96 PULMONIFERA.—HELICID&. 
one side, and a fresh secretion being thrown out, 
the layer of earth mixed with mucus is left. The 
animal then takes another layer of earth on the 
bottom of the foot, turns it also to the part where 
he intends to form the wall of his habitation, and 
leaves it in the same manner, repeating the process 
until the cavity is sufficiently large, and thus 
making the sides smooth, even, and compact. In 
forming the dome or arch of the form, a similar 
method is used, the foot collecting on its under 
surface a quantity of earth ; and the animal turning 
it upwards, leaves it by throwing out fresh mucus, 
and this is repeated until a perfect roof is formed. 
As I have very often watched this curious process, 
I am certain of the facts. On removing very care- 
fully a portion of the roof soon after its completion, 
I was enabled to see the formation of the operculum. 
In about an hour, or even less, after the hyberna- 
culum is covered in, the whole surface of the collar 
of the mantle instantaneously pours out the calca- 
reous secretion in considerable quantity. ‘This is 
at first as fluid as thick cream, but very soon 
acquires exactly the consistence of bird-lime, being 
excessively adhesive and tenacious, and in about 
an hour after it is poured out, it is perfectly solid.” 
M. Gaspard states that the labour of each indi- 
vidual continues for about two or three days, but 
that the whole of the month of October is occupied 
by the general closing of the shells of the species. 
He adds that, about the beginning of April, the 
hybernation ceases. ‘The mode by which their 
escape from confinement is effected is simple and 
easily comprehended. ‘The air which 1s contained 
in the different cells, and which had been expired 
on the animal withdrawing itself farther and 
