Sand Formation of the United States. 283 
BIVALVES. 
TEREBRATULA. 
1. T.. harlani. (S. G. M.) This fine species, which often attains 
a length of two inches and a half, is found in vast numbers at New 
Egypt, in New Jersey, where the only accompanying fossil is Gry- 
phea. (Ostrea, Say.) It is also common in many other places in 
the peninsula. 
2. T. fragilis. (S.G.M.) Found with the preceding, but is 
much more rare. 
3. T. Sayi. (S. G. M.) A small plicated species, occasionally 
found in the blue marls of New Jersey. This fossil was first descri- 
bed by Mr. Say,* under the name of T’. plicata, which name having 
been previously used by Lamarck for another species, was necessa- 
rily changed. 
A terebratula which I once thought might be the T’. perovalis of 
Sowerby, I am now convinced is only a variety of J’. harlani. 
cryvpHmA. Sowerby. 
1. G. convewa. (S.G.M.) ) These two species are found abund- 
2. G. mutabilis. (S. G. M.) i antly in almost every part of the 
marl region. Mr. Say was the first to notice them, which he did un- 
der the name of Ostrea convexa.t But as these fossils possess the 
characters of Gryphea as defined by Mr. Sowerby, I have ventured, 
though perhaps wrongly, to transfer them to that genus. 
Some varieties of G. mutabilis are so like Ostrea vesicularis, (Lam.) 
as to be easily mistaken for the same species. The O. vesicularis is 
characteristic of the European chalk. 7 
3. G. vomer. (S. G. M.) This species was described by me, to- 
gether with the two preceding, in the Jour. of the Academy, but the 
badness of the specimens enabled me to give but a very defective fig- 
ure. I afterwards even suspected that it might be a mere variety of 
G. convexa ; but I have lately received some perfect specimens which 
fully establish the correctness of the specific designation allotted to 
this fossil. I design giving an accurate drawing and description of it 
in the next number of this work. 
* Amer. Jour. Science, Vol. II. p. 43. t Idem Vol. IL. p. 42- 
