GEOGRAPHICAL DISTllIBUTION. J 35 



but probably it is merely because they are found, like 

 the shells of nuts Avhich are known to be eaten by the 

 former, near to logs. Frogs also, and toads, in their 

 excursions upon land, frequently meet with and prey 

 upon them, and it is quite a common occurrence to 

 find the shell of a Helix in the stomach of a froo-. 

 Some of the aquatic mammalia feed upon and destroy 

 great numbers of the Naiades, and there would, there- 

 fore, be nothing improbable in the supposition that some 

 of the smaller terrestrial quadrupeds feed upon the land- 

 mollusks. Indeed, we have been informed that a spe- 

 cies of field-mouse, probably a Sorex, burrows in the 

 deep snow that covers the ground in the winter, and 

 seeking the torpid Helices in their retreats, drags them 

 to the surface and devours them, leaving the broken 

 shells scattered upon the snow. 



Proximity of the Sea. Among the causes afibcting 

 the distribution of land-shells which have been noticed 

 in other comitries, the vicinity of the ocean has been 

 supposed to exercise very considerable influence. In 

 Great Britain it has been stated, that species are more 

 numerous, individuals multiplied to a greater extent, 

 varieties more common, and the shells larger, more 

 developed, and marked with more brilhant colors, on 

 sea-hanks than elsewhere. It seems to be thought, 

 though it is not so stated in terms, that the ocean pro- 

 duces a direct influence in this case, and no intimation 

 is given of its being an indirect climatal efiect. It is 

 said also, that the presence of sand aids the multiplica- 



