OF THE UNITED STATES. 71 



Length, about an inch and three fourths; breadth, three 

 fourths of an inch. 



Found in the lower friable strata at Egypt, New Jer- 

 sey. 



The general outline of this handsome species is similar 

 to that of T. Harlani ; from which, however, it is 

 readily distinguished by its strongly marked, ridges and 

 sinuses, the remarkable flatness of its upper valve, and 

 the extreme tenuity of its shell. It is more constant in 

 its form than any other bivalve of this formation. 



3. T. Sayi, (S. G. M.) PI. iii, fig. 3 and 4. 



Syn. T. plicata, Say. Amer. Journ. Science and Arts, vol. 

 ii, p. 43. 



Specific character. Suborbicular, with ten or twelve pro- 

 found longitudinal plicae in each valve, the two middle ones 

 most conspicuous, crossed by three or four transverse striae ; 

 upper valve subconvex, straight at the hinge margin ; low r er 

 valve convex; beak triangular, not incurved; foramen small. 



Length, three-fourths of an inch ; breadth a little more. 



The above description differs but little from that of 

 Mr. Say, who adds that this shell bears considerable re- 

 semblance to the T. crumena of Sowerby, (Min. Conch, 

 table lxxxiii, fig. 2 and 3.) 



The name plicata having been first used by M. La- 

 marck for another species, was necessarily changed ; I 

 therefore take the opportunity to dedicate this beautiful 

 fossil to my friend Mr. Thomas Say. 



Occurs in the marl of Burlington county, New Jersey, 

 more particularly at Woodward's Farm, near Walnford, 

 from whence it was first brought by Mr. Samuel R. 

 Wetherill. 



