tropical climates and seemed to be repelled only by the in- 

 hospitable rigor of the polar regions. 



Notwithstanding this wide range over the globe, they 

 may be recalled to mind, wherever the English language 

 is spoken, by the name of Snail shells^ and from their beau- 

 ty and diversity of forms, many persons who at first collec- 

 ted them for ornament, have been led by that circumstance 

 to devote their attention to this interesting science. 



The genus Helix, as originally instituted by Linne, 

 consisted of an unnatural assemblage of species of various 

 characters, habits and conformation. Those that reside on 

 the land and respire air only by means of a spiracle lead- 

 ing to a cavity for respiration, lined with a plexus of pul- 

 monary vessels, were associated with such as reside w^holly 

 in the water, and with others that are amphibious, as un- 

 like in their external character as in their anatomical struc- 

 ture. It was in reality a great reservoir for Molluscous an- 

 imals that correspond in some general appearances, all 

 of wiiich his generic definition, however comprehen- 

 sive, could not include. The present more natural con- 

 dition of this group is owing to the successive improve- 

 ments of Bruguiere, Draparnaud, Lamarck and Montfort, 

 who removed from it various species, of which they form- 

 ed the genera Vitrina, Bulimus, Carocolla, Pupa, Scara- 

 bus, Succinea, Planorbis, Lymneus, Paludina, Ampularia, 

 Melania, Janthina, Sigaretus, &c. Many of these Ferussac 

 has again restored to the genus Helix, forming various sub- 

 genera under new names which he has applied to them. — 

 Lamarck, as he has limited the genus, describes one hundred 

 and seven species of his own collection, but Ferussac, whose 

 boundaries are more comprehensive, being founded on the 



PLATE XIII. 



