$66 NORTH AMERICAN INDEX FOSSILS. 



LXXV. Onychocrinus Lyon and Casseday. 



Similar to Ichthyocrinus in general structure, but calyx depressed, 



arms spreading and talon-like, interbrachials present between the 



costals and posterior interray very different from the others, being 



composed of many minute pieces which enclose a row of small anal 



Fig. 1905. Onychocrinus exculptus, X Vz- (After Meek and Worthen 



plates, supporting a small tube above. Tegmen formed of almost 

 microscopic particles and very flexible. Arms 10, giving off arm- 

 lets in clusters. Mississippic. 



198. 0. exsculptus Lyon and Casseday. (Fig. 1905.) Mississippic. 

 Surface ornamented with minute granules. 

 Keokuk of Kentucky, Indiana and Illinois. 



LXXVL FoRBESiocRiNUS de Koninck and le Hon. 

 Similar to Taxocrinus, but differs in its anal area. Both IRA 

 and RA present. Interbrachials very numerous, sometimes in 12 

 or more rows. Arms long, bifurcating, with infolding tips. Mis- 

 sissippic. 



