Description.-" Shell subtriangular, convex, thick, obscurely undulated; with a fold on the posterior submargin and the extremity angular; basal margin acute; cardinal tooth very thick and elevated. Length, one inch." Conrad, 1833. Surface of left valve with obsolete concentric undulations, angular posteriorly; right valve with irregular, concentric undulations, beak more prominent and strongly curved than in lower valve; posterior submargin ridged, tooth massive. Length, 34 mm.; height, 29 mm.; diameter, 13 mm. Occurrence.-Choptank Formation. Governor Run,
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