The Spire Shells and - Flood Shells - Family Rissoidae

THE SPIRE SHELLS AND - FLOOD SHELLS - FAMILY RISSOIDAE Shell small, top-shaped or elongated; mouth rounded, scarcely channeled. A family of small marine mollusks living on seaweeds, to which they are suspended by a mucous thread.

Genus RISSOA, Freim.

Characters of the family. Two hundred species, abundant chiefly in shallow seas.

R. minuta, Totten, is a smooth, blunt-pointed shell, with rounded, finely striated whorls. It is yellowish brown and clings by a thread to the leaves of seaweeds. Length, inch.

Habitat.— New England to New Jersey.

R. acutilirata Cpr., to -I inch long, is worthy of ex amination under a lens. Its brownish yellow surface is marked by sharp intersecting ribs. 1 t is found on seaweed.

Habitat.— San Diego, Cal.

Genus RISSOINA, D'orb.

Resembles Rissoa except that the aperture and operculum are ear-shaped, and the latter has a blade-like projection on its inner surface. Warm coasts.

R. fenestrata,

Schwartz, is a white shell, blunt at apex, drawn in at base, its rounded whorls strongly ribbed longitudi nally and spirally, making the surface regularly "windowed," as the specific name implies. Length, to • inch.

Genus BARLEEIA, Clark Shell smooth, spiral elongated; aperture round; operculum not spiral; with internal projection.

B. haliotiphila,

Cpr., may be found in colonies comfortably quartered among the coralline tufts that flourish on the shell of 190 The Spire Shells and Flood Shells Haliotis, the Abalone, on the California coast. It is a simple conical shell inch long. Whether the Abalone is conscious of the burden it carries, I cannot say. Probably it counts these passengers as a part of its scheme of protective coloration. If so, then the little haliotis-lover pays for his lodging, and the migrations of the host help to keep the stationary guest mollusks supplied with food.

Genus AMNICOLA, Gld. and Hald.

Shell small, short, ovate or globose, thin, smooth; apex not acute; aperture broadly ovate, not oblique; lip thin, sharp; not projecting below; operculum horny, spiral. Foot short, broad, rounded behind; tentacles blunt; snout short; egg cases pod-like, short, one egg in each. A fresh-water snail of North

America. Species few.

A. limosa,

Say, the type, is dark horn-coloured, often en crusted with black, as it is found in muddy stream borders; the body is white, marked with brown above. Say found them numerous on the banks of Schuylkill and Delaware rivers, between high and low tides. Length, w inch.

Habitat.—Hudson Bay region to Wisconsin and Virginia.

Genus FLUMINICOLA,

Stimps.

Shell obliquely ovate, thick, smooth, spire blunt; inner lip flat and callous, outer lip spreading, especially below; operculum horny. Egg cases lens-shaped, containing many eggs. Found in fresh water in Oregon and California.

Nuttall's Flood Shell

(F. Nuttalliana, Lea) may be distin guished from neighbouring genera by its solid shell and sub-spiral operculum. It has been given five other generic names. The rivers of the two western states mentioned furnish plenty of specimens. Length, a inch.

A green species, F. virens, Lea, somewhat slender and oblique, but very thick, and a very stout, almost spherical one. F. fusca, Hald., reddish, with white lip, and the size of a pea, inhabits Oregon streams.

Genus POMATIOPSIS, Tryon.

Shell small, thin, elongated, of few very much rounded whorls; aperture round, lip continuous, extended or reflected; 191 The Spire Shells and Flood Shells operculum horny. Foot very broad; snout extensible; gill present, but the mollusk breathes air.

P.

lapidaria, Say, is a little pebble-like snail, scarce large enough to earn a name. It is found in moist situations, under stones, on river banks, and is able to crawl along the surface of the water with its shell hanging downward. But it is uncomfort able in water. On land it progresses by fastening the tip of the snout, and drawing the body up to it, thus taking "steps." Length, 1 inch.

Michigan and Missouri to Georgia and New York. P. Californica, PiIs., has a turreted-conic, thin, brown shell with a pit underneath the rounded whorls. Length, i inch. Small streams about San Francisco Bay.

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