Ii8 



NORTH AMERICAN INDEX FOSSILS. 



septa less crowded, and strongly curved downwards in lateral ex 

 pansions. 



Trenton of Illinois and Wisconsin. 



Fig. 1353. Gonioceras ancej>s, longitudinal Fig. 1354. Gonioceras occidentale, X %- (After 

 section showing small part of siphuncle, X K- Clarke, Pal. Minn.) 

 (After Hall, Pal. N. Y., I.) 



LXII. M^LONOCERAS Hyatt. 



Slender, very gradually enlarging, and regularly curved cyrto- 

 ceracones of subcircular or ovate section, with moderate living 

 chamber, and more or less nummuloidal siphuncle, which is situ- 

 ated near the ventral surface. Sutures with ventral and dorsal 

 saddles and slight lateral lobes. Shell with concentric striae, or 

 annulations, curved back on venter. Ordovicic-Siluric. 

 158. M. neleus Hall. (Fig. 1355.) Ordovicic. 



Slender, strongly curved, very gradually expanding, slightly 

 flattened on concave side ; septa close but not regular ; suture with 

 broad, ventral saddle; siphuncle subventran, comparatively large, 

 moderately nummuloidal; surface with rather strong concentric 

 striae or annulations, curved backwards on the venter. 



Stones River of Minnesota and Wisconsin. 



