OF CONCHOLOaY. 55 



ON CERTAIN GENERA AND FAMILIES OP ZOOPHAGOUS 

 GASTEROPODS. 



BY DR. WILLIAM STIMPSOX. 



Fara. CYSTISCID.E. 



The cliaracters of the soft parts, in the the new genus des- 

 cribed below, seem to warrant the establishment of a distinct 

 family for its reception, notwithstanding the great similarity 

 to the Marginellidas shown in the shell and lingnal dentition. 

 CYSTISCUS, nov. gen,— pi. 8, f. 2. 



Shell (plate 6, fig. 2, a, h,) resembling that of some ^largiaelUc 

 or Persiculse, small, thin, ovate, inflated, smooth and polished; 

 spire very short, but distinct; suture not impressed, but filled 

 up with a glossy deposit of shelly matter; aperture narrow; 

 columella with plaits on the anterior half. Foot (fig. 2. d^) elon- 

 gated, narrower than the shell, and truncated in front ; head 

 oblong, depressed, bifurcated in front to form the short, trian- 

 gular, flattened and horizontal tentacles; eyes at the lateral 

 margins of the head, a little behind the bases of the tentacles ; 

 mentura as broad as the head, but not extending beyond the 

 tips of the tentacles. Teeth of the lingual ribobn (fig. '2.6-,) in a 

 single row, 0' 1* 0, and resembling in form the rhachidian 

 teeth of the Muricidiie"", thick and strong, with seven unequal, 

 conical denticlesf on its upper surface, of which the central, 

 and two outer ones on either side are large, and project slightlv 

 beyond the anterior margin. 



In the examination of the living animal, it was unfortuna- 

 tely not determined whether the shell is covered externally 

 by an expansion of the mantle as in the Marginellidae, but 

 this is probably the case, judging by the character of the surface 

 of the shell and the filling up of the suture. This pallial en- 

 velope, if existing, must be very thin and delicate, and not 

 ornamented with tubercles or fringes, otherwise it would not 

 have easily escaped observation. The form of the respiratory- 

 siphon also remains to be ascertained. 



CttiscL'S CAPENSis, sp. unica, nov. (plate 8, fig. 2,) / 



Shell four-whorled, white, translucent ; the contained bluish 



viscera showing through in living examples. Columella with 

 * As restricted further on, to Miorex, Trophon^ etc. 



t There were eight denticles in the specimen figured, producing a want 

 of symmetry doubtless merely accidental. 



