CEPHALOPODA— ORTHOCHOANITES, 



49 



from six to nine to the inch; siphuncle changing from centren in 

 the young to more or less excentric in the adult. 



Trenton, Richmond and Maquoketa of Minnesota; Eden and 

 Maysville of Cincinnati region; Maquoketa of Iowa. 



21. 0. simulator Hall. Siluric. 



Fig. 1246. Orthoceras junceum, 

 fragments and end view. (After 

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



Fig. 1247, Orihoceras amplicameraiunit 

 side and end view of a fragment, X Yi' 

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



Cylindrical, gradually enlarging ; siphuncle subcentral ; septa 

 about one fourth diameter of shell apart; surface finely striated 

 transversely, often flattened. 



Niagaran (Waldron) shales of Indiana, etc. 



22. 0. rectum Worthen. Siluric. 



Medium sized, apical angle about 5° ; camerse large, from two 

 to three equalling the diameter of the shell; siphuncle centren. 

 4 



