PELECYPODA—TELEODESMACEA. 

 Common in Comanchic of Texas. 



543 



Fig. 742. Ptychomya ragsdalei, interior X/^* (After Shattuck.) 

 Fig. 743. Ptychomya ragsdalei; fragment of exterior. (After Shattuck.) 



CXLII. Corbjcula Megerle von Muhlfeld. 



Shell porcelaneous, with conspicuous epidermis- and marked with 

 concentric growth lines. Pallial line simple or with slight sinus. 

 Ligament prominent, external. Adductor scars nearly equal. 

 Hinge with anterior and posterior laterals distinctly separated from 

 the cardinals and sharply cross striated. Cardinal teeth bifid at 

 summit and usually three in each valve. Fresh and brackish 

 water. Cretacic-Recent. 

 507. C. durkei Meek. (Fig. 744, a-c.) Cretacic. 



Beaks very strongly incurved. 



Fig. 744. a-c, Corbicula durkei ; d-f, Sphcerium formosum, natural size and 

 enlargements ; g, h, Sph. planum. (After White. ) 



