Lamarck's Genera of Shells. 237 



rous and diversified than those of the gasteropoda. The greater 

 paft of them inhabit the sea, some live in fresli vrater, and 

 others on land. The shell of the latter is not at all, or only very 

 slightly, pearly, and generally has no other external projections 

 than the striae of growth. 

 Lamarck divides the irachelipoda into two sections. 



Section I. 

 Traciielitoda, without any Siphon. (Phytiphaga *.) 

 No projecting siphon ; animal generally breathes by a hole. 

 The greater part feed on vegetables, and are furnished with 

 jaws. 



Aperture of the shell entire ; base without any ascending dor- 

 sal notch, or canal. 

 This section contains ten families. 



1st Family. 

 CotiMACEA. (11 Genera.) 



Breathe air ; some furnished with an operculum, others not ; 

 "tentacula cylindrical. 



Shell spirivaive ; no external projecting parts, except the 

 striae of growth ; right margin of the aperture often curved 

 outwards. 



All the colimacea are land animals ; the first nine genera 

 have four tentacula, the two last, only two. 

 1. Helix f. 



Shell orbicular, convex, or conoidal, sometimes globular; 

 spire but little elevated. Aperture entire, transverse, very ob- 

 lique, contiguous to the axis of the shell ; margins disunited by 

 tlie projection of the penultimate whorl. 



The Helix is distinguished from the pupa, by the general 

 form of the shell, which Is never cylindrical, and by the borders 

 of the aperture being disunited ; from the bulinius, by the 

 aperture being rather transverse than longitudinal, and its plane 

 very oblique, and almost perpendicular to the axis of the spire; 

 and from the planorbis, by the left margin of the aperture 



» Hcfiitorotts. t A spiral line. 



