574 



NORTH AMERICAN INDEX FOSSILS. 



Very abundant in Bear River of Wyoming, Idaho and Utah. 



595. C. engelmanni Meek. (Fig. j%%, e,f) Cretacic. 

 Differs from C. piriformis in its smaller size, different outline, 



less convexity of valves and less incurving of beaks. 

 Bear River : Wyoming, Idaho. 



596. C. subtrigonalis Meek and Hayden. Cretacic. 



Fig. 788. a-d, Corbula pyriformis, right, cardinal, anterior views of complete shell 

 interior of left valve, e, f, C. engelmanni. (After White.) 



Outline triangular. Very convex. Average length .75 inch; 

 height .5 inch. Anterior end abruptly rounded ; posterior longer 

 and more angular. Umbonal angle about 90 . Beak incurved, 

 gibbous. Posterior umbonal slope subangular. Surface marked 

 with concentric lines and a few growth ridges. 



Especially abundant in the Montanan (brackish water beds) of 

 Wyoming, Montana, Assinib'oia. Also present in the Coloradoan 

 and Laramie. 



597. C. bisulcata Conrad. Cretacic. 

 Beak small, incurved. Surface crossed by fine concentric growth 



lines. 



Ripleyan of New Jersey (Cliffwood-Woodbury), North Caro- 

 lina, Mississippi, Arkansas. 



598. C. crassiplica Gabb. Cretacic. 

 Beaks large, inflated, enrolled, a little anterior of middle. Left 



valve much the less convex and without the strong concentric ribs 

 of the right valve. 



