Opisthostoma depauperatum E.A. Smith, 1894: 272; syntypes {"Barit Mountain, N.W. Borneo") BMNH 93.6.7.80-84/4.
Material seen. — SARAWAK. 5th Div.: G. Budah, Medalam Valley, trib. of Limbang R. (leg. Wilford, UF 194830/6; do. 194834/>10). "Barit Mountain, N.W. Borneo" BMNH/4, see above).
Shell often redddish-brown. Spire conical with slightly convex sides, or with convex sides near the apex, slightly concave lower down. Apex slightly oblique or not. Whorls 5 3/8-6 1/4, convex; last whorl rounded. Constriction with a parietalis, a longitudinal and a transverse palatalis, a distinct columellaris. Tuba gradually narrowed towards the constriction, rounded below. Radial ribs (moderately) spaced (3-5 ribs/0.5 mm on the penultimate whorl, 3-4 ribs/0.5 mm half-way on the tuba), not or very slightly sinuous. Spiral striation absent or inconspicuous. Umbilicus open, 0.20-0.25 mm across. Aper¬ture hardly tilted with regard to the coiling axis, circular, elliptic, or slightly angular. Peristome (widely) distant from the spire, rarely only slightly distant, double; outer peristome usually somewhat spreading beyond the inner, but gradually narrowed towards, and absent along the right side of the aperture, often slightly widened along the upper side; inner peristome usually moderately protruding from the outer, rarely only slightly protruding, spreading. Spire: height 1.5-2.3 mm; width 1.2-1.5 mm; index 1.3-1.6. Total width 2.2-2.6 mm. Height and width aperture 0.5-0.6 mm. Distribution. — Borneo: Sarawak, 5th Div.: Limbang Valley.

1. Variable. Specimens may have a distinctly higher spire than the depicted one, as well as less conspicuous, more densely placed ribs.
2. 0. inornatum and 0. decrespignyi have the inner peristome only slightly protruding from the outer; 0. baritense and 0. brevituba have the peristome at most slighdy distant from the spire.