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The snorkel snail genus Rhiostoma Benson, 1860 is comprised of terrestrial cyclophorid snails with wide-ranging species diversity and radiation in Southeast Asia. The typical characters of the genus are a depressed shell, a detached and descending portion of the last whorl with a distinctive peristomal breathing device attached, and a calcareous cup-shaped operculum. Herein, we have revised the systematics of extant species based on shell morphology combined with COI barcoding. From these thirty recognised species, twelve are described as new to science: R. ? amarapuraensesp. nov., R. anceyisp. nov., R. breviocollarsp. nov., R. ebenozosterasp. nov., R. cheliopegmasp. nov., R. furfurosumsp. nov., R. gnomus, sp. nov., R. lannaensesp. nov., R. laoensesp. nov., R. platymorphasp. nov., R. rhothonotaphrosasp. nov., and R. tigrinasp. nov. All conchological characters are provided via illustrations of type specimens and living snails, and descriptions of the shells and radulae. Phylogenetic analysis based on partial COI gene sequences strongly supports the designated morphospecies and a monophyletic Rhiostoma, confirming that all pterocyclinid snails with a calcareous, cup-shaped operculum belong to the same clade. A high intra-specific divergence was observed in R. jalorensis and R. housei populations from locations in close proximity, suggesting a lower dispersal and higher level of isolation. The low inter-specific divergence found in R. hainesi, R. samuiense, R. asiphon, and R. rhothonotaphrosasp. nov. supports their recent diversification and local adaptation, and is congruent with their marked morphological differences. Finally, nine formerly Rhiostoma-placed species were reclassified into either the genus Cyclotus or the genus Opisthoporus.

The genus Hirsuticyclus Neubauer, Xing and Jochum, 2019 was the first record of an exceptionally preserved land snail with dense periostracal hairs from mid-Cretaceous Kachin (Burmese) amber. Here, we document four newly-discovered shells from Kachin amber, one belonging to the type species Hirsuticyclus electrum Neubauer, Xing and Jochum, 2019 and the remaining three shells belonging to a new species, Hirsuticyclus canaliculatus sp. nov. Well-preserved morphological characteristics of these two species could be clearly demonstrated under light microscopy combined with modern micro-CT scans with computer 3D reconstructions. Our new material of the type species amends the generic diagnosis based on a better-preserved shell including the peristome and operculum. The new species shows distinctive shell characteristics such as numerous spiral keels and a flaring, folded peristome interrupted by two canals. These excellently preserved fossils contribute to our understanding of the morphological diversity and evolution of these ancient members of cyclophoroids.

The type series boundary and the name-bearing type designation of each cyclophorid taxon originally described by Godwin-Austen are clarified based on an interpretation that complies with the ICZN. Previous statuses of type specimens designated by previous authors are reconsidered. Lectotypes of Spiraculum oakesi Godwin-Austen, 1915, Spiraculum kempi Godwin-Austen, 1915, Pterocyclos aborensis Godwin-Austen, 1915, Pterocyclos miriensis Godwin-Austen, 1915, Pterocyclos brahmakundensis Godwin-Austen, 1915, Spiraculum luyorensis Godwin-Austen, 1915, Spiraculum putaoensis Godwin-Austen, 1915, and Theobaldius oakesi Godwin-Austen, 1915 are here designated to stabilize the existing nomenclature. In addition, the type specimens of Pterocyclos miriensis and Theobaldius oakesi are photographed and figured for the first time.

This study presents a list of land snails and slugs found on limestone hills in the District of Bau, the state of Sarawak in Malaysian Borneo. Systematic and random sampling for land snails was conducted at eight limestone outcrops, namely, Gunung Stulang, Padang Pan, Gunung Kapor, Gunung Lobang Angin, Gunung Doya, Gunung Batu, Bukit Sekunyit and Gunung Sebayat. A total of 122 land snail species was documented with photographs of each species. Of the 122 species collected, 13 are new to science, namely,Acmella bauensissp. nov.,Japonia bauensissp. nov.,Plectostoma margaretchanaesp. nov.,Microcystina arabiisp. nov.,Microcystina atonisp. nov.,Microcystina pariparisp. nov.,Microcystina liratasp. nov.,Microcystina oswaldbrakenisp. nov.,Microcystina kilatsp. nov.,Philalanka jambusanensissp. nov.,Everettia microrhytidasp. nov.,Everettia minutasp. nov., andParalaoma sarawakensissp. nov.

This study reviews theDicharaxspecies in Thailand. Altogether tenDicharaxspecies are reported, four of which are new to science and described herein. They areDicharax borealisJirapatrasilp & Páll-Gergelysp. nov.,Dicharax burchiJirapatrasilp & Páll-Gergelysp. nov.,Dicharax panhaiJirapatrasilp & Páll-Gergelysp. nov.andDicharax pongratiJirapatrasilp & Tongkerdsp. nov.Alycaeus davisiGodwin-Austen, 1914 is regarded as a junior subjective synonym ofAlycaeus cucullatusTheobald, 1870 (=D. cucullatus) based on a similar depressed-conical shell shape, a long sutural tube and a sharp swelling behind the peristome. Furthermore, the type locality ofAlycaeus pratatensisPanha & Burch, 1997 (=D. pratatensis) had to be amended. Most important characters to distinguishDicharaxspecies are the general shell shape and relative lengths of teleoconch regions, whereas the spiral striation of R1, the shape of swelling of R3, the outer peristome crenulation and protrusion, and the exterior opercular sculpture show large intraspecific variability.

A report is given on the genus Rhiostoma (Cyclophoridae) collected in Vietnam during recent fieldwork. Locality data, Vietnam distribution and general distribution are given for each species, including references to previously published records. Five named species are listed, of which a new species is described, Rhiostoma ningbien sp. nov., from Dien Bien, North-western Vietnam.

Through the present manuscript, we are reporting for the first time the presence of Cyclophorus pfeifferi Reeve, 1861 in India. Previously, this species of land snail was reported only from South-East Asian countries Malaysia, Thailand, Cambodia and Vietnam. The specimens were collected during field sur- veys in Dampa Tiger Reserve in Mizoram state, India. The presence of C. pfeifferi in India reveals the range expansion and long-distance dispersal abilities of the species. Here we discuss the taxonomy, ecology and possible routes of dispersal of the species in India.

Here, the clarification of the “type” status for Cyclophorus (Glossostylus) koboensis Godwin-Austen, 1915 catalogued by Nantarat et al. (2014) is corrected and briefly discussed.

Dicharax cyclostoma Páll-Gergely n. sp. Fig. 19 Material examined. Holotype: Thailand, Nakhon Ratchasima Province, 3.4 km W of Ban Mu Si, limestone hill, 14°32.016’N, 101°22.783’E, 380 m a.s.l., 5 May 1987, F.G. Thompson leg., UF 346812 (D: 2.54 mm, H: 1.54 mm). Paratypes: 18 shells, same data as holotype, UF 551219. Other material: 2 juvenile shells, same data as holotype, UF 551220. Etymology. This species is named for the very round aperture (Greek cyclo-, ring and stoma, mouth, opening, noun in apposition). Diagnosis. A small, depressed Dicharax species with glossy R1, protruding inner peristome, and round aperture; R2+R3 shorter than a quarter whorl, R2 half as long as R3. Description. Shell white, some specimens with very faint brownish or yellowish colouration; shell outline rounded or very slightly oval in dorsal view, shell depressed, spire only slightly elevated, body whorl rounded; protoconch low, glossy, 1.25–1.5 whorls; R1 of 1.25–1.75 whorls, glossy without sculptural elements; boundary between R1 and R2 conspicuous due to R2 ribs; R2 with ribs curved towards aperture, ca. 24–26 ribs present; spaces between R2 ribs narrower than ribs; R2+R3 less than quarter whorl (ca. 80˚); R2 half or less length of R3; R3 glossy, smooth; boundary between R2 and R3 distinct due to change in sculpture and moderately deep constriction; middle of R3 with rounded swelling; aperture strongly oblique to shell axis, round; boundary between inner and outer peristomes not conspicuous; inner peristome somewhat protruding, rather slim, outer peristome multi-layered, thickened and expanded, particularly toward umbilicus, but not reflected; umbilicus wide, slightly more than a third of shell width. Measurements. D: 2.22–2.68 mm, H: 1.31–1.56 mm. Operculum. Unknown. Differential diagnosis. Dicharax politus (W.T. Blanford, 1865) (examined material: Phungdo, Arakan, coll. Blanford, NHMUK 1906.4.4.178, 3 probable syntypes, Fig. 20C) is larger, has a more elevated spire, and longer R3. Dicharax (?) immaculatus Páll-Gergely, 2017 from Gansu Province, China is similar with low spire and smooth R1, but with shorter R2 without elevated ribs, and its peristome much thinner than that of new species. Some populations of D. cristatus (Möllendorff, 1886) possess a smooth R1 and a low spire, but it has a longer R2, and is always larger than the new species (Páll-Gergely et al. 2017). Distribution. This new species is known only from the type locality (Fig. 5)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 26-28, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Kobelt, W. & Mollendorff, O. F. von (1900) Zur Systematik der Pneumonopomen. Nachrichtsblatt der Deutschen Malakozoolo- gischen Gesellschaft, 32, 186.","Theobald, W. (1870) Descriptions of new species of land shells from the Shan States and Pegu. Journal of the Asiatic Society of Bengal, 39, 395 - 402.","Blanford, W. T. (1865) Contribution to Indian Malacology, No. V. Descriptions of new land shells from Arakan, Pegu, and Ava; with notes on the distribution of described species. Journal of the Asiatic Society of Bengal, 34 (2), 66 - 105.","Mollendorff, O. F. von (1886) Materialen zur Fauna for China. Jahrbucher der Deutschen Malakozoologischen Gesellschaft, 13, 156 - 210."]}

Dicharax (?) gnomus Páll-Gergely n. sp. Fig. 22 Material examined. Holotype: Thailand, Phrae Province, 4 km N of Ban Nim Rin, valley with limestone ridges, 18°10.133’N, 99°56.233’E, 200 m a.s.l., 16 May 1988, F.G. Thompson leg., leaf litter at base of boulders, UF 380401 (D: 1.65 mm, H: 1.15 mm). Etymology. The specific epithet gnomus (Medieval Latin for gnome) refers to the tiny shell that has unusual shell area ratios compared to most other species (to be used as a noun in apposition). Diagnosis. Tiny Dicharax species with wide, flat R1 ribs and fine spiral striation, short R2 with flat ribs, strongly reduced R3, and circular aperture. Description. Shell light grey, slightly semi-translucent; shell outline rounded in dorsal view; spire slightly elevated, body whorl rounded; protoconch low, finely granular, glossy, 1.5 whorls; R1 of 1.25 whorls, beginning with low ribs that appear curved anteriorly, developing into wide, flattened ribs separated by grooves, forming a smoothish, glossy surface; first whorl of R1 with some fine spiral striation; boundary between R1 and R2 not conspicuous due to similar rib morphology, although ribs become denser, ca. 30 R2 ribs present; R2+R3 less than quarter whorl (ca. 70–80˚); R3 considerably shorter than R2; boundary between R2 and R3 distinct due to sculpture change and rather deep constriction; R3 strongly reduced, represented only as a slight swelling just behind peristome; aperture almost parallel with shell axis, circular, round; peristome weak, very slightly thickened; boundary between inner and outer peristomes barely discernible; inner peristome weak, somewhat protruding and very slightly expanded, outer peristome very weakly developed, only indicated; umbilicus relatively narrow, less than one third of shell width. Measurements. D: 1.65 mm, H: 1.15 mm. Operculum. Unknown. Differential diagnosis. The R3 region practically absent in this species. No other low-spired alycaeid species has this trait in Thailand or Myanmar. The Dicharax species described as Awalycaeus Kuroda, 1951 in Japan also have a strongly reduced R3, but we consider this is a case of convergent evolution. Distribution. This new species is known only from the type locality (Fig. 17). Remarks. This species has unusual conchological characters, and therefore, its generic placement is unclear. The spiral striation on R1 and the lack of spiral striation on the protoconch suggests a relationship to Chamalycaeus, whereas the glossy shell surface, the flattened R2 ribs, and the low protoconch indicate a position in Dicharax. This study revealed other Dicharax species /populations that possess some spiral striae on R1 (see under Dicharax admirandus, n. sp. and D. omissus and Páll-Gergely et al. 2017). Thus, the placement of this species in Dicharax is justified., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 29-31, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Kuroda, T. (1951) On Awalycaeus abei gen. et. sp. nov. (Cyclophoridae). Venus, 16 (5 - 8), 73 - 74."]}

Dicharax ovatus Páll-Gergely & Auffenberg n. sp. Fig. 31A Material examined. Holotype: Thailand, Surat Thani Province, Highway 401, 2.7 km W junction Highway 4142 and 401, evergreen forest on rocky hillside, 9°10’N, 99°40’E, 90 m a.s.l., 19 April 1988, K. Auffenberg leg., below cliff, base of cliff, UF 345330 (D: 1.86 mm, H: 0.99 mm). Paratypes: 5 shells, same data as holotype, UF 551223. Other Material: 3 broken shells, same data as holotype, UF 551224. Etymology. Named for the ovate (Latin derivation: ovatus) shell shape (in dorsal view). Diagnosis. A tiny Dicharax species with depressed shell, finely ribbed R1, R2+R3 less than a quarter whorl, R2 with slightly curved ribs shorter than R2. Description. Shell off-white, light yellowish; shell outline oval in dorsal view, spire depressed, nearly flat; body whorl rounded; protoconch low, rather glossy, 1.25–1.5 whorls; R1 of 1.25 whorls; R1 with fine, regular, dense ribs, gradually become more widely-spaced and elevated toward R1 termination; boundary between R1 and R2 not conspicuous but discernible due to denser R2 ribs than those of R1; R2 with low ribs that slightly curve toward aperture, ca. 24–26 R2 ribs present; R2+R3 less than quarter whorl (ca. 80˚); R2 slightly shorter than R3; R3 with low ribs of similar density to those on R1; boundary between R2 and R3 clear due to change in rib density and shallow constriction; very low swelling on R3 only indicated; aperture slightly oblique to shell axis, rounded; boundary between inner and outer peristomes distinct; inner peristome thin, slightly protruding and expanded, rather narrow, outer peristome thicker than inner peristome, strongly expanded but not reflected; umbilicus wide, sigmoid, more than a third of shell width. Measurements. D: 1.81–1.95 mm, H: 0.93–1.1 mm. Operculum. unknown. Differential diagnosis. The most similar species regarding size and the dense, fine ribbing is the nearby occurring Chamalycaeus canaliculatus (examined material: Golf von Siam: Koh-Samui, coll. Möllendorff, SMF 109468, lectotype), which has a more pronounced constriction at border of R2 and R3, and a narrower swelling on R3. Chamalycaeus armillatus (Benson, 1856) has a more elevated spire, the first 1–1.5 whorls of the teleoconch are smooth and glossy, and the last whorl of R1 has spiral striation. Dicharax parvulus (Möllendorff, 1887) (examined material: Malakka: Bukit Pondong (Perak), coll. Möllendorff, SMF 109507, lectotype, Fig. 31B) is smaller, has a comparatively larger aperture, a more thickened peristome, and a shorter R2. Distribution. This new species is known only from the type locality (Fig. 3)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 41, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Benson, W. H. (1856) Characters of seventeen new forms of the Cyclostomacea from the British provinces of Burmah, collected by W. Theobald, Jun., Esq. The Annals and Magazine of Natural History, Series 2, 17, 225 - 233. https: // doi. org / 10.1080 / 00222935608697501","Mollendorff, O. F. von (1887) The landshells of Perak. Journal of the Asiatic Society of Bengal, 55, 299 - 316."]}

Chamalycaeus serratus Páll-Gergely & Auffenberg n. sp. Fig. 12 Material examined. Holotype: Thailand, Nakhon Si Thammarat Province, Khao Luang Park, 15.2 km S junction Highways 4186 and 4188, 1.3 km S Park Headquarters, 8°44’N, 99°43’E, 200 m a.s.l., 16 Apr. 1988, K. Auffenberg leg., UF 345204 (D: 2.35 mm, H: 1.67 mm). Etymology. Named for the serrated R2 ribs (Latin derivative serratus, notched like a saw). Diagnosis. A small Chamalycaeus species with R2+R3 being longer than a quarter whorl, R3 twice as long as R2, which bears characteristically serrulate R2 ribs. Description. Shell off-white, although dead-collected; shell outline rounded/slightly oval in dorsal view; spire elevated, conical; body whorl rounded with some depression inwardly in dorso-basal region; protoconch 1.5 whorls, elevated, finely granular, without spiral striation; R1 slightly more than 1.5 whorls, first ca. 0.75 whorl dominated by fine ribs, gradually becoming stronger toward R1 termination; spiral striation as strong as radial ribs at R1 termination; boundary between R1 and R2 conspicuous because of denser R2 ribs; R2+R3 more than quarter whorl (approximately 100˚); R2 ribs lamella-like, rather low, characteristically serrate with series of tiny spikes pointing anteriorly, ca. 28 R2 ribs present; R3 ca. twice as long as R2; R3 with rather strong spiral striation and weaker ribs than R1; boundary between R2 and R3 clear due to less pronounced R3 ribs, although constriction is shallow; aperture strongly oblique to shell axis, rounded; boundary between inner and outer peristomes distinct; inner peristome protruding, narrow, and relatively thin; outer peristome expanded, especially in basal and upper palatal directions; umbilicus narrow, ca. one fourth of shell width. Measurements. D: 2.35 mm, H: 1.67 mm. Operculum. Unknown. Differential diagnosis. This new species is very similar to Chamalycaeus hirpex n. sp. in terms of R2 morphology. However, it differs from that species in the long R3, which has an elongated, blunt swelling, and a more expanded aperture. Distribution. This new species is known only from the type locality (Fig. 3).

Genus Chamalycaeus Möllendorff, 1897 Alycaeus (Chamalycaeus) Möllendorff, 1897: 93. Chamalycaeus — Páll-Gergely et al. 2017: 5–7; Páll-Gergely et al. 2020: 34. Type species. Alycaeus (Chamalycaeus) fruhstorferi Möllendorff, 1897, by monotypy. Diagnosis. Genus characterized by the combination of a spirally striated teleoconch, protoconch without spiral striae, and wide umbilicus (see Páll-Gergely et al. (2020) for extended diagnosis and taxonomic remarks)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 5, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Mollendorff, O. F. von (1897) Neue Landschnecken von Java. Nachrichtsblatt der Deutschen Malakozoologischen Gesellschaft, 29, 89 - 97.","Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583"]}

Chamalycaeus krabiensis Páll-Gergely & A. Reischütz n. sp. Fig. 11 Material examined. Holotype: Thailand, Krabi Province, Phi-Phi Islands, Phi Phi Don Island, climbing rock at W end of beach in Ton Sai Bay, 7°44.011’N, 98°45.936’E, ca. 70 m a.s.l. (locality code: Th22), Mar. 2010, A. Reischütz leg., at base of limestone rocks in the forest, NHMW 113487 (D: 3.61 mm, H: 2.62 mm). Paratypes: 1 shell, same data as holotype; 1 shell, Thailand, Krabi Province, Phi-Phi Islands, Phi Phi Don Island, ascent to climbing rock at W end of beach in Ton Sai Bay, 7°44.049’N, 98°45.966’E, ca. 20 m a.s.l. (locality code: Th 21), Mar. 2010, A. Reischütz leg., at base of limestone rocks in forest, NHMW 113488 (photographed paratype: Fig. 11B, D: 3.73 mm, H: 2.37 mm); 9 shells, same data as preceding, RE; 2 shells, same data as preceding, CUMZ 5269; 7 shells, Thailand, Krabi Province, Phi-Phi Islands, Phi Phi Don Island, limestone rocks at Monkey Beach, 7°43.386’N, 98°46.135’E, ca. 10 m a.s.l. (locality code: Th 23), Mar. 2010, A. Reischütz leg., RE. Other material: 4 juvenile / broken shells, Thailand, Krabi Province, Phi-Phi Islands, Phi Phi Don Island, ascent to climbing rock at W end of beach in Ton Sai Bay, 7°44.049’N, 98°45.966’E, ca. 20 m a.s.l. (locality code: Th 21), Mar. 2010, A. Reischütz leg., at base of limestone rocks in forest, RE; 5 juvenile /broken shells, Thailand, Krabi Province, Phi-Phi Islands, Phi Phi Don Island, limestone rocks at Monkey Beach, 7°43.386’N, 98°46.135’E, ca. 10 m a.s.l. (locality code: Th 23), Mar. 2010, A. Reischütz leg., RE; 7 shells, 1.5 km SE of Ao Luek Tai, 8°22.386’N, 98°44.130’E, 40–45 m a.s.l., 16–19 Mar. 2020, S. Aiken leg., SA; 4 shells (one photographed here: Fig. 11C), 1.7 km SE of Ao Luek Tai, 8°22.020’N, 98°44.004’E, 25 m a.s.l., 19 Mar. 2020, S. Aiken leg., in dry debris on rock, at base of limestone cliff, SA. Etymology. This new species is named for the Thai province in which it occurs. Diagnosis. A medium-sized Chamalycaeus species with R2 and R3 of almost a quarter whorl each, blunt, elongated swelling on R3, protruding inner peristome, and strongly expanded outer peristome. Description. Shell off-white to light grey; shell outline slightly oval in dorsal view; spire elevated, conical; body whorl rounded or parabolic; protoconch somewhat elevated, finely granular, rather glossy, spiral striae lacking, 1.5 whorls; R1 of 1.75–2.5 whorls, with strong, narrow, elevated, regularly arranged ribs, spaces between ribs relatively wide, fine spiral striation between ribs; boundary between R1 and R2 distinct due to change in rib density; R2 ribs more elevated than those of R1, narrow, lamella-like; ca. 26–28 ribs present; R2 and R3 of comparable lengths, covering approximately a half whorl or slightly less; boundary between R2 and R3 distinct due to rather deep constriction and change in sculpture; R3 with elongated, convex, central swelling, posterior portion almost smooth, anterior bears ribs of similar density as on R1; aperture strongly oblique to shell axis, rounded, with a very small upper (parieto-palatal) incision; boundary between inner and outer peristomes conspicuous, inner peristome strongly protruding (extreme in some specimens) and slightly expanded; outer peristome slim, strongly expanded except in umbilical region; umbilicus narrow, ca. one fourth of shell width. Measurements. D: 3.41–3.81 mm, H: 2.34–2.62 mm (type samples). Operculum. Unknown. Differential diagnosis. Chamalycaeus reinhardti (Mörch, 1872) (examined material: Great Nicobar, coll. Godwin-Austen, NHMUK 1903.7.1.2711, 1 shell) and Chamalycaeus reinhardti sabangensis (Rensch, 1933) (examined material: Sumatra: Wald b. Sabang, Pulu Weh., exp. Rensch, 1927, SMF 6241, 1 paratype) both have a narrower swelling on R3 and a more elevated spire. Distribution. This species is known from the Phi-Phi Islands and the vicinity of Ao Luek Tai town, Krabi Province, Thailand (Fig. 3). Remarks. The shells from the two sites near Ao Luek Tai are slightly smaller (D: 2.8–3.3 mm), more depressed and conical from above, have overall denser ribs, lower R3 swelling, and the outer peristome is expanded in a smaller portion of the lip. However, although these differences occur, we consider them conspecific with those from Phi-Phi Islands due to the overall similar sculpture and proportions of shell regions., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 17, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Morch, O. A. L. (1872) Synopsis molluscorum a cl. J. Reinhardt letorum in circumnavigatione orbis terrarum Danicae navis Galatheae dictae. Oversigt over de af Prof. J. Reinhardt paa Corvetten Galatheas Reise omkring Jorden indsamlede Bloddyr. Videnskabelige meddelelser fra den Naturhistoriske forening i Kjobenhavn, 1872, 9 - 35.","Rensch, B. (1933) Die Molluskenfauna von Pulu Weh und ihre zoogeographischen Beziehungen. Zoologischer Anzeiger Leipzig, 102, 195 - 208."]}

Dicharax ebrius Páll-Gergely & Auffenberg n. sp. Fig. 21 Material examined. Holotype: Thailand, Mae Hong Son Province, 42 km NW of Pai, Road 1095, 19°32’N, 98°32’E, 750 m a.s.l., 20 Mar. 1988, K. Auffenberg leg., UF 345577 (D: 2.89 mm, H: 1.97 mm). Paratypes: 22 shells, same data as holotype, UF 551221. Other material: 9 juvenile shells, same data as holotype, UF 551222. Etymology. The dorsal view of the shell of this new species looks like a face of a drunken (ebrius in Latin) man due to glossy R3 swelling. Diagnosis. A small Dicharax species with a finely ribbed R1, glossy swelling on R3 situated far from peristome, thickened outer peristome and slightly fringed inner peristome. Description. Shell off-white to yellowish corneous, slightly translucent; shell outline slightly oval in dorsal view; spire slightly elevated, low conical, body whorl rounded; protoconch low, glossy, 1.25–1.5 whorls; R1 of 1.75–2 whorls, finely, regularly ribbed from beginning, ribs gradually become more widely-spaced toward R1 termination; boundary between R1 and R2 conspicuous due to dense R2 ribs; R2 ribs curved toward aperture, ca. 44–46 ribs present; R2 ribs almost adnate; R2+R3 slightly more than quarter whorl (ca. 100˚); R2 approximately as long as R3 or slightly shorter; boundary between R2 and R3 distinct due to change in sculpture and deep constriction; R3 with prominent, but rounded, glossy swelling situated close to constriction; between swelling and peristome with few fine ribs, in some specimens this area slightly swollen, seemingly forming secondary swelling; aperture strongly oblique to shell axis, rounded with basal incision; boundary between inner and outer peristomes indistinct; inner peristome strong, protruding, expanded, basal and palatal portions slightly fringed, outer peristome expanded, and reflected toward umbilicus; peristome edges merge to form a multi-layered, thickened apertural lip; umbilicus narrow, approximately one fourth of shell width. Measurements. D: 2.65–2.89 mm, H: 1.85–1.97 mm. Operculum. Outer surface concave, yellowish corneous, with some traces of a deciduous lamina; inner surface with a small, pointed, low central nipple. Differential diagnosis. The small shell size, blunt, but prominent, glossy swelling on R3 makes this new species easy to recognize. Dicharax notus (Godwin-Austen, 1914) is similar in overall shell shape, but has blunter, less glossy R3 swelling situated closer to peristome and a rounded aperture. Due to the weak traces of lower, secondary R3 swelling and overall shell shape, this new species is similar to D. birugosus (Godwin-Austen, 1893) (syn. Alycaeus canaliculus Godwin-Austen, 1914, see Páll-Gergely et al. 2020) from the Khasi Hills, India. However, the Indian species has shorter R2 and R3, the R2 ribs are more widely-spaced, and prominent secondary swelling. Distribution. This new species is known only from the type locality (Fig. 17)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 28-29, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583"]}

Chamalycaeus erawan Páll-Gergely & Hunyadi n. sp. Fig. 4 Material examined. Holotype: Thailand, Kanchanaburi Province, Erawan National Park, Erawan Falls Trail, 14°22.310’N, 99°8.699’E, 90 m a.s.l. (locality code: 2015/28), 17 Feb. 2015, A. Hunyadi leg., HNHM 104869 (D: 2.45 mm, H: 1.53 mm). Paratypes: 4 shells, same data as for holotype, HA; 1 shell, Thailand, 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., litter sample, UF 345935. Etymology. The specific epithet refers to the type locality (Erawan National Park). Diagnosis. A small Chamalycaeus species with bluntly angled body whorl, short R2, rounded aperture, and strongly expanded outer peristome. Description. Shell off-white to light grey, rather glossy, very slightly translucent; shell outline slightly oval in dorsal view; spire slightly elevated, conical-domed; body whorl rather bluntly angled, depressed inward basolaterally in apertural view; protoconch rather low, glossy, spiral striae lacking, 1.25–1.5 whorls; R1 of 1.5–1.75 whorls, with irregular, narrow, but rather low ribs and some weak spiral striation; boundary between R1 and R2 not distinct, but visible due to change in rib density; R2+R3 approximately a quarter whorl; R2 short, about one third of R3 length, only ca. 14–16 ribs; R2 ribs low, dorsally rounded; boundary between R2 and R3 distinct due to moderately deep constriction and almost smooth early R3; R3 with elongated, almost smooth (only a few low riblets/growth lines) central swelling; aperture oblique to shell axis, round; distance between inner and outer peristomes conspicuous, inner peristome protruding, thin, but robust, and slightly expanded; outer peristome strongly expanded, but not reflected, reduced in umbilical area; umbilicus narrow, less than one third shell width. Measurements. D: 2.25–2.45 mm, H: 1.49–1.56 mm. Operculum. Unknown. Differential diagnosis. This new species differs from Chamalycaeus irmatallus n. sp. in the larger size, longer R3, and more expanded peristome. Distribution. This species is known only from two nearby localities (Fig. 5)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 8-9, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958

Dicharax stuparum Páll-Gergely & Hunyadi, 2018 Fig. 32 Dicharax stuparum Páll-Gergely & Hunyadi, 2018: 62, figs 1F–K. New material examined. 7 shells, Thailand, Chiang Rai Province, Doi Thung; 20°20.533’N, 99°50.350’E, 1320 m a.s.l., 08 May 1988, F.G. Thompson leg., UF 347150. Type locality. Thailand, Chiang Rai Province, Doi Tung, 50 m before Wat Phra That Doi Tung, around the car park, 20°19.540’N, 99°49.987’E, 1350 m a.s.l. Operculum. The operculum was not described in the original description, but a live-collected specimen from the Florida Museum allows description. The operculum is extremely thin, translucent, concave; outer surface glossy, without any notable structures, inner surface with a low but pointed, central nipple. Remarks. The newly examined specimens were collected very near the type locality of D. stuparum (Fig. 17).

Dicharax (?) admirandus Páll-Gergely & Auffenberg n. sp. Figs 14–15 Material examined. Holotype: Thailand, Loei Province, 9.2 km NW Loei, Buddhist temple, up and N of main cave entrance, 17°35’N, 101°44’E, 250 m a.s.l., 28 Apr. 1988, K. Auffenberg leg., base of cliff under Georissa zone, UF 345861 (D: 2.9 mm, H: 1.9 mm). Paratype: 1 shell, same data as holotype, UF 551218. Etymology. The specific epithet admirandus (Latin for astonishing, remarkable, extraordinary) refers to several notable shell characters of this new species, namely the strong keel, strongly fringed aperture, and the spiral striation. Diagnosis. A medium-sized Dicharax species with strong peripheral keel, strongly ribbed and spirally striated R1, and strongly fringed aperture. Description. Shell off-white, although both available shells were somewhat eroded; shell outline slightly oval in dorsal view; spire slightly elevated, low conical, body whorl with conspicuous peripheral keel; protoconch somewhat elevated, finely granular, spiral striation lacking, 1.75 whorls; R1 of 1.5 whorls, first half whorl practically smooth, gradually changing to widely, regularly-spaced, strong ribs (ca. 30 ribs on last half whorl of R1), present on entire R1 except area between peripheral keel and outer edge of periumbilical keel, which has fine spiral striation; some spiral striation visible on dorsum of R1, and between ribs; boundary between R1 and R2 distinct due to dense R2 ribs; R2 ribs curved toward aperture, ca. 34–36 R2 ribs present; spaces between R2 ribs narrower than ribs; R2+R3 more than quarter whorl (ca. 110˚); R2 considerably shorter than R3, slightly more half its length; boundary between R2 and R3 distinct due to change in sculpture and deep constriction; R3 with rounded, elongated swelling situated closer to constriction than to peristome; aperture strongly oblique to shell axis, rounded with basal incision; boundary between inner and outer peristomes not conspicuous; inner peristome strong, somewhat protruding, expanded, basal and palatal portions strongly fringed, outer peristome weaker, expanded, but reflected only in direction of umbilicus; umbilicus funnel-shaped, relatively narrow, less than one third of shell width. Measurements. D: 2.9–3 mm, H: 1.9 mm Operculum. Unknown. Differential diagnosis. The angled body whorl, the funnel-shaped umbilicus, the flattened dorsal side, and the strongly convex R3 swelling distinguish this new species from the most similar D. fimbriatus (Bavay & Dautzenberg, 1912), which is known from Laos and Vietnam (Páll-Gergely et al. 2017). The R1 ribs of this species are stronger than those of most D. fimbriatus populations, and the new species has a spirally striated R1. Dicharax sylheticus (Godwin-Austen, 1914) (Examined material: S. Sylhet Hills, W. Channel leg., NHMUK 1903.7.1.55, holotype, Fig. 16) is similar, but has a more elevated spire, a less keeled body whorl, a longer R2 with less dense ribs, and a rounded aperture. Distribution. This new species is known only from the type locality (Fig. 17). Remarks. Similarly to some populations of D. omissus (Godwin-Austen, 1914), this species also possesses spiral striation on R1, which is very rare in Dicharax. Spiral striation on the teleoconch is characteristic for Chamalycaeus, but this species is classified in Dicharax due to the curved R2 ribs characterizing that genus and its overall shell shape. Possible homology of the spiral striation of these few Dicharax species and other alycaeid genera needs further investigation., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 21-23, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Bavay, A. & Dautzenberg, P. (1912) Description de coquilles nouvelles de l'Indo-Chine. Journal de Conchyliologie, 60, 1 - 54."]}

Dicharax verrucosus Páll-Gergely & Hunyadi n. sp. Fig. 34 Material examined. Holotype: Myanmar, Shan State, Taunggyi, hill above Aye Say Tee Pagoda, Dragon Cave, 20°47.489’N, 97°03.036’E, 1380 m a.s.l. (locality code: 2018/44), 08 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HNHM 104862 (holotype: D: 2.83 mm, H: 2.14 mm). Paratypes: 10 shells, same data as holotype, HA. Other material: 2 shells, Myanmar, Shan State, Hsihseng centre E ca. 6 km, right side of rd. + 400 m on unpaved rd., limestone hill, 20°7.983’N, 97°18.145’E, 1010 m a.s.l. (locality code: 2018/40), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA. Etymology. The specific epithet verrucosus (Latin for excrescence/wart) refers to the small swelling on R3, reminiscent of a wart. Diagnosis. A Dicharax species with a relatively high spire, glossy, smooth R1, R2+R3 about a quarter whorl (R3 shorter than R2), and blunt swelling on R3. Description. Shell light grey, possibly translucent when fresh; shell outline rounded in dorsal view, spire elevated, body whorl rounded; protoconch low, rather glossy, 1.5 whorls; R1 approximately 2.25 whorls, smooth, glossy, with occasional, weak growth lines; boundary between R1 and R2 conspicuous due to dense R2 ribs; R2 ribs curved toward aperture, ca. 36–38 R2 ribs present; R2 ribs situated close to each other, spaces between ribs much less than rib width; R2+R3 covers ca. quarter whorl; R3 very short; about half as long as R2; sculpture of R3 similar to R1, boundary between R2 and R3 distinct, indicated by deep constriction; middle of R3 with prominent, blunt swelling; aperture slightly oblique to shell axis; rounded, with slight upper incision in parieto-palatal region; boundary between inner and outer peristomes distinct, especially at columellar portion; inner peristome slim, slightly protruding, outer peristome strongly thickened, expanded and reflected, especially toward umbilicus (in sample 2018/40 more conspicuously than in 2018/44); umbilicus relatively narrow, less than a third of shell width. Measurements. D: 2.76–3.24 mm, H: 2.1–2.46 mm (2018/44); D: 3.21–3.55 mm, H: 2.46–2.5 mm (2018/40). Operculum. Unknown. Differential diagnosis. The combination of the elevated spire, smooth R2, short R3 with a prominent swelling distinguishes this species from all congeners. Distribution. Both known populations occur in the southeastern part of Shan States, Myanmar. The straightline distance between the two is ca. 77 km (Fig. 17). Remarks. The typical shells from Taunggyi are slightly smaller, and have less reflected peristomes than specimens from Hsihseng. However, since all other shell characters (shape, ratios of the shell regions, and shell sculpture) are identical, we treat them as the same species. Genus Metalycaeus Pilsbry, 1900 Alycaeus (Metalycaeus) Pilsbry, 1900: 382. Type species. Alycaeus (Metalycaeus) melanopoma Pilsbry, 1900 (synonym of Alycaeus nipponensis Reinhardt, 1877, see Minato 1988), by subsequent designation (Thiele 1929). Diagnosis. Metalycaeus is characterized by the presence of spiral striation on both the protoconch and teleoconch (Páll-Gergely et al. 2017, 2020). However, some shells of one Japanese species lacks spiral striation on the protoconch. Here we report a species (M. pygmachos n. sp.) lacking spiral striation on the entire shell, but based on other characters, is best assigned to this genus. Thus, examination of shell characters other than the spirally striated protoconch is also necessary., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 44-45, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Pilsbry, H. A. (1900) Notices of new Japanese land shells. Proceedings of the Academy of Natural Sciences of Philadelphia, 52, 381 - 384.","Reinhardt, O. (1877) [Herr Reinhardt legte eine Anzahl japanischer ...]. In: Peters, W. (1877) Sitzungs-Bericht der Gesellschaft naturforschender Freunde zu Berlin vom 20. Marz 1877. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin, 1877, pp. 67 - 70","Minato, H. (1988) A systematic and bibliographic list of the Japanese land snails. H. Minato, Shirahama, X + 294 pp., pls. 1 - 7.","Thiele, J. (1929) Handbuch der systematischen Weichtierkunde. Teil 1. Verlag von Gustav Fischer, Jena, 376 pp."]}

Nineteen new species of the alycaeid genera Chamalycaeus, Dicharax, and Metalycaeus are described from Thailand and Myanmar: Chamalycaeus buaboke Páll-Gergely & A. Reischütz, n. sp., C. erawan Páll-Gergely & Hunyadi, n. sp., C. hirpex Páll-Gergely & A. Reischütz, n. sp., C. irmatallus Páll-Gergely, n. sp., C. krabiensis Páll-Gergely & A. Reischütz, n. sp., C. serratus Páll-Gergely & Auffenberg, n. sp., C. spiratus Páll-Gergely, n. sp., Dicharax (?) admirandus Páll-Gergely & Auffenberg, n. sp., D. cyclostoma Páll-Gergely, n. sp., D. ebrius Páll-Gergely & Auffenberg, n. sp., D. (?) gnomus Páll-Gergely, n. sp., D. mirounga Páll-Gergely, n. sp., D. ovatus Páll-Gergely & Auffenberg, n. sp., D. subroseus Páll-Gergely, n. sp., D. verrucosus Páll-Gergely & Hunyadi, n. sp., Metalycaeus anas Páll-Gergely & A. Reischütz, n. sp., M. aries Páll-Gergely & Auffenberg, n. sp., M. bicarinatus Páll-Gergely & Hunyadi, n. sp., M. pygmachos Páll-Gergely & Hunyadi, n. sp. Alycaeus kengtungensis Godwin-Austen, 1914 is moved to the synonymy of Metalycaeus heudei (Bavay & Dautzenberg, 1900). We also report exact localities of Dicharax ataranensis (Godwin-Austen, 1914), Dicharax notus (Godwin-Austen, 1914), and Dicharax omissus (Godwin-Austen, 1914). The new records extend the known distribution of Chamalycaeus and Metalycaeus in Thailand.

Dicharax notus (Godwin-Austen, 1914) Figs 24–27 Alycaeus notus Godwin-Austen, 1914: 411, plate 155, fig. 12. Alycaeus (Dicharax) notus — Gude 1921: 262. Material examined. Lectotype (hereby designated): Myanmar, Shan State, “ Fort Stedman, Burma, coll. Woodthorpe ”, NHMUK 1903.7.1.3065.1. Paralectotypes: 14 shells, same data as for lectotype, NHMUK 1903.7.1.3065. Other Material: 1 shell (Fig. 25B), Myanmar, Mandalay State, Anesakhan, Dat Taw Gyaint Waterfall, 21°58.760’N, 96°23.116’E, 610 m a.s.l. (locality code: 2018/65), 18 Oct. 2018, A. Hunyadi leg., HNHM 104863 (D: 3.08 mm, H: 1.76 mm); 5 shells + 4 juvenile shells, same data as preceding, HA — Shan State; 15 shells + 6 strongly eroded shells, Myanmar, Mandalay State, Hopong, Sam Phu, Cave Ae-5 at ridge above village Ho Hwe, 20°41.103’N, 97°16.198’E (locality code: JG3), 02 Feb. 2019, J. Grego leg., JG; 21 shells + 1 juvenile shell, Myanmar, Mandalay State, Hsihseng centre E ca. 4.5 km, left side of rd. + 1.7 km on unpaved rd., limestone rocks, 20°9.359’N, 97°17.883’E, 1140 m a.s.l. (locality code: 2018/39), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA; 1 shell (photographed), Myanmar, Mandalay State, Hsihseng centre E ca. 6 km, right side of rd. + 400 m on unpaved rd., limestone hill, 20°7.983’N, 97°18.145’E, 1010 m a.s.l. (locality code: 2018/40), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HNHM 104864; 6 shells, same data as preceding, HA; 14 shells, Myanmar, Mandalay State, Hsihseng centre E ca. 6 km, right side of rd. + 500 m on unpaved rd., limestone hill, 20°8.002’N, 97°18.024’E, 1000 m a.s.l. (locality code: 2018/41), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA; 1 shell + 1 juvenile shell, Taunggyi, hill over Aye Say Tee Pagoda, Dragon Cave, 20°47.489’N, 97°3.036’E, 1380 m a.s.l. (locality code: 2018/44), 08 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA; 1 shell, Myanmar, Kayah State, Demoso, Demoso spring lake (locality code: JG109), 16 May 2019, J. Grego leg., JG; 8 shells + 3 broken/eroded shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Bo Pha Gu Cave sink, 19°21.121’N, 97°3.759’E (locality code: JG10), 10 Feb. 2019, J. Grego leg. JG; 33 shells + 13 juvenile shells, Myanmar, Kayah State, Demoso Distr., Han Li village, Lokalay Loku Gu Cave (Myaug a San Cave), 19°23.468’N, 97°01.372’E (locality code: JG11), 11 Feb. 2019, J. Grego leg., JG; 1 shell, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li village, under bridge over Phruno River, 19°22.966’N, 97°02.153’E (locality code: JG100), 12 Dec. 2019, J. Grego leg., HNHM 104865; 7 shells + 6 juvenile /broken shells, same data as preceding, JG; 26 shells + 4 juvenile /broken shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li Village, rocks above bridge over Phruno River, 19°23.011’N, 97°02.108’E (locality code: JG101), 12 Dec. 2019, J. Grego leg., JG; 50 shells + 17 juvenile /broken shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Entrance of Phruno River Cave, 19°22.744’N, 97°02.570’E (locality code: JG102), 12 Dec. 2019, J. Grego leg., JG; 7 shells, Thailand, Chiang Rai Province, Doi Tung, 50 m before Wat Phra That Doi Tung, around the car park, 20°19.540’N, 99°49.987’E, 1350 m a.s.l. (locality code: 2015/17), 12 Feb. 2015, A. Hunyadi leg., HA; 1 shell, Thailand, Chiang Rai Province, Doi Tung, 20°20.533’N, 99°50.350’E, 1320 m a.s.l., 08 May 1987, F.G. Thompson leg., UF 347139. Diagnosis. A variable Dicharax species with glossy shell, regularly ribbed R1, widely-spaced R2 ribs, blunt to somewhat narrow central swelling on R3, and strongly reflected outer peristome. Description. Shell yellowish, corneous, occasionally with some reddish/pinkish colouration on initial whorls, sometimes semi-translucent; shell outline rounded in dorsal view, spire rather low, only slightly elevated, but somewhat variable, body whorl rounded; protoconch low, glossy, 1.25–1.5 whorls; R1 approximately 1.75 whorls, sculpture variable, first 1–1.25 whorl with weak growth lines or finely ribbed, gradually becoming widely-spaced, rather prominent ribs; boundary between R1 and R2 not conspicuous but discernible because R2 ribs denser than R1; R2 ribs curved toward aperture, ca. 20–22 R2 ribs present; R2 ribs relatively widely spaced or densely arranged; R2+R3 ca. quarter whorl or more (90–110˚); R2 and R3 of comparable lengths, or R2 slightly shorter; R3 beginning smooth, glossy, anterior portion (between swelling and peristome) smooth or with few ribs similar to end of R1; boundary between R2 and R3 conspicuous due to sculptural change and rather deep constriction; middle of R3 with prominent, variably shaped swelling, high convex or low rounded; aperture strongly oblique to shell axis, rounded; boundary between inner and outer peristomes barely discernible, inner peristome not protruding; outer peristome strongly thickened and reflected in all directions, even to parietal shell wall; umbilicus relatively wide, slightly less than a third of shell width. A cross-sectional view of R2 was examined in one specimen (Fig. 27): anterior crust forms significantly elevated, sometimes hollow rib, with anterior and posterior projections of comparable sizes resulting in a T-shaped cross-section; anterior crust folds over much weaker posterior crust; posterior crust thick; cross-sectional view of microtunnel is nearly round; Measurements. D: 2.98–4.61 mm, H: 1.62–2.56 mm. Operculum. The outer surface of the opercula of two live-collected specimens could be examined: it has a closely-coiled lamina, similar to that of Dicharax species known from Vietnam (Páll-Gergely et al. 2017), although the lamina is seemingly deciduous since only remnants were visible. Differential diagnosis. Dicharax (?) bifrons (Theobald, 1870) (examined material: Shan States, NHMUK 1888.12.4.956–958, 3 syntypes, Fig. 20A) is rather dome-shaped, possesses two swellings on R3, and its outer peristome is not much reflected. Dicharax (?) woodthorpei (Godwin-Austen, 1914) (examined material: Fort Stedman, Burma, coll. Woodthorpe, NHMUK 1903.7.1.3064, 22 syntypes in two vials, Fig. 20B) is also somewhat similar to this species in terms of general shell and aperture shape, but it has a higher spire, a less convex swelling on R2, and R2 bears no elevated ribs, but has light and dark alternating colour stripes. Dicharax politus (W.T. Blanford, 1865) (examined material: Phungdo, Arakan, coll. Blanford, NHMUK 1906.4.4.178, 3 probable syntypes, Fig. 20C) is similar to this species in terms of general shell shape and sculpture, but differs in having a less thickened peristome, less expanded outer peristome, denser R2 ribbing, and glossier R1. See also under Dicharax omissus. Distribution. Dicharax notus is known from the Mandalay, Shan, and Kayah states of Myanmar, and from Chiang Rai Province, Thailand (Fig. 28). Remarks. This is a variable species in terms of shell size, R1 sculpture, density of R2 ribs, and the narrow width of the R3 swelling. See Table 2. The Japanese Metalycaeus vinctus (Pilsbry, 1902) and M. minatoi Páll-Gergely, 2017 are probably sister species to each other with ribbed and smooth R2s, respectively (Páll-Gergely & Asami 2017). Dicharax notus and D. woodthorpei may present a similar situation, because they are very similar in shell shape and have geographically adjacent distributions, differing mostly in the fine morphology of the R2 ribs, indicating that the character may be the subject of rapid evolutionary changes., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 32-37, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Gude, G. K. (1921) The Fauna of British India including Ceylon and Burma. Mollusca. III. Land operculates (Cyclophoridae, Truncatellidae, Assimineidae, Helicinidae). Taylor and Francis, London, 386 pp. https: // doi. org / 10.5962 / bhl. title. 12890","Theobald, W. (1870) Descriptions of new species of land shells from the Shan States and Pegu. Journal of the Asiatic Society of Bengal, 39, 395 - 402.","Blanford, W. T. (1865) Contribution to Indian Malacology, No. V. Descriptions of new land shells from Arakan, Pegu, and Ava; with notes on the distribution of described species. Journal of the Asiatic Society of Bengal, 34 (2), 66 - 105.","Pilsbry, H. A. (1902) New land molluscs from the Japanese Empire. The Nautilus, 16: 53 - 57.","Pall-Gergely, B. & Asami, T. (2017) A new species of Metalycaeus hitherto undistinguished from M. vinctus (Pilsbry, 1902). Venus, 75 (1 - 4), 1 - 16."]}

Metalycaeus aries Páll-Gergely & Auffenberg, n. sp. Figs 38, 39A, 40A–D Material examined. Holotype: Thailand, Loei Province, limestone knoll 1 km E Ban Huai Muang, top of knoll, 17°28.433’N, 101°53.333’E, 375 m a.s.l., 21 May 1987, F.G. Thompson leg., in leaf litter, UF 343786 (D: 2.48 mm, H: 1.49 mm). Paratypes: 12 shells, same data as holotype, UF 551225. Other material: 1 shell (Fig. 38B, D: 2.2 mm, H: 1.61 mm) + 5 shells + 4 juvenile shells, Thailand, Nakhon Sawan Province, limestone hill 4.0 km NW of Man Non San, 15°56.517’N, 99°52.400’E, 100 m a.s.l., 12 Jun. 1987, F.G. Thompson leg., UF 279699; 1 shell (Fig. 38C, D: 2.04 mm, H: 1.25 mm) + 3 shells, Thailand, Phetchabun Province, 24.4 km S Phetchabun on Highway 2275 evergreen forest in back of outcrop, base of cliff, 16°16’N, 101°10’E, 120 m a.s.l., 02 May 1988, K. Auffenberg leg., UF 346105. Etymology. The shape of the shell of this new species is reminiscent of a coiled ram’s horn (aries in Latin). The specific epithet is used as a noun in apposition. Diagnosis. A tiny Metalycaeus species with strongly ribbed R1, short combined R2+R3, dense, curved R2 ribs, and an angled R2 visible from dorsal side. Description of the type series. Shell off-white, light grey, although all available shells dead collected; shell outline slightly oval in dorsal view, R2 conspicuously swollen/angled; spire somewhat elevated, low conical; body whorl rounded with distinct lower, keel caused by angled ribs; protoconch of 1.5 whorls, elevated, first ca. 0.75 whorl finely granular and glossy, the last 0.75 whorl spirally striated; R1 of 1.5–1.75 whorls, with strong, equidistant, narrow ribs and fine, dense spiral striae between ribs; boundary between R1 and R2 distinct due to densely-placed R2 ribs; R2+R3 less than a quarter whorl (ca. 70˚); R2 swollen, forming blunt angle in dorsal view, and rounded in apertural view; R2 ribs curved toward aperture, nearly adnate, ca. 24–26 R2 ribs present; R2 and R3 of comparable length; R3 with spiral striation and weaker ribs than R1; boundary between R2 and R3 distinct due to lower R3 ribs and descending portion of R2 angle; aperture slightly oblique to shell axis, round; boundary between inner and outer peristomes distinct; inner peristome protruding and expanded, relatively thin; outer peristome thicker, wider, expanded, and very slightly reflected toward umbilicus; umbilicus moderately narrow, approximately one third of shell width. Measurements. 2.04–2.54 mm, H: 1.3–1.61 mm. Operculum. An operculum was present in one specimen (UF 279699). Outer surface multispiral without elevated lamina, originally covered with mud (a portion left on operculum for photography; Fig. 38B), inner surface with very small, low, central nipple. Differential diagnosis. The only similar species is M. bicarinatus n. sp., which has two distinct keels in R2, has slimmer, more elevated, and more widely-spaced ribs, and the protoconch lacks obvious spiral striae. Distribution. Three populations are known from the Thai provinces of Loei, Nakhon Sawan, and Phetchabun (Fig. 5). Remarks. The three populations classified as M. aries n. sp. show some conchological variability, which is compiled in Table 4., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 49-52, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Pilsbry, H. A. (1900) Notices of new Japanese land shells. Proceedings of the Academy of Natural Sciences of Philadelphia, 52, 381 - 384."]}

Metalycaeus heudei (Bavay & Dautzenberg, 1900) Fig. 41 Alycaeus (Charax) heudei Bavay & Dautzenberg, 1900a: 121–122. Alycaeus (Charax) heudei — Bavay & Dautzenberg 1900b: 458–459, plate 11, figs 15–18. Alycaeus paviei Bavay & Dautzenberg, 1912: 50–51, pl. 4, figs 5–8. Alycaeus paviei var. minor Bavay & Dautzenberg, 1912: 51, pl. 4, fig. 9. Chamalycaeus (Dicharax) compressicosta Zilch, 1957: 145–146, fig. 33. Chamalycaeus (Dicharax) fractus Varga, 1974: 165–167, figs 1–5. Alycaeus zhuangiyucuii Yang, Fan, Qiao & He, 2012: 32, fig. 2. Metalycaeus heudei — Páll-Gergely et al. 2017: 74–84, figs 49C–D, 50–52, 53C–D. (paviei Bavay & Dautzenberg, 1912, paviei var. minor Bavay & Dautzenberg, 1912, compressicosta Zilch, 1957, fractus Varga, 1974 and zhuangiyucuii Yang, Fan, Qiao & He, 2012 are synonyms; Inkhavilay et al. 2019: 16, fig. 6C. Alycaeus kengtungensis Godwin-Austen, 1914: 409, plate 139, figs 6, 6a. new synonym Material examined. Holotype: Myanmar, Shan State, “Kengtung, Siam Frontier, leg. Woodthorpe ”, NHMUK 1903.7.1.3037 (holotype of A. kengtungensis). For the examined type specimens of other taxa see Páll-Gergely et al. (2017). Other material: 4 shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Bo Pha Gu Cave sink, 19°21.121’N, 97°3.759’E (locality code: JG10), 10 Feb. 2019, J. Grego leg., JG; 2 shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li Village, under bridge over Phruno River, 19°22.966’N, 97°02.153’E (locality code: JG100), 12 Dec. 2019, J. Grego leg., JG; 1 shell, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li Village, rocks above bridge over Phruno River, 19°23.011’N, 97°02.108’E (locality code: JG101), 12 Dec. 2019, J. Grego leg., JG; 1 shell, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Entrance of Phruno River Cave, 19°22.744’N, 97°02.570’E (locality code: JG102), 12 Dec. 2019, J. Grego leg., HNHM 104867 (photographed shell: 4.77 mm, H: 3.66 mm); 17 shells, same data as preceding, JG. Diagnosis of specimens from Myanmar. A medium-sized to large species with very long R2 having typical Metalycaeus - type elevated, thin, widely spaced ribs, a narrow swelling on R3, and a rounded aperture. Measurements. D: 4.65–5.05 mm, H: 3.66–3.71 mm (newly collected specimens). Remarks. Metalycaeus heudei is a widely distributed, variable species reported from China, Vietnam and Laos. Alycaeus kengtungensis (Fig. 41B) from the eastern border of Shan State, Myanmar, and the newly collected shells from Kayah State (Fig. 5) fall within the known morphological variation of Metalycaeus heudei. Therefore, we consider A. kengtungensis a new synonym of M. heudei. With this, M. heudei is the most widely distributed alycaeid species known., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 53, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Bavay, A. & Dautzenberg, P. (1900 a) Diagnoses de coquilles nouvelles de l'Indo-Chine. Journal de Conchyliologie, 48, 108 - 122.","Bavay, A. & Dautzenberg, P. (1900 b) Description de coquilles nouvelles de l'Indo-Chine. Journal de Conchyliologie, 48, 435 - 460.","Bavay, A. & Dautzenberg, P. (1912) Description de coquilles nouvelles de l'Indo-Chine. Journal de Conchyliologie, 60, 1 - 54.","Zilch, A. (1957) Die Typen und Typoide des Natur-Museums Senckenberg, 20: Mollusca, Cyclophoridae, Alycaeinae. Archiv fur Molluskenkunde, 86 (4 / 6), 141 - 150.","Varga, A. (1974) Eine neue Chamalycaeus - Art aus Vietnam (Gastropoda: Cyclophoridae, Alycaeninae). Folia Historico Naturalia Musei Matraensis, 2, 165 - 167.","Yang, H., Fan, Z., Qiao, D. & He, J. (2012) Description of four landsnails from China. Shell Discoveries, 1 (1), 32 - 33.","Inkhavilay, K., Sutcharit, C., Bantaowong, U., Chanabun, R., Siriwut, W., Srisonchai, R., Pholyotha, A., Jirapatrasilp, P. & Panha, S. (2019) Annotated checklist of the terrestrial molluscs from Laos (Mollusca, Gastropoda). ZooKeys, 834, 1 - 166. https: // doi. org / 10.3897 / zookeys. 834.28800"]}

Metalycaeus bicarinatus Páll-Gergely & Hunyadi n. sp. Figs 39B, 40E–H Material examined. Holotype: Thailand, Phetchaburi Province, Khao Yoi, NE side of the hill, 13°14.316’N, 99°49.493’E, 30 m a.s.l. (locality code: 2015/39), 24 Feb. 2015, A. Hunyadi leg. HNHM 104868 (D: 2.33 mm, H: 1.63 mm). Paratype: 1 shell, same data as holotype, HA. Other Material: 4 juvenile /broken shells; same data as holotype, HA. Etymology. This new species is named after the most remarkable conchological character, the double keel of R2. Diagnosis. A tiny Metalycaeus species with a strongly ribbed R1, ribs narrow and elevated, short R2+R3, dense, curved R2 ribs, and an R2 with double keel, visible from lateral and ventral sides. Differential diagnosis. Due to the peculiarly carinated R2 no other alycaeid species is similar, except for M. aries n. sp. (see above). Description of the type series. Shell off-white, light grey, although available shells were dead collected; shell rounded in dorsal view; spire elevated, low conical; R1 body whorl rounded, R2 has distinct upper and lower keels separated by flattened zone, resulting in rectangular-shaped R2; protoconch consisting of 1.25 whorls, elevated, finely granular, last ca. quarter whorl with granules arranged into oblique striae; R1 of 1.75 whorls, with strong, narrow, elevated, equidistant ribs, areas between ribs with fine, dense spiral striae; boundary between R1 and R2 distinct because of denser R2 ribs; R2+R3 less than a quarter whorl (ca. 80˚); R2 very slightly swollen in dorsal view, and rectangular in lateral view due to upper and lower keels; R2 ribs curved toward aperture, nearly adnate, ca. 26 R2 ribs present; R2 somewhat longer than R3; R3 strongly reduced, with remnants of spiral striation and rough growth lines; R2 and R3 boundary distinct due to change in rib morphology and moderate constriction; aperture slightly oblique to shell axis; round; boundary between inner and outer peristomes barely discernible; inner peristome slightly protruding and expanded, relatively thin; outer peristome also thin, slightly expanded, not reflected; umbilicus moderately narrow, approximately one third of shell width. Measurements. D: 2.33–2.4 mm, H: 1.63–1.87 mm. Operculum. Unknown. Distribution. This new species is known only from the type locality (Fig. 5). Remarks. This species is assigned to Metalycaeus even though no spiral striation has been found on the protoconch. Since all available material was dead collected, we believe that the fine shell sculpture that exists between the ribs at the end of the protoconch is probably remnants of spiral striation. Also, the protoconch of Metalycaeus aries n. sp., the conchologically most similar species is clearly spirally striated (see above)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 52-53, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958

Chamalycaeus irmatallus Páll-Gergely n. sp. Figs 9, 10A Material examined. Holotype: Thailand, Surat Thani Province, limestone mtn., 6 km S of Na San, 8°39.583’N, 99°23.883’E, 100 m a.s.l., 3 Jun. 1987, F.G. Thompson leg., UF 279508 (D: 2.02 mm, H: 1.32 mm). Paratypes: 11 shells, same data as holotype, UF 551216. Other material: 6 shells, Myanmar, Thayet-myo, Pegu, coll. Blanford, NHMUK 1906.4.4.71; 1 shell, Thailand, Phang Nga Province, Phang Nga, Tham Nam Phud, 8°27.829’N, 98°32.617’E, 40 m a.s.l. (locality code: 2015/33), 20 Feb. 2015, A. Hunyadi leg., around the cave, HA. Etymology. The specific epithet is an anagram for armillatus, a species with which this new species has been confused (see Differential diagnosis). Diagnosis. A tiny Chamalycaeus species with glossy shell, irregularly, finely ribbed R1, very short R2 with blunt, low ribs, and somewhat longer R3 (the two latter regions are shorter than a quarter whorl combined). Description. Shell off-white, rather glossy, although available shells are somewhat eroded; shell outline slightly oval in dorsal view; spire slightly elevated, conical-domed; body whorl somewhat “parabolic” in apertural view; protoconch rather low, glossy, spiral striae lacking, 1.25 whorls; R1 of 1.5–1.75 whorls, with very indistinct, irregular, low and rounded, relatively wide ribs, and some weak spiral striation; boundary between R1 and R2 distinct due to change in intensity and strength of ribbing; R2 short, only ca. 16–20 ribs; R2+R3 less than quarter whorl (ca. 70–80˚); R3 up to twice as long as R2; boundary between R2 and R3 clear due to change in rib morphology, although constriction very shallow; R3 with very fine, rounded ribs, and low, convex, elongated central swelling; aperture round, slightly oblique to shell axis; boundary between inner and outer peristomes distinct, inner peristome strongly protruding, thickened, slightly expanded; outer peristome slightly weaker or as strong, also expanded, only slightly reflected toward umbilicus; umbilicus relatively narrow, ca. one third of shell width. Measurements. D: 1.75–2.02 mm, H: 1.15–1.32 mm. Operculum. Unknown. Differential diagnosis. Chamalycaeus armillatus (Benson, 1856) (material examined: Thayet-Mio, UMZC 102995, holotype, Fig. 10B) has a more rounded body whorl, longer R2 and R3, and a thicker peristome with greater distance between the edges of the inner and outer peristomes. Distribution. The type locality is in Thailand’s Surat Thani Province. A single shell was collected in the neighbouring Phang Nga Province (locality code: 2015/33, coll. HA). Shells collected more than 1,000 km north in Thayet, Myanmar are so similar to the Thai populations that they could not be separated (see below) (Fig. 3). Remarks. Chamalycaeus armillatus was described from an eroded specimen. Some spiral striations are visible on the holotype, but they might be the part of the lower shell layer. Thus, this species was provisionally assigned to Chamalycaeus in Páll-Gergely et al. (2020). Specimens from Thayet (NHMUK 1906.4.4.71, labelled as armillatus) have slightly less densely arranged R2 ribs than typical C. irmatallus n. sp. A single, eroded shell from Tham Nam Phud (Thailand) is somewhat larger than the holotype of C. irmatallus n. sp., and has a longer R2. Since all other shell characters are identical, we provisionally identify the Tham Nam Phud and Thayet specimens as C. cf. irmatallus n. sp., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 14, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Benson, W. H. (1856) Characters of seventeen new forms of the Cyclostomacea from the British provinces of Burmah, collected by W. Theobald, Jun., Esq. The Annals and Magazine of Natural History, Series 2, 17, 225 - 233. https: // doi. org / 10.1080 / 00222935608697501","Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583"]}

Chamalycaeus spiratus Páll-Gergely n. sp. Fig. 13 Material examined. Holotype: Thailand, Rayong Province, limestone range Khao San Ta, 2.0 km W of Ban Syaek Batan, 12°58.75’N, 101°40.00’E, 150 m a.s.l., 25 Apr. 1987, F.G. Thompson leg., UF 279157 (D: 1.8 mm, H: 1.16 mm). Paratypes: 5 shells, same data as holotype, UF 551217. Etymology. This new species is named for its conspicuous spiral striae. Diagnosis. A tiny Chamalycaeus species with strong, conspicuous spiral striations on entire teleoconch, R2+R3 slightly shorter than a quarter whorl, and distance between the edges of the inner and outer peristomes is great, outer peristome not reflected. Description. Shell off-white to yellowish-corneous, probably somewhat translucent when fresh; shell outline rounded in dorsal view; spire slightly elevated, low conical; body whorl rounded; protoconch somewhat elevated, glossy, finely granular, spiral striae lacking, 1.5 whorls; R1 of 1.25–1.5 whorls, with very strong, broad spiral striae on last 0.75–1.0 whorl, preceding area rather smooth; last ca. half whorl of R1 with strong but low ribs, similar strength to spiral striae, widely and irregularly spaced; boundary between R1 and R2 distinct due to change in rib density; R2 ribs curve toward aperture, spaces between ribs approximately as wide as ribs; ca. 18–20 ribs present; R2+R3 less than quarter whorl (ca. 70–80˚), comparable in length; boundary between R2 and R3 distinct due to change in rib morphology, constriction lacking; R3 practically without swelling, with similar spiral striae to that of R1, ribs virtually absent, replaced by very fine, weak growth lines; aperture slightly oblique to shell axis, round; boundary between inner and outer peristomes conspicuous, inner peristome strongly protruding and slightly expanded; edge of outer peristome thin, expanded weakly toward umbilicus, not reflected; umbilicus relatively narrow, approximately one third of shell width. Measurements. 1.72–1.93 mm, H: 1.07–1.16 mm. Operculum. Unknown. Differential diagnosis. The small size, prominent, thin outer peristome, strong ribs and spiral striae distinguish this species from all other congeners. The most similar species in size and sculpture are Chamalycaeus microconus (Möllendorff, 1887) (examined material: Malakka: Bukit Pondong (Perak), SMF 109493, lectotype, and SMF 109494, 2 paralectotypes) and Chamalycaeus mixtus Zilch, 1957 (examined material: Malakka: Bukit Pondong (Perak), SMF 109510, holotype, and SMF 109511, 4 paratypes) from the Malay Peninsula (Bukit Pondong), but they have higher spires, comparatively larger apertures, and shorter R3s. For comparisons, see photos in Páll-Gergely et al. (2020). Distribution. This new species is known only from the type locality (Fig. 5). Genus Dicharax Kobelt & Möllendorff, 1900 Charax Benson, 1859: 177. Dicharax Kobelt & Möllendorff, 1900: 186. (replacement name for Charax Benson, 1859, non Charax Scopoli, 1777 [Pisces]). Type species. Alycaeus hebes Benson, 1857, by subsequent designation (Gude 1921). Diagnosis. Typical Dicharax species possess R2 ribs curved toward aperture. Genus generally characterized by complete absence of spiral striation. Only two of 164 species assigned to genus by Páll-Gergely et al. (2020), have indication of spiral striation. A few other species reported to have striations by Jirapatrasilp et al. (2021). Despite occurrence of spiral striations in relatively few species, the absence of striations is generally a valuable character by which to recognize Dicharax species, although examination of additional characters is also critical., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 21, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Mollendorff, O. F. von (1887) The landshells of Perak. Journal of the Asiatic Society of Bengal, 55, 299 - 316.","Zilch, A. (1957) Die Typen und Typoide des Natur-Museums Senckenberg, 20: Mollusca, Cyclophoridae, Alycaeinae. Archiv fur Molluskenkunde, 86 (4 / 6), 141 - 150.","Kobelt, W. & Mollendorff, O. F. von (1900) Zur Systematik der Pneumonopomen. Nachrichtsblatt der Deutschen Malakozoolo- gischen Gesellschaft, 32, 186.","Benson, W. H. (1859) A sectional distribution of the genus Alycaeus, Gray, with characters of six new species and of other Cyclostomidae collected at Darjiling by W. T. Blanford, Esq. The Annals and Magazine of Natural History, Series 3, 3, 176 - 184.","Scopoli, J. A. (1777) Introductio ad historiam naturalem, sistens genera lapidum, plantarum et animalium hactenus detecta, caracteribus essentialibus donata, in tribus divisa, subinde ad leges naturae. Introductio ad historiam naturalem. Apud Wolfgangum Gerle, Prague, 506 pp. https: // doi. org / 10.5962 / bhl. title. 10827","Benson, W. H. (1857) Characters of Streptaulus a new genus and several species of the Cyclostomacea from Sikkim, the Khasi Hills Ava and Pegu. The Annals and Magazine of Natural History, Series 2, 19, 201 - 211. https: // doi. org / 10.1080 / 00222935708681840","Gude, G. K. (1921) The Fauna of British India including Ceylon and Burma. Mollusca. III. Land operculates (Cyclophoridae, Truncatellidae, Assimineidae, Helicinidae). Taylor and Francis, London, 386 pp. https: // doi. org / 10.5962 / bhl. title. 12890","Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583","Jirapatrasilp, P., Pall-Gergely, B., Sutcharit, C. & Tongkerd, P. (2021): The operculate micro land snail genus Dicharax Kobelt & Mollendorff, 1900 (Caenogastropoda, Alycaeidae) in Thailand, with description of new species. Zoosystematics and Evolution, 97 (1), 1 - 20. https: // doi. org / 10.3897 / zse. 97.59143"]}

Dicharax mirounga Páll-Gergely n. sp. Fig. 23 Material examined. Holotype: Thailand, Tak Province, Knoll 7 km E of Ban Huei Hin Fond, 16°46.350’N, 98°40.383’E, 610 m a.s.l., 02 May 1987, F.G. Thompson leg., UF 347421 (D: 3.13 mm, H: 2.08 mm). Etymology. The R3 shape of this species is reminiscent of the large proboscis of elephant seal males (genus Mirounga) (see Galimberti et al. 2019). Diagnosis. A medium-sized Dicharax species with glossy R1 having some widely-spaced, typical Dicharax -ribs, long R3 with an elongated swelling, strongly expanded outer peristome, and narrow umbilicus. Description. Shell white, with slightly yellowish colouration; shell outline oval in dorsal view; spire elevated, conical, body whorl rounded; protoconch low, glossy, slightly more than 1.25 whorls; R1 of 1.75 whorls, glossy, with widely-spaced ribs, strong only near suture and in umbilicus, represented as very fine axial lines on edge of peristome; boundary between R1 and R2 conspicuous due to dense R2 ribs; R2 ribs curved toward aperture, ca. 28 R2 ribs present; spaces between R2 ribs narrower than ribs; R2+R3 more than quarter whorl (ca. 110˚); R2 approximately half length of R3; R3 glossy, smooth, with very fine growth lines; boundary between R2 and R3 conspicuous due to change in sculpture, although constriction shallow; entire R3 with an elongated, inflated swelling reminiscent of an elephant seal proboscis; aperture strongly oblique to shell axis, round; boundary between inner and outer peristomes distinct; inner peristome somewhat protruding, rather thin, outer peristome extremely expanded, forming uniformly wide rim around aperture, slightly reflected over umbilicus, notched at the parieto-palatal edge; umbilicus very narrow. Measurements. D. 3.13 mm, H: 2.08 mm. Operculum. Unknown. Differential diagnosis. There are no other species recorded from Thailand, Myanmar, and neighbouring areas with such an expanded outer peristome. This trait, combined with the relatively small size, elevated spire, and smooth R1 makes this species easily recognizable. Distribution. This new species is known only from the type locality (Fig. 17)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 31, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Galimberti, F., Sanvito, S., Vinesi, M. C. & Cardini, A. (2019) \" Nose-metrics \" of wild southern elephant seal (Mirounga leonina) males using image analysis and geometric morphometrics. Journal of Zoological Systematics and Evolutionary Research, 57 (3), 710 - 720. https: // doi. org / 10.1111 / jzs. 12276"]}

Chamalycaeus buaboke Páll-Gergely & A. Reischütz n. sp. Figs 1A, 2 Material examined. Holotype: Thailand, Surat Thani Province, Ang Thong Islands, Wua Talap Island, ascent to Buaboke Cave, 9°37.993’N, 99°40.369’E, ca. 50 m a.s.l. (locality code: Th1), Sep. 2007, A. Reischütz leg., at base of limestone rocks, NHMW 113484 (D: 2.03 mm, H: 1.23 mm). Paratype: 1 shell, same data as holotype, RE. Etymology. The specific epithet (noun used in apposition) derives from the name of the cave where the new species was collected. Diagnosis. A tiny Chamalycaeus species with finely ribbed R1, elevated, narrow swelling on R3, and great distance between inner and outer peristomes. Description. Shell off-white, probably somewhat translucent when fresh; shell outline oval in dorsal view; spire slightly elevated, low conical; body whorl rounded; protoconch low, finely granular, spiral striae lacking, 1.25–1.5 whorls; R1 of 1.25–1.5 whorls, with strong, elevated, slim, densely, regularly arranged ribs, fine spiral striation between ribs; boundary between R1 and R2 distinct due to change of rib density; R2 ribs slightly curved towards aperture, spaces between ribs approximately as wide or slightly wider than ribs; ca. 26 ribs present; R2+R3 less than quarter whorl (ca. 80˚), R2 somewhat shorter than R3; boundary between R2 and R3 distinct due to deep constriction and ribless posterior portion of R3; R3 with short, narrow, ribbed central swelling; anterior slope of swelling steeper than posterior slope; aperture oblique to shell axis, rounded with small basal incision; boundary between inner and outer peristomes conspicuous, inner peristome strongly thickened, protruding, and slightly expanded; outer peristome thin, strongly expanded, distinctly reflected portion over umbilicus; distance between inner and outer peristomes significant, swelling of R3 and edge of outer peristome closely situated; umbilicus relatively narrow, ca. one fourth of shell width. Measurements. D: 2.03–2.29 mm, H: 1.23–1.33 mm. Operculum. Unknown. Differential diagnosis. The most similar species is Chamalycaeus canaliculatus (Möllendorff, 1894) (examined material: Golf von Siam: Koh-Samui, coll. Möllendorff, SMF 109468, lectotype, Fig. 1B), which was described from the nearby island, Koh Samui. The new species from Wua Talap Island is slightly smaller (C. canaliculatus D: 2.4 mm), has a more elevated R3, and much greater distance between the inner and outer peristomes. The new species differs from Dicharax ovatus n. sp. by the slightly smaller size, lower spire, very rounded body whorl and aperture, blunt swelling on R3, and the shorter distance between the inner and outer peristomes. Distribution. This new species is known only from the type locality (Fig. 3)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on page 5, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Mollendorff, O. F. von (1894) On a collection of land-shells from the Samui Islands, Gulf of Siam. Proceedings of the Zoological Society of London, 1894, 146 - 156."]}

Dicharax subroseus Páll-Gergely n. sp. Fig. 33 Material examined. Holotype: Thailand, Surat Thani Province, limestone hill right side off km. 105.2 rd. #401 (Suratthani—Takuapa), 8°53.622’N, 98°33.179’E (locality code: Th.119.00), Ch. & J. Hemmen leg., SMF 360000 (D: 2.79 mm, H: 1.83 mm). Paratype: 1 shell, same data as holotype, SMF 360001. Etymology. The specific epithet refers to the slight pinkish coloration of the available specimens. Diagnosis. A Dicharax species with a depressed shell, slight pinkish colouration, very widely spaced ribs on the last whorl of R1, a short R2 with straight, widely-spaced ribs, and a comparatively small, rounded aperture. Description. Shell whitish-yellowish with some pinkish colouration (holotype at the R2-R3 area, paratype on initial whorls); shell outline rounded in dorsal view; spire only slightly elevated; body whorl rounded; protoconch low, rather glossy, 1.25–1.5 whorls; R1 of 1.75–2 whorls; first whorl of R1 with only weak growth lines, gradually changing to strongly ribbed, spaces between ribs increase width rapidly (last half whorl of R1 with only 15–20 ribs); ribs straight, strong, narrow, but relatively low; boundary between R1 and R2 distinct due to denser R2 ribs; R2 with ca. 16, widely-spaced, low and rather narrow; R2+R3 approximately a quarter whorl or slightly more; R2 slightly shorter than R3; boundary between R2 and R3 conspicuous due to smooth R3 beginning and rather deep constriction; R3 with widely-spaced ribs, only anterior to constriction similar to those on R1, and blunt but prominent central swelling; aperture strongly oblique to shell axis, rounded, conspicuously small compared to shell size; boundary between inner and outer peristomes distinct; inner peristome prominent, protruding, relatively narrow; outer peristome as strong as inner peristome, strongly expanded, slightly reflected; umbilicus wide, approximately a third of shell width. Measurements. D: 2.74–2.79 mm, H: 1.7–1.83 mm. Operculum. The holotype possesses an operculum in the original position which appears to be separated into two layers. The outer layer, being partly broken, allows examination of the more deeply set layer. The outer surface is glossy without any surface structures. A central nipple is visible through the semi-translucent inner layer. Differential diagnosis. The combination of small size, widely-spaced R1 ribs, and a relatively small aperture is unlike any other species in the region. Distribution. This new species is known only from the type locality (Fig. 3)., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 41-43, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Pall-Gergely, B. & Hunyadi, A. (2018) Four new cyclophoroid species from Thailand and Laos (Gastropoda: Caenogastropoda: Alycaeidae, Diplommatinidae, Pupinidae). Zoosystema, 40 (4), 59 - 66. https: // doi. org / 10.5252 / zoosystema 2018 v 40 a 3"]}

Metalycaeus pygmachos Páll-Gergely & Hunyadi n. sp. Fig. 42 Material examined. Holotype: Myanmar, Mandalay State, near Maha Nandamu Peik Chin Myaung Cave & Waterfall, 22°05.762’N, 96°37.087’E, 740 m a.s.l. (locality code: 2018/66), 19 Oct. 2018, A. Hunyadi leg., HNHM 104866 (D: 4.8 mm, H: 2.91 mm). Paratype: 1 shell, same data as holotype, HA. Etymology. The specific epithet pygmachos (πυγμαχος: Greek for boxer) refers to the peculiarly shaped R3 resembling a boxer’s face after being punched. Diagnosis. A large Metalycaeus species with a long, swollen R2 having widely-spaced slim ribs, and a complex, conspicuous swelling on R3. Description. Shell off-white, although both available shells are eroded; shell outline oval in dorsal view due to conspicuously swollen R2; spire slightly elevated, domed; body whorl rounded; protoconch low, finely granular, spiral striae lacking, 1.25 whorls; R1 of 1.75–2 whorls, with strong, elevated, equidistant ribs and some faint, dense spiral striation; boundary between R1 and R2 not conspicuous because R1 and R2 ribs identical in shape and density; R2 with ca. 30–32 R2 ribs; R2+R3 almost half whorl (ca. 150–160˚); R2 slightly longer than R3; boundary between R2 and R3 indicated with very deep constriction; R3 characterized by very complex swelling strongly depressed dorsolaterally; this elongate depression parallel to constriction, corresponds with irregularly swollen ridge visible in oblique view in aperture; depression results in a U-shaped R3 swelling; upper rim of U, visible in dorsal view, more swollen than narrower lower rim, visible in lateral view; additional small depression just anterior to upper swollen rim, i.e. between upper, swollen rim and peristome, corresponding to a separate, knob-like swelling inside aperture; aperture strongly oblique to shell axis, rounded with slight upper and lower incisions; boundary between inner and outer peristomes barely discernible, inner peristome slightly protruding and expanded, outer peristome much stronger, wider, expanded, and reflected toward umbilicus, wide distance between inner peristome and edge of outer peristome resulting in strongly thickened lip; umbilicus relatively narrow, approximately less than one third of shell width. Measurements. 4.8–5.1 mm, H: 2.91–2.98 mm. Operculum. Unknown. Differential diagnosis. The peculiarly shaped R3 swelling is a unique feature distinguishing this species from all Chamalycaeus and Metalycaeus species. Distribution. This new species is known only from the type locality (Fig. 5). Remarks. This species is classified in the genus Metalycaeus due to its large size and the “depressed swelling” on R3 as in other Metalycaeus species. The lack of spiral striation on the protoconch is considered a secondary reduction. Concluding remarks Nineteen new species are described here (Fig. 43) collected by a few field biologists at a few isolated localities in Myanmar and Thailand, suggesting that still many undescribed species await discovery in Southeast Asia’s limestone outcrops. Biogeography In addition to the description of the new species and new data on the morphology and distribution of a few known species, this paper presents the following conclusions: - The Metalycaeus species described here represent the first records of that genus in Thailand, and the southernmost localities for Metalycaeus (Fig. 44; Páll-Gergely et al. 2020). - The numerous Chamalycaeus species recorded from southern Thailand indicate a diversity centre for the genus. - The numerous Dicharax species from northern Thailand clearly show that this genus retains high diversity continuously from the southeastern Himalaya east into northern Thailand. In contrast, the genus is much less diverse in neighbouring northern Laos (Fig. 44). - The distribution of Metalycaeus heudei ranges from Kayah Province, Myanmar east and north to Hubei Province, China, covering a distance of more than 1800 km. Metalycaeus heudei has the largest distributional area of all alycaeids and one of the largest among all terrestrial caenogastropods. - For Dicharax diminutus (Heude, 1885) and D. dolichodeiros (Heude, 1890), populations were found several hundred kilometres apart from each other without material from intervening areas (see Páll-Gergely et al. 2017). A similar situation for Chamalycaeus irmatallus n. sp. is reported here. Four hypotheses were outlined by Páll-Gergely et al. (2017) to explain the previously reported distributional gaps: 1) the gaps between known populations are due to poor collecting effort and the lack of material; 2) those species may have once had wider distributions that have become restricted into smaller, relict populations; 3) long distance dispersal events; or 4) convergent evolution of shell characters resulting in misidentifications and thus, incorrect distributions. Additional material and genetic/anatomical data will hopefully clarify our understanding of these species. Predation Some shells we examined had scraped predation holes (Fig. 45), possibly caused by Atopos Simroth, 1891 slugs (see Liew & Schilthuizen 2014; M. Schilthuizen, pers. comm.). Samples of Dicharax notus were large enough to provide meaningful information (see Table 5). This indicates that the predation pressure is highly variable between sites (0% for JG10, 4% in JG102 and 42% in JG11); in some cases almost half of the shells show signs of predation., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 55-59, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583","Heude, R. P. M. (1885) Memoires concernant l'histoire naturelle de l'empire chinois par des peres de la Compagnie de Jesus. Notes sur les Mollusques terrestres de la vallee du Fleuve Bleu. Vol. III. Mission Catholique, Chang-Hai, 44 pp. [pp. 89 - 132]","Heude, R. P. M. (1890) Memoires concernant l'histoire naturelle de l'empire chinois par des peres de la Compagnie de Jesus. Notes sur les Mollusques terrestres de la vallee du Fleuve Bleu. Vol. IV. Mission Catholique, Chang-Hai, 64 pp. [pp. 125 - 188]","Simroth, H. (1891) Uber das Vagulinidengenus Atopos n. g. Zeitschrift fur Wissenschaftliche Zoologie, 52 (4), 593 - 615. https: // doi. org / 10.1002 / ange. 18910042008","Liew, T. - S. & Schilthuizen, M. (2014) Association between shell morphology of micro-land snails (genus Plectostoma) and their predator's predatory behaviour. PeerJ, 2, e 329. https: // doi. org / 10.7717 / peerj. 329"]}

Chamalycaeus hirpex Páll-Gergely & A. Reischütz n. sp. Figs 6–8 Material examined. Holotype: Thailand, Krabi Province, N of Krabi, Wat Tham Suea (Tiger Cave Temple), along steps to the cave, 8°7.603’N, 98°55.466’E, ca. 90 m a.s.l. (locality code: Th 11), Sep. 2007, A. Reischütz leg., at base of limestone rocks, NHMW 113485 (D: 2.42 mm, H: 1.53 mm). Paratypes: 12 shells, same data as holotype, RE; 42 shells, Thailand, Krabi Province, Railay Beach West, Viewpoint Hill, 8°0.511’N, 98°50.248’E, ca. 30 m a.s.l. (locality code: Th 14), Sep. 2007, A. Reischütz leg., at base of limestone rocks, RE; 2 shells, same data as preceding, CUMZ 5268; 1 shell (Fig. 6C), Thailand, Krabi Province, E of Krabi, Khao Khanab Nam limestone hill, 8°4.707’N, 98°55.263’E, ca. 2 m a.s.l. (locality code: Th 15), Sep. 2007, A. Reischütz leg., at base of limestone rocks just above tidal influence, NHMW 113486; 17 shells, same data as preceding, RE; 3 shells, limestone hill at river Khanab Nam (Krabi Yai) at the northeastern city limits of Krabi, by the road Thanon Lan Gu (Mueang Kao), ca. 400 m E of crossing with road Thanon Thong Chai, S of road, 8°5.817’N, 98°55.068’E, ca. 10 m a.s.l. (locality code: Th 17), Mar. 2010, A. Reischütz leg., at base of limestone rocks, RE; 2 shells, Thailand, Krabi Province, Wat Tham Sua, 8°7.567’N, 98°55.496’E, 40 m a.s.l. (locality code: 2015/34), 21 Feb. 2015, A. Hunyadi leg., HA. Other material: 7 juvenile /broken shells; same data as holotype, RE; 6 juvenile /broken shells, Thailand, Krabi Province, Railay Beach West, Viewpoint Hill; 8°0.511’N, 98°50.248’E; ca. 30 m a.s.l. (locality code: Th 14), Sep. 2007, A. Reischütz leg., at base of limestone rocks, RE; 4 juvenile /broken shells, Thailand, Krabi Province, E of Krabi, Khao Khanab Nam limestone hill, 8°4.707’N, 98°55.263’E, ca. 2 m a.s.l. (locality code: Th 15), Sep. 2007, A. Reischütz leg., at base of limestone rocks just above tidal influence, RE; 2 juvenile /broken shells, Thailand, Krabi Province, limestone hill at river Khanab Nam (Krabi Yai) at northeastern city limits of Krabi, by road Thanon Lan Gu (Mueang Kao), ca. 400 m E of crossing with road Thanon Thong Chai, S of road, 8°5.817’N, 98°55.068’E, ca. 10 m a.s.l. (locality code: Th 17), Mar. 2010, A. Reischütz leg., at base of limestone rocks, RE; 3 juvenile /broken shells, Thailand, Krabi Province, Wat Tham Sua, 8°7.567’N, 98°55.496’E, 40 m a.s.l. (locality code: 2015/34), 21 Feb. 2015, A. Hunyadi leg., HA; 2 broken shells, Thailand, Krabi Province, granite rock in evergreen forest at Tone Nga Chang Waterfall, Cha Lung, Hat Yai, Songkhla, 6°56.810’N, 100°13.895’E (locality code: AC21), C. Sutcharit et al. leg., CUMZ 5271 (Fig. 8, identification questionable, not shown on Fig. 3). Etymology. The specific epithet refers to the R2 rib morphology, which, with the numerous tooth-like projections, is reminiscent of a harrow, an agricultural tool consisting of a framework with teeth used to break up plowed land (hirpex in Latin). Diagnosis. A small Chamalycaeus species with R2+R3 shorter than a quarter whorl and R2 with serrulate ribs. Description (based on the type series). Shell off-white, light grey to slightly yellowish; shell outline rounded in dorsal view, R2 conspicuously bulging/angled in dorsal view, but variable in some populations; spire rather depressed, but variable among populations, low conical; body whorl rounded or rather parabolic; protoconch elevated, finely granular, spiral striation lacking, 1.5 whorls (Figs 7C–D); R1 ca. 1.5 whorls, first ca. 0.75 whorl dominated by fine ribbing that gradually increases strength toward the R1 termination; spiral striation as strong as radial ribs at end of R1, while due to domination of ribs at end of R1, relative strength of spiral striae decreases; R1 and R2 boundary conspicuous due to denser R2 ribs; R2+R3 less than a quarter whorl (ca. 70–80˚); R2 bulging, forming a blunt angle in dorsal view, and rounded in apertural view; R2 ribs lamella-like, rather low, characteristically serrate (i.e. a series of tiny spikes pointing anteriorly, see Figs 7A–B), ca. 24–26 R2 ribs present; R2 and R3 of comparable lengths or R2 slightly shorter; R3 with spiral striation and weaker ribs than R1; boundary between R2 and R3 distinct due to lower R3 ribs, although constriction is shallow; aperture very strongly oblique to shell axis; rounded, with very weak upper (parieto-palatal) incision, a weak basal incision occasionally also indicated; boundary between inner and outer peristomes distinct; inner peristome protruding, rather sharp and relatively thin; outer peristome expanded except in umbilical area; umbilicus relatively wide, over one third shell width. A cross-sectional view of R2 was examined in one specimen (Figs 7E–H): anterior crust forms an elevated rib, which forms a series of hollow spikes (visible in cross-sectional image as widened tip) toward aperture, posterior crust low, adnate to anterior crust, which slightly folds over posterior crust; cross-sectional view of microtunnels nearly rounded, drop shaped, or somewhat triangular. Measurements. D: 2.00– 2.61 mm, H: 1.32–1.67 mm. Operculum. Strongly concave, outer surface with no structures, covered with thick mud layer; inner side with elevated central nipple (Fig. 6B). Differential diagnosis. The reticulated R2 sculpture distinguishes this species from all congeners except for C. serratus n. sp. See that species for comparisons. Distribution. This new species is known from four populations occurring in Krabi Province, Thailand (Fig. 3). Remarks. The examined populations show a degree of morphological variability, see Table 1., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 11-12, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958

Dicharax omissus (Godwin-Austen, 1914) Figs 29–30 Alycaeus omissus Godwin-Austen, 1914: 411, Plate 155, Fig. 13. Alycaeus (Chamalycaeus) omissus — Gude 1921: 231. Material examined. Lectotype (hereby designated): 1 shell, “ Siam & Shan boundary, coll. Woodthorpe ”, NHMUK 1903.7.1.1228.1. Paralectotype: 1 shell, same data as for lectotype, NHMUK 1903.7.1.1228. Other material: 1 shell (Fig. 29B, D: 2.94 mm, H: 1.94 mm) + 10 shells, Myanmar, Shan State, Hopong centre 5.8 km — Namsang, left side of rd. #4, near „Hopong Spring Cave”, 20°49.028’N, 97°13.469’E, 1110 m a.s.l. (locality code: 2018/35), 06 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA; 8 shells, Myanmar, Shan State, Taunggyi centre ca. 16 km — Hopong, rd. #4 N 1.5 km, „Shwe Pyi Aunchonda” monastery, 20°47.263’N, 97°8.239’E, 1110 m a.s.l. (locality code: 2018/46), 08 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA; 1 shell (Fig. 30A, D: 2.81 mm, H: 1.8 mm) + 7 shells, Thailand, Chiang Mai Province, 1.2 km N of Wat Tham Klaeb, 500 m side road from the junction, 19°33.918’N, 99°3.690’E, 650 m a.s.l. (locality code: 2015/08), 08 Feb. 2015, A. Hunyadi leg., HA; 1 shell (Fig. 30B, D: 2.69 mm, H: 1.75 mm) + 2 shells, Thailand, Mae Hong Son Province, 800 m from Tham Nam Lod toward the Buddhist temple, 19°33.928’N, 98°16.794’E, 650 m a.s.l. (locality code: 2015/12), 09 Feb. 2015, A. Hunyadi leg., HA. Type locality. “ Siam and Shan boundary”. Diagnosis. A variable Dicharax species with a relatively densely, regularly ribbed R1, rarely with spiral striation, dense R2 ribs, a rounded central swelling on R3, and an expanded, but not reflected outer peristome. Measurements. D: 2.52–2.87 mm, H: 1.71–1.89 mm (2018/08 and 2015/12); D: 2.89–3.23 mm, H: 1.88–2.3 mm (2018/35 and 2015/46). Differential diagnosis. Typical Dicharax notus and D. omissus are very similar, and since only eroded specimens of the latter species were available, the distinction of these two species was somewhat questionable until newly collected material became available. These specimens reveal that D. notus is generally larger, R1 bears denser ribs (although some populations of D. notus have less dense R2 ribs), and its outer peristome is more reflected. Distribution. Dicharax omissus is known from the Shan States of Myanmar and neighbouring Thai provinces of Chiang Mai and Mae Hong Son (Jirapatrasilp et al. 2021; Fig. 28). Remarks. The syntypes and the newly collected 4 samples (possibly 3 populations) show some variability in terms of the sculpture of R1 and R3, and the presence or absence of the notch at the basal portion of the aperture. However, all of these traits are rather minor and do not justify the distinction of species. The conchological differences of these populations are summarized in Table 3. The shells of the two samples from Hopong have some slight spiral striation on the R1, which is highly unusual in Dicharax. The spiral striae of this species might not be homologous with those of other alycaeid genera, although this requires further investigation., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 38-40, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Gude, G. K. (1921) The Fauna of British India including Ceylon and Burma. Mollusca. III. Land operculates (Cyclophoridae, Truncatellidae, Assimineidae, Helicinidae). Taylor and Francis, London, 386 pp. https: // doi. org / 10.5962 / bhl. title. 12890","Jirapatrasilp, P., Pall-Gergely, B., Sutcharit, C. & Tongkerd, P. (2021): The operculate micro land snail genus Dicharax Kobelt & Mollendorff, 1900 (Caenogastropoda, Alycaeidae) in Thailand, with description of new species. Zoosystematics and Evolution, 97 (1), 1 - 20. https: // doi. org / 10.3897 / zse. 97.59143"]}

Dicharax ataranensis (Godwin-Austen, 1914) Fig. 18 Alycaeus ataranensis Godwin-Austen, 1914: 426, plate 148, figs 4, 4a–b. Alycaeus (Dicharax) ataranensis — Gude 1921: 237. Dicharax ataranensis — Páll-Gergely et al. 2020: 77, fig. 18. Material examined. Holotype: Myanmar, Ataran, Burma, ex Dr. F. Stoliczka, NZSI M.8073 (holotype [single specimen mentioned in original description]). Other material: 1 shell, Myanmar, Kayin State, Mudon centre ESE ca. 51 km, Htimahto NE, NE point of Kwooprai Hill, 16°2.396’N, 97°58.200’E, 30 m a.s.l. (locality code: 2018/47), 10 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA. Type locality. “1 Ataran”. Diagnosis (emended based on a newly collected specimen). Protoconch relatively low, glossy, without spiral striation; R1 glossy, widely-spaced ribs near the suture and inside the umbilicus, edge of R1 smooth; R2+R3 over a quarter whorl long, R2 ca. half as long as R3; R2 ribs typical for Dicharax (curved towards the aperture); R3 smooth, with blunt, but large, conspicuous, elevated swelling. Remarks. Until recently the eroded holotype was the only known specimen of the species making the assignment to Dicharax questionable. The newly collected fresh shell allowed examination of shell sculpture which confirmed the assignment., Published as part of Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), pp. 1-61 in Zootaxa 4973 (1) on pages 25-26, DOI: 10.11646/zootaxa.4973.1.1, http://zenodo.org/record/4771958, {"references":["Gude, G. K. (1921) The Fauna of British India including Ceylon and Burma. Mollusca. III. Land operculates (Cyclophoridae, Truncatellidae, Assimineidae, Helicinidae). Taylor and Francis, London, 386 pp. https: // doi. org / 10.5962 / bhl. title. 12890","Pall-Gergely, B., Sajan, S., Tripathy, B., Meng, K., Asami, T. & Ablett, J. (2020) Genus-level revision of the Alycaeidae, with a catalog of the species (Gastropoda: Cyclophoroidea). ZooKeys, 981, 1 - 220. https: // doi. org / 10.3897 / zookeys. 981.53583"]}

The land area of Laos is composed of a large variety of undisturbed habitats, such as high mountainous areas, huge limestone karsts and the lower Mekong Basin. Therefore, Laos is expected to have a high species diversity, especially for the land snails. However, with respect to research on malacology, Laos is probably the least well-researched area for land snail diversity in Indochina (including Laos) over the past few centuries. The handful of species lists have never been systematically revised from the colonial period to the present, so these classifications are outdated. Herein we present the first comprehensive annotated checklist with an up-to-date systematic framework of the land snail fauna in Laos based on both field investigations and literature surveys. This annotated checklist is collectively composed of 231 nominal species (62 ‘prosobranch’ and 169 heterobranches), of which 221 nominal species are illustrated. The type specimens of 143 species from several museum collections and/or 144 species of newly collected specimens are illustrated. There are 58 species recorded as new to the malacofauna of the country, and two new replacement names are proposed asHemiplectalanxangnicaInkhavilay and Panha,nomen novum(Ariophantidae) andChloritiskhammouanensisInkhavilay and Panha,nomen novum(Camaenidae). Four recently described species of the genusAmphidromusfrom Laos, “thakhekensis”, “richgoldbergi”, “attapeuensis” and “phuonglinhae” are synonymized with previously described species. In addition, thirteen nominal species are listed as uncertain records that may or may not occur in Laos. This annotated checklist may inspire malacologists to carry on systematic research in this region.

Vietnam with its limestone ranges that are concentrated mainly in northern, north-central and southern parts, and many different limestone islands running along the coastline, has a phylogenetically-diverse land snails fauna dominated by endemic species. The genus Cyclophorus (Cyclophoridae) in Vietnam is studied. Sixty species and subspecies from various habitats of limestone areas throughout Vietnam are confirmed and recorded. New species and subspecies, Cyclophorus implicatus kanhoensis ssp. nov., from Northwestern Vietnam, and Cyclophorus tamdaoensis sp. nov., from Northern Vietnam are described and discussed. In this paper, the Cyclophorus courbeti var. leucostoma Dautzenberg et Fischer, 1905, is elevated to subspecies.