(Fig. 11)

Type material. Holotype (H: 1.41 mm, D: 1.84 mm, Fig. 11) (HNHM 104405), Laos, Khammouane Province, Tham Nam Dôn Cave, Earthquake Dome, sand sediments at bank of cave river, 160 m a.s.l., 17°33.815′N, 104°52.298′E (locality code: JG2 B), coll. J. Grego., 11 February 2017; 2 damaged paratypes (coll. JG), same data as preceding.

Diagnosis. A large Tonkinospira species with a depressed conical shell, rounded body whorl, fine radial growth lines and without spiral striation, a wide umbilicus, and a peristome that is not adnate to penultimate whorl.

Description. Shell large for the genus; depressed conical with rounded body whorl; shell wider than tall; 4.25 whorls, regularly increasing, separated by a very deep suture; whorls shouldered; protoconch consists of 1.5 whorls, with extremely fine radial growth lines and without spiral striation (on the first whorl of protoconch some spiral striae visible, but they are not regular, probably due to erosion of the shell surface); teleoconch overall weakly sculptured, with irregular, fine radial growth lines, and relatively dense, regular, obscure spiral striation, ca. 22 in number in the middle shell line from apertural view; aperture almost in alignment with penultimate whorl and very slightly oblique to shell axis in lateral view; aperture rounded-ovate, slightly free from the preceding whorl along the parietal margin; peristome very slightly expanded, not reflected; aperture not adnate to penultimate whorl, protruding into a truncated tuba (best seen from umbilical perspective); two weak, very low suggestions of parietal barriers are discernible; umbilicus wider than narrow.

Differential diagnosis. The most similar species in terms of shell size and the weak sculpture is T. tomasini, which has a much more elevated spire, and adnate peristome and a more oblique aperture to the shell axis.

Etymology. The specific epithet suturata refers to the deep suture of the new species.