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. 
Amphidesma punctata. — Shell orbicular, white, with very 
minute, numerous, concentric wrinkles, and very minute, numerous 
punctures ; lateral teeth none ; primary 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 much 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 slightly 
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 M. solida as presented on pi. 258, 
fig. 1, of the Encyc. Method., the proportions of the different 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 j 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 
