Plectostoma tonkinianum (Dautzenberg & Fischer, 1905)
Apex. Shape: distinctly convex.
Spire. Height: 3.1–3.8 mm. Width: 2.4–2.6 mm. Number of whorls: 4 3/4–4 7/8. Apical spire shape: depressed conical. Basal spire shape: ovoid. Whorl periphery: distinctly convex. Umbilicus: completely closed by tuba.
Constriction. Parietal teeth: two lamellae. Basal teeth: none.
Tuba. Coiling direction: type 3 and aperture visible in left lateral 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: simple peristome.
Spiral lines. Thick lines: absent. Thin lines: present.
Radial ribs. Rib density: 6–7 ribs per mm. Rib intensity: thin. Shape: slightly curved to single-humped. Inclination: orthoclin.
Data deficient. Some recent dead shells have been collected but no information is available on the habitat and population status.
ZMA 162136(1), V 10000(>25), V 10010(>25), V 10022(>25), V 11243(>25), V 11270(>25), V 11432(3), V 11502(>50), V 7937(5), V 9940(>10), V 9957(>25).