Hypselostoma venustum

Hypselostoma venustum (van Benthem Jutting, 1950) Figs 186 P, 215, 216, 223 Gyliotrachela transitans venusta van Benthem Jutting, 1950: 28–29, 47, fig. 16. Gyliotrachela transitans venusta — Maassen, 2001: 76. Gyliotrachela transitans helioscopia van Benthem Jutting, 1950: 29–31, fig. 17. syn. nov. Gyliotrachela transitans heliscopia [sic] — Maassen, 2001: 76. Type material examined. Malaysia • holotype of G. transitans venusta; Raffles Museum, Singapore ex. coll.; RMNH.Moll.137140 • 8 paratypes of G. transitans helioscopia; from the type locality; Raffles Museum, Singapore ex. coll.; 1947; RMNH.Moll.137144. Additional material examined. Malaysia • 3 shells; Pahang, 20 km southeast from Jerantut, Gua Kota Gelanggi, under Gua Balai; 03°54.000'N, 102°28.412'E; 115 m a. s. l.; 21 Jan. 2013; A. Hunyadi leg.; coll. HA. Type localities. “ Gunong Pondok, Padang Rengas, Perak ”, Malaysia (H. venustum); “ Kota Tongkat, Pahang ”, Malaysia (G. transitans helioscopia). Differential diagnosis. This species is similar to H. ophis sp. nov., from which it can be separated by narrower umbilicus and shorter and wavy parietal lamella. Hypselostoma transitans has more rough shell sculpture as well as the descending last whorl and a wider umbilicus. See also under H. vesovici sp. nov. Distribution. This species is known only from three localities in Peninsular Malaysia (Gunong Pondok, Kota Tongkat and Gua Kota Gelanggi). Remarks. Van Benthem Jutting (1950) recognised two additional subspecies of G. transitans, namely G. transitans helioscopia and G. transitans venusta. However, these two taxa should not be considered as subspecies since they differ from the nominotypical subspecies in several very important characters: last whorl is in nominotypical subspecies strongly descending near the aperture while in G. transitans venusta it is slightly ascending; whorls are more depressed in nominotypical subspecies; shell surface is also different, being more sandpaper-like in nominotypical subspecies and almost smooth to very finely sculptured in other two subspecies. Finally, umbilicus is wider in G. transitans. Because of all aforementioned clear differences, we conclude that H. venusta is a good species separated from H. transitans. Gyliotrachela transitans helioscopia is its junior synonym due to the virtually identical shell morphology. Van Benthem Jutting (1950) noted that in G. transitans venusta, the shell is less elevated, peripheral keel sharper and longitudinal grooves deeper than in G. transitans helioscopia. These differences are only minor and fall within the intraspecific variability, thus there are no clear characters which allow the separation of these two taxa.