PELECYPODA—TELEODESMACEA. 



571 



CLXXIV. Legumen Conrad. 



Equivalve, very inequilateral. Hinge with two slender teeth in 

 the right valve under the beak, and one posterior, very oblique, 

 and prominently lamelliform lateral tooth. Cretacic. 

 585. L. planulatum (Conrad). (Fig. 794.) Cretacic. 



Anterior muscle scar bounded posteriorly by a low ridge which 

 curves forward below. Surface covered with concentric growth 

 lines. 



Ripleyan of New Jersey (Merchant ville-Red Bank), Gulf region, 

 Montanan of Wyoming. 



CLXXV. Mactra Linne. 

 Nearly equilateral, rounded-triangular. Surface smooth or con- 

 centrically sculptured. Margins smooth. Valves equal. Cardi- 

 nal teeth in right valve two, soldered together dorsally ; one 

 cardinal in left valve. Lateral teeth elongate. Hinge plate well 

 developed. Resilifer subtriangular, excavated out of hinge plate 

 and separated from the scar of the external ligament by a thin 



Fig. 784. Mactra dathrodon, interior and exterior of left and interior of 

 right valve. (Md. Survey. ) 



raised plate, just posterior to the beak at the margin of the shell. 



Tertiary-Recent. 



586. M. clathrodon Lea. (Fig. 784.) Miocenic. 



Shell thin. Lateral teeth crossed by equidistant, minute striae. 



Maryland (St. Marys and Calvert). 



CLXXVI. Cymbophora Gabb. 

 Like Mactra but the ligament area and the resilifer are not 

 separated by a plate. Margins of the pit holding ligament and 

 resilium are elevated above the hinge line. Cretacic. 



