FOOD, HABITS, ETC. "73 
in sheltered positions in limestone rocks, where by 
frequent resort the Snails in course of years erode 
burrows in the stone, which in places becomes 
honeycombed by them. In all these resting-places 
they either fasten the mouth of the shell with mucus 
to some object or to a fellow-Snail’s shell; or, when 
isolated, close the aperture of the shell with a film of 
dried mucus to exclude the cold and retain their own 
moisture. This film is known as the “ epiphragm,” 
or “hybernaculum,” and has usually a small aperture 
left near the centre as an air-passage. In very cold 
weather, as the animal retreats farther into its shell, 
it will form a second and even a third epiphragm, 
with a space between each. In some cases such as 
the Roman Snail (Helix pomatia), this epiphragm is 
impregnated with lime salts to such an extent as to 
make it quite a solid lid (hence the name, from 
pomum, a lid). The operculate Land Snails have, of 
course, only to retreat into their shell and close the 
mouth with the operculum. 
In very hot weather (and, indeed, under any other 
adverse conditions) the Land Snails will similarly 
withdraw, and protect themselves in identical manner 
as against cold. Freshwater Snails burrow in the 
mud when the water dries up, while a Planorbis met 
with in the Bahamas, under these circumstances 
forms an epiphragm. Certain land operculates, 
belonging to the Cyclophoride, dwelling in Further 
India and Malaysia, have a peculiar provision for the 
