88 
Class CONCHIFERA. 
OsTREA SEMICYLINDRICA. — Sliell elongated, semieylindric, 
white, covered with a fuscous 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 Vulcella, 
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 Ascidia and our common Tlietliya, Lam. 
Pecten concentricus. — Shell suborbicular, with from eigh- 
teen to twenty elevated, rounded ribs, and very numerous simple 
transverse wrinkles ; longitudinal strise 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 Museum, 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 v/hite. 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 umbones and beaks ; the margins. 
