Plectostoma mengaburensis Liew, Vermeulen, Marzuki & Schilthuizen, 2014
Apex. Shape: moderately convex.
Spire. Height: 1.9–2.2 mm. Width: 1.4–1.6 mm. Number of whorls: 3 7/8–4 1/2. Apical spire shape: depressed conical. Basal spire shape: ovoid. Whorl periphery: distinctly convex. Umbilicus: open or half of the umbilicus closed by tuba.
Constriction. Parietal teeth: none. Basal teeth: none.
Tuba. Coiling direction: type 1 and aperture visible from back view. Tuba whorl length in proportion to spire last whorl: ca. 5/8. Proportion of tuba that attaches to spire: whole.
Aperture and peristome. Peristome: double peristomes. Outer peristome shape: same as inner peristome and uniformly projected all around, except the posterior part.
Spiral lines. Thick lines: present. Thin lines: present.
Radial ribs. Rib density: 7 ribs per mm. Rib intensity: thin. Shape: straight. Inclination: orthoclin.
Near Threatened. This species only occurs in the Mengabur limestone cluster, which is quite large (ca. 10 km2, estimated from Google Earth), and its vegetation cover is largely undisturbed. However, quarrying activities have started at the eastern part of the cluster and the whole limestone cluster is surrounded by plantation.
Holotype: BOR 5643(1). Paratypes: BOR 5574(>25), V8822 (6)
See discussion under Plectostoma christae.
Type locality. An unnamed small limestone hill in the plantation near the large Bukit Mengabur quarry (3°43'50"N, 102°49'40"E).
Distribution range. This species only occurs in the Mengabur limestone cluster (Figure 18D).