Plectostoma anisopterum (Vermeulen, 1994)
This species was found occur sympatrically with Plectostoma wallacei busauense.
Mount Nambi, near to Sireh Caves, Serian, Sarawak, Malaysia
This species was found occur sympatrically with Plectostoma wallacei busauense.
Mount Nambi, near to Sireh Caves, Serian, Sarawak, Malaysia
The specimens from Bukit Nambi slightly differ from the type specimen by its spineless ribs which confused with another close congener, P. wallacei wallacei. But the other characteristics agreed with the original description.
The area protected as the archeological site and most part of the hill (except the Sireh Caves) restricted for any visit activity by the local peoples.
The specimens can be found from the lower part of the hill until at the enterance of the Sireh Caves, upper part of the hill.
On the limestone surface covered with mosses.
[Jaap Vermeulen]
spire conical with flat to concave sides. Apex not obliwue. Whorls 5 1/4 - 5 7/8, (moderately) convex; last whorl rounded to angular. Constriction with a parietalis, a longitudinal and a transverse palatalis. Tuba gradually narrowed towards the constriction, slightly angular below. Radial ribs on the spire moderately to widely spaced (2-4 ribs/0.5 mm on the penultimate whorl), with a deeply trough-shaped projection half-way, abrading to a shallowly deeply looped scar, (projection of those close to the tuba double-channeled with both channels about equally deep or with the lower deepest, abrading to a scar with a double deep loop when the shell is observed in front view); those on the tuba widely spaced 91-2 ribs/0.5 mm half-way the tuba), below with an almost tubular, straight to slightly curved projection abrading to a scar with a deep, semi-circular loop. Spiral striation absent or inconspicuous, more distinct on the tuba. Umbilicus open, 0.10-0.30 mm across. Aperture tilted up to 30 degrees with regard to the coiling axis, circular to elliptic. peristome double; outer peristome spreading beyond the inner, either gradually narrowed towards the right side of the sperture or not; inner peristome hardly protruding from the outer, spreading. Spire: height 2.0-2.4 mm; width 1.2-1.6 mm; index 1.5-1.8. Total width 2.7-2.8 mm. Height aperture 0.6-0.7 mm; width 0.6-0.8 mm.