536 HISTORY OF SYSTEMS. 



(a) Inhabitants of the land. 



Les Colimacees. 



•i.i rw tentacula. 

 with 2 J 



(b) Inhabitants of the water, but ascending the surface 

 for air to breathe. Shell with the margins of the aperture 

 never reflected. 



Les Lymneens. 

 ** Trachelipods breathing water only. Branchiae project- 

 ing, in the form of filaments, laminae, or tufts, into the 

 branchial cavity. Shell often nacred, and often also 

 roughened with protuberances on the surface. 



(a) Shell ftuviatile, operculate, the left lip not imitating 

 a semipartition. 



-j- Shell with the lips of the aperture separate. 



Les Melaniens. 



-j-f Shell with the lips of the aperture continuous. 



Les Peristomiens. 



(b) Shell fiuviatile or marine, the left lip resembling a 

 semipartition. 



Les Neritaces. 



(c) Shell marine, the left lip not imitative of a semiparti- 

 tion. 



f Shell floating on the surface. 



Les Ianthines. 

 ff Shell not floating, the aperture very widely open ; 

 no columella. 



Les Macrostomes. 

 -j-ff Aperture not particularly open, with plaits on 

 the columella. 



Les Plicaces. 

 •f-j-f f No plaits or folds on the columella. 



§ Margin of the aperture continuous and circular. 



Les Scalariens. 

 §§ Margins of the aperture separate. 

 Les Turbinaces. 

 II. Section. T. with a projecting siphon to conduct the 

 water of respiration to the branchiae. All are marine, zoo- 

 phagous, destitute of jaws, and furnished with a retractile 

 proboscis. Shell spiral, enveloping, with an aperture either 

 canaliculate, or emarginate, or effuse at the base. (Les 

 Zoophages.) 



a. Shell with a more or less elongated canal at the base of 

 the aperture, of which the right lip undergoes no change 

 from age. 



Les Canaliferes. 







