198 MOLLUSKS: GASTEROPODS. 



glossy silicious teeth, which are arranged in rows in 

 the most regular manner, and differently in different 

 kinds. The tongue of some kinds contains one hun- 

 dred and sixty rows of teeth, and one hundred and 

 eighty teeth in each row, or more than twenty-eight 

 thousand in all ! 



Many of the Gasteropods 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 365-377. Some of these feed upon dead 

 animals which they find; others attack living moUusks; 

 and though the latter are shut tightly within their 

 shells, the hungry Gasteropod, with its rasp-like tongue, 

 files a neat roimd hole through the shell, and then 

 leisurely feasts upon its contents. Thus clams and 

 other large mollusks fall a prey even to some of the 

 very small carnivorous gasteropods. 



The Gasteropods are divided into Air-breathers or 

 Pulmonifers, as Land-Snails, and the Water-breathers 

 or Branchifers, as the Sea-Snails and River-Snails. The 

 first look like the parents, only smaller, as soon as they 

 are born ; the young of the latter differ from their par- 

 ents, and, instead of creepmg, swim with a pair of fins 

 springing from the sides of the head. 



STROMBS, CONCHS, OR WING-SHELLS, &c. 



These are large marine shells, some of them the 

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

 tain Shell, is extensively used for making shell-cameos; 

 three hundred thousand of this kind were carried from 

 the West Indies to Liverpool in a single year. The 

 interior of the conch is of the richest rosy hue. 



