88 



Class CONCHIFERA. 



OsTREA SEMICYLINDRICA. — Stell elongated, semlcylindrie, 

 white, covered with a fascous epidermis ; sides parallel ; base and 

 tip rounded, equally obtuse ; inferior valve very convex • superior 

 valve flat; within white, somewhat perlaceous; muscular impres- 

 sion large, white. 



Length seven-twentieths of an inch. Inhabits the coast of 

 Greorgia and Florida, imbedded in sponges. Cabinet of the Aca- 

 demy and Philadelphia Museum. 



This species has the habit and manners of the genus. Vidcella, 

 but differs from it in having very unequal valves and beaks, and 

 at the same time it differs from the Ostreas in being unattached. 

 I found several specimens imbedded in sponges, or interposed be- 

 tween large A&cidia and our common Tliethya, Lam. 



Pecten concentricus. — Shell suborbicular, with from eigh- 

 teexi to twenty elevated, rounded ribs, and very numerous simple 

 transverse wrinkles ; longitudinal striae none ; one valve somewhat 

 ventricose, pale-yellow, fasciated concentrically with reddish-fus- 

 cous or blackish ; the other valve convex, brownish-cinereous ; 

 auricles subequal ; hinge margin rectilinear in each valve ; within 

 white. 



Length two inches and nine-tenths. Breadth three inches and 

 one-tenth. Inhabits the coast of New Jersey. Cabinet of the 

 Academy and Philadelphia Mixseum, and Mr. Hyde's collection. 



Var. a. Somewhat more compressed, variegated. 



Although this shell is a large species, and is one of our most 

 common shells, yet I cannot perceive that it has been either figured 

 or described distinctly in any work to which I can refer. The 

 inner margin, particularly between the ribs, is sometimes of a dirty 

 reddish-brown color. I have not seen this species on the southern 

 coast. 



The variety occurs on the coast of New England, and several 

 specimens are preserved in Mr. William Hyde's cabinet. One 

 specimen is of a fine bright orange-color, and on one of the valves 

 only are the concentric bands of blackish ; the margins, which 

 decline from the beaks, are transversely mottled with white. An- 

 other has one valve blackish-brown, with about a dozen rather 

 large white spots on the disk, longitudinally disposed, and white 

 transverse variegations on the umboncs and beaks; the margins. 



