Hypselostoma transitans Mollendorff 1894

Hypselostoma transitans Möllendorff, 1894 Figs 186 O, 213, 214, 223 Hypselostoma transitans Möllendorff, 1894: 16, figs 12, 13. Hypselostoma translucidum [sic] — Fischer and Dautzenberg 1904: 408. Gyliauchen transitans — Pilsbry 1917: 214–215, pl. 36, figs 5–8. Gliotrachela transitans [sic] — Laidlaw 1933: 214. Gyliotrachela transitans transitans — van Benthem Jutting 1950: 47; van Benthem Jutting 1950: 28; Thompson and Upatham 1997: 233. Gyliotrachela transitans — Zilch 1984: 166; Hemmen and Hemmen 2001: 41; Panha and Burch 2008: 85, fig. 74; Dumrongrojwattana and Wongkamhaeng 2024: 324, fig. 8. Hypselostoma transitans — Fischer and Dautzenberg 1904: 408. Type material examined. Thailand • 1 lectotype; SMF 4589 • 8 paralectotypes; from the type locality; SMF 4590. Additional material examined. Thailand • 2 shells; Chumphon Province, 2.5 km northeast from Pathio, Tham Khao Phlu; 10°43.851'N, 99°19.242'E; 23 Feb. 2015; A. Hunyadi leg.; coll. HA • 22 fragments and 1 complete shell; Suratthani Province, Angthong islands, Wia Talap island, steep path to Buaboke cave, at the base of limestone rocks; 8°7.603'N, 98°55.466'E; 50 m a. s. l.; Sep. 2007; A. Reischütz leg.; coll. REI. Type locality. “ Samui islands, Gulf of Siam ”, Thailand. Differential diagnosis. Hypselostoma torticollis is similar due to the down-turning aperture and same arrangement of the apertural barriers but this species has a much wider umbilicus, more enlarged last whorl and is spirally striated. Hypselostoma fungus sp. nov. is spirally striated, has merged angular and parietal lamellae, more down-turning last whorl and a much wider umbilicus. See also under H. venustum. Distribution. This species in known from Chumphon and Suratthani provinces in Thailand. Remarks. In some paralectotypes, a lamella between the columellar and parietal was positioned much deeper in the aperture. We have examined a distinct form of this species from Tham Khao Phlu (Chumphon province). This form had a wider umbilicus and a sharper keel as well as more enlarged last whorl in comparison to previous ones. However, we decided not to treat it as distinct species due to the fact that we have also found a transitional form between the typical H. transitans (close to its type locality) and the one from Tham Khao Phlu.