Vianinae Baker, 1922

Subfamily Vianinae Baker, 1922 View in CoL

Calybium Morlet, 1892 View in CoL

Calybium Morlet, 1892: 316 View in CoL , 317; 1893: 326, 327. Calybium View in CoL – Dautzenberg, 1896: 19; Wagner, 1907: 15;

Zilch, 1979: 381.

Type species. Calybium massiei Morlet, 1892 View in CoL (by monotypy).

Diagnosis. Calybium is characterized by a dex- tral, depressed conical, coarse shell, and sharply keeled body whorl. The aperture is parallelogram, the peristome discontinuous, thickened, expanded, and somewhat reflected.Apertural dentition always with six parietal lamellae, other lamellae may be present including one palatal lamella and one basal lamella.

Remarks. Apertural dentition with six lamellae on the parietal wall is always present, distinguishing the genus Calybium Morlet, 1892 from all other helicinid genera.

The genus Geotrochatella P. Fischer, 1891 , with a distribution range in Vietnam, Laos, Thailand, Cam- bodia, and South China [ Pfeiffer, 1863; Morlet, 1892; Wagner, 1907; Inkhavilay et al., 2019], is similar to the genus Calybium due to the depressed conical shell and sharply keeled body whorl, coarse dorsal surface with raised riblets or wrinkles, and the almost closed umbilicus, but differs from it by having six lamellae on the parietal wall or maybe other lamellae on the palatal and basal wall [ Wagner, 1907; this study].

The shell shape of Calybium is somewhat similar to the genus Geophorus P. Fischer, 1885 , and Aphanoconia Wagner, 1905 in general shell shape and closed umbilicus. However, Calybium differs from two genera mentioned here in having lamellae on the parietal wall (or maybe lamellae on the palatal and basal wall) [P. Fischer, 1885; Wagner, 1905, 1907].