WILD LIFE OF ORCHARD AND FIELD 



visible on all the larger specimens. Various other 

 signs indicate youth or adult age in the shell. 



Mollusks prosper best, other things being equal, 

 in a broken landscape, with plenty of lime in the 

 soil. The reason, no doubt, why the West India 

 Islands, the Cumberland Mountains, and similar 

 regions are so peculiarly rich in shells of every 

 sort is that a ravine-cut surface and a wide area 

 of limestone rocks characterize those districts; on 

 the other hand, it is not surprising that I found 

 nine-tenths of the Rocky Mountain species to be 

 minute, since the geology is represented by sand- 

 stone and volcanic rocks." Hot springs are very 

 likely to be inhabited by mollusks, even when the 

 temperature exceeds 1 00° Fahr. and the waters are 

 very strongly impregnated with mineral salts. 



Snails are mainly vegetarians, and all their 

 mouth-parts and digestive organs are fitted for 

 this diet. Just beneath the lower tentacles is the 

 mouth, having on the upper lip a crescent-shaped 

 jaw of horny texture, with a knife-like, or some- 

 times saw-like, cutting edge. The lower lip has 

 nothing of this kind, but in precisely the same atti- 

 tude as our tongue is arranged a lingual mem- 



* See Dr. Hayden's Report of the United States Geological 

 Survey, 1874, and Popular Science Monthly, July, 1875. 



301 



