ECHINODERMATA—CRINOIDEA. 5 5 1 



LX. GiLBERTSOCRiNUS Phillips. 

 (OUacrinus Cumberland, Goniasteroidocrinus, Lyon and Casseday.) 



Calyx composed of delicate plates. Dorsal cup greatly exceed- 

 ing the tegmen, elongate, cylin- 

 drical. IB 5, frequently hidden 

 by the column. B and IR large, 

 the latter rapidly decreasing in 

 size upward. From the last axil- 

 lary spring two tufts of small, 

 branching, pinnule-bearing arms ; 

 these are either folded over the 

 tegmen or they bend downward 

 with the ventral side exposed to 

 view, the pinnules being directed 

 upward. Tegmen flat or low 

 hemispherical, with five interra- 

 dial pits and its margin extended 

 into 10 tubular appendages pass- 

 ing outward and downward. 

 Plates smooth or ornamented. 

 Anus subcentral, opening di- 

 rectly through the tegmen. 

 Column circular. 



Differs from Rhodocrinus in 

 the presence of the tubular ap- ^^^- '^^°- Lyriocrinus dactyius. 

 pendages. Devonic-Mississippic. 

 163. G. spinigerus (Hall). (Fig. 1881.) Devonic. 



Tegmen flat. Rays marked by ridges proceeding to the arm 

 openings. R, first costals, and first IR ex- 

 tended into sharp nodes or small spines. 

 Hamilton of Ontario. 



164. G. typus Hall. Mississippic. 



Agrees with G. spinigerus in general out- 

 line, projecting rim around the upper mar- 

 gin and presence of spines, but is larger, 

 with slightly convex tegmen. 



Upper Burlington and Burlington-Keokuk transition bed of 

 Iowa; Upper Burlington of Missouri. 



Fig. 1 88 1. Gilbertsocrinus 

 spinigerus. ( After Whitf . ) 



