POND-SNAIL. A snail of the pu]monate family Limmeidle, which inhabit the fresh wa ters of temperate regions. All are vegetable eaters and seek their food beneath the water. They lay their eggs in clusters surrounded by a clear gelatin-like substance, and attached to plants and other objects beneath the water. The typical pond-snails are those of the genus Lim fwea, which have thin, horny shells forming a slender spiral with a large aperture. not pro tected by an operculmn. When the ponds are frozen or dry up. they bury themselves in the mud, and become dormant until released. The largest species (Linine-a Rtagnalis) is scattered abundant ly over most of the Northern Hemisphere. and may 1;ecome two inches in length. Many other species are known in North America. most of them less than an inch long. A smaller, less drawn-out shell, differing from Limnpea primarily in the fact that it is sinistral, while the shells of Limmea follow the ordinary method of turning from left to right, is that of the genus Physa. It is more south erly in its distribution than Limmea, hut several species are found throughout the United States.
one of which (Physa heterostropha) is exceeding ly abundant. (See PIIYSA.) Another prominent genus, with a large number of familiar species. is Planorbis, so called because its shell is coiled in a flat spiral like a roll of tape: none exceed three-fonrths of an inch in diameter. Among other genera may be mentioned Ancylus and Gundlachia, which are shaped nearly like lim pets. and have similar habits. although they inhabit fresh water alone, and are not larger than grains of rice. All the pond-snails are infested with parasites. and certain of them regularly form the hots of the liver-flukes of the genus Distoma during one stage of their development. Pond-snails are not only interest ing objects in an aquarium, but of much utility in keeping the glass free from confervoidgrowths. which they constantly feed upon. Consult : Cooke. "Shells." vol. iii. of Cambridge Natural His tory (London. 1S9S) : Binney. Land and Frcsh Water Shells of North America. Part ii. (Smithsonian Institution. Washington. 1865.. See PULMONATA ; SNAIL.