218 
ous species of various types of organization and exterior cliaracterj 
although Lister had already circumscribed the boundaries with 
correctness. From Linne’s genus^ Bruguiere separated Pectert^ 
Perna and Pedum^ which are provided with a byssus. Lamarck 
conducted the analysis still further and formed the genera Gry- 
pliseay Lima and Malleus. Of these the two latter are attached by 
a byssus. Lamarck gives the following characters to his family of 
Ostracea : Ligament interior or half interior. Shell irregular, 
foliaceous, sometimes papyraceous.^^ It comprehends his genera 
Gryphsea, Ostrea, Vulsella, Placuna and Anomia. The two 
latter have the ligament interior, and Vulsella, which is closely 
allied, is imbedded in sponges, and has a cardinal callosity in each 
valve, extending somewhat interior. Gryphsea is now by most 
authors considered as a group of the present genus, distinguished 
from the others only by the curved umbo, and I may remark that 
I possess an individual of 0 . virginica, which has the incurved 
apex of Gryphsea. 
In the generic character we have mentioned but one muscular 
impression. There is, however, at least one other, which is very 
small, and situated near the hinge for the support of the back of 
the animal. 
Ostrea equestris.— D esc. Shell small, with transverse wrin- 
kles, and more or less deeply and angularly folded longitudinally; 
ovate-triangular, tinted with violaceous ; lateral margins near the 
hinge with from six to twelve denticulations of the superior 
valve received into corresponding cavities of the inferior valve ; 
superior valve depressed but slightly folded ; inferior valve con- 
vex, attached by a portion of its surface, the margins elevated, 
folds unequal, much more profound than those of the superior 
valve ; hinge very narrow, and curved laterally and abruptly. 
Ohs. This small species is remarkable for the very abrupt lateral 
curvature of the beak, the continued line of which may be 
traced in favorable specimens on the exterior and inferior part of 
the umbo. 
I obtained several specimens on the coast of Florida, attached 
to various objects, and Dr. Eavenel of Charleston sent me the 
individual represented in the upper part of the plate. It is 
seated on a Gonopea elongata, S., which is attached to a branch of 
our common Grorgonia. He obtained it at Sullivan’s island. The 
