PLATYCEINID^ Roejier. 



Monocyclic. Brachials and interbrachials only slightly represented in the 



DORSAL cup ; THE LOWER BRACHIALS TAKING MORE OR LESS THE FORM OF FREE 

 ARM PLATES; THE LOWER INTERRADIALS IN PART INTERAMBULACRAL IN POSITION, 

 BARELY ENTIRELY INTERBRACHIAL. EaDIALS IN CONTACT ALL AROUND, THERE BEING 

 Nt) SPECIAL ANAL PLATE. BaSALS FORMING A PENTAGON. 



Analysis of the Genera. 



B. 



Basals 3, unequal, frequently anchylosed. 

 COSTALS TWO. 



1. Column circular. 



a. Disk almost completely occupied hy the orals ; ambulacra 

 sultegminal ; orals separated from radials hy only one 

 ring of interradials. 



Orals symmetric; arms apparently delicate . . . Coccocrinus. 



Orals asymmetric ; arms heavy, biserial .... CuUcocrinus. 



h. Disk co9nposed of numerous plates ; ' orals not observed ; 



arms uniserial, or slightly interlocking Cordylocrinus. 



CoSTALS ONE. 



1. Orals occupying but a small part of the disk, and asymmetri- 

 cally arranged ; ambulacra exposed ; arms biserial. 



a. Column circular; canal large, quinquelobate ; distichals 



one when more than one bifurcation Marsupiocrinus. 



b. Column elliptic ; canal small, round ; distichals two. 



Arms branching by alternate bifurcation .... Platycrinus. 



Eays extended into tubular appendages giving ofi 



the arms Eucladocrinus. 



