444 NORTH AMERICAN INDEX FOSSILS. 



Montanan of Kansas, Wyoming, Alberta ; also Coloradoan of 

 South Dakota. 



217. I. nebrascensis Owen. Cretacic. 

 Beak about one fifth the length of the shell from the anterior 



border. Average length and height 5 inches. Anterior side 

 short, making a very broad, oblique curve from beak to base. 

 Posterior and basal margins broadly rounded. Hinge rather short. 

 Differs from /. proximus in its larger size and coarser concentric 

 undulations. 



Montanan of the Plains and Rocky Mountain regions. 



218. I. proximus Tuomey. (Fig. 584.) Cretacic. 

 Hinge line about two thirds the length of the shell. Basal and 



posterior margins broadly rounded. Average length and height 

 about two inches. Differs from /. barabini in being more com- 



Fjg. 584. Inoceramus proximus. (After Whitfield, Pal. N. J., I.) 



pressed, less oblique, and in having more regular and closely 

 arranged concentric undulations. 



Pierre : South Dakota, Colorado. Ripleyan of New Jersey 

 and the Gulf region. 

 219. I. vanuxemi Meek and Hayden. Cretacic. 



Subcircular. Hinge short. Beaks located a little in advance 

 of the middle. Valves slightly convex. Surface marked with 

 regular, coarse concentric undulations. Average length 5 inches ; 

 height 4.5 inches. Distinguished from /. nebrascensis by its much 

 less convex and nearly circular form, its less prominent and more 



