98 LAND AND FRESH-WATER MOLLUSKS. 
Many mollusks are found in every situation 
and on every variety of soil, while others are to 
be found only in particular habitats. 
The geological pecuharity of a district influ- 
ences the distribution of land shells much more 
than geographical distribution. Thus, the 
majority of the snails occur throughout the 
length and breadth of Great Britain; of the 
remainder, those that are peculiar to the South 
of England flourish on soils derived from chalk 
and oolitic limestones. And the fact that 
a large portion of the life of the mollusk is 
passed in a state of hybernation, when the influ- 
ence of climatical peculiarity is scarcely felt, 
accounts for the absence of any striking differ- 
ence in the land molluscan fauna of the two 
opposite extremities of our island. 
The British species are collected with advan- 
tage in the autumn, when they are full grown; 
the winter rains destroy much of the original 
beauty of the shells. 
Land and fresh-water snails may be killed with 
boiling water, and the animals may be removed ~ 
from their shells by the aid of a bent pin; Olau-— 
silice, Helicelloe, &c., which retire too far to be 
reached by this ordinary expedient, may be killed 
by placing them in tepid water, and adding — 
gradually hot water; the animals may then be ~ 
partially removed. The shells should be well 
