Prehistoric sites have uncovered piles of this gastropod mollusk'S spiral shell, indicating that snails were popular early on. They were greatly favored by ancient Romans, who cultivated special vineyards on which the snails could feed and fatten. The best-known varieties today are the vineyard or Burgundy snail and the petit-gris. The vineyard snail has a diet of grape leaves and, though it grows slowly and is somewhat difficult to raise, is considered the best eating. It grows to about 1 3/4 inches, has a streaked, dull, yellowish brown shell and mottled flesh. The smaller (about 1 inch) French petit-gris is now being cultivated in the United States and has a brownish-gray shell and flesh. Other varieties are cultivated in Algeria, Turkey, China, Indonesia and Africa but are not as highly esteemed as the vineyard snail and petit-gris. Fresh snails are available year-round and can be found in specialty markets. Fresh American-cultivated snails do not require the purification period that European snails do but should be used the same day they're purchased. Snails are usually boiled before being baked or broiled in the shell with a seasoned butter. Canned snails and packaged snail shells are available in gourmet markets and many supermarkets. See also snail plate; snail tongs; shellfish.