56 



NORTH AMERICAN INDEX FOSSILS. 



39. P. lamarckii (Billings). (Fig. 1255.) Ordovicic. 



Very gently expanding (i mm. in 20), often slightly bent; annu- 

 lations rounded, narrow, with wider concave interspaces ; distance 

 of septa similar to annulations; siphuncle large, excentric. 



Fig. 1258. Cycloceras nicolletti, 

 X K- (After Clarke, Pal. Minn.) 



Fig. 1259. Cycloceras randolphense, 

 two views of same specimen. (After 

 Meek & Worthen, 111. Pal., II.) 



Beekmantown (Cassin) beds of Lake Champlain, and similar 

 beds of Mingen Island and Newfoundland. 



