The Helicider or family of true snails is an immense one, the typical genus alone in its un restricted sense embracing about 6,500 species. They abound in moist places and have very sim ilar habits the world over. They feed chiefly on vegetable substances, though they are very indiscriminate in their appetite and even devour the dead of their own kind. The mischief which they do to garden crops is too well known; and gardeners lay down cabbage leaves and the like to attract them, in order that they may be destroyed. Snails delight in warm, moist weather; in dry weather, their chief time of activity is during the night, and they hide themselves by day; but after rain they come forth at any hour in quest of food. At the ap proach of winter or in very dry weather they dose the mouth of the shell with a membrane (epipihragm), formed by the drying of the mucous substance which they secrete, and be come inactive and torpid. Snails retreat into crevices for the winter, or into holes which they make in the earth, and which are roofed over with earth, dead leaves, etc., agglutinated by secreted mucus. The eggs are deposited in moist earth, the snails often burrowing beneath the surface for this purpose and they have no jelly but only a slightly adhesive covering. Among the most plentiful of our native species are Helix albolabris and H. alternata and the minute Zonites milium (not closely related) found everywhere in damp woods. Several of the large European species have been intro duced. The great vine snail, or edible snail (Helix pomatia), a European species, was con sidered by the ancient Romans one of their table luxuries. In some countries, as Switzerland and parts of France, they still form a consider able article of commerce. Together with H. aspersa, they are fed by thousands in places called "escargatoires," which are made on pur pose for them. Preserved snails are imported into the United States for table use, and the demand has increased sufficiently to induce a few persons to inaugurate the business of rais ing them, particularly in California. On ac
count of its large size and gregarious habits the European H. pomatia is best suited to this purpose. Another family of water snails (Paludittickr) belongs to a quite different di vision of the GasteroPoda, the order Prosobran chiata. In these forms the usually single ctenidium is placed anterior to the heart, and the visceral nervous loop is twisted into a figure 8. The order is a very extensive one, most of the members of which are marine. With the flavour, Ampullarie, which are re lated fresh-water forms often placed in distinct families, the species of Paludina and Vivipara have the left ctenidium only and a single kidney and heart auricle. The shell is usually stout, more or less pyriform and has a well-developed operculum. The single pair of non-retractile tentacles bear the eyes upon lobes near their bases and the edge of the mantle forms a pair of short tubes by which water is directed over the gill. The sexes are always separate and the young are produced alive. Common species are P. inteora. -P. intertexta ana P. vivipara, which live on the mud at the bottom of ponds and sluggish streams. They are, at least in part, carnivorous. Other important fresh-water families are the Pleurocerida• and Melaniidcr, including chiefly oviparous forms which have the thick shell variously ornamented with spines and tubercles. Of the numerous forms found in the mountain streams and eastern tributaries of the Mississippi and elsewhere the large and variable lo spinosa is an example.
Bibliography.— Pilsby and Tryon, 'Manual of Conchology> (Philadelphia 1878-1904) ; Bin ney and Gould, 'Terrestrial Air-breathing Mol lusks of the United (Boston 1851 to 1859) ; Binney, Bland, Prime and Tryon, 'Land and Fresh-water Shells of North (Smithsonian Institution, Washington, 1865 73) ; Cooke, 'Cambridge Natural (Vol. III, London 1895) ; and for an excellent popular account Ingersoll, 'Wild Life in Orchard and Field) (New York 1903) See GASTF.ROPODA.