94 Gaspard's Memoir on the 



cretes a large quantity of very white fluid over its whole surface, 

 which instantly sets uniformly, like plaster of Paris, thus forming 

 a solid covering, about half a line in thickness. When this oper- 

 culum is hardened, the animal separates its mantle from it, by 

 another mucus web stronger than the former ; and after a few 

 hours, expelling a portion of the air it had previously taken into the 

 lungs, it retires by this means a little farther into the shell, forms 

 another lamina of mucus, retires again expiring another quantity 

 of air, and thus sometimes forms a fourth, fifth, and even sixth 

 partition, with intermediate cells filled with air.* 



§. 2. The labour of each individual continues for about two or 

 three days. But the whole of the month of October is occupied 

 by the general closing of the shells of the species, and after the 

 very commencement of November, we find none of them, except 

 perhaps a few diseased individuals, which, not being capable of hi- 

 bernating, perish with the first frosts. 



If from any obstacle the orifice of the shell is not brought to a 

 horizontal position, but is found more or less inclined, it often 

 happens that the calcareous fluid before it is completely fixed, sub- 



* The account here given by M. Gaspard does not completely explain the 

 manner in which the excavation is formed. It is not by the pressure of the foot 

 and the turning round of the shell that this is principally effected. A large 

 quantity of very viscid mucus it 3ecreted on the under surface of the foot, to 

 which a layer of earth or dead leaves adheres ; this is turned on 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 carefully a portion of the roof soon after its completion, I was 

 enabled to see the formation of the operculum. In about an hour or evenlessafter 

 thehibernaculum is covered in, the whole surface of the collarof the mantle in- 

 stantaneously pours out the calcareous 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. T. B. 



