MIOCENE MOLLUSCA AND CRUSTACEA. 29 
White, in his Non-Marine Molluscan Fauna of the West,’ and in his work 
on the Fossil Ostreidze of the United States. 
Formation and locality: Fossil in the Miocene near Shiloh and at 
Elwell’s marl pits at Jericho, N. J. 
OSTREA PERCRASSA. 
Pl. 1m, figs. 1-4. 
Ostrea percrassa Conrad: Medial Tert. Foss., p. 58, Pl. xxv, fig. 1. Meek, Smith 
Check List, p. 3. White, Fam. Ostreide; p. 313, Pl. Lxvm, fig. 3. 
Shell rather large, very thick and heavy in appearance; subcircular in 
outline, or obscurely broad subovate, being widest in front of the middle 
of the length; the lower valve often highly convex on the outside and deep 
within. Hinge-area large and strongly lamellose, striate transversely; 
ligamental groove broad and deep. Upper valve less deep than the lower, 
also less convex on the outer surface. Muscular scars very large, semi- 
lunate or semi-elliptical; extending far beneath the shell at the back edge, 
forming a deep cavity beneath it. Margin of the shell outside of the pallial 
area smooth. Substance of the shell very strongly lamellose, the lamellae 
being separated by a minutely vesiculose interlamellar substance, as in 
Gryphea vesicularis Lam. 
The New Jersey forms of this shell which have come under my notice 
are not nearly so large and ponderous as those which I have seen from 
South Carolina. Mr. Conrad’s figure given in his Medial Tertiary fossils is a 
very fair representation of the general run of the examples from New Jersey. 
While many of those from the more southern localities have grown longer 
with advanced age, but not wider in the same proportion, still one or two 
examples from the Santee River in South Carolina, now in the collection of 
the American Museum of Natural History in New York, are very broad and 
not so thickened; while the outer surface of the upper valve is almost flat 
and comparatively smooth. A peculiar feature of this species, seen in the 
New Jersey specimens but not in those from South Carolina, is the finely 
vesicular, interlamellar structure, which, when the upper layer of pearly 
shell is removed from the one beneath, presents a very fine froth-like 
1Fourth Annual Rept. U. 8. Geol. Surv. 
