CEPHALOPODA— ORTHOCHOANITES. 



63 



52. 0. cornu-oryx (Whitfield). (Fig. 1268.) Ordovicic. 



Internal annulations faint, distant, and separated by shallow- 

 spaces ; section depressed, elliptical ; camerae short. Surface smooth. 



Beekmantown (Fort Cassin) of Vermont and New York. 



XVI. Spyroceras Hyatt. 



Like Protocycloceras but with the longitudinal ridges persisting 

 into the adult, together with the pronounced annulations. Ordo- 

 vicic-Carbonic. 



53. S. bilineatum Hall. (Fig. 1269.) 



Ordovicic. 



^P^l 



Fig. 1269. Spyroceras bilineatum^ ribbed Fig. 1270. Spyroceras anellus. 

 apical portion passing into annulated part. (After Clarke, Pal. Minn.) 

 (After Clarke, Pal. Minn.) 



Early portion non-annulated ; annulse of later part strong, round, 

 slightly oblique. Longitudinal ridges strong with finer ones be- 

 tween; camerse short. 



Stones River and Black River of Minnesota; Black River of 

 Cincinnati region; Black River and Trenton of Canada; Trenton 

 of New York and Tennessee. 



54. S. anellus Conrad. (Fig. 1270.) Ordovicic. 



Differs from the preceding in the more uniformly and regularly 

 rounded annulations with similar interspaces, and in the fine, regu- 

 lar, longitudinal striae. 



