194 



ECHINODERMATA— PELMATOZOA 



PHYLÜM IV 



quadrangular. Structure otherwise substantially as in the preceding. 

 Ordovician (Cincinnatian) ; Ohio. 



Compsocrinus S. A. Miller. Basais four. Arms simple or branching. 

 Basais and radials more evenly rounded and less excavate laterally, but other- 

 wise differing little from Xenocrinus. Ordovician (Cincinnatian) ; Ohio. 



Jcacocrinus W. and Sp. Interbrachials few, definitely arranged, not in 

 strongly depressed areas, and brachials and anals not in prominent ridges. 

 First primibrach (costal) quadrangular. Arms uniserial, slender, unbranched, 

 with cuneate ossicles tending to interlock at the tips. Calyx rather low and 

 rotund. Basais three. Silurian ; Indiana and Kentucky. 



Carpocrinus Müller (PJioenicocrinus Austin ; Abracrimis d'Orb. ; Habro- 

 crinus, Pionocrinus, Lepiocrinus Ang.) (Fig. 295). Calyx as in the preceding. 



.,,„,. Arms simple, heavy, 



usually not exceeding 

 ten, with very short, 

 wide ossicles, slightly 

 cuneiform, the longer 

 face bearing two pin- 

 nules, the shorter but 

 one. Silurian ;Gotland, 

 England. 



Desmidocrinus Ang. 

 (Fig. 296). Like the 

 preceding but with arms 

 fifteen to twenty, ossi- 

 cles longer and quad- 

 rangular, bearing one 

 pinnule to each side. 

 Silurian ; Gotland and 

 England. 



Abacocrinus Ang. 



(Carolicrinus Waag. and Jahn). Basais four. Calyx rotund. Interbrachials 

 rather numerous, definitely arranged, not in depressed areas ; brachials and 

 anals not in prominent ridges. First primibrach hexagonal. Arms branch- 

 ing, biserial from the calyx up. Silurian ; Gotland. 

 Macarocrinus Jaekel. Devonian ; Germany. 



Penechocriniis Austin (Geocrinus d'Orb.; Pyxidocrinus Müller; Trochocrimis 

 Portlock ; Pradocrinus de Verneuil). Basais three. Calyx elongate, expanding 

 to arm bases ; plates thin and long, usually with narrow median ridges along 

 the brachial series, which bifurcate two or three times within the calyx, lead- 

 ing to twenty-five or thirty arms, which are biserial beyond the calyx and do 

 not branch after becoming free. First primibrach (costal) hexagonal. Inter- 

 brachials numerous, definitely arranged. Silurian ; England and Gotland. 



Saccocrinus Hall. Like the preceding, but the arms branch from about 

 twenty openings after becoming free, and are biserial both below and above the 

 bifurcations. Silurian to Lower Carboniferous (Upper Burlington) ; North 

 America and (?) Gotland. 



Fig. 295. 



a, Carpocrinus comtus (Ang.). Silurian ; Got- 

 land. Crown viewed from the anal side, natural 

 size. b, H. ornatus (Ang.). Tegmen showing cover- 

 ing pieces of the ambulacra (after Angelin). 



Fig. 296. 



Desmidocrinus 

 heterodactylus (Ang. ). 

 Silurian ; Gotland. 

 Natural size (after 

 Angelin). 



that they do not pass dowii to the basals in eitlier species. This leaves no character to separate it 

 from the Batocrinidae, and the present reviser agrees with Bather in placing it with Tanaocrinus 

 and Compsocrinus as the primitive forms of that faniily. 



