325 Bulletin 5 55 



FOSSIL SHELLS. 1 49 



umbones, and much crowded on the basal half ; 

 several very obtuse longitudinal undulations, of 

 which that on the middle is more profound : basal 

 viargin deeply undulated in compliance with the 

 undulations of the disk : wit/mi crenate on the 

 edge : anterior margin flattened, and simply wrin- 

 kled. 



lycngth nearly five, breadth six inches. 



Smallest specimen, three inches and seven- 

 tenths long, and four inches and a half wide. 



This extraordinary shell has so unusual an ap- 

 pearance, that I should almost have been disposed 

 to regard a single specimen as a monstrosity. The 

 examination of several individuals proves that the 

 species varies somewhat in form, and in the locality 

 of the undulations. 



2. V. paphia ? Lam. 



CYTHEREA. 



C. convexa. PI. xii. fig. 3. Shell subcordate ; 

 elevated convex, concentrically wrinkled, inequi- 

 lateral ; posterior tooth and fosset not striated ; 

 edge not crenated ; umbo rather prominent ; lunule 

 dilated, cordate, marked by a simple line. 



Length one inch and a tenth, breadth more than 

 one inch and three-tenths. 



On the inner surface of the shell is a prominent 

 line in one valve, proceeding from the extremity 

 of the impression of the retractor muscle, and 



[J. A. N. S., Phila., ist Ser., Vol. IV, 1824.] 



