MIOCENE MOLLUSC A AND CRUSTACEA. 29 



White, ill his Koii-Marine Molluscan Fauna ut' the West, ' and in his work 

 on the Fossil Ostreidse of the United States. 



Formation, and localitif: Fossil in the JMiocene near Shiloh and at 

 Elwell's luarl pits at Jericho, N. J. 



OSTBEA PEECRASSA. 



PI. Ill, tigs. 1-4. 



Ostrea percrussa Conrad: Medial Tert. Foss., p. 58, PI. xxv, tig. 1. Meek, Smith 

 Check List, p. 3. White, Earn. Ostreid*; p. 313, PI. lxtiii, fig. 3. 



Shell rather large, very thick and heavy in appearance; subcirciilar in 

 outline, or obseui'ely 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; 

 ligainental 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 strongh^ lamellose, the lamellse 

 being separated by a minutely vesiculose interlamellar substance, as in 

 Gryphcea vesicularis Lam. 



The New Jersey forms of this shell which have come under my notice 

 are not nearly 'so large and 25onderous as those which 1 have seen from 

 South Carolina. Mr. Com-ad'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 tliose 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 

 niit so thickened; while the outer surface of the ujiper valve is almost flat 

 and comparatively smooth. A peculiar feature of this species, seen in the 

 New Jersey specimens but not in those fn^n South Carolina, is the finely 

 vesicular, interlamellar strirctui'e, which, when the upper layer of ])early 

 shell is removed from the one beneath, presents a very fine froth-like 



K 1 Fourth Annual Rept. U. S. Geol. Surv. 



