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- 

 ph?ea. (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 T. harlani. 

 GRYPH^A. Sowerby, 



1. G. convexa. (S. G. M.) ') These two species are found abund- 



2. G. mutabilis. (S. G. M.) ) 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. f But as these fossils possess the 

 characters of Gryphcea 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. 



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. II. p. 42, 



