456 University of Kansas Geological Survey. 



the base ; posterior basal extremity prominently rounded ; pos- 

 terior margin broadly rounded or subtruncated ; dorsal and 

 anterior margin diverging from the beaks at an angle of about 

 ninety degrees ; hinge short ; moderately prominent and nearly 

 terminal, that of the left valve rather strongly incurved and 

 directed obliquely forward, while in the right it is straighter 

 and less elevated ; umbonal axis ranging at an angle of about 

 seventy degrees to the hinge line. Surface of both valves (in 

 the condition of casts) ornamented by regular strong, sub- 

 angular, concentric undulations, separated by wider rounded 

 depressions. Height from the most prominent part of the base 

 to the hinge margin, 2.90 inches; height to top of umbo, 3.36 

 inches ; convexity of left valve, 1.84 inches." 



This species occurs in the Fort Benton limestone, but it is not 

 abundant. Specimens seen were imperfect casts only. 



Inoceramus subconvexus, n. sp. Plate cxviii, fig. 1. 



Description : Shell oblong oval, nearly if not entirely equi- 

 valve, convex, greatest convexity in anterior region ; anterior 

 margin triangular ; margin opposite hinge curved ; hinge 

 straight, long in comparison with length of shell ; posterior 

 margin rounded and extended into a narrow, flat flange. Shell 

 curving abruptly upward from the narrowly pointed beaks, 

 then curving gradually backward and downward ; beaks ter- 

 minal, apparently not rising above the hinge and slightly 

 incurved. Surface marked by moderately prominent undula- 

 tions and rather closely crowded striations. Length of longi- 

 tudinal axis, fifty mm. ; maximum breadth, thirty mm. ; 

 diameter at point of greatest convexity, fifteen mm. 



This species seems most nearly related to Inoceramus labiatus, 

 to which species I was inclined to ascribe it on first examina- 

 tion, thinking it was a young individual. On comparing the 

 specimen with young individuals of Inoceramus labiatus, how- 

 ever, I was able to note specific differences. These differences 

 are greater convexit} T , pointed beak, and abrupt anterior curve 

 of shell. 



A right and left valve of this shell were found by the writer 



