Material seen. — KALIMANTAN, Kalimantan Selatan; Batu Tungga near Sarungga, W. of road Batulicin-Benualawas (V 3265/>10, HOLOTYPE RMNH 56914); limestone escarpments along road Benualawas-Limbungan (V 2859/5).
Spire cylindrical. Apex oblique. Whorls 3 1/4-3 3/8, convex; the penultimate obtusely angular on the right side if the shell is observed in front view, the ultimate obtusely angular. Constriction with a parietalis which continues far into the tuba; with a distinct, short angularis covering the suture, with a transverse palatalis. Tuba touching the spire over its entire length, slightly bulging and rather abruptly narrowed towards the constriction, obtusely angular below. Radial ribs on the spire moderately spaced (4-5 ribs/0.5 mm on the penultimate whorl), not sinuous; those on the tuba widely spaced (2-3 ribs/0.5 mm half-way the tuba), with a shallow, semicircular loop below. Spiral striation present. Umbilicus open, 0.1 mm across, but often (almost) entirely covered by the tuba. Aperture tilted up to 15° with regard to the coiling axis, its upper margin widely above the level of the apex, elliptic, with the continuation of the parietalis clearly visible along its lower side if the aperture is observed in front view. Peristome double, outer peristome widely spreading beyond the inner, but gradually narrowed towards, and absent along the right side of the aperture; inner peristome protruding from the outer, somewhat spreading, its outer surface and the upper surface of the outer peristome with closely placed, slightly irregular lamellae. Spire: height 1.1-1.3 mm; width 1.2-1.3 mm; index 0.9-1.0. Total width 1.7-1.8 mm. Height aperture 0.4-0.6 mm; width 0.5-0.6 mm.
Distribution. — Borneo: Kalimantan, K. Selatan, karst areas E. of the Meratus Mts.
Notes. — 1. Differs from 0. subconicum, O. hailei as well as 0. cryptodon in lacking a tooth along the upper side of the aperture. The aperture somewhat resembles a human ear, hence the name.