216 



in appearance from the usual fornij that Grmelin considered it a 

 variety of vestiarius, L., the type of the genus Rotella, and I ob- 

 served it in a cabinet, arranged with species of that genus, from 

 which it is in reality so widely distinct. 



Nassa unicincta, S., Jour. Acad. Nat. Sci. vol 5, p. 211. 



Obs. I am indebted to the late Mr. Stephen Elliott for this 

 species, who found it on the coast of South Carolina. In the col- 

 lection of the Academy of Natural Sciences of Philadelphia is a 

 shell from the Antilles, resembling this, and although the striae of 

 the labrum are double in the former, yet it is probable that the 

 two shells will be found to constitute one species when more 

 specimens shall be examined and compared. Plate 57, f. la. 



Nassa vibex, S., Jo^ir. Acad. Mat. Sci., vol. 2, p. 231. 



Obs. I obtained a few specimens on our southern coast, and 

 my brother brought me one from the coast of New Jersey. I have 

 since received a very perfect individual from the Academy of 

 Natural Sciences, and several specimens from Dr. Ravenel, of 

 Charleston, a gentleman who has devoted much attention to the 

 shells of that region and to whom I am indebted for numerous in- 

 teresting species. Plate 57, f. 2. 



Nassa acuta, S., Jo^ir. Nat. Sci., vol. 2, p. 234, pi. 5, fig. 3. 



OsTREA. — Shell bivalve, attached, foliaceous, inaequivalve, ir- 

 regular ; apices becoming very unequal by age, the position of 

 the superior valve being gradually changed with respect to the 

 lower valve produces a corresponding elongation of the inferior 

 apex ; superior valve depressed ; inferior valve larger, concave ; 

 hinge without teeth, tripartite, the middle portion in the inferior 

 valve being a longitudinal groove for the reception of the cartilage, 

 corresponding with a convexity of the upper valve ; ligament at- 

 tached to the lateral portions ; muscular impression one, large, 

 subcentral. 



Animal depressed, margins of the mantle thick, not adherent, 

 retractile, with a double range of short and numerous tentacular 

 filaments; labial palpi long triangular ; foot none; muscle bipartite, 

 subcentral, no prominent syphon and no byssus. 



Obs. Oysters are familiar to the knowledge of all those who re- 

 side in maratime districts, in almost every part of the globe. Under 

 a rugged and irregular exterior is included an animal which supplies 



