GEOGRAPHICAL DISTRIBUTION. 135 
but probably it is merely because they are found, like 
the shells of nuts which are known to be eaten by the 
former, near to logs. Frogs also, and toads, hi 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 frog. 
Some of the aquatic mammaha 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 Sorer, 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 affecting 
the distribution of land-shells which have been noticed 
in other countries, 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 brilliant colors, on 
sectrbanks 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 effect. It is 
said also, that tho presence of sand aids the multiplica- 
