CEPHALOPODA— ORTHOCHOANITES. 



57 



XI. Cycloceras McCoy. 



Like the preceding but with discontinuous longitudinal ridges. 

 Annulations often become obsolete in old age. Ordovicic. 



40. C. lesueuri Clarke. (Fig. 1256.) Ordovicic. 

 Small, nearly cylindrical, with sHghtly oblique, rounded annula- 

 tions; sutures coincide with constrictions. 



Stones River of Minnesota; Stones River and Black River of 

 the Cincinnati region. 



41. C. olorus Hall. (Fig. 1257.) Ordovicic. 

 Larger than preceding, with more widely separated, sharply 



Fig. 1260. Dawsonoceras an- 

 nulatutn. (After Barrande. ) 



Fig. 1 26 1. Dawsonoceras annu- 

 latum. (After Kindle, Ind., 28.) 



rounded and somewhat flexuous annulations and deeply convex 

 septa. 



Stones River and Trenton of Minnesota; Stones River of Cin- 

 cinnati ; Trenton of New York ; Bighorn of Wyoming. 



