The Xenophoridæ have the singular habit of cementing to the exterior of their shell, stones, pieces of coral, and fragments of other shells; hence they have been called “Carrier-shells,” and, according to the kind of material chosen, have been named “Conchologists” and “Mineralogists.” Beyond acting as a disguise, and consequently as a protection, there does not appear to be any special utility in thus adding to the weight of their own shells. The animals do not glide like most other molluscs, but scramble along like the Strombs, the form of their foot being small, divided into a front, expanded, and a hind, tapering portion admirably adapted to the nature of the ground on which they live, which usually consists of broken and dead shells.
Cases 49–52.
The “Wing-shells” (Strombidæ) are the largest of the Gastropods with a proboscis or non-retractile snout. They do not crawl like most other Gastropods, but progress by a sort of hopping movement. They act as scavengers, feeding on decomposing animal matter.
The Strombus gigas, or “Fountain-shell,” occurs in great numbers in the West Indies, and is a very heavy solid shell. It is a favourite ornament for rockwork and fountains in gardens, and, like the Helmet-shells, is used for cameo-carving. It is also employed in the manufacture of porcelain, as many as 300,000 having been imported into Liverpool in one year for that purpose.
Cases 51–52.
The Scorpion-shells, or “Spider-claws,” as they are sometimes called (Pterocera), possess singular claw-like projections, which are developed on the outer lip of the shells.
Cases 53–54.
The “Trumpet-shells” (Lotoriidæ) have varices or strengthening ribs at intervals, like the Murices; the largest species, Lotorium variegatum, is used by South-Sea Islanders as a horn or trumpet. A hole is made in the upper part of the spire to blow through, and the sound produced can be modulated or varied by inserting the hand in the aperture or mouth of the shell.
Cases 55–56.
The “Helmet-shells” (Cassididæ) are used for cameo-carving; they consist of differently coloured layers, so that the ground-colour of the carving is of a different tint from the subject engraved. The most artistic shell-cameos are produced in Italy, whence the art has been introduced into France and England. The Cassis madagascariensis (Fig. 12 on p. [19]) is in special request by shell-carvers on account of the strong contrast of the white upper layer with the dark ground beneath. Extinct forms of Cassis are found fossil in Tertiary formations, but none of them equal in size the largest living species.