WATER-BREATHING SNAILS. 211 



lar manner, and differently in different kinds. The 

 tongue of some kinds contains one liundred and sixty 

 rows of teeth, and one liundred and eighty teetli in 

 eacli row, or more than twenty-eight thousand in all. 

 The tongue is used like a rasp to scrape the animal's 

 food to pieces. 



Many of the Gastropods feed upon vegetable sub- 

 stances, and these have the aperture of the shell en- 

 tire. The others feed upon animal substances, and 

 have the aperture notched, or drawn out into a canal, 

 as in Figures 363-375. Some of these feed upon dead 

 animals ; others attack living mollusks, though shut 

 tightly within their shells, for the Gastropod, with its 

 rasp-like tongue, files a round hole through the shell, 

 then leisurely feasts upon its contents. Thus clams 

 and other large mollusks fall a prey even to some of 

 the very small carnivorous Gastropods, which are among 

 the most dangerous enemies of the oyster, and cause 

 heavy losses every year to the oystermen. 



The Gastropods are divided into Air-breathers, as 

 Land Snails and Pond Snails ; and Water-breathers, 

 as Sea Snails and River Snails. The young of the 

 former are like the parents, only smaller ; the young of 

 the latter differ from their parents, and swim with a 

 pair of fins springing from the sides of the head. 



Water-breathing Snails. 



Strombs and Conches, or Wing-shells, etc. 



These are large marine shells, some of them the 

 largest of the Gastropods. One kind, called the Foun- 

 tain Shell, is extensively used for making shell cameos ; 



