CLASS HI 



CRINOIDEA 



199 



§ 1. Rays with ttoo or more primibrachs (cosfals). 



Coccocrinus Joh. Miiller. The simplest form of the Camerata, the calyx 

 consisting only of three basals, five radials, 2x5 costals, five interbrachials and 

 five orals. Calyx small, rotund ; basals and radials forming almost the entire 

 dorsal cup. Tegmen almost completely occupied by five large, triangular, 

 symmetrical orals, forming a pyramid. Anal opening in the interradio- 

 oral suture. Arms delicate, branching once, uniserial with cuneate joints. 

 Column round. Silurian ; North America. Devonian ; Eifel. 



Oulicocrinus Joh. Miiller. Transitional between Coccocrinus and Platycrinus ; 

 generally similar to the former. Orals asymmetrical. Arms heavy, biserial. 

 Column round. Middle Devonian ; Eifel. 



Hapalocrinus Jaekel em. Bather {Jgriocrimis, Thallocrinus and Clematocrinus 

 Jaekel). Orals small ; interambulacra visible. Arms uniserial, Avith cuneate 

 joints ; branching once or twice. Column round, with strong cirri. Silurian ; 

 England, Australia, North America. Devonian ; Germany. 



Corclijlocrinus Angelin. Tegmen composed of numerous plates. Arms 

 uniserial, or slightly interlocking. Column round, with long cirri. Silurian ; 

 Gotland. Devonian ; North America. 



§ 2. Bays with only one primibrach (costal). Orals occupying but a small part of 

 the tegmen, asymmetrical ; ambulacral plates well defined. 



Marsipocrinus Bather (pro Marsupiocrinus Phill., non Blv.'). (Syn. Cypellocrinus 

 vel Cupellaecrimis Shumard, ex Troost, non Steininger.) Brachials to axillary 

 distichal usually incorporated in cup. Arms biserial, ten or twenty. Column 

 round. Axial canal large. Silurian ; England, Gotland, North America. 



.^.'T> 



Fig. 300. 



Platycrinus subsjnnosus (Hall), 

 ous ; Burlington Group, Iowa, 

 cup, omitting anal inturray. h, 

 I, Costals ; ir, Interbrachials 

 and Springer). 



Lower Carbonifer- 



Analysis of dorsal 



Basals ; R, radials ; 



(after Wachsmuth 



Fig. 301. 



Platycrinus tnijintidactylus 

 (Austin). Lower Carbonifer- 

 ous ; Tournay. Belgium (re- 

 stored, after de Koninck). 



Platycrinus Miller (Centrocrinus, Pleurocrinus Austin; Edwardsocrinns d'Orb.) 

 (Figs. 300, 301). Calyx rotund. Eadials large with crescent-shaped facets. 

 First interbrachials at the level of the arm bases ; consisting of three plates 

 horizontally arranged, usually partly interambulacral, but sometimes succeeded 

 by one or more ranges incorporating the distichals ; plates of anal interradius 

 usually more numerous than those of the other sides. Orals usually large, 

 asymmetrical, occupying but a small part of the tegmen. Ambulacra rigid, 



