Say on Shells, &c. 43 
of the shell abovementioned, and indeed, with the exception 
of the less elevated umbo, it is almost as closely related to 
Gryphea as the G. dilatata of Sowerby. 
Genus Exogyra. 
Shell inequivalve, equilateral ; cicatrix one, large, deep- 
ly impressed, subcentral ; inferior valve convex, attached, 
umbo spiral, spire lateral, prominent, hinge with two parallel, 
transverse grooves; superior valve discoidal operculiform, 
umbo not prominent, revolving spirally within the margin, 
hinge with a single groove on the edge. 
EE. costata, apex lateral, with about two volutions ; infe- 
suor valve convex, costate, transversely corrugated, coste of 
the disk somewhat dichotomous, sometimes fornicated ; 
within, a single profound cicatrix placed rather nearer to 
the inner side; hange with two nearly parallel, profoundly 
excavated grooves, of which the inner one is shortest, and 
corrugated ; superior valve flat, slightly concave, destitute of 
coste, outer half exhibiting the increments, outer edge ab- 
ruptly reflected from the imferior surface to the superior, but 
not elevated above it; hinge with a single groove on the 
edge ; cicatrix profound. 
Length four inches, breadth three and a half—Cabinet 
of the Acad. of Nat. Sciences.—Peale’s Museum. 
This interesting shell is the largest and most perfect of 
its class, which has yet been found in the Ancient Alluvial 
deposit of New-Jersey. It is not uncommon. I have seen 
many specimens. ‘They vary somewhat in the coste, being 
sometimes almost antiquated, sometimes nearly smooth. 
The aged shells became extremely thick and ponderous. 
It seems to differ from the genus Gryphea by having 
been attached, and by the lateral situation of the spire ; the 
hinge grooves also are parallel with the edge, so as to be 
transverse with respect to the shell, bearing some resem- 
blance to those of some species of Chama. 
Genus Terebratula. 
T. plicata, suborbicular, convex, ten or twelve profound, 
longitudinal plice, the two middle ones of the siphunculated 
valve, slightly more elevated, and the corresponding ones 
