58 HELICID^. 



size, form, and color. But I find differences in the shells 

 of the two continents in these respects, -n-hich are con- 

 stant. The American shell is more globose ; the plane of 

 the aperture is more oblique, and the basal portion of the 

 lip sweeps round from the columella in a rapidly cur\ang 

 arc, instead of stretching off almost horizontally ; indeed, 

 the whole aperture is more rounded. These differences 

 become quite conspicuous when the shell is greatly 

 enlarged. The color of the European species is always 

 more or less green or yellow, wiereas, all the American 

 specimens are colorless, and decidedly thinner. In size, 

 our shells are about one quarter smaller than the foreign 

 ones, and invariably have half a whorl less, two and a 

 half, even when shells of the same size are compared. 

 The suture, in the true V. pellucida when closely exam- 

 ined, is foimd to be much excavated, and barred with 

 transverse septa. Mere vestiges of these charactei-s 

 appear in the American shell. It is more nearly like 

 V. sub-globosa, Mich., which, however, has the spire 

 much more elevated, and its basal face much more 

 inflated. 



These differences, in a genus where marked specific 

 characters are rarely found, together with the fact that 

 our shell inhabits a remote continent, on which it ranges 

 for more than a thousand miles inland, it appears to me 

 are sufficient to authorize us to regard it as distmct from 

 the European shell ; and I would propose for it the name 

 of V. limpida, in the expectation that my diagnosis will 

 be confirmed by the observations of others. — g.] 



