101 



Length two-fifths of an inch. Inhabits the southern coast. Cabi- 

 net of the Academy and Philadelphia Museum. 

 A small species, not very commonly found. 

 Ampiiidksma punctata. — Shell orbicular, white, with very 

 minute, numerous, concentric wrinkles, and very minute, numerous 

 punctures ; lateral teeth none ; primaiy teeth two in each valve, of 

 which one has a deep groove, which gives it a bifid appearance ; 

 groove of the interior cartilage not very distinct; within a small 

 projecting rim or elevated line near the edge extends from the 

 hinge to the basal margin. 



Length about seven-twentieths of an inch. Breadth mucli the 

 same. Inhabits the southern shores. Cabinet of the Academy. 



This shell bears a strong resemblance to the preceding, on an 

 exterior and transient view of its valves ; but on examination it 

 will be perceived to be more orbicular and less oblique, and that 

 the surface is less polished. By the aid of a magnifier, the surface 

 will be observed to exhibit a remarkable punctured appearance. 



Mactra SIMILIS. — Shell subtrigonate, smooth, or very slight^ 

 wrinkled, white on the disk or upon the umbones, and dirty light 

 brownish color on the margin ; umbones nearly central ; lateral 

 teeth strongly and regularly crenated on the side next the recipient 

 cavity. 



Length one inch and three-twentieths, nearly. Width one inch 

 and two-fifths. Inhabits the coast of the United States. Cabinet 

 of the Academy. 



The specimens which I obtained from the coast of New Jersey 

 seem closely allied to Var. a. of 31. solida as presented on pi. 258, 

 fig. 1, of the Encyc. Method., the proportions of the difi"erent parts 

 of the shell nearly corresponding with those of that figure. But 

 upon comparing it with several specimens of M. solida sent to the 

 Academy by Mr. O'Kelly of Ireland, I find its proportions to be 

 altogether different, being longer and not so wide. 



Mactra lateralis. — Shell triangular, very convex, of a 

 smooth appearance, but with very minute, transverse wrinkles ; 

 lateral margins flattened, cordate, with a rectilinear, sometimes 

 concave profile, one margin rounded at the tip, the other longer 

 and less obtuse ; umbo nearly central, prominent. 



Length half an inch. Breadth thirteen-twentieths of an inch. 

 Thickness seven-twentieths of an inch. Inhabits the coast of the 



