164 



SHELLS AND SHELL-FISH. 



and comparatively slender. Our analysis of the Helicince 

 not having been yet completed, we are only acquainted 

 with the four following genera ; the fifth, which should 

 intervene between Helicella and Pupa, being yet unde- 

 termined. In the first, or Helix proper, we have the 

 great proportion of shells usually so called, of which 

 the Helix hortensis is a good example ; they are strictly 

 turbinated shells, the spire being very slightly elevated ; 

 the body- whorl ventricose ; the aperture without teeth ; 

 and the base of the pillar never separated from the outer 

 lip : this is the typical genus. The second, or sub- 

 typical, is Geotrochus, where the spire is always elevated, 

 and composed of more than four whorls *, generally of 

 five, and sometimes of six: the typical species are trochi- 

 form ; but the sub- genus Pithohelix puts on the aspect 

 of a Bulimus or Achatina. The third is Pupa, where the 

 spire reaches its full development, and the aperture 

 becomes nearly circular : by this character Pupa may 

 be readily distinguished from Clausilia and all its sub- 

 ordinate types. Our fourth genus is composed of the 

 remaining portion of Ferussac's HeliceUcB, typically 

 represented by those disk-like shells which are destitute 

 of a pillar; the spire very short, and often sunk below the 

 level of the margins (as in Planorhis) ; the body-whorl 

 ventricose ; and the outer lip considerably thickened : 

 this group has no indications whatever of the incipient 

 teeth seen in Hemiodon, and yet it connects the land- 

 volutes and the present sub-family of HelicincB in the 

 most perfect manner. We shall not in this place offer 

 any conjectures regarding the fifth type, but proceed 

 at once to give our analysis of the two typical genera. 

 Helix and Geotrochus, so far as it has yet extended. 



(155.) The sub-genera of Helix appear to us to be 

 as follows : — The first, on leaving Helicella, is Hemi- 

 cycla, distinguished from Helix proper by the broad and 

 flattened margin of its outer lip, and by the absence of 

 the inner, except occasionally a little tubercle, sufficient 

 to point out its analogy to the Lucernince ; but there 



* The last, or body-whorl, being excluded. 



