Plectostoma cyrtopleuron (Vermeulen, 1994)  

Vermeulen (1994)'s description

"Spire conical with flat to concave sides. Apex slightly oblique or not. Whorls 5 1/8 - 6 3/4, convex; last whorl rounded to slightly angular at the periphery, slightly convex above and below. Constriction with or without a parietalis, with a transverse palatalis, with or without a columerallaris. Tuba free from spire rather closely placed to widely spaced (3-6 ribs/0.5 mm on the penultimate whorl), (slightly) sinuous, sometimes flattened and inconspicuous on the upper half of the whorls; those on the tuba widely spaced (2-3 ribs/0.5 mm half-way), sinuous below or not, or with a shallowly concave to deeply trough-shaped projection, abrading to a scar with a shallow to deep, semi circular loop. Spiral striation present, sometimes fine. Umbilicus open, 0.25-0.40 mm across. Aperture tilted up to 30 degree with regard to the coiling axis, its upper margin widely below the level of the apex, circular to elliptic. Peristome double, outer peristome slightly distinctly spreading beyond the inner, but gradually narrowed towards, and absent along the right side of the aperture, often slightly to distinctly widened along the upper side; inner peristome slightly to distinctly protruding from the outer, (moderately) spreading. Spire: Height 1.7-2.5 mm; width 1.2-1.6 mm; index 1.3-1.7. Total width 2.6-3.1 mm. Height and width aperture 0.6-0.8 mm."