agi ButLETIN 5 21 



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 

 Gryphcea as the G. dilatata of Sowerby. 



Genus Exogyra. 



Shell inequivalve, inequilateral ; 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. 



E. costaia, apex lateral, with about two volutions ; infe- 

 rior valve convex, costate, transversely corrugated, costae of 

 the disk somewhat dichotomous, sometimes fornicated ; 

 within, a single profound cicatrix placed rather nearer to 

 the inner side ; hinge with two nearly parallel, profoundly 

 excavated grooves, of which the inner one is shortest, and 

 corrugated ; superior valve flat, slightly concave, destitute of 

 costae, outer half exhibiting the increments, outer edge ab- 

 ruptly reflected from the inferior 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 costae, being 

 sometimes almost antiquated, sometimes nearly smooth. 

 The aged shells became extremely thick and ponderous. 



It seems to differ from the genus Gryphcea 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 plicae, the two middle ones of the siphunculated 

 valve, slightly more elevated, and the corresponding ones 

 [A. J. S., 1st Sen, Vol. II.] 



