218 



ous species of various types of organization and exterior character, 

 although Lister had already circumscribed the boundaries with 

 correctness. From Linne's genus, Bruguiere separated Pecten, 

 Perna and Pedum, which are provided with a byssus. Lamarck 

 conducted the analysis still further and formed the genera Gri/- 

 phsea, Lima and Malleus. Of these the two latter are attached by 

 a byssus. Lamarck gives the following characters to his family of 

 Osiracea : " Ligament interior or half interior. Shell iiTegular, 

 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. Grypli?ca 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. — Desc. 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 eon- 

 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. Ilavcnel of Charleston sent me the 

 individual represented in the upper part of the plate. It is 

 seated on a Conopea elongata, S., which is attached to a branch of 

 our common Grorgonia. He obtained it at Sullivan's island. The 



