NORTH AMERICAN INDEX FOSSILS. 



oval section ; living chamber comparatively long, slightly contracted 

 towards the aperture in the gerontic stages, but aperture open; 

 siphuncle more or less nummuloidal without organic deposits. 

 Ordovicic-Devonic. 



1 60. C. cassinense (Whitfield). (Fig. 1357.) 



Ordovicic. 



Fig. 1357. Cyclostomiceras cas- 

 sinense^ dorsal and septal views, X 

 %. ( After Ruedemann, Bull. 90, N. 

 Y. State Mus.) 



Fig. 1358. Cyclostomiceras orodes, 

 showing shell. (After Whiteaves, Pal. 

 Foss., III.) 



Very gently curved, rapidly expanding; aperture slightly con- 

 tracted; living chamber half the length of the shell; apertural mar- 

 gin straight with shallow, wide hyponomic sinus ; siphuncle large, 

 propiodorsan, slightly nummuloidal. 



Beekmantownian (Fort Cassin) beds of Lake Champlain region. 



161. C. orodes (Bilhngs). (Figs. 1358-60.) Siluric. 



Very gently curved cyrtoceracones, rapidly expanding, with ven- 

 tral, scarcely nummuloidal siphuncle ; surface smooth ; apertural 

 contraction moderate. 



Guelph of Canada and New York ; Upper Monroe of Canada. 



