194 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



quadrangular. Structure otherwise substantially as in the preceding. 

 Ordovician (Cincinnatian) ; Ohio. 



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

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

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



Acacocrinus 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. Basals three. Silurian ; Indiana and Kentucky. 



Carpocri7ius Miiller (PJwenicocrinus Austin ; Ahracrimis d'Orb. ; Habro- 

 crinus, Pionocrimis, 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 

 (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 



Ang. 



Flo. 296. 



Pio. 295. 



a, CarpocrinU'S comtits (Aug.). Siluinan ; (!ot- 

 land. Crown viewed from the anal side, natural 

 size. 6, //. or»a<!ts (Aug.). Tegnien showing cover- 

 ing pieces of the ambulacra (after Angelin). 



Desmidocrinus 

 heterodactyhis (Ang.). 

 Silnrian ; Gotland. 

 Natural size (after 

 Angelin). 



England. 



Abacocrinus Ang. 



(Carolicrinus Waag. and Jahn). Basals 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. 



Macarocr'mns Jaekel. Devonian ; Germany. 



Periechocrinus Austin {Geocrinus d'Orb.; Pyxidocrinus Miiller; Trochocriuus 

 Portlock ; Pradocrinus de Verneuil). Basals 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. 



that they do not pa.ss down to the basals in either species. This leaves no character to separate it 

 from the Batocriuirlae, and the present reviser agrees with Batlier in placing it with Tanaocrinus 

 and Gompsocrittns as the primitive forms of that family. 



