Materia) seen. — KALIMANTAN. Kalimantan Selatan: limestone escarpments along road Benualawas-Limbungan (V 2857/>10, HOLOTYPE RMNH 56916).

Spire cylindrical. Apex not or slightly oblique. Whorls 3 1/4-3 1 /2, convex; last whorl rounded. Constriction with a transverse palatalis. Tuba touching the spire over its entire length, gradually narrowed towards the constriction, rounded below. Radial ribs not sinuous, on the spire rather densely placed (7-8 ribs/0.5 mm on the penultimate whorl); on the tuba widely spaced (3 ribs/0.5 mm half-way the tuba). Spiral striation present, fine. Umbilicus open, 0.10-0.15 mm across. Aperture tilted 15-45° with regard to the
coiling axis, its upper margin slightly to widely below the level of the apex, about circular to elliptic. Peristome double, outer peristome spreading beyond the inner, but gradually narrowed towards, and absent along the right side of the aperture; inner peristome distinctly protruding from the outer, somewhat spreading, on the right side of the aperture either spreading over the widest whorl of the spire as well as the whorl above; or touching the widest whorl only, but then only a narrow gap present between the peristome and the whorl above the widest. Spire: height 0.8-1.0 mm; width 0.8-0.9 mm; index 1.0-1.2. Total width 1.2-1.3 mm. Height aperture 0.25-0.30 mm; width 0.35-0.40 mm.
Distribution. — Borneo: Kalimantan, K. Selatan, karst area E. of the Meratus Mts.
Notes. — 1.0. ballorum has the aperture similarly attached to the spire. Both 0. ballorum and O.javanicum differ in having only low radial ribs on the last whorl and the tuba.
2. The name refers to the distinct radial ribs (from the Greek *delos meaning: distinct).