1881.] NATURAL SCIENCES OF PHILADELPHIA. 233 



that of a compound oral plate in Platycrinus, as against a simple 

 one in Coccocrinus. 



Zittel has arranged this genus with Haplocrinus under a separate 

 family. 



Generic Diagnosis. — Body small, globose; calyx constructed 

 like that of Platycrinus ; vault composed of five oral plates, resting 

 upon five smaller interradial pieces. 



Basals three ; two of them equal, the third smaller by half, the 

 suture between the two equal plates directed toward the right 

 posterior ray ; the two sutures in connection with the smaller one 

 directed to the anterior and left lateral rays, thereby disturbing 

 the general sj-mmetr^'^ of the calyx, which otherwise would be perfect. 



Radials 2X5; the first large, quadrangular, its upper corners 

 slightly truncate for the reception of the interradial, and its 

 upper side slightly convex. Second radials narrower by half 

 than the first, and very short ; they are almost quadrangular — 

 although bifurcating plates — on account of the very obtuse angle 

 upon which they support the arms. 



Arms unknown, only a single joint having been discovered, 

 which is small and round. 



Interradials, one to each area resting upon the corners of the 

 first, and between the second radials ; its upper part truncate, 

 deflected towards the summit, and supporting another somewhat 

 larger plate, giving five in the vault, which form a low pyramid. 

 The latter, which are oral plates, do not join laterally, nor in the 

 centre, but leave a median space and lateral slits, which, in perfect 

 specimens, were doubtless closed, the one b}^ the apical dome 

 plates and the slits by small marginal pieces. Posterior side only 

 distinguished by the anal opening, which is placed within the 

 suture of the interradial and oral plate. 



Column small, cylindrical ; central canal round and narrow. 



Coccocrinus differs from HajDlocrinus in having the first radials 

 simple instead of compound, and in the oral plates, which in the 

 latter are formed into compartments for the reception of the arms. 

 It differs from Platycrinus and Gordylocrinus in the summit 

 structure, and from the former also in having the column round 

 instead of elliptical and twisted. 



Geological Position^ etc. — Of the two species referred to this 

 genus, one is from the Lower Silurian of Tennessee, the other 

 from the Devonian of the Eifel, Germany. 



