OF THE UNITED STATES. 259 



Length seven-twentieths of an inch. 



Inhabits the coast of Georgia and Florida, im- 

 bedded in sponges. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



This species has the habit and manners of the 

 genus Vulcella, but differs from it in having very un- 

 equal valves and beaks, and at the same time it dif- 

 fers from the Ostreas in being unattached. I found 

 several specimens imbedded in sponges, or interposed 

 between a large Ascidia and our common Thethya, 

 Lam. 



PECTEN, Lam. 



1. P. *concentricus. Shell suborbicular, with 

 from eighteen to twenty elevated, rounded ribs, and 

 very numerous simple transverse wrinkles ; longitu- 

 dinal striae, none ; one valve somewhat ventricose, 

 pale-yellow, fasciated concentrically with reddish- 

 fuscous or blackish ; the other valve convex, brown- 

 ish-cinereous ; auricles subequal ; hinge margin rec- 

 tilinear in each valve; within white. 



Length two inches and nine-tenths. 



Breadth three inches and one-tenth. 



Inhabits the coast of New Jersey. 



Var. a. Somewhat more compressed, variegated. 



Cabinet of the Academy and Philadelphia Mu- 

 seum, and Mr. Hyde's collection. 



Although this shell is a large species, and is one 

 of our most common shells, yet I cannot perceive that 



