MARYLAND GEOLOGICAL SURVEY 693 



Description. " Shell moderately large, elongate ; beaks central, ele- 

 vated, anterior end produced, rounded; base very slightly convex; pos- 

 terior end subangulated below, arched above ; a strong umbonal ridge runs 

 from the beaks to the angle. Surface destroyed on the only specimen I 

 have seen. Length 2.6 in., width 1.25 in. The impression of the hinge is 

 preserved in the matrix, and the shell is so strongly characterized by its 

 form that I have not hesitated to describe it. It is from Pataula Creek, 

 Georgia, in a hard calcareous marl." Gabb, 1876. 



" The dimensions of two specimens are : Length 32 mm. and 46 mm., 

 height 16 mm. and 23 mm. Shell very broadly subtriangular in outline, 

 the beaks nearly central and pointing a little backward, the greatest 

 anterior extension at considerably below the middle. The anterior and 

 posterior cardinal margins meeting at the beak in an angle of about 140 

 to 150, curving gently downward in front and behind ; anterior margin 

 rather sharply rounded; ventral margin very long and gently convex; 

 postero-basal extremity sharply rounded or subangular ; posterior margin 

 nearly vertically subtruncate below, curving forward above and passing 

 into the cardinal margin. Valves depressed convex, with a subangular 

 umbonal ridge extending from the beak to the postero-basal extremity, 

 the surface sloping with a very gentle convex curve to the anterior, pos- 

 terior and ventral margins ; curving much more abruptly to the cardinal 

 margins, but just before reaching the margin the surface is deflected in 

 the casts so as to form a rather narrow flattened area extending from the 

 beak in each direction and gradually dying out before reaching the ante- 

 rior and posterior extremities of the shell; just beneath the beak this 

 flattened area bears the impressions of the hinge teeth. Surface of the casts 

 smooth, except for a few very faint and indistinct radiating costae just 

 above the postero-cardinal slope of the valves. Pallial sinus very deep, 

 extending beyond the middle of the shell. Hinge teeth small and weak, 

 situated just beneath the beak, a single one in the left valve with a socket 

 on either side, and two in the right valve with a deep socket between. "- 

 Weller, 1907. 



The two casts which have been referred to this species are by no means 

 conclusive evidence of its former existence in Maryland. 



