Spire conical with slightly convex sides. Apex oblique. Whorls 4 5/8-5 3/8, convex; last whorl rounded. Constriction with an inconspicuous transverse palatalis, an inconspicuous columellaris. Tuba free from the spire but usually touching it again near the apex, bulging and then abruptly narrowed towards the constriction, rounded below. Radial ribs on the spire rather closely placed to moderately spaced (3-8 ribs/0.5 mm on the penultimate whorl), often widened and flattened on the lowermost part of the whorls, with a (shallowly) concave projection on the lower half of the whorls, usually abraded to a (slightly) sinuous to shallowly looped scar, but often to a hardly sinuous scar on the last whorl; those on the tuba closely placed to moderately spaced (5-9 ribs/0.5 mm half-way), not or slightly sinuous below. Spiral striation absent. Umbilicus open, 0.15-0.20 mm across. Aperture tilted up to 60° with regard to the coiling axis, its upper margin slightly below the level of the apex to widely above it, circular to elliptic. Peristome touching the spire or slightly distant from it, double; outer peristome only slightly spreading beyond the inner, but gradually narrowed towards, and absent along the right or lower side of the aperture; inner peristome slightly protruding from the outer, moderately spreading. Spire: height 1.4-1.6 mm; width 1.0-1.2 mm; index 1.3-1.6. Total width 1.2-1.5 mm. Height aperture 0.4-0.6 mm; width 0.5 mm.
Distribution. — Borneo: Sarawak, 4th Div., Tatau Valley.
Notes. —
1. 0. tuba has a wider umbilicus, the spire with flat to slightly concave sides and less sinuous radial ribs, as well as the tuba entirely free from the spire.
2. The name refers to the trumpet-shaped tuba.