Plectostoma heteropleuron (Vermeulen, 1994)  

By Vermeulen (1994)

"Spire conical with (slightly) concave sides. Apex not oblique. Whorls 4 3/4 - 5, convex; last whorl obtusely angular at the periphery, slightly concave above, almost flat to slightly convex below. Constriction with a transverse palatalis. Tuba gradually narrowed towards the constriction, obtusely angular or with an obtuse ridge below. Radial ribs on the spire rather closely placed (5-6 ribs/0.5 mm on the penultimate whorl), distinctly sinuous, but those on the last whorl widely spaced (2 ribs/0.5 mm half-way), with a deeply trough-shaped projection on the periphery, abrading to a scar with a single deep loop when the shell is observed in front view; those on the tuba widely spaced (2-3 ribs/0.5 mm half-way), similar but with a long, slightly curved projection. Spiral striation present often rather coarse. Umbilicus open, 0.15-0.30 mm across. Aperture tilited 30-45 degrees with regard to the coiling axis, its upper margin at most about level apex, circular. Peristome distant from spire, double; outer peristome widely spreading beyond the inner, but narrowed towards, and absent along the right side of the aperture, with a distinct, obtuse (rounded but not widely so) wing with a truncated or cancave right margin along the upper side of the aperture, and with or without a similar but less distinct wing along the lower side; inner peristome (moderately) protruding from the outer, spreading. Spire: height 1.4-1.7 mm; width 1.0-1.1 mm; index 1.4-1.7. Total width 2.3-2.4 mm. height and width aperture 0.6 mm"