Cerithium reticulatum receives its generic name from its appearance to a small horn, and the specific name refers to the netted appearance of its surface due to the presence of numerous little tubercles arranged in rows—a feature that serves to distinguish it from the small Turret shells. It is a common shell, as is also the other representative of the family illustrated, but the latter is rendered conspicuous by the enormously expanded lip that has earned for it the popular name of Spout Shell. Its scientific name is Aporrhais pes-pelicani, and the application of the specific term will be understood when the shell is viewed from above, for the expanded lip is drawn out into long finger-like lobes that suggest the foot of a bird. This is a very solid shell, sometimes reaching a length of two inches; and the animal inhabiting it is carnivorous.
Fig. 176.—Aporrhais pes-pelicani, showing both shell and animal
We have yet some turreted shells to deal with, belonging to the family Pyramidellidæ, but they need not be confused with the preceding groups if carefully examined. In the first place, the aperture of the shell is very small; and the operculum, instead of being spiral, as in the turreted shells before mentioned, is imbricated or made up of parallel layers denoting that the growth took place on one side only. Another distinguishing feature is seen in the nucleus—that small portion of the spire that was developed within the egg—which is sinistral or left-handed. In addition to this, the animal has broad, ear-like tentacles, a retractile proboscis, and a lingual ribbon without teeth.
The British species of this family belong principally to the genera Odostomia, characterised by a tooth-like fold of the columella; Eulima, containing small, white, polished shells with numerous level whorls; and Aclis, with little polished shells not unlike Turritella.
Fig. 177.—1. Odostomia plicata. 2. Eulima polita. 3. Aclis supranitida
The last family of the Holostomata is the Naticidæ, the shells of which are almost globular, with only a few whorls, and a small, blunt spire. The mouth is semilunar in form, and the lip sharp. The proboscis of the animal is long and retractile, and the foot large; but perhaps the most characteristic feature is the presence of large mantle lobes which hide some of the shell when the animal is crawling. In Natica (fig. 155), the typical genus, the shells are somewhat thick and smooth, with a large umbilicus. As the animal crawls a large fold of the mantle is reflected back over the head, completely covering it, and apparently obstructing its view; but this is not the case, for the creature has no eyes. Natica is very abundant on some sandy beaches, where it devours small bivalves and other animals; and it is frequently washed up alive by the waves. Its shell is also a favourite one with hermit crabs. Its eggs, all connected together in a spiral band, may often be seen stranded on sandy coasts. Several species of Natica are found on our shores. An allied mollusc—Velutina lævigata, so called on account of the velvety epidermis that clothes the shell, completely surrounds the shell by its mantle folds when creeping.