Plectostoma sinyumensis (Maassen, 2001)  

Apex. Shape: moderately convex.

Spire. Height: 1.6–1.9 mm. Width: 1.2–1.3 mm. Number of whorls: 3–3 3/4. Apical spire shape: depressed conical. Basal spire shape: ellipsoid. Whorl periphery: distinctly convex. Umbilicus: almost completely closed by tuba.

Constriction. Parietal teeth: none. Basal teeth: none.

Tuba. Coiling direction: type 1 and aperture visible between right lateral and back view. Tuba whorl length in proportion to spire last whorl: ca. 5/8–3/4. 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: absent. Thin lines: present.

Radial ribs. Rib density: 9–10 ribs per mm. Rib intensity: thin. Shape: straight. Inclination: orthoclin.