93 
A remarkable species and readily recognised. 
Aeca pexata. — Shell covered with a hairy epidermis, trans- 
versely subovate, with from thirty-two to thirty-six ribs, placed 
nearer to each other than the length of their own diameters ; um- 
bones moderate ; apices approximate, placed far backward Yeij 
near the posterior termination of the hinge ; posterior edge round- 
ed, destitute of an angle ; anterior edge rounded, with an angle at 
the termination of the hinge ; inferior edge regularly rounded. 
Length one inch and seven-tenths. Breadth two inches and 
three-tenths. Inhabits the coast of the United States. Cabinet 
of the Academy and Philadelphia Museum. 
A common species, distinguished by the name of the bloody 
clam. It is covered with a hairy epidermis, and when violently 
opened, an effusion of a red sanies proceeds from the animal. In 
the young shell, an angle is perceptible on. the posterior edge, at 
the termination of the hinge margin, but this disappears with 
age, 
Arca incongrua. — Shell somewhat rhomboidal, with from 
twenty-six to twenty-eight ribs, placed nearer to each other than 
the length of their own diameters, and crossed by elevated, ob- 
tuse, equal and equidistant lines, which are altogether wanting on 
ten rays of the disk of the left valve ; apices opposite to the middle 
of the hinge, distant from each other, with a lanceolate space be- 
tween them, of which the breadth is about one-third of its length ; 
extremities of the hinge margin angulated ; posterior edge rounded ; 
inferior edge rounded, that of the right valve extended a little be- 
yond the regular curve in the middle ; anterior margin cordate, 
flattened ; anterior edge nearly rectilinear. 
Length two inches Breadth rather more than two inches. In- 
habits the estuaries of the United States. Cabinet of the Academy 
and Philadelphia Museum. 
This species, which is very abundant on our coast, strongly re- 
sembles A. rliomhea, but agreeably to the figure in the Eneyc. 
Meth., it differs in the width of the space on the hinge margin, in 
the width of the spaces between the ribs, and in its more recti- 
linear anterior edge. 
Auca TRANS versa. — Shell transversely oblong, rhomboidal, 
with from thirty-two to thirty-five ribs, placed at nearly the length 
of their own diameters distant from each other ; apices separated 
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