Page:Natural History, Mollusca.djvu/94

 them. There is an umbilicus behind the pillar; the operculum is hard, horny externally, and marked with a single, depressed, spiral line.

This Mollusk lives on vegetable matter, like the snails, and is found in damp places, on a chalky soil. It is not very generally distributed, but is said to be abundant on the warm chalk hills, covered with brushwood, at Caversham, near Reading, in Berkshire. It is common also in the Isle of Portland, where I have seen it numerous in April, crawling on the twigs of shrubs, with the operculum carried behind, in a curious manner.

The characters of this family are the following :&mdash; The animal has a lengthened foot, a lengthened ringed muzzle, two somewhat cylindrical tentacles, with eyes near their bases on the inner side. The body is spiral, placed on the centre of the foot, and invested with a thin mantle, with a thickened edge. There is an ample spiral shell, the pillar of which is plaited at all periods of its life.

Mr. Gray observes of these Mollusca, which are feebly represented in Britain by some three or four small species comprised in three genera, that they appear, by their habit and character, to be exactly intermediate between the land and the fresh-water Univalve Mollusca. They have the sessile eyes of the Pond-snails, placed behind instead of in front of the tentacles, and the subcylindrical tentacles of the Land-snails; but the tentacles are not retractile under the skin of the neck. In the same manner, the Carychia and the Acmea are terrestrial, living in damp moss; the Conovuli live in