Page:Natural History, Mollusca.djvu/158

146 to disappear, pale colours are displayed by the shell, and its texture is stony. Its form is more or less rolled upon itself, but without a salient or produced spire, and the mouth is usually ample and widely expanded.

The animal is large, fleshy, and often slimy. The gills are concealed, the tentacles are so much shortened, widened, and separated, that their form is well-nigh obliterated, and they constitute a large square fleshy veil, beneath which are placed the eyes. The stomach is complicated, and in some species there is a shelly gizzard, with a peculiar grinding apparatus of great strength, needful for the demolition of the shells of other species of Mollusca on which the Bulladæ feed. They are very voracious, and sometimes swallow bivalves so large as quite to distort their own form, and render it almost unrecognisable. The shelly gizzard of Scaphander lignarius, a large species not uncommon on our coasts, was described by Gioeni, a Sicilian naturalist, as a new genus of multivalve shells, to which he gave his own name, calling it Gioenia. He even went so far as to describe the habits of the pretended animal, which was actually received into the catalogues of science by some of the most eminent names in conchology, until at length the imposture was detected and exposed.

The animals of this family generally inhabit deep water, that is to say, below the range of low tide. Occasionally, however, they stray within tide-marks.