102 
HELICID^. 
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 ; 
Muller calls it the operculum liyhernum^ 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. 
(An?i. 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 (Limnmts and Plan-- 
orhis\ 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 
