216 
in appearance from the usual form, that G-melin 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. Set. vol 6, 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., Jour. Acad. Nat. Sci., vol 2, p. 231. 
Ohs. 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. Eavenel, 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., Jour. Nat, JSci., vol 2 yp . 234, pi. 5, fig. 3. 
OsTREA. — Shell bivalve, attached, foliaceous, insequivalve, 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. 
Ohs. 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 
