The Valve Shells - Family Valvatidae

THE VALVE SHELLS - FAMILY VALVATIDAE. Shell depressed, often almost discoidal, umbilicated; oper culum round; epidermis green. Animal with long snout and tentacles; foot cleft in front; branchial plume long, branched, thrust partially out when the mollusk is walking. Teeth of radula in seven series, broad, hooked. Fresh water or terrestrial mol lusks.

Genus VALVATA, MUM Characters of the family. Small, thin, flat-coiled shells, found in slow-running brooks and ditches, or ponds, in Europe and North America. The eggs are laid in a single globular capsule. The capsules are fastened to pebbles or stems of plants.

The

Valve Shell (V. tricarinata, Say) exhibits three coils, each of which bears a keeled shoulder. The mouth is round, expanding like a bell; the operculum is spiral with a central nucleus. When progressing, the gill plume is lifted above the head. Diameter, inch.

Habitat.— Delaware River.

V. sincera,

Say, similar in most particulars to the preceding, has rounded whorls. The ,pit is larger.

Habitat.— Northwest Territory.

The Green Valve Shell (V. virens, Tryon), a minute, swollen top shell, bright green, is a inch in diameter. Clear Lake, Cal.

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