. Natural history. Zoology. 634 MOLLUSCAâCLASS IV.âGASTROPODA, up with a shelly deposit termed the callus. The operculum is either horny or shelly. The animal of Natica is blind and has an extension of the fore- part of the foot that projects over its head when the animal is crawling ; extensions of the side of the foot also partially envelop the shell. The Naticas prey on bivalves, boring a small hole right through the shell. Several species are British. The Lambllariid^ have a delicate shell over which the mantle is reflected to a greater or less degree. The aperture is very large and rounde
. Natural history. Zoology. 634 MOLLUSCAâCLASS IV.âGASTROPODA, up with a shelly deposit termed the callus. The operculum is either horny or shelly. The animal of Natica is blind and has an extension of the fore- part of the foot that projects over its head when the animal is crawling ; extensions of the side of the foot also partially envelop the shell. The Naticas prey on bivalves, boring a small hole right through the shell. Several species are British. The Lambllariid^ have a delicate shell over which the mantle is reflected to a greater or less degree. The aperture is very large and rounded, and there is no operculum. The TmcHOTKOPiDiE have a conical shell; the whorls are keeled, and the periostracum, where it covers these, is fringed with hairs. They are northern forms and come from moderately deep water. The operculum is short and claw-shaped. The NAKiciDiE have shells shaped like Naiica, but covered with a velvety periostracum, whilst the shell itself is marked with spiral and transverse ridges, forming a kind of network sculpturing. The operculum is thin and horny. The majority of the Xbnophorid^ may be recognised at once by their curious habit of building into their own shells those or parts of others, stones, corals, or what- ever may happen to be lying on the sea-bottom â where they dwell (Fig. 15). The shell in the Capdlidje is limpet-like. In Capulus, the cap-of-liberty shells, it has a little curly apex; whilst in the cup-and-saucer limpets (Crucibidum, etc.) there is an internal shelly projection which serves for muscular attachments. The HippoKiciD^ have also limpet-like fig. 16.âXbnophoea. shells, but the mouth is closed by an accu- rately-fitting shelly plate attached to some fixed object. This plate is secreted by a kind of second mantle that envelopes the under surface of the animal and represents the foot, of which there is none properly so-called. A great horse-shtie-shaped muscle holds the shell to its base. The four next families are all
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