from Massachusetts Bay. 123 
Shell ovate, transverse, equivalve, inflated, gaping at 
both extremities, with numerous, very distinct, concentric 
lines of increment, covered with a yellowish-green, 
polished epidermis in young specimens, concealed under 
a black pigment, which readily rubs off in the recent 
specimen, giving a sooty appearance to thefingers. In the 
adult shell the epidermis is rather a dirty brown. Beaks 
slightly prominent over hinge margin. An obtuse angle, 
more elevated and wider at its lower half, runs obliquely 
from the umbones to the posterior base of the shell, 
serving as a boundary to the anterior inflated portion. 
Posterior portion of shell much compressed, its epidermis 
is of a lighter color, and the strie of increase are much 
more apparent, than upon the anterior portion. Anterior 
margin, rounded ; posterior, somewhat truncated. With- 
in, perlaceous. Teeth, numerous and peculiar; those 
contiguous to hinge, small, those farther removed 
fosset, very strong, sharp, angulated, higher than wide; 
the teeth of one valve shutting very closely into the exca- 
vated teeth of the opposite valve, form a very powerful 
hinge. Fosset capacious. : 
This shell, of which I have seen but one perfect speci- 
men, and which, in its general outline, resembles some- 
what a Thracia, I took from the stomach of a Platéssa— 
the dentata of Mitchill—called by our fishermen, Sand 
- dab :—this fish was caught off Provincetown, Cape Cod, 
in about thirty fathoms of water, and was brought to our 
market the last of December, 1837. I am thus minute, 
because it is usually thought sufficient to state that a 
shell is taken from a “fisks stomach” without the 
slightest attention being paid to the species of fish, or the 
season of the year, in. which the fish is taken, and con- 
sequently but little light is shed upon its probable local- 
