Genus POTAMIDES, Bron.
Shell imperforate, turreted, angled, tubercled or spiny, with thick epidermis, apex often decollated; operculum horny; foot nearly circular, blunt behind; siphon fringed. A genus of tropical brackish water species which are able to live for long periods suspended above the water by threads spun from the foot.
A species, P. palustris, Brug., lives in the salt marshes of the Eastern Archipelago. The natives collect these in quan tities for food. They are roasted, then the contents of the shell are sucked out, the spire being broken off first.
In Borneo the large P. telescopium, Brug., 8 to to inches long, is an article of food. Near Calcutta this species is so abundant that the shells are burned for lime. The live mollusks are first heaped in the sun to die.
Genus BITTIUM, Leach ' Shell elevated; whorls many and granular, with irregular varices; anterior canal short, not recurved; outer lip not reflected, usually with an exterior rib; foot narrow, square in front. Small mollusks, in temperate seas.
181 The Horn Shells B. filosum, Gld., has about eight whorls, each lined with four ridges, forming a graceful spire, i to i of an inch long. It is thin, of horny texture, brownish to white, and found attached to stones at low tide. Small hermit crabs often take possession of the dead shells. Sitka to Monterey, Cal.
Habitat.— New England to Florida.
whorls of its graceful slender spire. Length, about * inch. Habitat.— Southern California.
Sub-Genus CERITHIOPSIS, Forbes and Hanley Shell small, rather cylindrical, narrow, tubercled; whorls numerous, narrowing toward base; aperture small ; canal short, straight; foot narrow. Inhabits northern and temperate seas.
Habitat.— Massachusetts to Florida, West Indies.
C. tubercularis, Montg., is the European horn shell found also in Florida and on the west coast of North America. It is half an inch long, however, in the New World form, twice as large as the European type. It is a dark brown shell with three rows of strong, regular tubercles. The sutures are well marked, the apical whorls smooth.
Habitat.—Europe, Vancouver Island to Southern California.
Habitat.— Massachusetts to West Indies.
Genus TRIFORIS, Desh.
Shell spiral, elongated, granular, coiled to the left, whorls numerous, aperture small with short canal. One hundred species.
182 The Horn Shells Peculiar in retaining the larval form until quite large, especially when living far from shore.
Habitat.— Florida, West Indies.
A Californian form of the European T. perversa, Linn., is var. adversa. Its ribbed and beaded, yellowish brown spire coils to the left, distinguishing it from other genera of the horn shells. It is about the same size as T. decorata.