Page:Natural History, Mollusca.djvu/95

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83
LUNG-BREATHING MOLLUSKS.


the mud at the mouths of rivers, or in the sea: they seldom leave salt, or at least brackish water. There are some foreign species which live in ponds, and have all the habits of our Pond-snails, only that their pillar is more distinctly plaited.

The family may be represented by Conovulus denticulatus, an oblong, spiral shell, rarely exceeding half an inch in length, of a brown or purplish hue. Its last whorl is long and compressed; the pillar is grooved, with several spiral plates; the throat is also grooved. A remarkable character of this shell is, that the pillar extends no farther than the upper part of the last whorl, the upper whorls being destitute of any pillar or internal spiral division. This character is common to most species of the family, and forms, as Mr. Gray observes, one of its best technical distinctions. It is attributed to the animal's absorbing the partitions which separate the upper whorls, and thus converting the spire into a single cavity.


THE DENTICULATED CONOVULUS.
(Nat. size and magnified.)
This little Mollusk is by no means common; it has been found in the marshes near Faversham, at the roots of rushes. It is said also to inhabit the clefts of rocks, near high water-mark, as well as the mud left bare by the tide, at the mouths of rivers. The animal feeds, according to M. Bouchard Chantreux, on the detritus of marine plants and rotten wood. It lays twelve or thirteen eggs in the months of June and September, united by a viscid matter into a small mass, which is fixed under the more