J62 



THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Calyx rotundate ; anal tube moderately 

 small, about central ; arm openings twelve 

 to twenty; arms long, single or paired, 

 often in the same species ; respiratory 



pores not visible Dizygoorinus. 



2. Anus without a tube. 



a. Calyx lobed ; arms arranged in ffroujys. 



Calyx more or less elongate. 



Arms heavy, one from each opening. 



Arms ten, recumbent on the dorsal cup ; pin- 

 nules infolding Barrandeocrinus. 



Arms one only from each opening, erect, 



rather heavy Aorocrinus. 



Arms slender, paired ; upper arm joints 

 spiniferous ; posterior oral and proximal 

 radial dome plates extended into spines . Dorycrirms. 



b. Calyx hemispheric or pyramidal. 



Dorsal cup from very slightly convex to 

 concave ; arms heavy. Orals and radial 



dome plates prominent Agaricocrinus. 



B. Akms uniserial. 



1. Basals three. Interbrachials not numerous. Col- 

 umn ROUND. 



a. Arms delicate, joints cuneate, alternately arranged, 



only interlocking at the tips Acacocrmus. 



h. Arms heavy, joints quadrangular. 



Arms ten Sabrocrinus. 



Arms more than ten (?) Desmidocrimis. 



2. Basals four ; column quadrangular. 



Arms slender, joints cuneate ; plates deli- 

 cate and highly ornamented. Interbrach- 

 ials and interdistichals very numerous . Compsocrinus. 



II. 



Ventral disk composed of small, irregularly arranged plates, 



WITH OR without ORALS. AkMS GENERALLY BRANCHING 



beyond the calyx Periechockinites. 



A. Arms biserial from the calyx up. 

 1. Basals three ; anal area wide. 



Calyx elongate, urn-shaped ; plates thin and 

 elongate ; arms grouped. Orals indistin- 

 guishable. The column with large cen- 

 tral canal Periechocriniis. 



Calyx depressed globose, plates short and 

 heavy. Arms branching, given off in 

 pairs, their facets contiguous ; orals gen- 

 erally represented ; central canal large . Megistoerinus. 



Calyx low, strongly lobed at the arm regions, 

 plates thin, highly ornamented. Arms 

 arranged in clusters. Central canal of 

 moderate size Gennmocrinus. 



