84 PULMONIFERA.—LIMNEAD&. 
humid stones. The eggs are globular, yellowish, 
and quite diaphanous: they are hatched about the 
fifteenth day, and the animals reach their full size 
about the end of the second year. They do not 
hybernate. 
Famity LIMNEADA, 
(Pond-Snails.) 
The Fresh-water Snails were scattered by Lin- 
neus and his followers among various marine and 
terrestrial genera, on account of the diversity which 
is found in the shape and appearance of their shells. 
Since more attention has been paid by conchologists 
to the structure of the animal inhabiting a given 
shell, the close similarity which subsists between 
them has prompted their union into one family, 
and that one of the most natural of all those into 
which the Mollusca are divided. ‘They are distin- 
guished by the following characters :— 
The animals have a lengthened foot, a spiral 
body, a short, broad muzzle, two large tentacles, 
triangular and compressed, or awl-shaped, with the 
eyes near their outer bases. The tongue is fur- 
nished with rows of hooked teeth. The mantle, 
which is ample, has a thin edge, and is protected 
by a shell of exceedingly variable form, being 
spiral, turreted, discoid, or simply conical. Those 
which are spiral are sometimes regular, and some- 
times reversed. The colour is generally pale 
brown, uniform in hue, and the surface is closed 
with a hard olive skin, technically called the 
pertostraca, or that which is around the shell. | 
They are destitute of an operculum. 
The habits of these Mollusca are as identical as 
