Spire conical with flat to distinctly convex sides. Apex slightly oblique or not. Whorls 5 3/4-6 7/8, convex; last whorl rounded. Constriction with a parietalis, a longitudinal and a transverse palatalis, a distinct columellaris which continues as a ridge-shaped transverse basalis or not. Tuba gradually to rather abruptly narrowed towards the constriction, rounded below. Radial ribs on the spire rather closely placed to widely spaced (1-7 ribs/0.5 mm on the penultimate whorl), sinuous, often with a shallowly concave projection half-way, abrading to a (slightly) sinuous scar, those on the tuba moderately to widely spaced (2-3 ribs/0.5 mm half-way), below with a shallowly concave projection, abrading to a not or slightly sinuous scar. Spiral striation absent. Umbilicus open, 0.15-0.25 mm across. Aperture tilted up to 30° with regard to the coiling axis, circular. Peristome double; outer peristome (widely) spreading beyond the inner, but rather abruptly narrowed towards, and absent along the right side of the aperture, with a distinct, widely rounded to obtuse wing along the upper side, and usually a similar but less conspicuous wing along the lower side; inner peristome hardly to distinctly protruding from the outer, spreading. Spire: height 2.4-3.5 mm; width 1.6-2.2 mm; index 1.4-1.6. Total width 3.0-4.0 mm. Height and width aperture 0.7-1.0 mm.
Distribution. — Borneo: Sarawak, 4th Div., G. Mulu Nat. Park.

1. Shows variability in the size of the shells, the shape of the spire (its sides varying from straight to distinctly convex because of a tightly coiled last whorl), the size of the tuba (short in some specimens, long and prominent in others), and the presence or absence of a basalis.
2. Similar to 0. dipterum, see the notes under that species.