MOLLUSCA. 9] 
Physade may have the same power. The passage to the next family seems 
to be through Gray’s genus Chélina, which is a Limnea with folds upon the 
columella. 
Fam. 6. Auriculide. In this monoicous family there are two tentacles, 
and the eyes are at their external and posterior base. Some species inhabit 
land, and others plants near the sea, and salt water marshes. Awrecula mid 
(pl. 76, fig. 1) is the largest species of the genus, being four inches long, 
and of a solid texture. 
Fam. 7. Helicidew. This family includes most of the numerous species 
of land snails with an external spirivalve shell. All breathe free air, are 
monoicous and inoperculate, and have two large tentacles, with an eye upon 
the apex, capable of being retracted by being turned within itself. Besides 
these, there is an inferior and smaller pair of tentacles present in most cases, 
although in some of the minute species they have not been detected. Most 
of the land shells of Europe and North America belong to Helia, a very 
extensive genus, containing upwards of 500 species from various parts of 
the globe, including the islands of the Pacific, all the continents, high 
mountains, and cold climates, although the larger species are intertropical. 
They vary in size from about a tenth of an inch to four inches. The 
shells vary much in form; the aperture is sometimes reduced to a narrow 
fissure, or armed with teeth, in such a manner as to lead one to think it 
impossible for the animal to get out or in. They hybernate under ground, 
closing the aperture with a temporary operculum. Among the genera may 
be mentioned Bulomus (pl. 75, figs. 93, 94), Clausilia (fig. 100), which has 
a peculiar operculum attached to the shell within the aperture, Pupa, 
Streptaxis, &c. Their food is fresh or decaying vegetable matter, and some 
feed upon fungi. The large European species are cooked and eaten, and 
the Romans fattened them for the table. 
Fam. 8. Iimacide. This family includes the naked snails without a 
turbinated shell, but some of them have an internal shell, or a small external 
one which is little more than an appendage. The head, tentacles, organization, 
habits, and food, do not differ essentially from those of the preceding family. 
The genus Limazx (pl. 77, figs. 19-21) is destructive to the plants cultivated 
by the farmer and gardener in Europe, and new modes of destroying them 
are continually sought after. The species which occur in North America 
have not yet proved injurious, and the same remark applies to the snails, 
which are troublesome to gardeners in Europe. The body of Limax is 
very contractile, but when moving on its lower surface or foot, it is rather 
slender, thickest in the middle, and tapering towards the extremity. Upon 
the back is a kind of fleshy shield, beneath which the head can be drawn. 
Class 3. Cephalopoda. 
This class was named Malakia by Aristotle, and Dfollia by Pliny. It 
includes certain dioicous marine mollusca, which have the feet or arms 
around the mouth at the extremity of the head. The body is soft, the 
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