FAMILY OSTRACID^E — OSTREA. 171 



punctures are often seen through the shell, produced by various marine animals ; the most 

 common and destructive of these, according to the oystermen, is the Drill, or Fusus cinereus. 

 I have examined several oysters on which were numerous drills ; and upon detaching them, 

 observed, in the centre of a circular abraded spot, a minute puncture not larger than a pin- 

 hole, extending into the body of the shell, but not perforating it entirely through ; occasion- 

 ally these punctures would be very numerous, and apparently communicate with each other, 

 the whole interior being eroded, and the shell itself rotten and brittle. In such cases, the 

 oyster itself would be poor and destitute of flavor, and, as might naturally be inferred, pe- 

 rishes sooner or later. I am informed that when these drills abound in an oyster bed, a great 

 mortality among the oysters is observed. 



(EXTRALIMITAL. ) 



O. semicylindrica. Say, Ac. Sc. Vol. 2, p. 228.) Shell elongated, semicylindrical : sides parallel; 

 base and tip rounded, equally obtuse; inferior valve very convex ; upper valve flat. Muscular im- 

 pression large, white. Color, white, with a fuscous epidermis. Length, 0*35. Attached to 

 Sponges. Georgia, Florida. 



O. equestris. (Id. Am. Conch, pi. 58.) Small, ovate-triangular, with transverse wrinkles, and more 

 or less deeply and angularly folded longitudinally. Lateral margin near the hinge, with 6 - 12 

 denticulations of the superior valve, received into corresponding cavities of the lower valve : upper 

 valve depressed, but slightly folded. Lower valve convex, attached by a portion of its surface, the 

 margins elevated ; folds unequal, much more profound than those of the upper valve. Hinge very 

 narrow, and curved laterally and abruptly. South Carolina, Florida. 



22" 



