Description
Author: Jan Delsing
Text ID: 128947
Text Type: 1
Page: 0
Created: 2023-12-30 20:19:33 - User Delsing Jan
Language: EN
Text function: [[t:1955829,textblock=128947,elang=EN;Description]]
Spire conical with about flat sides. Apex slightly oblique. Whorls 4 1/4-5 1/4; top whorls convex; last whorl obtusely angular at the periphery, flat to slightly convex above and below. Constriction with a transverse palatalis. Tuba slightly bulging and then abruptly narrowed towards the constriction, obtusely angular or with an obtuse ridge below. Radial ribs on the spire either entirely absent, or present on the top whorls only, or present on the entire spire, if present rather closely placed to moderately spaced (3-5 ribs/0.5 mm on the penultimate whorl), distinctly sinuous on the lower half of the whorls; but those close to the tuba with a single deep loop on the periphery when the shell is observed in front view; those on the tuba (moderately) spaced (2-4 ribs/0.5 mm half-way), below with a short, but deeply trough-shaped projection, abrading to a deeply looped scar. Spiral striation absent. Umbilicus open, 0.20-0.30 mm across. Aperture tilted up to 30° with regard to the coiling axis, its upper margin usually below the level of the apex, sometimes slightly above, about circular. Peristome widely distant from the spire, double; outer peristome somewhat spreading beyond the inner, but gradually narrowed towards, and absent along the right side of the aperture; inner peristome slightly protruding from the outer, widely spreading. Spire: height 1.5-2.2 mm; width 1.1-1.5 mm; index 1.2-1.6. Total width 2.2-3.1 mm. Height and width aperture 0.5-0.8 mm.
Distribution. — Borneo: Sarawak, 4th Div., G. Subis only.
Notes. — May have a distinctly higher spire than the depicted specimens.
Vermeulen, J. J., 1994. Notes on the non-marine molluscs of the island of Borneo 6. The genus Opisthostoma (Gastropoda Prosobranchia: Diplommatinidae), part 2.