Plectostoma dipterum (Vermeulen, 1994)  

Vermeulen (1994)'s description

"Spire conical with flat to slightly convex sides. Apex slightly oblique or not. Whorls 5 1/8 - 5 7/8, convex; last whorl rounded. Constriction with a palatalis, a longitudinal and a transverse palatalis, with or without a very inconspicuous columellaris. Tuba gradually narrowed towards the constriction, rounded below. Radial ribs moderately spaced (3-4 ribs/0.5 mm on the penultimate whorl, 3 ribs/0.5 mm half-way on the tuba), Those on the spire sinuous; those on the tuba (slightly) sinuous below. Spiral striation fine. Umbilicus open, 0.15-0.20 mm across. Aperture hardly tilted with regard to the coiling axis, circular. Peristome double; outer peristome spreading beyond the inner, but rather abruptly narrowed towards, and absent along the right side of the aperture, with a distinct, obtuse (rounded but not so wide so) wing along the upper side, and usually a similar but less conspicuous wing along the lower side; inner peristome slightly protruding from the outer spreading. Spire: height 1.7-2.1 mm; width 1.2-1.4 mm; index 1.4-1.6. Total width 2.1-2.3 mm. Height aperture 0.5-0.6 mm; width 0.5 mm"