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 

 pomufn, 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 Cyclophoridae, dwelling in Further 

 India and Malaysia, have a peculiar provision for the 



