PELECYPODA—TELEODESMACEA. 



541 



plate heavy, flat, with two cardinal teeth in each valve ; lateral 

 teeth present, one (posterior) in each valve, with a small anterior 

 lateral at times in the right valve. Free margins of valves crenate. 

 Adductor impressions deep. Pallial line simple. Cretacic-Recent. 



500. C. alaeformis (Conrad). (Fig. 740, a % b.) Eocenic. 



Fig. 740. 



a, b, Cr as satellites alceformis % left and right valves ; 

 and cardinal views. (Md. Surv.) 



d, C. aquiana, left 



Base of attenuated posterior portion varying from broadly convex 

 to broadly concave ; sculpture strong. 



Very abundant in the Aquia of Maryland. 



501. C. aquianus (Clark). (Fig. 740, c y d.) Eocenic. 

 Differs from C. alceformis in its shorter and broader posterior 



extremity, its higher umbos, and the absence of deep prominent 

 furrows on the umbos. 

 Aquia of Maryland. 



502. C. gabbi SafTord. (Fig. 741.) Eocenic. 

 Surface marked with heavy concentric ribs which become faint 



at the posterior umbonal slope. 

 Midway : Gulf region. 



