CEPHALOPODA— CYRTOCHOANITES. 



119 



Fig. 1355. MiBlonoceras neleus, X Vz- ( After Clarke, Pal. Minn.) 



159. M. arcticameratum Hall. (Fig. 1356.) Siluric. 



Slender, regularly and moderately curved and gradually and reg- 

 ularly expanding to the living chamber, which may contract very 

 slightly towards the aperture ; section transversely oval to circular ; 



Fig. 1356. McBlonoceras arcticameratum, y^Y-^. (After Clarke and Ruedemann. ) 



septa slightly convex; siphuncle small, ventral; surface with con- 

 centric striae, recurving ventrally. 



In the Guelph of Canada, New York and Wisconsin. 



LXIIL Cyclostomiceras Hyatt. 

 Slender but short endo- or exo-gastric cyrtoceracones (rarely 

 orthoceracones), of circular or slightly compressed, transversely 



