Spire conical with about flat to concave sides. Apex not oblique. Whorls 5 5/8-6, convex; last whorl rounded. Constriction with a transverse palatalis. Tuba gradually narrowed towards the constriction, slightly angular below. Radial ribs on the spire widely spaced (2 ribs/0.5 mm on the penultimate whorl), with a (deeply) trough-shaped projection on the lower half of the whorl, abrading to a (deeply) looped scar, those on the last whorl with a straight projection abrading to a scar with a single deep loop when the shell is observed in front view; those on the tuba widely spaced (1-2 ribs/0.5 mm half-way), with a longer, curved projection, otherwise similar. Spiral striation present. Umbilicus open, 0.15-0.20 mm across. Aperture tilted 30-45° with regard to the coiling axis, its upper margin below the level of the apex, circular to elliptic. Peristome distant from the spire, double; outer peristome slightly to moderately spreading beyond the inner, usually gradually narrowed towards, and narrow or absent along the right side of the aperture; inner peristome slightly protruding from the outer, (widely) spreading. Spire: height 2.1-2.5 mm; width 1.3-1.4 mm; index 1.5-1,9. Total width 2.8-3.1 mm. Height aperture 0.6-0.9 mm; width 0.7-0.8 mm.
Distribution. — Borneo: Sarawak, 4th Div., Beluru area.
Notes. — 1.0. everetti and 0. anisopterum have the projections on the radial ribs close to the tuba abrading to a scar with a double loop; next to this, 0. anisopterum has a longitudinal palatalis. Also similar to 0. heteropleuron; see the note under that species.
2. The name refers to the narrow umbilicus.