Plectostoma tuba (Vermeulen, 1994)
Bukit Sarang, Lower Tatau River valley, Sarawak, Malaysia.
Bukit Sarang, Lower Tatau River valley, Sarawak, Malaysia.
By Vermeulen (1994)
"Spire conical with flat to slightly concave sides. Apex oblique or not. Whorls 5 - 5 3/4. convex; last whorl rounded. Constriction with a transverse palatalis, sometimes an inconspicuous columellaris. Tuba free from spire, rarely close to it again near the apex, gradually to abruptly narrowed towards the constriction, rounded below. Radial ribs on the spire moderately spaced (4 ribs/0.5 mm on the penultimate whorl), (slightly) sinuous; but those close to the tuba rather closely placed to moderately spaced (4-8 ribs/0/5 mm), not or hardly sinuous; those on the tuba closely placed to moderately spaced (6-11 ribs/0.5 mm half-way), not sinuous below. Spiral striation absent. Umbilicus open, 0.30-0.40 mm across. Aperture tilted up to 30 degree with regard to the soiling axis, its margin slightly below the level of the apex to widely above it, circular to elliptic. Peristome distant from spire, double; outer peristome only slightly spreading beyond the inner, but grdually narrowed towards, and absent along the right or lower side of the aperture; inner peristome slightly protruding from the outer, moderately spreading. Spire: height 1.4-1.7 mm; width 0.9-1.0 mm; index 1.4-1.7. Total width 1.5-1.6 mm. Height aperture 0.5-0.6 mm; width 0.5 mm."