Helicostoa E. Lamy, 1926

Helicostoa E. Lamy, 1926

Type species: Helicostoa sinensis E. Lamy, 1926 , by original designation.

Diagnosis: shell 2.68 to 11.80 mm in width, broad protoconch, 2.5 to 4 whorls, teleoconch whorls with dense fine ribs, for the sessile individuals on the middle of the last half whorl upper end and lower end of outer lip extending and merging together, enclosing an opening, seam between both ends of outer lip clearly visible.

Taxonomic remarks: Helicostoa sinensis used to be considered as the only species of the genus Helicostoa , which was assigned to the monotypic family Helicostoidae Pruvot-Fol, 1937 . However, both Wilke et al. [ 16] and our molecular phylogeny support a position of Helicostoa within Bithyniidae , and Helicostoidae must consequently be regarded as a junior synonym of Bithyniidae . Our study of operculum, radula and genital characters supports this taxonomic revision as well. There are two known species of Helicostoa . The description of Helicostoa sinensis is a redescription incorporating our new results.