Material seen. — KALIMANTAN. Kalimantan Selatan: limestone escarpment W. of km 6 road Benualawas-Batulicin (V 3368/>10, HOLOTYPE RMNH 56915); limestone escarpments along road Benualawas-Limbungan (V 2858/>10).
Spire conical with distinctly convex sides, or almost cylindrical. Apex slightly oblique. Whorls 3 3/8-3 5/8, convex; the penultimate rounded or slightly angular on the right side if the spire is observed in front view, the ultimate obtusely angular. Constriction with a thick parietalis which continues far into the tuba; with a transverse palatalis, with a columellaris. Tuba touching the spire over its entire length, gladually narrowed towards the constriction, obtusely to almost sharply angular below. Radial ribs on the spire rather closely placed to moderately spaced (5-8 ribs/0.5 mm on the penultimate whorl), not sinuous; those on the tuba (rather) closely placed (6-10 ribs/0.5 mm half-way the tuba), with a shallow to rather deep, semi-circular loop below. Spiral striation present. Umbilicus open, 0.20-0.25 mm across. Aperture tilted up to 45° with regard to the coiling axis, its upper margin slightly below the level of the apex, subtriangular with rounded edges, with the continuation of the parietalis just visible along its lower side if the aperture is observed in front view, with a distinct tooth along the upper side. 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, little spreading, its outer surface and the upper surface of the outer peristome with closely placed, slightly irregular lamellae. Spire: height 1.1-1.5 mm; width 1.1-1.2 mm; index 1.0-1.3. Total width 1.8-2.0 mm. Height aperture 0.4-0.5 mm; width 0.5-0.6 mm.
Distribution. — Borneo: Kalimantan, K. Selatan, karst areas E. of the Meratus Mts.
Notes. — 1. Differs from 0. hailei as well as 0. cryptodon in having a more conical rather than a cylindrical spire (hence the name), as well as in having loops in the radial ribs on the lower surface of the tuba. These loops are most distinct about half-way the tuba.