GASTEROPODA PULMONEA. 241 



Those which possess no apparent shell, form in the Linnaean system the 

 genus 



LIMAX, Linnceus, 



Which is now divided into Limax, Arion, Lima, Vaginulus, Testacella, and 

 Parmacella. These animals are known by the common name of slugs. 



In the terrestrial Pulmonea with, complete and apparent shells, the edges of 

 the aperture in the adult are usually iumid. 



HELIX, Linnaeus. 



To this genus Linnaeus referred all those species in which the aperture of 

 the shell, somewhat encroached upon by the projection of the penultimate 

 whorl, assumes a crescent-like figure. 



Helix pomatia, Lin., common in the gardens and vineyards of France, with 

 a reddish shell marked with paler bands, an animal which in some places is 

 considered a delicious article of food. The genus is now variously subdivided. 

 The animals are what we term snails. 



The AQUATIC PULMONEA have but two tentacula; they are continually 

 compelled to rise to the surface for the purpose of breathing, so that they 

 cannot inhabit very deep water ; they are usually found in fresh water or salt 

 ponds, or at least in the vicinity of the sea coast and of the mouths of rivers. 

 Some of them have no shell, such as those of the genus ONCHIDIUM. 



The aquatic Pulmonea, with complete shells, were also placed by Linnaeus 

 in his genera HELIX, BULLA, and VOLUTA, from which it has been found 

 necessary to separate them. 



In the first were comprised the two following genera, where we find the 

 internal edge of the aperture crescent-shaped, as in Helix. 



PLANORBIS, Brugueir. 



The Planorbes are distinguished from the Helices by 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 it is 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. In stagnant waters. The 



LIMN.IEUS, Lamarck, 



Has, like a Bulinus, an oblong spire and the aperture higher than it is wide ; 

 but the margin, like that of a succinea, is not reflected, and there is a longitu- 

 dinal 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 inhabit stagnant waters in great numbers ; they also abound with the 

 Planorbes in certain layers of marl or calcareous strata, which they evidently 

 prove were deposited in fresh water. 



