The shells of this genus are small, solid, planorboid in shape with flattened or slightly depressed spires; adults range in maximum diameter from 2 to 11 mm., are usually twice as wide as high, and are deeply and widely umbilicated. Whorls 2 to 4 in number. Nuclear whorl of 1/2 turn, glassy white, minutely creased with one or more fine spiral lines on the top surface. In fresh specimens, the old peristome of the last nuclear whorl flares, so that its remnant may be seen as a minute, raised scale projecting slightly over the beginning of the first postnuclear whorl. In adults, the spiral sculpturing consists of several moderately developed carinae. Axial sculpture either very weak or of quite strong ribs which often become nodular as they cross the spiral carinae. Frosted appearance over the outer shell is due to many, closely packed, axial, laminated threads. Peristome continuous, round internally, and often thickened externally into a heavy varix. Operculum multispiral, concave externally, with a chitinous base on the inside, and with many revolving rows of tinraised, calcareous beads on the external side. Often between the rows of beads, and always on the outer rim of the operculum, there are many small, hair-like bristles forming a sparse or sometimes dense matting. The radula is rhipidoglossate as shown from examination of specimens of Cyclostrema discoideum Reeve.

Shell depressed, suborbicular, distinctly spirally and radially sculptured, white or uniformly coloured ; aperture nearly circular ; peristome acute, continuous ; umbilicus deep, boimded by a carina ; operculum circular, horny, multispiral, each volution obliquely striated.
Distribution.—Nearly universal.