Opisthostoma otostoma Boettger, 1893: 194; lectotype ("Borneo, Brunei, Labuan") leg. Staudinger, SMF 104951 Material seen. — SABAH. Interior Zone: "Brunei": small islands around Labuan (NMW/6; SMF 104951/1 see above). "North Borneo" (UF 160195/8).
Spire conical with flat sides. Apex slightly oblique. Whorls 5 1/2-6 1/8, convex; last whorl rounded. Constriction with a longitudinal and a transverse palatalis, and an inconspicuous columellaris. Tuba somewhat abruptly narrowed towards the constriction, rounded. Radial ribs moderately spaced (3-4 ribs/0.5 mm on the penultimate whorl, 3 ribs/0.5 mm half-way the tuba), on the spire slightly sinuous, those close to the tuba not sinuous; those on the tuba not or slightly sinuous below. Spiral striation present. Umbilicus open, 0.15-0,30 mm across. Aperture hardly tilted with regard to the coiling axis, circular to elliptic. Peristome double; outer peristome spreading beyond the inner but gradually narrowed towards, and absent along the right side of the aperture, with a distinct, but small wing along the upper side which often has a somewhat concave right margin; inner peristome slightly protruding from the outer, spreading. Spire: height 2.0-2.2 mm; width 1.5-1.6 mm; index 1.3-1,4. Total width 2.4-2.7 mm. Height aperture 0.6-0.7 mm; width 0.6 mm.
Distribution. — Sabah, Interior Zone, small limestone islands around Labuan. Prob¬ably extinct due to habitat destruction: the limestone has been quarried for the con¬struction of the Labuan airfield.