34 CLASS GASTEROPODA. 
placed by Linneus in his genera HELIX, BULLA, and Vo- 
LUTA, from which it has been found necessary to separate 
them. 
In the first were comprized the two following genera, where 
we find the internal edge of the aperture crescent-shaped, as 
in helix. 
PLANORBIS, Brug. 
The planorbes had been already distinguished from the 
helices by Bruguiéres, and even previously by Guettard, on 
account of the slight increase of the whorls of their shell, the 
convolutions of which are nearly in one plane, and because 
the aperture is wider than itis high. It contains an animal 
with long, thin, filiform tentacula, at the inner base of which 
are the eyes, and from the margin of whose mantle exudes a 
quantity of a red fluid, which is not, however, its blood. Its 
stomach is muscular, and its food vegetable, like that of the 
Limnzi, of which, in all our stagnant waters, it is the faithful 
companion. (Hel. vortex, H. cornea, H. spirorbis, &c.) 
LIMNZUS, Lam., 
Separated from the bulimi of Bruguiére by M. de Lamarck, 
has, like a bulimus, an oblong spire, and the aperture higher 
than it is wide ; but the margin, like that of succinea, is not 
reflected, and there is a longitudinal fold in the columella, 
which runs obliquely into the cavity. ‘The shell is thin; the 
animal has two compressed, broad, triangular tentacula, near 
the base of whose inner edge are the eyes. They feed on 
plants and seeds, and their stomach is a very muscular giz- 
zard, preceded by acrop. Like all the pulmonariz, they are 
hermaphrodites, and the female organ of generation being far 
from the other, they are compelled so to copulate, that the in- 
dividual which acts as a male for one serves as a female for 
a third ; long strings of them may be observed in this position. 
