108 
beneath ; posterior margin, ixom a line extending from the beak to 
the inferior angle of the truncature, destitute of the strise and 
iniitic ; hinge callous, formed of the duplicature of the hinge mar- 
gin, and destitute of cells, a small tooth upon the inner margin, 
projecting backward ; dentiform process curved, prominent, slender, 
flat. 
Length three-fourths of an inch. Breadth one inch and seven- 
tenths. Inhabits the southern coast. Cabinet of the Academy 
and Philadelphia Museum. 
A common shell. Pennant, in his observations upon P. parva, 
says, I have a piece (of wood) filled with them, which was found 
near Pensacola, in West Florida.’^ May this not have been the 
young of our truncata ; or have we in reality the parva to add to 
our catalogue ? Pennant’s figure (volume iv. British Zool.', pi. 40, 
fig. 13,) of that species does not represent a truncature at the pos- 
terior side of the shell ; otherwise ours might be supposed to be a 
variety of it, although it attains to a much larger size. 
Pholas cuneiformis. — Shell subcuneiform; anterior margin 
' nearly closed, transversely truncated from the hinge ; the surface 
transversely striated in an undulated manner, with elevated, 
minutely crenate lines; the interstitial lines smooth; these lines 
partially interrupt a profoundly impressed longitudinal sulcus, 
which passes from the beak to near the middle of the base ; the 
inferior portion of this margin is destitute of striae; posterior margin 
attenuated by nearly rectilinear edges, to a rounded tip ; surface 
transversely wrinkled ; hinge callous, composed of the reflected mar- 
gin, which forms a cavity before, and is destitute of cells ; denti- 
form process incurved, slender, filiform ; hinge plate ovate-trian- 
gular, with a short projecting angle on the anterior middle, and 
subacute behind ; within, disk slightly contracted by an elevated 
line corresponding with the external sulcus. 
Length nine-twentieths of an inch. Width four-fifths of an inch. 
Inhabits the southern coast. Cabinet of the Academy and Phila- 
delphia Museum. 
Is often cast ashore in old wood, which it penetrates. It bears 
some resemblance in form to the shell represented in the Encyc. 
Method., t. ITfl, fig. 5, &c. Its longitudinal sulcus is very similar 
to that of P. crispata, but in many other respects it is closely al- 
lied to P. pmillus, and like that species it is distinguished by two 
