Page:Natural History, Mollusca.djvu/198

186, exclusively marine, and generally inhabits deep water. It is an open-mouthed shell, about half an inch in diameter, of a dull reddish hue, covered with a furry epidermis. Messrs. Forbes and Hanley distinguish it from its fellow species by affirming that it is not membranaceous, but this does not agree with my own experience; the specimens that have fallen under my notice having been quite flexible and membranaceous, especially near the margin. Nothing is known of its habits.

The shell in this family is globose, with the spire minute and scarcely raised; the surface is generally smooth, and often covered with a porcelain-like polish; the aperture is large and semi-circular; the pillar is always thick and solid, and its exposed part, constituting what is technically known as the inner lip, is often very broad.

The animal is large in proportion to the shell, yet capable of being wholly withdrawn into it. The mouth is not extended into a proboscis, but is concealed beneath a broad hood or veil. When the eyes can be recognised, they are placed at the bases of the tentacles. The mantle is entire, that is, its edges are not cut into filaments. An operculum is always present, sometimes horny in texture, sometimes shelly, but invariably closing the wide aperture of the shell.

Though the genera comprised in this family are few, the constituent species are numerous, and widely scattered in geographical distribution. For