TAXOCRTNIDAE 421 



Of the fifteen described species belonging to this genus, five are synonyms or insuffi- 

 ciently defined for identification. The remaining ten may be arranged as follows : 



The Species of Onychocrinus 

 I. Exsculptiis Group. 



iBr numerous and well-developed. 



Ramules unilateral, outside of dichotom. IBr 3 O. asteriaeformis. 



Ramules bilateral, alternating on both sides of dichotom. 

 IBr 4 ; rami strongly diverging. 



Rami short, with few divergent clusters of stout ramules. 

 Ramules at intervals of 3 or more. 



Anal tube small O. diversus. 



Rami longer, rays short and robust, clusters of stout ramules 

 more than 5 in number. 



Anal tube large 0. ulrichi. 



Rami longer than main rays below, slender and gradually 

 tapering. 



Ramules delicate and clusters numerous 0. exsculptiis. 



II. Ramiilosits Group. 



iBr few ; areas chiefly filled by perisome. 

 Ramules bilateral, alternating. 



Rami much longer than main rays below. 

 Small iBr frequent in higher axils. 

 Rami strong. 



Ramules not divergent, long, branching at long intervals 

 and not forming clusters ; united to main ramus for 

 several brachials or connected by small iBr. 



IBr 3 ; IIBr 4 or more. 0. ramulosus. 



Small iBr rare in higher axils. 

 Rami slender. 



Ramules divergent ; delicate, in clusters at intervals of 3, 

 or 2 in upper part. 

 IBr variable, 3 or 4 ; IIBr 3. 



Rays massive 0. magnus. 



Rays relatively slender 0. distensits. 



Rami strong ; ramules thick, not in clusters, at intervals of 3 

 and 2. 



IBr 3. IIBr 3 and 2 0. pulaskiensis. 



IBr 4. IIBr 2 ; ramules at intervals of 3, 2 and 1 0. wrighti. 



IBr 5 or more. 



Ramules unilateral, inside of dichotom O. polvdactylus. 



Insufficiently defined r O. semiovatus. 



