Hypselostoma circumcarinatum Gojsina, Auffenberg & Pall-Gergely 2025, sp. nov.

Hypselostoma circumcarinatum Gojšina, Auffenberg & Páll-Gergely sp. nov. Figs 111 K, 125, 126, 154 Type material. Holotype. Thailand • 1 shell (SH: 2.3 mm; SW: 2.2 mm); Kanchanaburi Province, 4.3 km SW Kanchanaburi, Taoist Buddhist temple; 13°59'N, 99°31'E; 40 m a. s. l.; 13. May 1988, K. Auffenberg leg.; UF 345933. Paratypes. Thailand • 1 shell; same data as for holotype; CUMZ 14456 • 3 shells (2 whole and 1 with complete aperture); same data as for holotype; UF 591336. Additional material examined. Thailand • 4 shells (damaged, without last whorl, not paratypes); same data as for holotype; UF 583722. Type locality. Kanchanaburi Province, 4.3 km SW Kanchanaburi, Taoist Buddhist temple; 13°59'N, 99°31'E; 40 m a. s. l. Diagnosis. Hypselostoma species with very deep sutures and spirally striated whorls. Penultimate and the last whorl are keeled. Last whorl not detached from the penultimate. Aperture equipped with six barriers (angulo-parietal, upper palatal, lower palatal, basal, columellar and a small infraparietal). Umbilicus initially narrow, abruptly widening at the last whorl. Description. Shell conical-ovoid, consisting of 4–4.5 whorls separated by a deep suture. Protoconch pitted, showing some spiralling pattern, the same colour as the rest of the shell, consisting of ~ 1.5 whorls. Teleoconch surface sculptured with coarsely spaced radial lines crossed by much stronger and dense spiral striae. Spacing between two spiral striae approximates the width of one or two striae. First teleoconch whorl rounded. All other teleoconch whorls strongly keeled, last one the most prominent. Surface above the keel on the penultimate whorl is almost flat, (like a platform) but is much more steep (sloping) on the last whorl. Last whorl adnate to the penultimate and slightly ascending near the aperture (~ 5–10 ° compared to the shell axis). Peristome not very strong but expanded, not reflected. It is forming a weak callus on the parietal side. Aperture equipped with five main barriers (angulo-parietal, upper palatal, lower palatal, basal and columellar) and one small infraparietal lamella which is knob-like (although it can be absent as well). Angulo-parietal lamella is the strongest in the aperture, consisting of larger parietal part and indistinct angular part so that it appears slightly bilobed. Upper palatal plica short, weaker than the lower palatal and slightly bent towards it. Lower palatal plica roughly as strong as the columellar, situated halfway between upper palatal and basal plica. Basal plica small, slightly weaker than the upper palatal. Columellar lamella strong, directed towards the upper palatal plica and almost reaching the expanding peristome. Peristome is weakly swollen in front of the columellar lamella. Surface of all apertural barriers is finely granulated to almost smooth. Sinulus wide and not distinctly separated from the rest of the aperture. Umbilicus initially very narrow and then abruptly widening at the last whorl, measuring ~ 1 / 5–1 / 6 of the shell width. A weak groove is visible running alongside the umbilicus but it is getting lost near the middle part of the last whorl. Differential diagnosis. See under H. sculpturatum and H. khmerianum. Measurements (in mm, n = 4). SH = 1.93–2.46; SW = 2.09–2.24; AH = 1.02–1.16; AW = 1.05–1.18. Etymology. The two largest whorls (last and the penultimate) are keeled which gives the initial impression that the whole shell is keeled, hence the specific epithet. Distribution. This species is known only from the type locality. Remarks. Some specimens had a more depressed shell which was even slightly wider than high.