ECHINODERMATA—CRINOIDEA. 



549 



LVI. Hercocrinus Hudson. 

 Base of calyx with narrow concavity. IB very small and nearly 

 covered by the stem joints. R nearly equal in size to B (exposed 

 part). Costals two; the next few succeeding brachials each giving 

 off a large pinnule which is in- 

 corporated into the dorsal cup, 

 those of adjoining rays being 

 in conjunction, or meeting to 

 form web-like extensions o^ the 

 arm bases. Arms to, biserial. 

 IR of variable plates, not form- 

 ing part of the ventral disk. 

 Tegmen of numerous small 

 plates. Anus nearly central, 

 elevated (Fig. 1878). Ordo- 

 vicic. 



157. H. elegans Hudson. 



Ordovicic. 



Small (one half inch wide), 

 pyriform. Base flattened, rather pentangular. R prominently 

 triangular at contact with base. IR convex, numerous, polished 

 and jewel-like ; three or more IR separate the R. B with a smooth 

 transverse ridge. 



Chazy of Lake Champlain. 



158. H. ornatus Hudson. Ordovicic. 

 More nearly globular than H. elegans. B with rough trans- 

 verse ridge, forming a circular border to the base. R and bra- 

 chials similarly roughened by ridges. R separated by two IR. 



Chazy of Lake Champlain region. 



Fig. 1878. Hercocrinus, analysis of 

 calyx. (After Hudson.) 



LVII. Rhodocrinus Miller. 



Calyx small, globose. Dorsal cup flat or concave below, con- 

 stricted above. IB 5, small. B 5, large, truncated above. R 

 smaller than B. Costals two, often coalesced into a single plate. 

 Distichals free in part. Arms in pairs and bifurcating. Tegmen 

 narrow, but slightly elevated above the dorsal cup. Anus excen- 

 tric, sometimes marginal. Column round. Devonic-Mississippic. 



