102 



Helices. On the approach of warm or damp weather, 

 the animal softens the adhesion that has taken place 

 between the lid and the edge of the mouth of its 

 shell, by emitting a small quantity of fluid mucus ; 

 and the cover is thus easily thrown off by the pressure 

 of the foot. When another is required by external 

 circumstances, the process is commenced afresh. This 

 lid gives the name Pomatia to our largest snail. 

 Lister called the lid the operculum saliva confectum ; 

 Miiller calls it the operculum hybernum, or winter lid ; 

 and more recently it has been named by Draparnaud 

 the epiphragm : the latter name has been generally 

 adopted. Montagu has been blamed for calling it an 

 hybernaculum ; but this arises from a mistake. Mon- 

 tagu intended by the latter name the hole in which 

 the animal buries itself, as is proved by his use of the 

 term at p. 407. 



The Helices will eat meat and other extraordinary 

 substances. I have often observed the common 

 garden snail ( H. aspersa) eating the posting-bill from 

 the walls of the environs of London after a shower. 

 (Ann. and Mag. N. H. ii. 310., 1839.) 



The power of forming this kind of epiphragm, 

 and the thickening of the outer lip, has been consi- 

 dered a peculiar character of the land Mollusca ; but 

 it is now known that pond snails (Limnceus and Plan- 

 orbis), when left dry by the evaporation of the water 

 in which they have been living, thicken the edge of 

 the lip, and form a distinct epiphragm. 



Though the British species are not very numerous, 

 it has been thought advisable to divide them into 

 several sections, to facilitate their determination, and 



