Plectostoma goniostoma (Vermeulen, 1994)  

Vermeulen (1994)'s description

"Spire conical with distinctly convex sides. Apex (distinctly) oblique. Whorls 3 5/8 - 4 convex; last whrol rounded. Constriction with a transverse palatalis. Tuba touching the spire over its entire length, gradually narrowed towards the constriction, rounded below. Radial ribs not sinuous, on the spire moderately spaced (4 ribs/0.5 mm on the penultimate whorl); those on the tuba moderately to widely spaced (2-3 ribs/0.5 mm half-way), with numerous, much finer radial riblets in between. Spiral striation absent. Umbilicus open, 0.15-0.20 mm across. Aperture tilted 30-45 degree with regard to the coiling axis, its upper margin widely to slightly below the level of the apex, subrectangular with the upper and lower edge grooved, the left and right side well rounded. Peristome double; outer peristome slightly spreading beyond the inner, but graudally narrowed towards, and absent along the right side of aperture, with a slight widening with an obtuse (not widely rounded) top along the upper edge of the aperture; inner peristome moderately protruding from the outer, often with fine riblets outside, spreading. Spire: height 1.7-1.8 mm; width 1.5-1.6 mm; index 1.1-1.2. Total width 2.5-2.7 mm. height aperture 0.9 mm; width 0.7 mm"