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Shell minute, thin, depressed, umbillicate, and with 3 to 4 subtubular whorls. The umbilicus has rather flattened walls and is usually bounded by a spiral cord. The rounded aperture is oblique, with a thin lip, its upper margin arching forward. Columella only moderately thickened. Operculum corneous, thin, multispiral. There are many species in American waters with quite a number of genera and subgenera. The family is undergoing considerable change under the current research by H. A. Pilsbry. We are including only three examples of this interesting group. Consult recent numbers of The Nautilus.

2 mm. in diameter, planorboid, 4 whorls, spire moderately raised. Translucent-white, glossy, smooth. Umbilicus round, very deep, moderately wide, bounded by a small, spiral, smoothish thread. Wall of umbilicus flattish. Columella strong, braced on the whorl above by a small, spreading callus. Outer lip thin, sharp. Not uncommon in shallow water. This is the type of the genus.

5 mm. in diameter, planorboid, well-compressed, 4 whorls, opaque-white, with a glossy sheen. Outer surface covered with numerous, crowded, spiral, incised lines. Umbilicus with rounded sides, deep, rather narrow. 50 to 100 fathoms. Locally common.