RHODOCRINID^ Roemer (1855). 



DiCYCLic. Lower brachials and interbrachials forming an important part op 



THE dorsal cup. RaDIALS SEPARATED ALL AROUND BY AN INTERRADIAL PLATE 

 WHICH IS FOLLOWED BY WELL-DEFINED, REGULARLY ARRANGED INTERBRACHIALS. 



Analysis of the Genera. 



Infrabasals 5. Basals 5. 



A. Anal interradius generally with additional plates. 



1. Arms uniserial. 



a. Arms not branching. 



Basals exposed in a side view Rhaphanocrinus- 



2. Arms hiserial. 



a. Arms hranchirig. 



Calyx obovate ; anus without a tube ; interbracMals 

 numerous, two in second row ; interdisticlials gen- 

 erally present Arch^ocrinus. 



Calyx depressed globular, anus at end of a tube, first 

 interradials frequently separated from basals by 

 supplementary pieces. No interdistichals. Arms 

 probably given off from brachial prolongations of 



the calyx Diabolocrinus. 



Calyx globose, flattened or concave below ; two or three 

 interbrachials in second and succeeding rows ; no 

 interdistichals. 



Ventral disk narrower than dorsal cup . . . Rhodocrinus. 

 Ventral disk equal to, or exceeding dorsal cup ; 

 tubular appendages suspended from mar- 

 gin of disk Gilbertsocrinus. 



b. Arms not branching. 



Calyx globose, arms long and heavy ; interdistichals 



numerous Thylacocrinus. 



B. Anal interradius without additional plates. 

 1. Arms biserial. 



a. Arm,s not branching, dorsal cup broadly truncate at the bot- 



tom, radials sometimes not all separated; arm facets 



directed upward Lyriocrinus. 



b. Arms branching. 



One costal ; interdistichals few Anthemocrinus. 



Two costals ; rays produced into long trunks giving off 



armlets from opposite sides Ripidocrinus. 



C. Anal interradius unknown. 



Arms uniserial, branching frequently ; infrabasals very small . Diamenocrinus. 



