurus, but without showing positive evidence as to their nature. Metuops oF LIFE. This is a subject upon which much can be inferred, but little proved. Without trying to cover all possibilities, it may be profitable to see what can be deduced from what is known of the structure of the external test, the internal anatomy, and the appendages. This can, to a certain extent, be controlled by what is inferred from the strata in which the specimens are found, the state of preservation, and the associated animals. (For other details, see the discussion of “Function of the Appendages” in Part I.) LOCOMOTION. 99 HABITS OF LOCOMOTION. The methods of locomotion may be deduced with some safety from a study of the ap- pendages, and, as has repeatedly been pointed out, all trilobites could probably swim by their use. This swimming was evidently done with the head directed forward, and could prob- ably be accomplished indifferently well with either the dorsal (gastronectic, Dollo) or the ventral (notonectic) side up. If food were sought on the bottom by means of sight, the animal would probably swim dorsal side up, for by canting from side to side it could see the bottom just as easily as though it were ventral side up, and at the same time it would be in position to drop quickly on the prey. In collecting food at the surface, it might swim ventral side up. All trilobites could probably crawl by the use of the appendages, and, as has already been pointed out, there are great differences in the adjustment of the appendages to different methods of crawling. Some crawled on their “toes,” some by means of the entire endopo- dites, and some apparently used the coxopodites to push themselves along. That the normal direction of crawling was forward is indicated by the position of the eyes and sensory anten- nules. There is no evidence that their mechanism was irreversible, however, and the position of the mouth and the shape of the hypostoma indicate that they usually backed into feeding position. The caudal rami of Neolenus were evidently sensory, and the animal was pre- pared to go in either direction. The use of the pygidium as a swimming organ, suggested by Spencer (1903, p. 492) on theoretical grounds, developed by Staff and Reck (1911, p. 141) from a mechanical stand- point, and elaborated in the present paper by evidence from the ontogeny, phylogeny, and musculature, provided the animal with a swifter means of locomotion. By a sudden flap of this large fin, a backward darting motion could be obtained, which would be invaluable as a means of escape from enemies. Staff and Reck seem to think that in this movement the two shields were clapped together, and that the animal was projected along with the hinge- like thorax forward. This might be a very plausible explanation in the case of the bivalve- like Agnostidz, and it is one I had suggested tentatively for that family before I read Staff and Reck’s paper. In the case of the large trilobites with more segments, however, it would be more natural to think of a mode of progression in which there was an undulatory move- ment of the body and the pygidium, up-and-down strokes being produced by alternately contracting the dorsal and ventral muscles. Bending the pygidium down would tend to pull the animal backward, while bringing it back into position would push it forward. It fol- lows, therefore, that one of these movements must have been accomplished very quickly, the other slowly. If the muscle scars have been interpreted properly, the ventral muscles were probably the more powerful, an indication that the animal swam backward, using the cephalon and antennules as rudders. The chief objection to the theory of swimming by clapping the valves together is that where the thorax consists of several segments it no longer acts like the hinge of a bivalve, and a sudden downward flap of the pygidium would impart a rotary motion to the animal. Take, for example, such nearly spherical animals as the Illenidz, and it will readily be seen that there is nothing to give direction to the motion if the pygidium be brought suddenly against the lower surface of the cephalon. A lobster, it is true, progresses very well by this method, but it depends upon its great claws and long antenne to direct its motions. The whole shape of the trilobite is of course.awkward for a rapidly swimming animal. It could keep afloat with the minimum of effort and paddle itself about with ease, but it was not built on the correct lines for speed. 100 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Dollo (1910, p. 406), and quickly following his lead, Staff and Reck (1911, p. 130), have published extremely suggestive papers, showing that by the use of the principle of correlation of parts, much can be inferred about the mode of life of the trilobites merely from the structure of the test. Dollo studied the connection between the shape of the pygidium and the position and character of the eyes. As applied by him, and later by Clarke and Ruedemann, to the euryp- terids, this method seems most satisfactory. He pointed out that in Eurypterida like Sty- lonurus and Eurypterus, where there is a long spine-like telson, the eyes are back from the margin, so that a Limulus-like habit of pushing the head into the sand by means of the limbs and telson was possible. Erettopterus and Pterygotus, on the other hand, have the eyes on the margin, so that the head could not be pushed into the mud without damage, and have a fin-like telson, suggesting a swimming mode of life. In carrying this principle over to the trilobites, Dollo was quite successful, but Staff and Reck have pointed out some modifications of his results. The conclusions reached in both these papers are suggestive rather than final, for not all possible factors have been considered. The following are given as examples of interesting speculations along this line. Homalonotus delphinocephalus, according to Dollo, was a crawling animal adapted to benthonic life in the euphotic region, and an occasional burrower in mud. ‘This is shown by well developed eyes in the middle of the cephalon, a pointed pygidium, and the plow-like profile of the head. This was as far as Dollo went. From the very broad axial lobe of Homalonotus it is fair to infer that, like [sotelus, it had very long, strong coxopodites which it probably used in locomotion, and also very well-developed longitudinal muscles, to be used _ in swimming. From the phylogeny of the group, it is known that the oldest homalonotids had broad unpointed pygidia of the swimming type, and that the later species of the genus (Devonian) are almost all found in sandstone and shale, and all have wider axial lobes than the Ordovician forms. It is also known that the epistoma is narrower and more firmly fused into the doublure in later than in earlier species. These lines of evidence tend to confirm Dollo’s conclusion, but also indicate that the animals retained the ability to swim well. On the same grounds, Olenellus thompson and Dalmamites limulurus were assigned the same habitat and habits. Both were considered to have used the terminal spine as does Linulus. Olenellus thompsom is generally considered to be unique among trilobites in having a Limulus-like telson in place of a pygidium. This “telson” has exactly the position and characteristics of the spine on the fifteenth segment of Mesonacis, and so long ago as 1896, Marr (Brit. Assoc. Ady. Sci., Rept. 66th Meeting, page 764) wrote: The posterior segments of the remarkable trilobite Mesonacis vermontana are of a much more delicate character than the anterior ones, and the resemblance of the spine on the fifteenth “hody segment” of this species to the terminal spine of Olenellus proper, suggests that in the latter subgenus posterior segments of a purely membranous character may have existed devoid of hard parts. This prophecy was fulfilled by the discovery of the specimens which Walcott described as Pedeunias transitans, a species which is said by its author to be a “form otherwise identical with O. thompsom, [but] has rudimentary thoracic segments and a Holmuia-like pygidium posterior to the fifteenth spine-bearing segment of the thorax.’’ A good speci- men of this form was found at Georgia, Vermont, associated with the ordinary specimens of Olenellus thompsom, and I believe that it is merely a complete specimen of that species. LOCOMOTION. TOI Olenellus gilberti, which was formerly supposed to have a limuloid telson, has now been shown by Walcott (Smithson. Misc. Coll., vol. 64, 1916, p. 406, pl. 45, fig. 3) to be a Mesonacis and to have seven or eight thoracic segments and a small plate-like pygidium back of the spine-bearing fifteenth segment. All indications are that the spine was not in any sense a pygidium. Walcott states that Olenellus resulted from the resorption of the rudimentary segments of forms such as Mesonacis and Pedewmuias, leaving the spine to function as a pygidium. This would mean the cutting off of the anus and the posterior part of the alimentary canal, and developing a new anal opening on the spine of one of the thoracic segments! If the spine of the fifteenth segment is not a pygidium, could it be used, as Dollo postulates, as a pushing organ? Presumably not, for though in entire specimens of Olenellus (Pedeumias) it extends back beyond the pygidium, it probably was borne erect, like the similar spines in Elliptocephala, and not in the horizontal plane in which it is found in crushed specimens. While this removes some of the force of Dollo’s argument, his conclusion that Olenellus was a crawling, burrowing animal living in well lighted shallow waters was very likely cor- rect. The long, annelid-like body indicates numerous crawling legs, there is no swimming pygidium, and the fusion of the cheeks in the head makes a stiff cephalon well adapted for burrowing. Staff and Reck have pointed out that Dalmanites limulurus was not entirely a crawler, but, as shown by the large pygidium, a swimmer as well. This kind of trilobite probably represents the normal development of the group in Ordovician and later times. The Pha- copide, Proétidee, Calymenide, and other trilobites of their structure could probably crawl or swim equally well, and could escape enemies by darting away or by “digging them- selves in.” Cryptohthus tessellatus (Trinucleus concentricus) is cited by Dollo as an example of an adaptation to life in the aphotic benthos, permanently buried in the mud. In this case he appealed to Beecher’s interpretation of the appendages, and pointed out that while the adult is blind, the young have simple eyes and probably passed part of their life in the lighted zone. It needs only a glance at the very young to convince one that the embryos had swimming habits, so that in this form one sees the adaptation of the individual during its history to all modes of life open to a trilobite. The habits of the Harpedidze may have been similar to those of the Trinucleidze, but the members of this family are supplied with broad flat genal spines. It has been suggested that these served like pontoons, runners, or snow-shoes, to enable the animal to progress over soft mud without sinking into it. Some such explanation might also be applied to the similar development in the wholly unrelated Bathyuride. The absence of compound eyes and the poor development of ocelli in the Har- pedidze suggest that they were burrowers, and from these two families, Trinucleide and Harpedidz, it becomes evident that a pygidial point or spine is not a necessary part of the equipment of a burrowing trilobite. In fact, from the habits of Limulus it is known that the appendages are relied upon for digging, and that the telson is a useful but not indis- pensable pushing organ. Deiphon is an interesting trilobite from many points of view. Its pleural lobes are reduced to a series of spines on either side of the body, and its pygidium is a mere spinose vestige. Dollo considered this animal a swimmer in the euphotic zone, because its eyes are on the anterior margin, its body depressed, its glabella globose, and its pygidium flat 102 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. and spinose. That such a method of life was secondary in a cheirurid was indicated to him by the fact that the more primitive members of the family seemed adapted for crawl- ing. Staff and Reck have gone further and shown that the pygidium is only the vestige of a swimming pygidium, and that the great development of spines suggests a floating rather than a swimming mode of life. They therefore argue for a planktonic habitat. A similar explanation is suggested for Acidaspis and other highly spinose species. The Aeglinidz, or Cyclopygide as they are more properly called, present the most re- markable development of eyes among the trilobites. In this, Dollo saw, as indeed earlier writers have, an adaptation to a region of scanty light. ‘The cephalon is not at all adapted to burrowing, but the pygidium is a good swimming organ, and one is apt to agree that this animal was normally an inhabitant of the ill lighted dysphotic region, but also a nocturnal prowler, making trips to the surface at night. Similar habits and habitat are certainly indi- cated for Telephus and the Remopleuride, but whether Nileuws and the large-eyed Bumastus are capable of the same explanation is doubtful. Finch (1904, p. 181) makes the suggestion that “Nileus’ (Vogdesia) vigilans, an abundant trilobite in the calcareous shale of the Maquoketa, was in the habit of burying itself, posterior end first. He found a slab containing fifteen entire specimens, all of which had the cephalon extended horizontally near the surface of the stratum, and the thorax and pygidium projecting downward. The rock showed no evidence that they were in burrows, and the fact that all were in the same position indicates that the attitude was voluntarily assumed. ‘They appear to have entrenched themselves by the use of the pygidia, which are incurved plates readily adapted for such use, and, buried up to the eyes, awaited the coming of prey, but were, apparently, smothered by a sudden influx of mud. The form of the eye in Vogdesia vigilans bears out this supposition of Finch’s. Not only are the eyes unusually tall, but the palpebral lobe is much reduced, so that many of the lenses look upward and inward,-as well as outward, forward and backward. ‘The particular food required by V. vigi- lans must have been very plentiful in the Maquoketa seas of Illinois and Lowa, for the species was very abundant, but that its habits were self-destructive is also shown by the great num- ber of complete enrolled specimens of all ages now found there. The soft mud was appar- ently fatal to the species before the end of the Maquoketa, for specimens are seen but very rarely in the higher beds. Vogdesia vigilans is shaped much like Bumastus, Illenus, Asaphus, Onchometopus, and Brachyaspis, and it may be that these trilobites with incurved pygidia had all adopted the habit of digging in backward. As noted above, their pygidia are not very well adapted for swimming, and most of them have large or tall eyes. Dollo’s comparison of the Cyclopygidz to the huge-eyed modern amphipod Cystosoma is instructive. This latter crustacean, which has the greater part of the dorsal surface of the carapace transformed into eyes, is said to live in the dysphotic zone, at depths of from 40 to 100 fathoms, and to come to the surface at night. It swims ventral side down. The kinds of sediments in which trilobites are entombed have so far afforded little evi- dence as to their habitat. Frech (Lethza paleozoica, 1897-1902, p. 67 et seq.) who has collected such evidence as is available on this subject, places as deeper water Ordovician deposits the “Trinucleus-Schiefer” of the upper Ordovician of northern Europe and Bohemia, the ‘““Triarthrus-Schiefer” of America, the “Asaphus-Schiefer’ of Scandinavia, Bohemia, Portugal, and France, and the Dalmania quartzite of Bohemia. Cryptolithus and Triarthrus, although not confined to such deposits, are apt to occur FEEDING. 103 chiefly in very fine-grained shales, in company with graptolites. These latter are distributed by currents over great distances within short periods. It is somewhat curious that the nearly blind burrowing Trinucleide, the dysphotic, large-eyed Remopleuride and Telephus, the blind nektonic Agnostidz and Dionide, and the planktonic graptolites should go together and make up almost the entire fauna of certain formations. Yet, when the life history of each type is studied, a logical explanation is readily at hand, for all have free-swimming larvee. A list of the methods of life noted above is given by way of summary, with examples. Planktonic Ki Primarily Earliest protaspis of all trilobites | 1 Secondarily Deiphon, Odontopleura, etc. Pelagic Primarily Later protaspis of all trilobites. Naraoia | | Probably many thin-shelled trilobites with large pygidia Nektonic i (only partially nektonic) Secondarily j | Cyclopygide és : Rempniearide: ‘ (nektonic dysphotic) Crawlers and Most trilobites with small pygidia. Triarthrus, Para- 7 slow swimmers doxides, etc. Crawlers and Most trilobites with large pygidia. Jsotelus, Dal- Benthonic active swimmers manites, etc. Crawlers, slow : swimmers, and Trinucleide, Harpedide, some Mesonacide, etc. burrowers < FOOD AND FEEDING METHODS. This subject has been less discussed than the methods of locomotion. The study of the appendages has shown that while the mouth parts were not especially powerful, they were at least numerous, and sufficiently armed with spines to shred up such animal and vegetable substances as they were liable to encounter. It having been ascertained that the shape of the glabella and axial lobe furnishes an indication of the degree of development of the alimen- tary canal it is possible to infer something of the kind of food used by various trilobites. The narrow glabellz and axial lobes of the oldest trilobites would seem to indicate a carnivorous habit, while the swollen glabellze and wider lobes of later ones probably denote an adaptation to a mixed or even a vegetable diet. This can not be relied upon too strictly, of course, for the swollen glabellee of such genera as Deiphon or Spherexochus may be due merely to the shortening up of the cephalon. Walcott (1918, p. 125) suggests that the trilobites lived largely upon worms and con- ceives of them as working down into the mud and prowling around in it in search of such prey. While there can be no doubt that many trilobites had the power of burying them- selves in loose sand or mud, a common habit with modern crustaceans, most of them were of a very awkward shape for habitual burrowers, and how an annelid could be successfully pursued through such a medium by an animal of this sort is difficult to understand. In fact, the presence of the large hypostoma and the position of the mouth were the great handicaps of the trilobite as a procurer of live animal food, and coupled with the rela- tively slow means of locomotion, almost compel the conclusion that errant animals of any size were fairly safe from it. This restricts the range of animal food to small inactive creatures and the remains of such larger forms as died from natural causes. The modern Crustacea are effective scavengers, and it is probable that their early Palzeozoic ancestors were equally so. It is a common saying that in the present stressful stage of the world’s history, very few wild animals die a natural death. In Cambrian times, competition for 104 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. animal food was less keen, and with the exception of a few cephalopods, a few large anne- lids, and a few Crustacea like Sidneyia, there seem to have been no aggressive carnivores. In consequence, millions of animals must have daily died a natural death, and had there been no way of disposing of their remains, the sea bottom would soon have become so foul that no life could have existed. For the work of removal of this decaying matter, the carniv- orous annelids and the Crustacea, mostly trilobites, were the only organisms, and it is prob- able that the latter did their full share. After prowling about and locating a carcass, the trilobite established himself over it, the cephalon and hypostoma on one end and the pygidium on the other enclosing and protecting the prey, which was shredded off and passed to the mouth at leisure by means of the spinose endobases. Even in Middle Cambrian times some trilobites (e. g., Paradowxides) seem to have en- larged the capacity of the stomach and taken vegetable matter, but later, in the Upper Cambrian and Ordovician, when the development of cephalopods and fishes caused great competition for all animal food, dead or alive, most trilobites seem to have become omniv- orous. This is of course shown by the swollen glabella, with reduced lateral furrows, and, in the case of a few species (Calymene, Ceraurus), the known enlargement of the stomach. Cryptolithus is the only trilobite which has furnished any actual evidence as to its food. From the fact that the alimentary tract is found stuffed from end to end with fine mud, and because it is known to have been a burrower, it has been suggested by several that it was a mud feeder, passing the mud through the digestive tract for the sake of what organic matter it contained. Spencer (1903, p. 491) has suggested a modification of this view: The phyllopods appear to feed by turning over whilst swimming and seizing with their more posterior appendages a little mud which swarms with infusoria, etc. This mud is then pushed along the ventral groove to the mouth. Casts of the intestine of trilobites are still found filled with the mud. Cerawrus and Calymene also must have occasionally swallowed mud in quantity, other-— wise the form of the alimentary canal could not have been preserved as it is in a few of Doctor Walcott’s specimens. TRACKS AND TRAILS OF TRILOBITES. Tracks and trails of various sorts have been ascribed by authors to trilobites since these problematic markings first began to attract attention, but as the appendages were until re- cently quite unknown, all the earlier references were purely speculative. The subject is a difficult one, and proof that any particular track or trail could have been made in only one way is not easily obtained. Since the appendages have actually been described, compara- tively little has been done, Walcott’s work on Protichnites (1912 B, p. 275) being the most important. Since the first description of Protichnites by Owen (Quart. Jour. Geol. Soc., London, 1852, vol. 8, p. 247), it has been thought that these trails were made by crustaceans, and the only known contemporaneous crustaceans being trilobites, these animals were natu- rally suggested. Dawson (Canadian Nat. Geol., vol. 7, 1862, p. 276) ascribed them, with reserve, to Paradoxides, and Billings (1870, p. 484) suggested Dikelocephalus or Aglaspis. Walcott secured well preserved specimens which showed trifid tracks, and these were readily explained when he found the legs of Neolenus, which terminated with three large spines. Similar trifid terminations had already been described by Beecher, and clearly pictured in his restoration of Triarthrus, but the spines and the tracks had somehow not previously been connected in the mind of any observer. Walcott concluded that the tracks had been made TRACKS AND TRAILS. 105 by a species of Dikelocephalus, possibly by D. hartti, which occurs both north and south of the Adirondacks. In a recent paper, Burling (Amer. Jour. Sci., ser. 4, vol. 44, 1917, p. 387) has argued that Protichnites was not the trail of a trilobite, but of a “short, low-lying, more or less heavy set, approximately 12-legged, crab-like animal,’ which had an oval shape, toed in, and was either extremely flexible or else short and more or less flexible in outline. This seems to describe a trilobite. Climactichnites, the most discussed single trail of all, has also been ascribed to trilo- bites,—by Dana (Manual of Geology, 1863, p. 185), Billings (1870, p. 485), and Packard (Proc. Amer. Acad. Arts and Sci., vol. 36, 1900, p. 64),—though less frequently than to other animals. The latest opinion (see paper by Burling cited above) seems to be against this theory. Miller (1880, p. 217) described under the generic name Asaphoidichnus two kinds of tracks which were such as he supposed might be made by an Asaphus (Isotelus). In re- ferring to the second of the species, he says: “Some of the toe-tracks are more or less fringed, which I attribute to the action of water, though Mr. Dyer is impressed with the idea that it may indicate hairy or spinous feet.” The type of this species, A. dyeri, is in the Museum of Comparative Zoology, and while it may be the trail of a trilobite, it would be difficult to explain how it was produced. Ringueberg (1886, p. 228) has described very briefly tracks found in the upper part of the Medina at Lockport, New York. These consisted of a regularly succeeding series of ten paired divergent indentations arranged in two diverging rows, with the trail of the pygid- ium showing between each series. The ten pairs of indentations he considered could have been made by ten pairs of legs like those shown by the specimen of Jsotelus described by Mickleborough, and the intermittent appearance of the impression of the pygidium suggested to him that the trilobite proceeded by a series of leaps. Walcott (1918, pp. 174-175, pl. 37-42) has recently figured a number of interesting trails as those of trilobites, and has pointed out that a large field remains open to anyone who has the patience to develop this side of the subject. IPVAURIC IEE RELATIONSHIP OF THE TRILOBITES TO OTHER ARTHROPODA. It can not be said that the new discoveries of appendagiferous trilobites have added greatly to previous knowledge of the systematic position of the group. Probably none will now deny that trilobites are Crustacea, and more primitive and generalized than any other group in that class. The chief interest at present lies in their relation to the most nearly allied groups, and to the crustacean ancestor. Trilobites have been most often compared with Branchiopoda, [sopoda, and Merostom- ata, the present concensus of opinion inclining toward the notostracan branchiopods (Apod- idee in particular) as the most closely allied forms. It seems hardly worth while to burden these pages with a history of opinion on this subject, since it was not until the appendages were fully made out, from 1881 to 1895, that zoologists and palzontologists were in a position to give an intelligent judgment. The present status is due chiefly to Bernard (1894). Beecher (1897, 1900, et seg.), and Walcott (1912, et seq.). The chief primitive characteristics of trilobites are: direct development from a pro- taspis common to the subclass; variability in the number of segments, position of the mouth, and type of eyes; and serially similar biramous appendages. The recent study has modified the last statement slightly, since it appears that in some trilobites there was a modification of the appendages about the mouth, suggesting the initia- tion of a set of tagmata. In comparing the trilobites with other Crustacea, the condition of the appendages must be especially borne in mind, for while these organs are those most intimately in contact with the environment, and most subject to modification and change, yet they have proved of greatest service in classification. Appendages have been found on trilobites from only the Middle Cambrian and Middle and Upper Ordovician, but as the Ordovician was the time of maximum development of the group, it is probable that trilobites of later ages would show degradational rather than pro- gressive changes. All the genera which are known show appendages of the same plan, and although new discoveries will doubtless reveal many modifications of that plan, general infer- ences may be drawn now with some assurance. The chief characteristics of the appendages are: first, simple antennules, a primitive fea- ture in all Crustacea, as shown by ontogeny; second, paired biramous appendages, similar to each other all along the body, the youngest and simplest in front of the anal segment, the oldest and most modified on the cephalon. The endobases are retained on all the coxopo- dites, except possibly, in some species, the anterior ones, and these gnathobases are modi- fied in some genera as mouth-parts, while in others they are similar throughout the series. With these few fundamentals in mind, other Crustacea may be examined for likenesses. The differences are obvious. CRUSTACEA. BRANCHIOPODA. The early idea that the trilobites were closely related to the Branchiopoda was rejuve- nated by the work of Bernard on the Apodidz (1892) and has since received the support BRANCHIOPODA. 107 of most writers on the subject. Fundamentally, a great deal of the argument seems to be that Apus lies the nearest of any modern representative of the class to the theoretical crus- tacean ancestor, and as the trilobites are the oldest Crustacea, they must be closely related. Most writers state that the trilobites could not be derived from the Branchiopoda (see, how- ever, Walcott 1912 A), nor the latter from any known trilobite, but both subclasses are be- lieved to be close to the parent stem. Viewed from the dorsal side, there is very little similarity between any of the branchi- opods and the trilobites, and it is only in the Notostraca, with their sessile eyes and depressed form, that any comparison can be made. The chief way in which modern Bran- chiopoda and Trilobita agree is that poth have a variable number of segments in the body, that number becoming very large in Apus on the one hand and Mesonacis and Pedeumias on the other. In neither are the appendages, except those about the mouth, grouped in tagmata. Other likenesses are: the Branchiopoda are the only Crustacea, other than Trilo- bita, in which gnathobases are found on limbs far removed from the mouth; the trunk limbs are essentially leaf-like in both, though the limb of the branchiopod is not so primitive as that of the trilobite; caudal cerci occur in both groups. If the appendages be compared in a little more detail, the differences prove more strik- ing than the likenesses. In the Branchiopoda, the antennules are either not segmented or only obscurely so. In trilobites they are richly segmented. In Branchiopoda, the antenne are variable. In the Notostraca they are vestigial, while in the males of the Anostraca they are powerful and often complexly developed claspers. Either condition might develop from the generalized biramous antenne of Trilobita, but the present evidence indicates a tendency toward obsolescence. Claus’ observations indicate that the antennze of the Anostraca are developments of the exopodites, rather than of the endopodites. The mandibles and maxilla of the Branchiopoda are greatly reduced, and grouped closely about the mouth. Only the coxopodites of the Trilobita are modified as oral appen- dages. The trunk limbs of Apus are supposed to be the most primitive among the Branchio- poda, and comparison will be made with them. Each appendage consists of a flattened axial portion, from the inner margin of which spring six endites, and from the outer, two large flat exites (see fig. 34). This limb is not articulated with the ventral membrane, but attached to it, and, if Lankester’s interpretation of the origin of schizopodal limbs be correct, then the limb of Apus bears very little relation to that of the Trilobita. In Apus there is no distinct coxopodite and the endobases which so greatly resemble the similar organs in the Trilobita are not really homologous with them, but are developments of the first endite. Beecher’s comparison of the posterior thoracic and pygidial limbs of Triarthrus with those of Apus can not be sustained. Neither Triarthrus nor any other trilobite shows any trace of phyl- lopodan limbs. Beecher figured (1894 B, pl. 7, figs. 3, 4) a series of endopodites from the pygidium of a young Triarthrus beside a series of limbs from a larval Apus. Superficially, they are strikingly alike, but while the endopodites of Triarthrus are segmented, the limbs of Apus are not, and the parts which appear to be similar are really not homologous. The similarity of the thoracic limbs in the two groups is therefore a case of parallelism and does not denote relationship. 108 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Geologically, the Branchiopoda are as old as the Trilobita, and while they did not have the development in the past that the trilobite had, they were apparently differentiated fully as early. Anostraca, Notostraca and Conchostraca, three of the four orders, are represented in the Cambrian by forms which are, except in their appendages, as highly organized as the existing species. Brief notes on the principal Middle Cambrian Branchiopoda follow: _Burgessia bella Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 177, pl. 27, figs. 1-3; pl. 30, figs. 3, 4. This is the most strikingly like the modern Branchiopoda of any species described by Walcott from the Middle Cambrian, and invites comparison with Apus. The carapace is long, loosely attached to the body, and extends over the greater part of the thorax. The eyes are small, sessile, and close to the anterior margin. The appendages of the head consist of two pairs of antennze, and three pairs of slender, jointed legs. Both pairs of antennz are slender and many-jointed, the antennules some- what smaller than the antennz. The exact structure of the limbs about the mouth has not yet been made out, but they are slender, tapering, endopodite-like legs, with at least three or four segments in each, and probably more. There are eight pairs of thoracic appendages, each limb having the form of the endopo- dite of a trilobite and consisting of seven segments and a terminal spine. The proximal three segments of each appendage are larger than the outer ones, and have a flattened triangular expansion on the inner side. Walcott also states that “One specimen shows on seven pairs of legs, small, elongate, oval bodies attached near the first joint to the outer side of the leg. These bodies left but slight impression on the rock and are rarely seen. They appear to represent the gills.” They are not figured, but taken in connection with the endopodite-like appearance of the segmented limbs, one would expect them to be vestigial exopodites. A small hypostoma is present on the ventral side, and several of the specimens show wonderfully well the form of the alimentary canal and the hepatic ceca. The main branches of the latter enter the mesenteron just behind the fifth pair of cephalic appendages. Behind the thorax the abdomen is long. limbless, and tapers to a point. It is said to consist of at least thirty segments. Compared with Apus, Burgessia appears both more primitive and more specialized. The carapace and limbless abdomen are Apus-like, but there are very few appendagiferous segments, and the appendages are not at all phyllopodan, but directly comparable with those of trilobites, except, of course, for the uniramous character of the cephalic limbs. A closer comparison may be made with Marrella. Waptia fieldensis Walcott. Tllustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 181, pl. 27, figs. 4, 5. The carapace is short, covering the head and the anterior part of the thorax. The latter consists of eight short segments with appendages, while the six abdominal segments, which are similar to those of the thorax, are without limbs except for the last, which bears a pair of broad swimmerets. The eyes are marginal and pedunculate. The antennules are imperfectly known, but apparently short, while the antennz are long and slender, with rela- tively few, long, segments. The mandibles appear to be like endopodites of trilobites and show at least six segments. As so often happens in these specimens from British Columbia, BRANCHIOPODA. 109 the preservation of the other appendages is unsatisfactory. As illustrated (Walcott, 1912 A, pl. 27, fig. 5), both endopodites and exopodites appear to be present, and the shaft of the exopodite seems to be segmented as in Tviarthrus. Walcott considers WV/aptia as a transitional form between the Branchiopoda and the Malacostraca. Yohoia tenuis Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 172, pl. 20, figs. 7-13. This species, though incompletely known, has several interesting characteristics. The head shows, quite plainly in some specimens, the five segments of which it is composed. The eyes are small, situated in a niche between the first and second segments, and are described as being pedunculate. The eight segments of the thorax all show short triangu- lar pleural extensions, somewhat like those of Remopleuyides or Robergia. The abdomen consists of four cylindrical segments, the last with a pair of expanded caudal rami. The antennules appear to be short, while the antennz are large, with several segments, ending in three spines, and apparently adapted for serving as claspers in the male. The third, fourth, and fifth pairs of cephalic appendages are short, tapering, endopodite-like legs similar to those of Burgessia. The appendages of the thorax are not well preserved, and there seem to be none on the ° abdomen. This species is referred by Walcott to the Anostraca. Opabina regalis Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 167, pl. 27, fig. 6; pl. 28, fig. 1. This most remarkably specialized anostracan is not well enough known to allow com- parison to be made with other contemporaneous Crustacea, but it is worthy of mention. There is no carapace, the eyes are pedunculated, thorax and abdomen are not differ- entiated, and the telson is a broad, elongate, spatulate plate. There seem to be sexual dif- ferences in the form of the anterior cephalic and caudal appendages, but this is not fully established. The most remarkable feature is the long, large, median cephalic appendage which is so suggestive of the proboscis of the recent Thamnocephalus platyurus Packard. The appendages are not well enough preserved to permit a determination as to whether they are schizopodal or phyllopodan. Summary. Walcott referred Burgessia and Waptia to new families under the Notostraca, while Yohowa and Opabina were placed with the Anostraca. Except for the development of the carapace, there is a striking similarity between /Vaptia and Yohoia, serving to connect the two groups. The Branchiopoda were very highly specialized as early as Middle Cambrian time, the carapace of the Notostraca being fully developed and the abdomen limbless. Some (Bur- gessia) had numerous segments, but most had relatively few. The most striking point about them, however, is that so far as is known none of them had phyllopodan limbs. While the preservation is in most cases unsatisfactory, such limbs as are preserved are trilo- bite-like, and in the case of Burgessia there can be no possible doubt of the structure. An- other interesting feature is the retention by Yohoia of vestiges of pleural lobes. The Middle I10 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Cambrian Branchiopoda are more closely allied to the Trilobita than are the modern ones, but still the subclass is not so closely related to that group as has been thought. Modern Apus is certainly much less like a trilobite than has been supposed, and very far from being primitive. The Branchiopoda of the Middle Cambrian could have been derived from the trilobites by the loss of the pleural lobes, the development of the posterior margin of the cephalon to form a carapace, and the loss of the appendages from the abdominal segments. Modern branchiopods can be derived from those of the Middle Cambrian by the modifica- tion of the appendages through the reduction of the endopodite and exopodite and the growth of the endites and exites from the proximal segments. Carpenter (1903, p. 334), from his study of recent crustaceans, has already come to the conclusion that the Branchiopoda are not the most primitive subclass, and this opinion is strengthened by evidence derived from the Trilobita and from the branchiopoda of the Middle Cambrian. COPEPODA. The non-parasitic Eucopepoda are in many ways much nearer to the trilobites than any other Crustacea. These little animals lack the carapace, and the body is short, with typi- cally ten free segments and a telson bearing caudal furca. The head is composed of five segments (if the first thoracic segment is really the fused first and second), is often flat- tened, and lacks compound eyes. Pleural lobes are well developed, but instead of being flattened as in the trilobite, they are turned down at the sides or even incurved. A labrum is present. The antennules, antennee, and mandibles are quite like those of trilobites. The anten- nules are very long and made up of numerous segments. The antennz are biramous, the junction between the coxopodite and basipodite is well marked, and the endopodite consists of only two segments. The mandibles are said to “retain more completely than in any other Crustacea the form of biramous swimming limbs which they possess in the nauplius.” The coxopodites form jaws, while both the reduced endopodite and exopodite are furnished with long setee. The maxillule are also biramous, but very different in form from those of the trilobite, and the maxillae are phyllopodan. The first thoracic limb is uniramous and similar to the mawxille, but the five following pairs are biramous swimming legs with coxopodite, basipodite, exopodite, and endopodite. Both the exopodite and endopodite are shorter than in the trilobites, but bear setze and spines. The last pair of thoracic limbs are usually modified in the male into copulatory organs. In some females they are enlarged to form plates for the protection of the eggs, in others they are unmodified. In still others they are much reduced or disappear. The abdomen is without appendages. The development in Copepoda is direct, by the addition posteriorly to the larval form (nauplius) of segments, and the appendages remain nearly unmodified in the adult. Altogether, the primitive Copepoda seem much more closely allied to the Trilobita than any other modern Crustacea, but unfortunately no fossil representative of the subclass has been found. This is not so surprising when one considers the habits and the habi- tat of most of the existing species. Many are parasitic, many pelagic in both fresh and marine waters, and many of those living on the bottom belong to the deep sea or fresh water. Most free-living forms are minute, and all have thin tests. ARCHICOPEPODA. III The eyes of copepods are of interest, in that they suggest the paired ocelli of the Har- pedidee and Trinucleide. In the Copepoda there are, in the simplest and typical form of these organs, three ocelli, each supplied with its own nerve from the brain. Two of these are dorsal and look upward, while the third is ventral. In some forms the dorsal ocelli are doubled, so that five in all are present (cf. some species of Harpes with three ocelli on each mound). In some, the cuticle over the dorsal eyes is thickened so as to form a lens, as appears to be the case in the trilobites. These peculiar eyes may be a direct inheritance from the Hypoparia. : ARCHICOPEPODA. Professor Schuchert has called my attention to the exceedingly curious little crustacean which Handlirsch (1914) has described from the Triassic of the Vosges. Handlirsch erected a new species, genus, family, and order for this animal, which he considered most closely allied to the copepods, hence the ordinal name. Euthycarcinus kessleri, the species in question, was found in a clayey lens in the Voltzia standstone (Upper Bunter). Associated with the new crustacean were specimens of Estheria only, but in the Voltzia sandstone itself land plants, fresh and brackish water animals, and occasionally, marine animals are found. The clayey lens seems to have been of fresh or brackish water origin. All of the specimens (three were found) are small, about 35 mm. long without including the caudal rami, crushed flat, and not very well preserved. The head is short, not so wide as the succeeding segments, and apparently has large compound eyes at the posterior lateral angles. The thorax consists of six segments which are broader than the head or abdomen. The abdomen, which is not quite complete in any one specimen, is interpreted by Hand- lirsch as having four segments in the female and five in the male. Least satisfactory of all are traces of what are interpreted by the describer as a pair of long stiff unsegmented cerci or stylets on the last segment. The ventral side of one head shield shows faint traces of several appendages which must have presented great difficulty in their interpretation. A pair of antennules appear to spring from near the front of the lower surface, and the remainder of the organs are grouped about the mouth, which is on the median line back of the center. Handlirsch sees in these somewhat obscure appendages four pairs of biramous limbs, antennze, mandibles, maxillule, and maxilla, both branches of each consisting of short similar segments, endopodites and exopodites being alike pediform. Each segment of the thorax has a pair of appendages, and those on the first two are clearly biramous. The endopodites are walking legs made up of numerous short segments (twelve or thirteen according to Handlirsch’s drawing), while the exopodite is a long breath- ing and rowing limb, evidently of great flexibility and curiously like the antennules of the same animal. The individual segments are narrow at the proximal end, expand greatly at the sides, and have a concave distal profile. A limb reminds one of a stipe of Diplograptus. Both branches are spiniferous. No appendages are actually present on the abdomen, but each segment has a pair of scars showing the points of attachment. From the small size of these, it is inferred that the limbs were poorly developed. This species is described in so much detail because, if it is a primitive copepod, it has a very important bearing on the ancestry of that group and is the only related form that has been found fossil. 112 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The non-parasitic copepods have typically ten (eleven) free segments, including the telson, and the four abdominal segments are much more slender than the six in front of them. In this respect the agreement is striking, and the presence of five pairs of appen- dages in the head and six free segments in the thorax is a more primitive condition than in modern forms where the first two thoracic segments are apparently fused (Calman, 1909, Pp. 73)- The large compound eyes of this animal are of course not present in the copepods, but as vestiges of eyes have been found in the young of Calanus, it is possible that the ancestral forms had eyes. The greatest difficulty is in finding a satisfactory explanation of the appendages. The general condition is somewhat more primitive than in the copepods, for all the appendages are biramous, while in the modern forms the maxillipeds are uniramous and the sixth pair of thoracic appendages are usually modified in the male as copulatory organs. In the cope- pods the modification is in the direction of reduction, both endopodites and exopodites usu- ally possessing fewer segments than the corresponding branches in the trilobites. The endopodite of Euthycarcinus, on the contrary, possesses, if Handlirsch’s interpretation is correct, twice as many segments as the endopodite of a trilobite. If the Copepoda are descended from the trilobites, as everything tends to indicate, then Euthycarcinus is certainly not a connecting link. The only truly copepodan characteristic of this genus is the agree- ment in number and disposition of free segments. The division into three regions instead of two, the compound eyes, and the structure of the appendages are all foreign to that group. With the Limulava fresh in mind, one is tempted to compare Euthycarcinus with that ancient type. The short head and large marginal eyes recall Sidmeyia, and the grouping of the appendages about the mouth also suggests that genus and Emeraldella. In the Limu- lava likewise there is a contraction of the posterior segments, although it is behind the ninth instead of the sixth. There is no likeness in detail between the appendages of the Limulava and those of Euthycarcinus, but the composite claws of Sidneyia show that in this group there was a tendency toward the formation of extra segments. If this fossil had been found in the Cambrian instead of the Triassic, it would prob- ably have been referred to the Limulava, and is not at all impossible that it is a descendant from that group. As a connecting link between the Trilobita and Copepoda it is, however, quite unsatisfactory. OSTRACODA. The bivalved shell of the Ostracoda gives to this group of animals an external appear- ance very different from that of the trilobites, but the few appendages, though highly modi- fied, are directly comparable. The development, although modified by the early appearance of the bivalved shell within which the nauplius lies, is direct. Imperfect compound eyes are present in one family. The antennules are short and much modified by functioning as swimming, creeping, or digging organs. They consist of eight or less segments. ‘The antennze are also locomotor organs, and in most orders are biramous. The mandibles are biramous and usually with, but sometimes without, a gnathobase. The maxillule are likewise biramous but much modified. The homology of the third post-oral limb is in question, some considering it a maxilla and others a maxilliped. It has various forms in different genera. It is always much modi- MALACOSTRACA. i 113 fied, but exopodite and endopodite are generally represented at least by rudiments. The fourth post-oral limb is a lobed plate, usually not distinctly segmented, and the fifth a uni- ramous pediform leg. The sixth, if present at all, is vestigial. Very little comparison can be made between the Ostracoda and Trilobita, other than in the ground-plan of the limbs, but the presence of biramous antenne is a_primi- tive characteristic. CIRRIPEDIA. Like the ostracod, the adult cirriped bears little external resemblance to the trilobite. The form of the nauplius is somewhat peculiar, but it has the typical three pairs of appen- dages, to which are added in the later metanauplius stages the maxille and six pairs of thoracic appendages. In the adult, the antennules, which serve for attachment of the larva, usually persist in a functionless condition, while the antennz disappear. The mandibles, maxillule, and maxille are simple and much modified to form mouth parts, and the six pairs of thoracic appendages are developed into long, multisegmented, biramous appendages bearing numerous sete which serve for catching prey. Paired eyes are present in later metanauplius stages, but lost early in the development. The relationship to the trilobite evi- dently is not close. MALACOSTRACA. 1. Phyllocarida. The oldest malacostracans whose appendages are known are species of Hymenocaris. One, described as long ago as 1866 by Salter, has what seem to be a pair of antennz and a pair of jaw-like mouth-parts. Another more completely known species has recently been reported by Walcott (1912 A, p. 183, pl. 31, figs. 1-6). This latter form is described as haying five pairs of cephalic appendages: a pair of minute antennules beside the small pedunculated eyes, a pair of large uniramous antennz, slender mandibles and maxillulze, and large maxilla composed of short stout segments. There are eight pairs of biramous thoracic limbs, the exopodites setiferous, the endopodites composed of short wide segments and ending in terminal claw-like spines. These appendages are like those of trilobites. Hymenocaris belongs to the great group of extinct ceratocarid Crustacea which are admitted to the lowest of the malacostracan orders, Phyllocarida, because of their resem- blance to Nebalia, Paranebalia, Nebaliopsis, and Nebaliella, the four genera which are at present living. The general form of the recent and fossil representatives of the order is strikingly similar. The chief outward difference is that in many of the fossils the telson is accompanied by two furcal rami, while in the modern genera it is simple. It now be- comes possible to make some comparison between the appendages of Hymenocaris of the Middle Cambrian and the Nebaliidz of modern seas. In both there are five pairs of cephalic and eight of thoracic appendages, while those of the abdomen of Hymenocaris are not known. In both, the antennules are less developed than the antenna. In the Nebaliidze the antennules show evidence of having been originally double (they are obviously so in the embryo), while they are single in Hymenocaris. In both, the antennz are simple. The remaining cephalic organs are too little shown by the specimen from the Middle Cambrian to allow detailed comparison. The mandibles, maxillule, and maxillee of Nebalia are, how- ever, of types which could be derived from the trilobite. 114 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. In three of the genera of the Nebaliidee, the eight pairs of thoracic limbs are all simi- lar to one another, though those of the genera differ. All are biramous. The limbs of Hymenocaris can apparently be most closely correlated with those of Nebalia antarctica, in which the endopodite consists of short flattened segments, and the exopodite is a long seti- ferous plate. Epipodites are present in both Nebalia and Hymenocaris. So far as the appendages of Hymenocaris are known, they agree very well with those of the Nebaliidze, and since they are of the trilobite type, it may safely be stated that the Trilobita and Malacostraca are closely related. 2. Syncarida. Walcott (1918, p. 170) has compared the limbs of Neolenus with those of the syn- carid genera Anaspides and Koonunga. ‘These are primitive Malacostraca without a cara- pace, but as they have a compressed test and Anaspides has stalked eyes, their gross anatomy does not suggest the trilobite. The thoracic appendages are very trilobite-like, since the endopodite has six segments (in Anaspides) and a multisegmented setiferous exopodite. The coxopodites, except of the first thoracic segment, do not, however, show endobases, and those which are present are peculiar articulated ones. The cephalic appendages are special- ized, and the antennules double as in most of the Malacostraca. [External epipodites are very numerous on the anterior limbs. This group extends back as far as the Pennsylvanian and had then probably already become adapted to fresh-water life. It may be significant that the Palzeozoic syncarids appear to have lacked epipodites. While differing very considerably from the Trilobita, the Syncarida could have been derived from them. 3. Isopoda. Since the earliest times there has been a constant temptation to compare the depressed shields of the trilobites with the similar ones of isopods. Indeed, when Serolis with its Lichadian body was first discovered about a hundred years ago, it was thought that living trilobites had been found at last. The trilobate body, cephalic shield, sessile eyes, abdom- inal shield, and pleural extensions make a wonderful parallel. This similarity is, however. somewhat superficial. The appendages are very definitely segregated in groups on the vari- ous regions of the body, and while the pleopods are biramous, the thoracic legs are with- out exopodites (except in very early stages of development of one genus). The Isopoda arose just at the time of the disappearance of the Trilobita, and there seems a possibility of a direct derivation of the one group from the other. It should be pointed out that while the differences of Isopoda from Trilobita are important, they are all of a kind which could have been produced by the development from a trilobite-like stock. For example: Isopoda have a definite number of segments. There is less variation in the number of segments among the later than the earlier trilobites. Isopoda have no facial suture. In at least three genera of trilobites the cheeks become fused to the cranidium and the sutures obliterated. Isopoda have one or two segments of the thorax annexed to the head. While this is not known to occur in trilobites, it is possible that it did. ; Most Isopoda have a fairly stiff ventral test. The ventral membrane of trilobites would probably have become stiffened by impregnation of lime if the habit of enrollment had been given up. MARRELLA SPLENDENS. 115 In Isopoda the antennze are practically uniramous sensory organs. The second cephalic appendages of trilobites are capable of such development through reduction of the exopodite. In the Isopoda the coxopodites are usually fused with the body, remaining as free, movably articulated segments only in a part of the thoracic legs of one suborder, the Asellota. Endobases are entirely absent. This is of course entirely unlike the condition in Trilobita, but a probable modification. In Isopoda there is a distinct grouping of the appendages, with specialization of func- tion. The trilobites show a beginning of tagmata, and such development would be expected if evolution were progressive. In both groups, development from the embryo is direct. Rudiments of exopodites of thoracic legs have been seen in the young of one genus. The oldest known isopod is Oxyuropoda ligioides Carpenter and Swain (Proc. Royal Irish Acad., vol. 27, sect. B, 1908, p. 63, fig. 1), found in the Upper Devonian of County Kilkenny, Ireland. The appendages are not known, but the test is in some ways like that of a trilobite. The thorax, abdomen, and pygidium are especially like those of certain trilo- bites, and there is no greater differentiation between thorax and abdomen than there is be- tween the regions before and behind the fifteenth segment of a Pédeunuas or Mesonacis. The anal segment is directly comparable to the pygidium of a Ceraurus, the stiff unseg- mented uropods being like the great lateral spines of that genus. The interpretation of the head offered by Carpenter and Swain is very difficult to under- stand, as their description and figure do not seem to agree. What they consider the first thoracic segment (fused with the head) seems to me to be the posterior part of the cephalon, and it shows at the back a narrow transverse area which is at least analogous to the nuchal segment of the trilobite. If this interpretation can be sustained, Osywropoda would be a very primitive isopod in which the first thoracic segment (second of Carpenter and Swain) is still free. According to the interpretation of the original authors, the species is more specialized than recent Isopoda, as they claim that two thoracic segments are fused in the head. The second interpretation was perhaps made on the basis of the number of segments (nineteen) in a recent isopod. MARRELLA SPLENDENS WALCOTT. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 192, pls. 25, 26. Among the most wonderful of the specimens described by Doctor Walcott is the “lace crab.’ While the systematic position was not satisfactorily determined by the describer, it has been: aptly compared to a trilobite. The great nuchal and genal spines and the large marginal sessile eyes, coupled with the almost total lack of thoracic and abdominal test, give it a bizarre appearance which may obscure its real relationships. The cephalon appears to bear five pairs of appendages, antennules, and antennz, both tactile organs with numerous short segments, mandibles, and first and second maxille. The last three pairs are elongate, very spinose limbs, of peculiar appearance. They seem to have seven segments, but are not well preserved. These organs are attached near the posterior end of the labrum. j There are twenty-four pairs of biramous thoracic appendages, which lack endobases. The endopodites are long and slender, with numerous spines; the exopodites have narrow, thin shafts, with long, forward pointed sete. The anal segment consists of a single plate. 116 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Further information about this fossil will be eagerly awaited. None of the illustra- tions so far published shows biramous appendages on the cephalon. This, coupled with the presence of tactile antennze, makes its reference to the Trilobita impossible, but the present interpretation indicates that it was closely allied to them. SeTT ee © ZY] Oi 6 Zl ‘a Yi s S777 OD) H D2 2S Wy ey OH SSH FY, xX KS NS X SS Sr a Fig. 32—WMarrella splendens Walcott. photographs and descriptions published by Walcott. Restoration of the ventral surface, based upon the Although all the limbs of the trunk appear to be biramous, only endopodites are placed on one side and exopodites on the other, for the sake of greater clearness in the illustration. Drawn by Doctor Elvira Wood, under the supervision of the writer. >< about 6. Restoration of Marrella. (Text fig. 32.) The accompanying restoration of the ventral surface of Marrella is a tentative one, based on Doctor Walcott’s description and figures. The outline is taken from his plate 26, figure 1; the appendages of the head from plate 26, figures 1-3, 5, and plate 25, figures 2, 3; the endopodites, shown on the left side only, from figures 3 and 6, plate 25. studied actual specimens, and the original description is very incomplete. The restoration is therefore subject to revision as the species becomes better known. I have not ARACHNIDA. 117 ARACHNIDA. No attempt will be made to pass in review all of the subclasses of the arachnids. Some of the Merostomata are so obviously trilobite-like that it would seem that their relationship could easily be proved. The task has not yet been satisfactorily accomplished, however, and new information seems only to add to the difficulties. So far as I know, the Aranez have not previously been compared directly with trilobites, although such treatment consists merely in calling attention to their crustacean affinities, as has often been done. Carpenter’s excellent summary (1902, p. 3 of the relationship of the Arachnida to y ) the trilobites may well be quoted at this point: The discussion in a former section of this essay on the relationship between the various orders of Arachnida led to the conclusion that the primitive arachnids were aquatic animals, breathing by means of appendicular gills. Naturally, therefore, we compare the arachnids with the Crustacea rather than with the Insecta. The immediate progenitors of the Arachnida appear to have possessed a head with four pairs of limbs, a thorax with three segments, and an abdomen with thirteen segments and a telson, only six of which can be clearly shown by comparative morphology to have carried appendicular gills. But embryological evidence enables us to postulate with confidence still more remote ancestors in which the head carried well developed compound eyes and five pairs of appendages, while it may be supposed that all the abdominal segments, except the anal, bore limbs. In these very ancient arthropods, all the limbs, except the feelers, had ambulatory and branchial branches; and one important feature in the evolution of the Arachnida must have been the division of labour between the anterior and posterior limbs, the former becoming specialized for locomotion, the latter for breathing. Another was the loss of feelers and the degeneration of the com- pound eyes. Thus we are led to trace the Arachnida (including the Merostomata and Xiphosura) back to ancestors which can not be regarded as arachnids, but which were identical with the primitive trilobites, and near the ancestral stock of the whole crustacean class. TRILOBITES NOT ARACHNIDA. While no one having any real knowledge of the Trilobita has adopted Lankester’s scheme of the inclusion of the group as the primitive grade in the Arachnida, reference to it may not be amiss. This theory is best set forth in the Encyclopedia Britannica, Eleventh Edition, under the article on Arachnida. It is there pointed out that the primitive arachnid, like the primitive crustacean, should be an animal without a fixed number of somites, and without definitely grouped tagmata. As Lankester words it, they should be anomomeristic and anomotagmatic. The trilobites are such animals, and he considers them Arachnida and not Crustacea for the following reasons: Firstly and chiefly, because they have only one pair (apart from the eyes) of pre-oral appendages. “This fact renders their association with the Crustacea impossible, if classifi- cation is to be the expression of genetic affinity inferred from structural coincidence.”’ Secondly, the lateral eyes resemble no known eyes so closely as the lateral eyes of Limulus. Thirdly, the trilobation of the head and body, due to the expansion and flattening of the sides or pleura, is like that of Limulus, but ‘“‘no crustacean exhibits this trilobite form.” Fourthly, there is a tendency to form a pygidial or telsonic shield, “a fusion of the pos- terior somites of the body, which is precisely identical in character with the metasomatic carapace of Limulus.’ No crustacean shows metasomatic fusion of segments. Fifthly, a large post-anal spine is developed “in some trilobites” (he refers to a figure of Dalmanites). 118 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. Sixthly, there are frequently lateral spines on the pleura as in Limulus. No crustacean has lateral pleural spines. These points may be taken up in order. 1. If trilobites have one appendage-bearing segment in front of the mouth, they are Arachnida; if two, Crustacea. This is based on the idea that in the course of evolution of the Arthropoda, the mouth has shifted backward from a terminal position, and that as a pair of appendages is passed, they lose their function as mouth-parts and eventually become simple tactile organs. Thus arise the cheliceree of most arachnids, and the two pairs of tactile antennze of most Crustacea. This theory is excellent, and the rule holds well for modern forms, but as shown by the varying length of the hypostoma in different trilobites, the position of the mouth had not become fixed in that group. In some trilobites, like Triar- thrus, the gnathobases of the second pair of appendages still function, but in all, so far as known, the mouth was back of the points of attachment of at least two pairs of appendages, and in some at least, back of the points of attachment of four pairs. As pointed out in the case of Calymene and Ceraurus, the trilobites show a tendency toward the degeneration of the first and second pairs of biramous appendages, particularly of the gnathobases. They are in just that stage of the backward movement of the mouth when the function of the antennz as mandibles has not yet been lost. If the presence of functional gnathobases back of the mouth, rather than the points of attachment in front of the mouth, is to be the guide, then Triarthrus might be classed as an arachnid and Calymene and Isotelus as crustaceans. In other words, the rule breaks down in this primitive group. 2. Superficially, the eyes of some trilobites do look like those of Limulus, but how close the similarity really was it is impossible to say. The schizochroal eyes were certainly very different, and Watase and Exner both found the structure of the eye of the trilobite unlike that of Limulus. . 3. The importance of the trilobate form of the trilobite is very much overestimated. It and the pygidium are due solely to functional requirements. The axial lobe contained practically all the vital organs and the side lobes were mechanical in origin and secondarily protective. That the crustacean is not trilobate is frequently asserted by zoologists, yet every text-book contains a picture of a segment of a lobster with its axial and pleural lobes. It is a fundamental structure among the Crustacea, obscured because most of them are com- pressed rather than depressed. 4. The pygidium of trilobites is compared with the metasomatic shield of Limulus. No homology, if homology is intended, could be more erroneous. The metasomatic shield of Limulus is, as shown by ontogeny and phylogeny, formed by the fusion of segments formerly free, and includes the segments between the cephalic and anal shields, or what would be known as the thorax of a trilobite. No trilobite has a metasomatic shield. The pygidium of a trilobite, as shown by ontogeny, is built up by growth in front of the anal region, and since the segments were never free, it can not strictly be said to be composed of fused segments. Some Crustacea do form a pygidial shield, as in certain orders of the Isopoda. 5. The post-anal spine of Dalmanites and some other trilobites is similar to that of Limulus, but this seems a point of no especial significance. That a similar spine has not been developed in the Crustacea is probably due to the fact that they do not have the broad depressed shape which makes it so difficult for a Limulus to right itself when once turned on its back. Relatively few trilobites have it, and it is probably correlated with some special adaptation. MEROSTOMATA, - 119 6. There is nothing among the trilobites comparable to the movable lateral spines of the metasoma of Limulus. While, as classifications are made up, the Trilobita must be placed in the Crustacea rather than the Arachnida, there is no reason why both the modern Crustacea and the Arach- nida should not be derived from the trilobites. MEROSTOMATA. It has been a custom of long standing to compare the trilobite with Limulus. Packard (1872) gave great vitality to the theory of the close affinity of the two when he described the so called trilobite-stage in the development of Limulus polyphemus. His influence on Walcott’s ideas (1881) is obvious. Lankester has gone still further, and associated the Trilobita with the Merostomata in the Arachnida. The absence of antennules at any stage in development allies Limulus so closely with the Arachnida and separates it so far from the Trilobita that in recent years there has been a tendency to give up the attempt to prove a relationship between the merostomes and trilo- bites, especially since Clarke and Ruedemann, in their extensive study of the Eurypterida, found nothing to indicate the crustacean nature of that group. A new point of view is, how- ever, presented by the curious Sidneyia imexpectans and Emeraldella brocki described by Walcott from the Middle Cambrian. Sidneyia inexpectans Walcott. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1911, p. 21, pl. 2, fig. 1 (not figs. 2, 3); pls. 3-5; pl. 6, fig. 3; pl. 7, fig. 1. ; The body of this animal is elongate, somewhat eurypterid-like, but with a broad telson supplied with lateral swimmerets. The cephalon is short, with lateral compound eyes. The trunk consists of eleven segments, the anterior nine of which are conspicuously wider than the two behind them, and the telson consists of a single elongate plate. On the ventral side of the head there is a large hypostoma and five pairs of appendages. The first pair are multisegmented antennules. The second pair have not been adequately described. ‘The third are large, complex claws, and the fourth and fifth suggest broad, stocky endopodites. Broad gnathobases are attached to the coxopodites of the third to fifth pairs of appendages and form very strong jaws. The first nine segments of the thorax have one pair each of broad filiform branchial appendages, suggestive of the exopodites of trilobites, but no endopodites have been seen. The tenth and eleventh.segments seem to lack appendages entirely. Emeraldella brocki Walcott. Illustrated: Sidneyia inexpectans Walcott partim, Smithson. Misc. Coll., vol. 57, 1911, pl. 2, figs. 2, 3 (not fig. 1) ;—Ibid., 1912, p. 206, text fig. 10. Emeraldella brocki Walcott, Ibid., 1912, p. 203, pl. 30, fig. 2; text fig. 8;—Ibid., vol. 67, 1918, p. 118 (correction). Emeraldella has much the same shape as Sidneyia and the same number of segments, but instead of a broad flat telson, it has a long Limulus-like spine. The cephalon is about as wide as long, and eyes have not yet been seen. The body consists of eleven segments and a telson (Walcott says twelve and a telson but shows only eleven in the figures). Nine of the segments, as in Sidneyia, are broad, the next two narrow. 120 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The ventral side of the cephalon has a long hypostoma, and five pairs of appendages. The first pair are very long multisegmented antennules and the next four pairs seem to be rather slender, spiniferous, jointed endopodites. Whether or not gnathobases were present is not shown by the figures, but owing to the long hypostoma the appendages are grouped about the mouth. All the segments of the body, unless it were the telson, seem to have borne appendages. On the anterior end, they were clearly biramous (1912, p. 206, text fig. 10), and that they were present along the body is shown by figure 2, plate 30, 1912. The present state of knowledge of both these peculiar animals leaves much to be desired. The indications are that the cephalic appendages are not biramous, and that only one pair of antennz, the first, are developed as tactile organs. The thoracic appendages of Emeraldella are biramous, and also possibly those of Sidneyia. In the latter, the last two abdominal seg- ments seem to have been without appendages, while in Emeraldella at least one branch of each appendage, and possibly both, is retained. These animals, which may be looked upon as the last survivors of an order of pre- Cambrian arthropods, have the appearance of an eurypterid, but their dominant character- istics are crustacean. The features which suggest the Eurypterida are: elongate, obovate, non-trilobate, tapering body; telson-like posterior segment; marginal, compound, sessile eyes; claw-like third cephalic appendages; and, more particularly, the general resemblance of the test to that of an eurypterid like Strabops. In form, Sidneyia agrees with the theoretical prototype of the Eurypterida reconstructed by Clarke and Ruedemann (Mem. 14, N. Y. State Mus., vol. 1, 1912, p. 124) in its short wide head with marginal eyes, and its undiffer- entiated body. There is, moreover, no differentiation of the postcephalic appendages. The crustacean characteristics are seen in the presence of five, instead of six, pairs of appendages on the head, the first of which are multisegmented antennules, and in the bira- mous appendages on the body of Emeraldella. It should be noted that these latter are typically trilobitic, each consisting of an endopodite with six segments and a setiferous exopodite. Clarke and Ruedemann (1912, p. 406) have discussed Sidneyia briefly, and conclude: It seems to us probable that the Limulava [Sidneyia and Amiella] as described are not eurypterids but constitute a primitive order, though exhibiting some remarkable adaptive features. This order possibly belongs to the Merostomata, but is distinctly allied to the crustaceans in such important characters as the structure of the legs and telson, and is therefore much generalized. The specialization of Sidneyia consists in the remarkable development of a highly com- plex claw on each of the third cephalic appendages, and in the compound tail-fin, built up of the last segment and one or more pairs of swimmerets. These two characteristics seem to preclude the possibility of deriving the eurypterids from Sidneyia itself, but it seems entirely within reason that they may have been derived from another slightly less specialized member of the same order. That Sidneyia is descended from any known trilobite seems highly improbable, but that it was descended from the same ancestral stock as the trilobites is, I believe, indicated by the presence of five pairs of appendages on the cephalon and trilobitic legs on the abdomen. Molaria and Habelia. Other so called Merostomata found by Walcott in the Middle Cambrian are the genera Molaria and Habelia, both referred to the Cambrian family Aglaspidee. These genera seem to conform with Aglaspis of the Upper Cambrian in having a trilobite-like cephalon without ARANEA. T21 facial sutures, a trilobite-like thorax of a small but variable (7-12) number of segments, and a Limulus-like telson. Neither of them has yet been fully described or figured, but (Walcott 1912 A, p. 202) Habelia appears to have five pairs of cephalic appendages, the first two pairs of which are multisegmented antennz. The thoracic appendages are likewise none too well known, but they appear to have been biramous. The endopodites are better preserved than the exopodites, but in at least one specimen of Molaria the exopodites are conspicuous. If these genera are properly described and figured, their appendages are typically crus- tacean, and fundamentally in agreement with those of Marrella. The relation to the Trilo- bita is evidently close, the principal differences being the absence of facial sutures and the presence of true antenne. 1 am therefore transferring the Aglaspide from the Merosto- mata to a new subclass under the Crustacea. 5 ARANE#. The spiders have the head and thorax fused, the abdomen unsegmented except in the most primitive suborder, and so appear even less trilobite-like than the insects. The appen- dages likewise are highly specialized. The cephalothorax bears six pairs of appendages, the first of which are the preoral cheliceree, while behind the mouth are the pedipalpi and four pairs of ambulatory legs. The posterior pairs of walking legs belong to the thorax, but the anterior ones are to be homologized with the maxille of Crustacea, so that the spiders are like the trilobites in having functional walking legs on the head. The chief likenesses are, however, seen in the very young. On the germ band there appear a pair of buds in front of the rudiments of the cheliceree which later unite to form the rostrum of the adult. At the time these buds appear, the chelicerze are postoral, but afterward move forward so that both rostrum and cheliceree are in front of the mouth. The rostrum is therefore the product of the union of the antennules, and the chelicerz are to be homologized with the antenne. There seems to be some doubt about the homology of the pedipalps with the mandibles, as at least one investigator claims to have found rudi- ments of a segment between the one bearing the chelicerze and that with the pedipalps. Jaworowski (Zool. Anzeiger, 1891, p. 173, fig. 4) has figured the pedipalp from the germ band of Trochosa singoriensis, and called attention to the fact that it consists of a cox- opodite and two segmented branches which may be interpreted as exopodite and endopodite. He designated as exopodite the longer branch which persists in the adult, but since the ambu- latory legs of Crustacea are endopodites, that would seem a more likely interpretation. As the figure is drawn, the so called endopodite would appear to spring from the proximal seg- ment of the “exopodite.” If the two terms were interchanged, the homology with the limb of the trilobite or other crustacean would be quite perfect. In the young, the abdomen is segmented and the anterior segments develop limb-buds, the first pair of which become the lung books and the last two pairs the spinnerets of the adult. There seems to be some question about the number of segments. Montgomery (Jour. Morphology, vol. 20, 1909, p. 337): reviewing the literature, finds that from eight to twelve have been seen in front of the anal segment. The number seem to vary with the species studied. This of course suggests connection with the anomomeristic trilobites. The oldest true spiders are found in the Pennsylvanian, and several genera are now known. The head and thorax are fused completely, but the abdomen is distinctly seg- 122 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. mented. Some of the Anthracomarti resemble the trilobites more closely than do the Aranez, as they lack the constriction between the cephalothorax and abdomen. The spiders of the Pennsylvanian have this constriction less perfectly developed than do modern Aranez, and occupy an intermediate position in this respect. In the Anthracomarti, the pedipalpi are simple, pediform, and all the appendages have very much the appearance of the coxopodites and endopodites of trilobites. Cheliceree are not known, and pleural lobes are well devel- oped in this group. Anthracomarti have not yet been found in strata older than the Penn- sylvanian, but they seem to be to a certain extent intermediate between true spiders and the marine arachnid. INSECTA. Handlirsch (in several papers, most of which are collected in “Die Fossilen Insekten,” 1908) has attempted to show that all the Arthropoda can be derived from the Trilobita, and has advocated the view that the Insecta sprang directly from that group, without the intervention of other tracheate stock. At first sight, this transformation seems almost an impossibility, and the view does not seem to have gained any great headway among ento- mologists in the fourteen years since it was first promulgated. If an adult trilobite be com- pared with an adult modern insect, few likenesses will be seen, but when the trilobite is stripped of its specializations and compared with the germ-band of a primitive insect, the theory begins to seem more possible. Handlirsch really presented very little specific evidence in favor of his theory. In fact, one gets the impression that he has insisted on only two points. Firstly, that the most ancient known insects, the Palzeodictyoptera, were amphibious, and their larve, which lived in water, were very like the adult. Secondly, that the wings of the Palzeodictyoptera prob- ably worked vertically only, and the two main wings were homologous with rudimentary wing-like outgrowths on each segment of the body. These outgrowths have the appear- ance of, and might have been derived from, the pleural lobes of trilobites. He figured (1908, p. 1305, fig. 7) a reconstructed larva of a palzeodictyopterid as haying biramous limbs on each segment, but so far as I can find, this figure is purely schematic, for there seems to be no illustration or description of any such larva in the body of his work. That the insects arose directly from aquatic animals is of course possible, and Hand- lirsch’s first argument has considerable force. It may, however, be purely a chance that the oldest insects now known to us happen to be an amphibious tribe. The Palzodictyoptera are not yet known to antedate the Pennsylvanian, but there can be no doubt that insects existed long before that time, and the fact that their remains have not been found is good evidence that the pre-Pennsylvanian insects were not aquatic. Comstock, who has recently investigated the matter, does not believe that the Palzeodictyoptera were amphibious (The Wings of Insects, Ithaca, N. Y., 1918, p. 91). The second argument, that wings arose from the pleural lobes of trilobites, is exceedingly weak. Where most fully set forth (1907, p. 157), he suggests that trilobites may occasion- ally have left the water, climbed a steep bank or a plant, and then glided back into their native element, taking advantage of the broad flat shape to make a comfortable and gentle descent! This sport apparently became so engaging that the animal tried experiments with flexible wing tips, eventually got the whole of the pleural lobes in a flexible condition, and selected those of the second and third thoracic segments for preservation, while discarding the remainder. ‘The pleural lobes of trilobites are not only too firmly joined to the axial portion INSECTA AND CHILOPODA. 123 of the test to be easily transformed into movable organs, but they are structurally too unlike the veined wings of insects to make the suggestion of this derivation even worthy of con- sideration. Tothill (1916) has recently reinvestigated the possible connection between insects, chi- lopods, and trilobites, and, from the early appearance of the spiracles in the young, came to the conclusion that the insects Were derived from terrestrial animals. He suggested that they may have come through the chilopods from the trilobites. The hypothetical ancestor of the insects, as restored by Tothill from the evidence of embryology and comparative anatomy, is an animal more easily derived from the Chilopoda than from the Trilobita. Five pairs of appendages are present on the head, and the trunk is made up of fourteen similar segments, each with a pair of walking limbs and a pair of spiracles. Only the maxille and maxillule are represented as biramous. If the ancestor of the Insecta was, as seems possible, tracheate, this fact alone would rule out the trilobites. Among tracheates, the Chilopoda are certainly more closely allied to the Insecta than are any other wingless forms. If the ancestors of the insects were not actually chilopods, they may have been chilopod-like, and there can be little doubt that both groups trace to the _ same stock. As to the ancestry of the Chilopoda, it is probable that they had the same origin as the other Arthropoda. Tothill has pointed out that in the embryo of some chilopods there are rudiments of two pairs of antennz and that the two pairs of maxillc and the maxilli- peds are biramous. This would point rather to the Haplopoda than directly to the trilobites as possible ancestors, and may explain why the former vanish so suddenly from the geological record after their brief epoca ance in the Middle Cambrian. They may have gone on to the land. There seem to be no insuperable obstacles to prevent the derivation, indirectly, of the insects from some trilobite with numerous free segments, and small pygidium. The anten- nules and pleural lobes must be lost, the antennze and trunk limbs modified by loss of exopo- dites. Wings and trachez must be acquired. Handlirsch places the date of origin of the Insecta rather late, just at the end of the Devonian and during the “Carboniferous.” By that time most families of trilobites had died out, so that the possibilities of origin of new stocks were much diminished. If the haplopod-chilopod-insect line is a better approximation to the truth, then the divergence began in the Cambrian. — CHILOPODA. The adult chilopod lacks the antennules, and all of the other appendages, with the ex- ception of the maxillula, are uniramous. The walking legs are similar to the endopodites of trilobites, and usually have six or seven segments. The appendages are therefore such as could be derived by modification of those of trilobites by the almost complete loss of the exopodites and shortening of the endopodites of the head. The position of the postoral ap- pendages, the posterior ones outside those closest the mouth, is perhaps foreshadowed in the arrangement of those of Triarthrus. The Chilopoda differ from the Hexapoda in developing the antennze instead of the antennules as tactile organs, but this can not be used with any great effect as an argument that the latter did not arise from the ancestors of the former, since it is entirely possible that in early Paleozoic times the pre-Chilopoda possessed two pairs of antenne. The first pair are still recognizable in the embryo of certain species. a 124 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. The oldest chilopods are species described by Scudder (Mem. Boston Soc. Nat. Hist., vol. 4, 1890, p. 417, pl. 38) from the Pennsylvanian at Mazon Creek, Grundy County, Illinois. Only one of these, Latzelia primordialis Scudder (pl. 38 fig. 3), is at all well preserved. This little animal, less than an inch long, had a depressed body, with a median carina, exceed- ingly long slender legs, and about nineteen segments. The head is very nearly obliterated. DrIpPLopoDA. The diplopods, especially the polydesniids with their lateral outgrowths, often have a general appearance somewhat like that of a trilobite, but on closer examination few like- nesses are seen. The most striking single feature of the group, the possession by each seg- ment of two pairs of appendages, is not in any way foreshadowed in the trilobites, none of which shows any tendency toward a fusion of pairs of adjacent segments. The anten- nules are short, antennz absent, mandibles and maxillulee much modified, the latter possibly biramous, and the maxillz absent. The trunk appendages are very similar to those of chi- lopods, and could readily be derived from the endopodites of trilobites. The oldest diplopods are found in the Silurian (Ludlow) and Devonian (Lower Old Red) of Scotland, and three species belonging to two genera are known. ‘The oldest is Archidesmus loganensis Peach (1889, p. 123, pl. 4, fig. 4), and the Devonian species are Archidesmus macnicoli Peach and Kampecaris forfarensis Page (Peach 1882, p. 182, pl. 2, fig. 2, 2a, and p. 179, pl. 2, figs. 1-1g). All of these species show lateral expansions like the recent Polydesmidz, and these of course suggest the pleural lobes of trilobites. All three of the species are simpler than any modern diplopod, for there is only a single pair of appendages on each segment. No foramina repugnatoria were observed, and the eyes of Kampecaris forfarensis as described are singularly like those of a phacopid. Peach says: “The eye itself is made up of numerous facets which are arranged in oblique rows, the posterior end of each row being inclined downwards and outwards, the facets being so numerous and so close together that the eye simulates a compound one.’’ There is also a protecting ridge which somewhat resembles a palpebral lobe (1882, pl. 7, fig. Ia). Peach comments on the strength of the test, and from his description it appears that it must have been preserved in the same manner as the test of trilobites.. It was punctate, and gran- ules and spines were also present. The presence of the lateral outgrowths in these ancient specimens would seem to indicate that they are primitive features, and may have been in- herited. While possibly not homologous with the pleural extensions of trilobites, they may be vestiges of these structures. The limbs are made up of seven segments which are circular in section and expand at the distal end. The distal one bears one or two minute spines. They are most readily com- pared with the endopodites of Jsotelus. The resemblance is, in fact, rather close. The sternal plates are wider and the limbs of opposite sides further apart than in modern diplo- pods. Except for one pair of antennz, no cephalic appendages are preserved. While these specimens do not serve to connect the Diplopoda with the Trilobita, they do show that most of the specializations of the former originated since Lower Devonian times, and lead one to suspect that the derivation from marine ancestors took place very early, perhaps in the Cambrian. If no very close connection with the trilobites is indicated, there is also nothing to show that the diplopods could not have been derived from that group. PRIMITIVE CHARACTERISTICS OF TRILOBITES. 125 PRIMITIVE CHARACTERISTICS OF TRILOBITES. TRILOBITES THE MOST PRIMITIVE ARTHROPODS. The Arthropoda, to make the simplest possible definition, are invertebrate animals with segmented body and appendages. The most primitive arthropod would appear to be one composed of exactly similar segments bearing exactly similar appendages, the segments of the appendages themselves all similar to one another. It is highly improbable that this most primitive arthropod imaginable will ever be found, but after a survey of the whole phylum, it appears that the simpler trilobites approximate it most closely. That the trilobites are primitive is evidenced by the facts that they have been placed at the bottom of the Crustacea by all authors and claimed as the ancestors of that group by some; that Lankester derived the Arachnida from them; and that Handlirsch has consid- ered them the progenitors of the whole arthropodan phylum. Specializations among the Arthropoda, even among the free-living forms, are so numer- ous that it would be difficult to make a complete list of them. In discussing the principal groups, I have tried to show that the essential structures can be explained as inherited from the Trilobita, changed in form by explainable modifications, and that new structures, not present in the Trilobita, are of such a nature that they might be acquired independently in even unrelated groups. The chief objections to the derivation of the remainder of the Crustacea from the trilo- bites have been: first, that the trilobites had broad pleural extensions; second, that they had a large pygidium; and lastly, that they had only one pair of tactile antennz. It has now been pointed out that many modern Crustacea have pleural extensions, but that they usually bend down at the sides of the body, and also that in the trilobites and more especially in Marrella, there was a tendency toward the degeneration of the pleural lobes. A glance at the Mesonacidz or Paradoxidz should be convincing proof that in some trilo- bites the pygidium is reduced to a very small plate. In regard to the second antennz standard text-books contain statements which are actu- ally surprising. A compilation shows that the antennz are entirely uniramous in but a very few suborders, chiefly among the Malacostraca; that they are biramous with both exopodite and endopodite well developed in most Copepoda, Ostracoda, and Branchiopoda; and that the exopodite, although reduced in size, still has a function in some suborders of the Malacostraca. The Crustacea could not possibly be derived from an ancestor with two pairs of uniramous antenne. Although I have defended the trilobites, perhaps with some warmth, from the impu- tation that they were Arachnida, my argument does not apply in the opposite direction, and I believe Lankester was right in deriving the Arachnida from them. If the number of appendages in front of the mouth is fundamental, then the trilobites were generalized, primi- tive, and capable of giving rise to both Crustacea and Arachnida. As shown on a previous page. (p. 119), the “connecting links’’ so far found tend to disprove rather than to prove the thesis, but the present finds should be looked upon as only the harbingers of the greater ones which are sure to come. ; LIMBS OF TRILOBITES PRIMITIVE. The general presence, in an adult or larva, of some sort of biramous limbs through- out the whole class Crustacea has led most zoologists to expect such a limb in the most 126 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. primitive crustaceans, and apparently the appendage of the trilobite satisfies the expectation. It is well, perhaps, as a test, to consider whether by modification this limb could produce the various types of limbs seen in other members of the class. In the first place, it is necessary to have clearly in mind the peculiarities of the appendage to be discussed. It should first of all be remembered that the limb is articulated with the dorsal skeleton in a manner which is very peculiar for a crustacean. The coxopodite swings on a sort of ball-and-socket joint, and at the outer end both the exopodite and the basipodite articulate with it. Since the exopodite articulates with the basipodite as well as with the coxopo- dite, the two branches are closely connected with one another and there is little individual freedom of movement. This is, of course, a necessary consequence of their articulation with a segment which is itself too freely movable to provide a solid base for attachment of muscles. The relation of the appendifer, coxopodite, and two rami is here shown dia- grammatically (fig. 33), the exopodite branching off from the proximal end of the basipo- dite at the junction with the coxopodite. In all trilobites the endopodite consists of six segments, and the coxopodite of a single segment the inner end of which is prolonged as an endobase. There does not seem to be any variation from this plan in the subclass, although individual segments are variously Fig. 33.—Diagrammatic representation of an appendage of the anterior end of the thorax of Triarthrus becki Green, to show relation of exo- podite and endopodite to each other and to the coxopodite. Much enlarged. modified. The exopodites are more variable, but all consist of a flattened shaft with setee on one margin. No other organs such as accessory gills, swimming plates, or brood pouches have yet been found attached to the appendages, the evidence for the existence of the vari- ous epipodites and exites described by Walcott being unsatisfactory (see p. 23). In the Ostracoda the appendages are highly variable, but it is easily seen that they are modifications of a limb which is fundamentally biramous. In most species, both exop- odite and endopodite suffer reduction. The exopodite springs from the basipodite and that segment is closely joined to the coxopodite, producing a protopodite. In some cases the original segments of the endopodites fuse to form a stiff rod. While highly diversified, these appendages are very trilobite-like, and some Ostracoda even have biramous antenne. The non-parasitic Copepoda have limbs exceedingly like those of trilobites. Many of them are biramous, the endopodites sometimes retaining the primitive six segments. Coxop- odite and basipodite are generally united, and endopodite and exopodite variously modified. Like some of the Ostracoda, the more primitive Copepoda have biramous antenne. As would be expected, the appendages of the Cirripedia are much modified, although those of the nauplius are typical. The thoracic appendages of many are biramous, but both branches are multisegmented. In the modern Malacostraca the ground plan of the appendages is biramous, but in most orders they are much modified. In many, however, the appendages of some part of the body are biramous, and in many the endopodites show the typical six segments. From the coxopodites arise epipodites, some of which assist in swimming, and some in respiration. PRIMITIVE CHARACTERISTICS OF TRILOBITES. 127 Because of the many instances in which such extra growths arise, and because of the form of the appendages of the Branchiopoda, it has been suggested that the primitive crustacean leg must have been more complex than that of the trilobite. In looking over the Malacos- traca, however, one is struck by the fact that epipodites generally arise where the exopo- dites have become aborted or are poorly developed, and seem largely to replace them. The coxopodite and basipodite are usually fused to form a protopodite, and a third segment is sometimes present in the proximal part of the appendage. In the Branchiopoda are found the most complex crustacean limbs, and the ones most difficult to homologize with those of trilobites. In recent years, Lankester’s homologies of the parts of the limbs of Apus with those of the Malacostraca have been quite gener- ally accepted, and the appendages of the former considered primitive. Now that it is known that the Branchiopoda of the Middle Cambrian (Burgessia et al.) had simple trilo- bite-like appendages, it becomes necessary to exactly reverse the opinion in this matter. The same homologies stand, but the thoracic limbs of Apus must be looked upon as highly specialized instead of primitive. MAEM a eee Cy ee NG \ Fig. 34——One of the appendages of the anterior part of the trunk of Apus, showing the endites (beneath) and exites (above). The proximal endite forms a gnathobase which is not homologous with the gnatho- base (or endobase) of the trilobite. Copied from Lankester. Much enlarged. Lankester (Jour. Micros. Sci., vol. 21, 1881) pointed out that the axial part of the thoracic limb of Apus (fig. 34) is homologous with the protopodite in the higher Crus- tacea, that the two terminal endites corresponded to the exopodite and endopodite, and that the other endites and exites were outgrowths from the protopodite analogous to the epip- odites of Malacostraca. There seems to be no objection to retaining this interpretation, but with the meaning that both endopodite and exopodite are much reduced, and their func- tions transferred to numerous outgrowths of the protopodite. One of the endites grows inward to form an endobase, the whole limb showing an attempt to return to the ancestral condition of the trilobite. The limbs of some other. branchiopods are not so easy to under- stand, but students of the Crustacea seem to have worked out a fairly satisfactory compari- son between them and A pus. The discovery that the ancestral Branchiopoda had simple biramous appendages instead of the rather complex phyllopodan type is another case in which the theory of “recapitu- lation” has proved to hold. It had already been observed that in ontogeny the biramous limb preceded the phyllopodan, but so strong has been the belief in the primitive character of the Apodidze that the obvious suggestion has been ignored. Even in such highly special- ized Malacostraca as the hermit crabs the development of certain of the limbs illustrates the change from the schizopodal to the phyllopodan type, and Thompson (Proc. Boston Soc. Nat. Hist., vol. 31, 1903, pl. 5, fig. 12) has published an especially good series of drawings 128 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. showing the first maxilliped. In the first to fourth zoez the limb is biramous but in the glaucothoe a pair of broad processes grow out from the protopodite, while the exopodite and particularly the endopodite become greatly reduced. In the adult the endopodite is a mere vestige, while the flat outgrowths from the protopodite have become very large and bear sete. Summary. The limbs of most Crustacea are readily explained as modifications of a simple bira- mous type. These modifications usually take the form of reduction by the loss or fusion of segments and quite generally either the entire endopodite or exopodite is lacking. Modifi- cation by addition frequently occurs in the growth of epipodites, “endites,” and “exites” from the coxopodite, basipodite, or both. A protopodite is generally formed by the fusion of coxopodite and basipodite, accompanied by a transference of the proximal end of the exopodite to the distal end of the basipodite. A new segment, not known in the trilobites (precoxal), is sometimes added at the inner end. Among modern Crustacea, the anterior cephalic appendages and thoracic appendages of the Copepoda and the thoracic appendages of certain Malacostraca, Syncarida especially, are most nearly like those of the trilobite. The exact homology, segment for segment, be- tween the walking legs of the trilobite and those of many of the Malacostraca, even the Decapoda, is a striking instance of retention of primitive characteristics in a specialized group, comparable to the retention of primitive appendages in man. NUMBER OF SEGMENTS IN THE TRUNK. Various attempts have been made to show that despite the great variability, trilobites do show a tendency toward a definite number of segments in the body. Emmrich (1839), noting that those trilobites which had a long thorax usually had a short pygidium, and that the reverse also held true, formulated the law that the number of segments in the trunk was constant (20-+-1). Very numerous exceptions to this law _ were, however, soon discovered, and while the condition of those with less than twenty-one segments was easily explained, the increasing number of those with more than twenty-one soon brought the idea into total disrepute. Quenstedt (1837) had considered the number of segments of at least specific impor- tance, and both he and Burmeister (1843) considered that the number of segments in the thorax must be the same for all members of a genus. As first shown by Barrande (1852. p. 191 et seq.), there are very many genera in which there is considerable variation in the number of thoracic segments, and a few examples can be cited in which there is variation within a species, or at least in very closely related species. Carpenter (1903, p. 333) has tabulated the number of trunk segments of such trilo- bites as were listed by Zittel in 1887 and finds a steady increase throughout the Paleozoic. His table, which follows, is, however, based upon very few genera. Period | No. of Genera Average No. of body-segments © Cambrian 12 17.66 Ordovician 2 18.58 Silurian 160 19.34 Devonian 10 | < 20.70 Carboniferous 2 » 20.75 SEGMENTS IN TRUNK. 129 Due chiefly to the efforts of Walcott, an increasingly large number of Cambrian genera are now represented by entire specimens, and since these most ancient genera are of great- est importance, a few comments on them may be offered. The total number of segments can be fairly accurately determined in at least nineteen genera of trilobites from the Lower Cambrian. These include eight genera of the Meson- acide (Olenellus was excluded) and Eodiscus, Goniodiscus, Protypus, Bathynotus, Atops, Olenopsis, Crepicephalus, Vanuxemella, Corynexochus, Bathyuriscus, and Poliella. The ex- tremes of range in total segments of the trunk is seen in Eodiscus (g) and Pedeumias (45+), and these same genera show the extremes in the number of thoracic segments, there being 3 in the one and 44+ in the other. Pedeimias probably shows the greatest var- iation of any one genus of trilobites, various species showing from 19 to 44+ thoracic seg- ments. The average for the nineteen genera is 13.9 segments in the thorax, 3.7 segments in the pygidium, or a total average of 17.6 segments in the trunk. Crepicephalus with 12-14 segments in the thorax and 4-6 in the pygidium, and Protypus, with 13 in the thorax and 4-6 in the pygidium, are the only genera which approach the average. All of the Mes- onacide, except one, Olenelloides, have far more thoracic and fewer pygidial segments than the average, while the reverse is true of the Eodiscide, Vanuxemella, Corynexochus, Bath- yuriscus, and Poliella. The eight genera of the Mesonacide, Nevadia, Mesonacis, Elliptocephala, Callavia, Holmia, Wanneria, Pedeumias, and Olenelloides, have an average of 20.25 segments in the thorax and 1.5 in the pygidium, a total of 21.75. If, however, the curious little Olenelloides be omitted, the average for the thorax rises to 22.14 and the total to 23.84. Olenelloides is, in fact, very probably the young of an Olenellus. Specimens are only 4.5 to tr mm. long, and occur in the same strata with Olenellus (see Beecher 1897 A, p. 191). Thirty-three genera from the Middle Cambrian afford data as to the number of seg- ments, the Agnostidze being excluded. The extreme of variation there is smaller than in the Lower Cambrian. The number of thoracic segments varies from 2 in Pagetia to 25 in Acrocephalites, and these same genera show the greatest range in total number of trunk segments, 8 and 29 respectively. The average of thoracic segments for the entire thirty-three genera is 10.5, of pygidial segments 5.9, a total average of 16.4. It will be noted that the thorax shows on the average less and the pygidium more segments than in the Lower Cambrian. If the Agnostidz could be included, this result would doubtless be still more striking. Of the genera considered, Asaphiscus with 7-11 thoracic and 5-8 pygidial segments, Blainia with 9 thoracic and 6-11 pygidial, Zacanthoides with 9 thoracic and 5 pygidial, and Anomocare with 11 thoracic and 7-8 pygidial segments came nearest to the average. Only a few departed widely from it. The genera tabulated were Acrocephalites, Alokistocare, Crepicephalus, Karlia, Hamburgia. Corynexochus, Bathyuriscus, Poliella, Agraulos, Dolichometopus, Ogygopsis, Orria, Asaphis- cus, Neolenus, Burlingia, Blainia, Blountia, Marjumia, Pagetia, Eodiscus, Goniodiscus, Albert- ella, Oryctocara, Zacanthoides, Anomocare, Anomocarella, Coosia, Conocoryphe, Ctenoce- phalus, Paradoxides, Ptychoparia, Sao, and Ellipsocephalus. Enough genera of Upper Cambrian trilobites are not known from entire specimens to furnish satisfactory data. Excluding from the list the Proparia recently described by Wal- cott, the average total trunk segments in ten genera is 18, but as most of the genera are Olenidze or olenid-like, not much weight can be attached to these figures. For the Cambrian as a whole, the average for sixty-two genera is between 17 and 18 trunk segments, which is surprisingly like the result obtained by Carpenter from only twelve 130 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. genera, and tends to indicate that it must be somewhere near the real average. If the 5 or 6 segments of the head be added, it appears that the “average” number of segments is very close to the malacostracan number 21. Genera with 16 to 18 trunk segments are Cal- lavia, Protypus, Bathynotus, Crepicephalus, Bathyuriscus, Ogygopsis, Burlingia, Orria, Asa- phiscus, Blainia, Zacanthoides, Neolenus, Anomocare, Conocoryphe, Saukia, Olenus, and Eurycare. The order Proparia originated in the Cambrian, and Walcott has described four genera, one from the Middle, and three from the Upper. The number of segments in these genera is of interest. Burlingia, the oldest, has 14 segments in the thorax and 1 in the pygidium. Of the three genera in the Upper Cambrian, Norwoodia has 8-9 segments in the thorax and 3-4 in the pygidium ; Millardia 23 in thorax and 3-4 in pygidium; and Menomomia 42 in thorax and 3-4 in pygidium. It is of considerable interest and importance to note that the very elon- gate ones are not from the Middle but from the Upper Cambrian. Forty genera of Ordovician trilobites known from entire specimens were tabulated, and it was found that the range in the number of segments in the thorax and pygidium was surprisingly large. Agnostus, which was not included in the table, has the fewest, and Eoharpes, with 29, the most. While the range in number of segments in the thorax is 2 to 29, the range of the number in the pygidium, 2 to 26, is almost as great. A species of Dionide has 26 in the pygidium, while Remopleurides and Glaphurus have evidence of only 2. The average number of segments in the thorax for the forty genera was 10.15, in the pygidium 8.81, and the average number for the trunk 10. Genera with just 19 segments in the trunk appear to be rare in the Ordovician, a species of Ampya being the only one I have happened to notice. Calymene, Tretaspis, Triar- thrus, Asaphus, Ogygites, and Goldius come with the range of 18 to 20. Goldius, with IO segments in the thorax and (apparently) 8 in the pygidium, comes nearest to the averages for these two parts of the trunk. Goldius, Amphilichas, Bumastus, Acidaspis, Actinopeltis, and Spherexochus are among the genera having 10 segments in the thorax, and there are many genera which have only one or two segments more or less than 10. In most Ordovician genera, thirty-five out of the forty tabulated, the number of seg- ments in the thorax is fixed, and the variation is in any case small. In four of the five genera where it was not fixed, there was a variation of only one segment, and the greatest variation was in Pliomerops, where the number is from 15 to 19. This of course indicates that the number of segments in the thorax tends to become fixed in Ordovician time. The variation in the number of segments in the pygidium is, however, considerable. It is difficult in many cases to tell how many segments are actually present in this shield, as it is more or less smooth in a considerable number of genera. Extreme cases of variation within a genus are found in Encrinurus, species of which have from 7 to 22 segments in the pygidium, Cybeloides with 10 to 20, and Dionide with 10 to 26. As the number in the thorax became settled, the number in the pygidium became more unstable, so that not even in the Ordovician can the total number of segments in the trunk be said to show any tendency to become fixed. The genera used in this tabulation were: Eoharpes, Cryptolithus, Tretaspis, Trinucleus, Dionide, Raphiophorus, Ampyx, Endymionia, Anisonotus, Triarthrus, Remopleurides, Bath- yurus, Bathyurellus, Ogygiocaris, Asaphus, Ogygites, Isotelus, Goldius, Cyclopyge, Amphili- chas, Odontopleura, Acidaspis, Glaphurus, Encrinurus, Cybele, Cybeloides, Ectenonotus, Calymene, Ceraurus, Pliomera, Pliomerops, Pterygometopus, Chasmops, Eccoptochile, Acti- nopeltis, Spherexochus, Placoparia, Pilekia, Selenopeltis, and Calocalymene. SEGMENTS IN TRUNK. 131 Only sixteen genera of Devonian trilobites were available for tabulation, and it is not always possible to ascertain the exact number of segments in the pygidium, although genera with smooth caudal shields had nearly all disappeared. The number of segments in the thorax had become pretty well fixed by the beginning of the Devonian, Cyphaspis with a range of from 10 to 17 furnishing the only notable exception. The range for the sixteen genera is from 8 to 17, the average 11, the number exhibited by the Phacopidee which form so large a part of the trilobites of the Devonian. The greater part of the species have large pygidia, and while the range is from 3 to 23, the average is 11.2. Probolium, with 11 in the thorax and 11-13 in the pygidium, and Phacops, with 11 in the thorax and 9-12 in the pygidium, approach very closely to the “average’’ trilobite, and various species of other genera of the Phacopide have the same number of segments as the norm. In every genus, however, the number of segments in the pygidium is variable, the greatest variation being in Dalmanites, with a range of from 9 to 23. The number of segments in the pygidium was therefore not fixed and was on the average higher than in earlier periods. The genera used in the tabulation were: Calymene, Dipleura, Goldius, Proétus, Cyphas- pis, Acidaspis, Phacops, Hausmama, Coronura, Odontochile, Pleuracanthus, Calmonia, Pen- naia, Dalmanites, Probolium, and Cordania. The trilobites of the late Paleozoic (Mississippian to Permian) belong, with two pos- sible exceptions, to the Proétide, and only three genera, Proétus, Phillipsia, and Griffithides, appear to be known from all the parts. I am, however, assuming that both Brachymetopus and Anisopyge have 9 segments in the thorax, and so have tabulated five genera. The range in the number of segments in the pygidium is large, from 10 in some species of Proétus to 30 in Anisopyge, and the average, 17.3, is high, as is the average for total num- ber in the trunk, 26.3. Anisopyge, a late Permian trilobite described by Girty from Texas, is perhaps the last survivor of the group. It seems to have had 39 segments in the trunk, making it, next to the Cambrian Pedeumias and Menomonia, the most numerously segmented of all the trilobites. The above data may be summarized in the following table: | I I re oD on = fs 3 2 5 Period | = A a & st o Tay | oo Bae S oa ar Set p= a | ts) A iS) Agee A 2 3 pa po > bo A ) 2 5) Ww 0D 2 oS —»)» LY ‘pore ee - wan 2» VY yw») » By > >” ° »)- > a >D s ‘ vows > &: bppy >”) ae ~ se > , a5 > ® >> 2 a “ >) J >) » pop nya >> yy Dy ni 3S} ze y Siam })). wW BD | » » » oe yp A = Pp as a & ‘>. Z Jd DD . ) » 5 a) a >> w)) >» 3 /\)»@Pp ~ > Drv Pp» BR 2 ») D>) WoW) > >> MD» D: »y = D*. ) » y Fs verte Ad et oe he’ Se] ore - w on Al vie a =~) | =~ dh Abd ACA, yg Nees Ne Ny Nay Ne Ne es mAs AF yh A | Ad Abin beth Ne 7 D> Dp Dd 4 VL + Be > on 2) Dy > DD. Noa ‘yy SEXES © wh. Le wh wi Yew v c NA ww SS VAT IS . AS te A A ses | | ed's we ww ke Sh q Sub © WH ee ISS ed — Dp | 2 Ie om DD | > —< IP IDD)) PR »> >. +2 DP ): » yy) » yd Yy > > » » > WP PW yy » > p sD. yD b “* re? ic PD > >I» 2 i‘ iy » SS ‘ » YD > Dp sh >» D> 5 Dy ww ww . 2am >. yy )) am : ie hy) » s Bs) &® > Nn» => pr> wy map? BWaYy>D YP WWM °* > 3D BD yo 9 yaa’ = D> > DED SP YED »»>? Hor ») »)) > 2» >» DD >» >» > Pop ) > 1 Y or | oi 4 To Sp nt ae hos? 3 3 x . < DA ~ = > )) “yD D> » » JB > oe ») s > RP » >» > e oe 22 BP > VD >» DD. yD Dy >) o> dD > s 5 pr» » yD A > “a »> vy Iw»»D I yy Oy te Pp. 2 » ee Pie : > Db ID »y» »YD »») an >) >. ) dF 2 Be ~ ID hp _ vy » Br? ? he , _— a i a OP a as wv 1351 6802