﻿Revision of the carnivorous land snail family Streptaxidae (Stylommatophora, Achatinina) in Myanmar, with description of four new species

﻿Abstract The carnivorous terrestrial snail family Streptaxidae, recognized by having a regular to eccentric shell with complex apertural dentition, remains little-known and largely unexplored in Myanmar. This article presents historically recorded species and provides new data on this family. A total of eighteen species in five genera, namely Carinartemis, Discartemon, Haploptychius, Oophana, and Perrottetia from the southeastern and eastern parts of Myanmar, is examined herein. Among these, Haploptychius is the most diverse with eight species, while the remaining genera are comprised of fewer than five species each. Streptaxisbirmanica and Streptaxisblanfordianus are herein synonymized with Haploptychiusblanfordi, while Streptaxishanleyanus is synonymized with Carinartemissankeyi. Furthermore, the first genitalia and radula descriptions for three previously known species, D.tonywhitteni, C.exacutus, and C.sankeyi, are provided. Using comparative morphological and anatomical approaches, four new species are described: D.paurodeviatussp. nov., H.heliakosussp. nov., H.tenasserimicussp. nov., and H.karenorumsp. nov. This present study enhances the understanding of the land snail fauna in Myanmar, specifically the streptaxids, and highlights that limestone areas are important for biodiversity conservation.


Introduction
Having the greatest land area in mainland Southeast Asia, Myanmar, formerly known as Burma, is recognized as having a high level of ecosystem diversity that can support a diverse variety of organisms and is part of the Indo-Burma biodiversity hotspot (Myers et al. 2000;FAO 2010;Asian Development Bank 2012). Intensive surveys of the malacofauna in Myanmar were performed in the mid-nineteenth to early twentieth centuries and were mainly conducted by American and European naturalists (see Pholyotha et al. 2020;Grego et al. 2021). However, the investigation on mollusks did not receive much attention after the independence of Myanmar in the 1940s. Fortunately, since Myanmar became more open in the 1990s, studies of several groups of Burmese land snails have gradually been published, i.e., Streptaxoidea Gray, 1860(Páll-Gergely et al. 2020aSutcharit et al. 2020), Helicarionoidea Bourguignat, 1877(Pholyotha et al. 2020Sutcharit et al. 2020;Sutcharit and Panha 2021), Pupinidae Pfeiffer, 1853(Páll-Gergely et al. 2015; Páll-Gergely and Grego 2019), Plectopylidae von Möllendorff, 1898 (Páll-Gergely 2018), Camaenidae Pilsbry, 1895(Páll-Gergely et al. 2020b, 2022, and Clausiliidae Gray, 1855(Nordsieck 2002aGrego et al. 2021;Szekeres et al. 2021a, b).
The members of family Streptaxidae Gray, 1860 are known as carnivorous land snails and are characterized by an eccentric to cylindrical shell with complex apertural dentition, genitalia with hook-like structures, and living animals usually having bright yellow to red or greenish bodies (Blanford and Godwin-Austen 1908;van Benthem Jutting 1954;Berry 1963;Schileyko 2000;Verdcourt 2000;Rowson et al. 2009;Siriboon et al. 2013Siriboon et al. , 2014a. This group is distributed worldwide across the tropical and subtropical areas of South America, Africa, and Asia (van Bruggen 1967;Schileyko 2000;Sutcharit et al. 2010;Rowson et al. 2010). As in many predator-prey relationships, most streptaxid taxa are abundant in limestone microhabitats where their preferred food items are also abundant (Siriboon et al. 2013(Siriboon et al. , 2014aInkhavilay et al. 2016). In Southeast Asia, karsts cover an area of approximately 400,000 square kilometers and are known to host high levels of animal diversity and endemism . Currently, ten genera and approximately 140 nominal species of streptaxid snails are recognized in the region (Blanford and Godwin-Austen 1908;van Bruggen 1972;Richardson 1988;Schileyko 2000;Siriboon et al. 2013Siriboon et al. , 2014aDo and Do 2015;Inkhavilay et al. 2016;MolluscaBase 2021).
In Myanmar, the most recent reports on the superfamily Streptaxoidea (Streptaxidae and Diapheridae Panha & Naggs, 2010) were published more than one hundred years ago (see Blanford and Godwin-Austen 1908). While only a few land snail groups have been systematically revised in Myanmar (Páll-Gergely et al. 2020a;, the systematic revision of the streptaxid snails in several other countries of mainland Southeast Asia (i.e., Laos, Vietnam, and Thailand) has advanced during the past decade (Siriboon et al. 2013(Siriboon et al. , 2014aInkhavilay et al. 2016;Do 2017;Bui et al. 2019;Siriboon et al. 2020;Sutcharit et al. 2020).
During land snail expeditions in Myanmar in 2015 and 2016, streptaxid species were discovered in several localities in southeastern (Mon State, Kayin State, and Tanintharyi Region) and eastern (Shan State and Mandalay Region) parts of Myanmar under the cooperation of the Forest Department of Myanmar (FDM), Fauna & Flora International (FFI), and Chulalongkorn University. Herein, we discuss the taxonomy of the carnivorous terrestrial snail family Streptaxidae collected in Myanmar. The molecular phylogeny by Siriboon et al. (2020) suggests that some genera are non-monophyletic, especially Oophana Ancey, 1884 andHaploptychius von Möllendorff, 1906. However, in this study the traditional concept based on morphological characters is applied, without acknowledging their respective type species. Therefore, this research aims to 1) revise the systematics of the streptaxid species with eccentric shell shape based on the shell, radula morphology and genital anatomy (if available), especially the penial hooks; and 2) record all species of streptaxid species with an eccentric shaped shell that have been reported from Myanmar based on the literature and historical museum collections.

Materials and methods
Streptaxid specimens were collected during 2015 and 2016 by the Animal Systematics Research Unit (ASRU) members, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand. These field surveys were conducted under a MOU between the Forest Department, Ministry of Natural Resources and Environmental Conservation and Forestry, Myanmar and Fauna & Flora International (FFI) with Letter No. 0092. The field surveys focused on non-limestone and limestone areas in Shan State, Mon State, Kayin State, Mandalay Region, and Tanintharyi Region. The coordinates were recorded using GPS. Approximate collection localities are presented in Table 1 and Figure 1.
For anatomical studies, living specimens were photographed, euthanized following the protocol by the American Veterinary Medical Association (2020), and then preserved in 70% ethanol (v/v). Taxonomic identifications were made based on Kobelt (1905Kobelt ( -1906, Blanford and Godwin-Austen (1908), Schileyko 2000;Siriboon et al. (2013Siriboon et al. ( , 2014a, Inkhavilay et al. (2016), and Sutcharit et al. (2020). Shell height, shell width and whorl count were measured, and the height/width ratio was calculated following Siriboon et al. (2013). The shells were photographed using a Nikon camera with a Nikon 105 Macro lens. One to five adult specimens in ethanol were dissected, and the genitalia were examined under a stereomicroscope. A representative specimen was illustrated with the aid of a camera lucida. The buccal masses were removed, and the radulae were soaked in 10% (w/v) NaOH, and then cleaned in distilled water. Radula, penial hooks, and vaginal hooks were examined and photographed using scanning electron microscopy (SEM; JEOL, JSM-5410 LV).
All the nominal species names described as new to science in this work are attributed to the first and last authors (Man & Panha). Thus, a complete citation of the authors is Man & Panha in Man et al.

Species, localities and CUMZ no. Number of specimens
Ranges, mean ± S.D. in mm.

NHM
The Natural History Museum, London; NHMUK when citing specimens deposited in the NHM; SMF Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main.
Diagnosis. Shell flattened to globose-heliciform. Last whorl rounded to angular, less distorted, and often with peripheral keel; whorls regularly to rapidly expanded. Apertural dentition varied, ranging from only one parietal lamella to additional dentition: upper palatal, palatal, basal, columellar and supracolumellar lamellae. Genitalia with short to long penis, sometimes with penial appendix and penial sheath covering entire penis length. Penial hooks present and vaginal hook absent.
Remarks. This genus was recently revised in both shell and genital diagnostic characters, and the intrageneric relationship was discussed (Siriboon et al. 2014a(Siriboon et al. , 2020. At present, the genus Discartemon comprises thirty recognized species, including a new species described herein  Diagnosis. This species was clearly described in Sutcharit et al. (2020). Shell is depressed-heliciform, white and translucent, spire low conical to convex with wide and depressed suture. Shell surface glossy, with fine transverse ridges that diminish below  periphery; varices present. Embryonic shell large, ~ 2½ whorls with smooth surface; following whorls in regularly expanding coil. Last whorl usually angular; widely open umbilicus. Apertural dentition with one strong parietal, one palatal, one basal, one columellar and one supracolumellar lamella (Fig. 3A, B).
Vagina (v) short, ~ 1/3 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) long, ~ 2 times of vagina length. Oviduct (ov) slender and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) ca. twice as long as the length from talon to branching point of seminal vesicle (Fig. 4A).
Distribution. Discartemon tonywhitteni is the southernmost distributed species and, currently, is known as the only form from the type locality ( Fig. 1), which is an isolated limestone outcrop in Tanintharyi Region, southern Myanmar .
Remarks. Sutcharit et al. (2020) described D. tonywhitteni based only on shells. Fortunately, seven alcohol-preserved specimens collected near the type locality were sent by the FFI staff after the species was published. These additional specimens allow us to describe the genitalia and radular morphology of this species herein.  (Sykes, 1902) from Malaysia by having a larger shell, rounded last whorl, semi-ovate and slightly reflected aperture, and sometimes supracollumellar lamellae are present. Compared with D. vandermeermohri van Benthem Jutting, 1959 andD. mekalostraka Siriboon &Panha, 2014 from Thailand, this new species has a slightly extended last whorl from the penultimate whorl, last whorl slightly axially deflected, widely open umbilicus, and semi-ovate aperture. The genital organs of D. paurodeviatus sp. nov. differ from D. mekalostraka by having corrugated atrium without pore, short penis, dense brownish and long slender penial hooks located on penial papillae, and short vagina with thickened and reticulated vaginal folds.
Vagina (v) very short and stout, ~ 1/7 of penis length. Gametolytic duct (gd) a long and slender tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) convoluted and distally long and thick, ~ 3 times of vagina length. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing short and thickened seminal vesicle (sv) and ca. same length as from talon to branching point of seminal vesicle (Fig. 4C).
Vaginal wall generally with thickened reticulated vaginal folds, smooth surface, and vaginal pores present (Fig. 6A, G).
Etymology. The specific name paurodeviatus is derived from the Greek word pauros meaning little or few and the Latin word devius meaning out of the way. It refers to the last whorl of the new species as being slightly axially deflected and extruded from the penultimate whorl.
Distribution. The species is only known from the type locality in southern Myanmar (Fig. 1).
Remarks. Variation occurs in the possession of supracolumellar lamellae in some specimens. Currently, two species of Discartemon (D. paurodeviatus sp. nov. and D. tonywhitteni) have been recognized from Myanmar ). These two species are noticeably different in shell morphology and internal structure of genitalia and found in distant localities from each other.
Remarks. The genus Oophana shares the ovate shell shape with the Haploptychius. However, Oophana can be distinguished by generally having a greater number of apertural dentitions (parietal, palatal, basal and columellar lamellae), while Haploptychius has only one parietal lamella (Schileyko 2000;Inkhavilay et al. 2016).
Generally, despite Oophana and Indoartemon Forcart, 1946 possessing an ovate shell with a blunt spire, the former can be distinguished by its parietal, palatal, basal, and columellar lamellae, while the latter possesses only one parietal and one palatal lamella (Schileyko 2000;Siriboon et al. 2014a). Oophana can be distinguished from Discartemon and Perrottetia Kobelt, 1905 by its globosely ovate shell, axially deflected last whorl, and penultimate whorl more or less extended from the last whorl. In comparison, Discartemon has a flattened to a globose-heliciform shell, regularly to rapidly growing last whorl that is less deflected, and penultimate whorl does not extend from the last whorl (Siriboon et al. 2014a). Perrottetia possesses a sub-heliciform and depressed shell, with longitudinal furrows behind the apertural lip, and a less deflected last whorl (Siriboon et al. 2013;Inkhavilay et al. 2016). Moreover, Oophana can easily be separated from the Carinartemis Siriboon & Panha, 2014 by their rounded penultimate whorl with more apertural dentition, whereas the latter genus has a sharply keeled penultimate whorl, and without or with only one parietal lamella (Siriboon et al. 2014b).
Generally, Oophana shows high variability in shell form, and apertural dentition with upper palatal and supracolumellar lamellae occurring in some species (Siriboon et al. 2020). However, examination of the genitalia in most species including the type species is still limited, making comparisons with other congeners difficult.
The phylogenetic relationships of the Oophana s.l. from Thailand were recently shown to be polyphyletic and comprised of three groups. These polyphyletic groups could possibly be recognized as distinct genera supported by their unique shell and genital characters (Siriboon et al. 2020). Furthermore, the oblique-heliciform shell and apertural dentition with four lamellae are shared among these three polyphyletic groups. Nevertheless, without the information on the type species, these characters are insufficient to restrict the true Oophana s.s., and so, in this revision we place the streptaxids that have an oblique-ovate shell and apertural dentition with four lamellae within the genus Oophana s.l.

Oophana elisa (Gould, 1856)
Streptaxis elisa Gould, 1856: 13.  Remarks. The shell is oblique-heliciform with convex spire and a distinct suture. Whorls 7 and shell surface with transverse ridges that diminish below the periphery. Shell periphery is keeled, and last whorl axially deflected. Umbilicus open and deep. Aperture is subquadrangular, peristome reflected. Apertural dentition with one parietal, one basal, two weak palatal, and one columellar lamella. This species is known only from the type locality, in the southern part of Myanmar. No fresh materials were collected in this survey. Herein, the description of this species is based only on the original description. Gould (1856) received the specimen from Rev. J. Benjamin and described it without providing any figures. In the description, Gould compared O. elisa with two species: Seychellaxis souleyetianus (Petit, 1841) and Haploptychius pyriformis (Pfeiffer in Philippi, 1845). In differentiating the three, Gould noted that O. elisa has a larger and a more depressed shell than S. souleyetianus, and that O. elisa has a more elongated shell that is two-fold larger in size and posterior denticle (presumably parietal lamella) smaller than H. pyriformis. Based on this comparison, we assume that the shell of O. elisa differs from all other known congeners from Myanmar and Peninsular Malaysia by its largely deflected last whorl, discoid spire and keeled penultimate whorl. Besides probably having the same distribution range, O. elisa is similar to D. paurodeviatus sp. nov. in having a quite straight and parallel aperture lip, and four apertural dentitions. However, O. elisa seems to have an oblique-ovate shell with more deflected last whorl, keeled penultimate whorl, and discoid spire. Meanwhile, D. paurodeviatus sp. nov. possesses a globose shell with less deflected last whorl, and penultimate whorls being rounded. To date, no specimens or illustrations have been found after the first record.
Oophana mouhoti (Pfeiffer,   Diagnosis. Oophana mouhoti can be distinguished from O. obtusus (Stoliczka, 1871) by its higher spire, expanded aperture lip, deflected last whorl, and slightly angulate penultimate whorl. In contrast, O. obtusus exhibits a narrow aperture, spire convex, periphery of penultimate whorl usually equal to last whorl, strong columellar lamella, and small tubercle near the posterior angle of aperture.
Description. Shell oblique-ovate, white, and translucent; whorls 6½; spire elevated conical with distinct suture. Shell surface glossy with fine transverse ridges that diminish below the periphery; following whorls regularly coiled. Shell periphery rounded and last whorl axially deflected. Aperture subcircular; peristome expanded, thickened, discontinuous, and reflected. Apertural dentition with one strong parietal, one small upper palatal, one small palatal, and one basal lamella. Umbilicus open and deep (Fig. 7A, B).
Distribution. This species has been recorded from several localities in Peninsular Thailand (Siriboon et al. 2020) along the southeastern part of the Tenasserim Range. However, only one specimen was collected in Myanmar from the Tanintharyi Region.
Remarks. The only shell was collected from the limestone hills at Buddha Cave, Tanintharyi Region; it matches well with this species. Oophana mouhoti was originally described based on specimens in the collection of H. Cuming with the very brief collection locality given as Siam. The NHM, London holds a lot of three specimens in the Cuming collection collected by H. Mouhot but has Camboja as the collection locality. This specimen lot does not have Pfeiffer' handwriting on the label; therefore, they are considered possible syntypes. However, Mouhot's recorded localities were generally imprecise. No additional specimens for this species are available, nor are records or literature references from Cambodia, other than peninsular Thailand . A similar situation of imprecise type locality records with Mouhot-collected specimens have been clarified in the case of helicarionid species (see Pholyotha et al. 2020). The recent works on land snails from Thailand confirmed that the specimens from the limestone hills along peninsular Thailand identified as O. mouhoti match well with the possible syntype. Therefore, peninsular Thailand (Petchaburi and Prachuap Khiri Khan provinces) are possibly the collecting locality for this species. Furthermore, H. Mouhot visited Petchaburi Province once from May to August in 1860 [see travel routes map in Mouhot (1864a, b)]. Additionally, Streptaxis johswichi Martens, 1864 was described based on specimens collected from Petchaburi Province, Thailand. Later, Martens (1867)  Description. Shell oblique-ovate, white, translucent; whorls 6-7; spire convex with distinct suture. Shell surface glossy with fine transverse ridges, nearly smooth with few transverse ridges near peristome. Embryonic shell ~ 2½ whorls with smooth surface; following whorls regularly coiled. Shell periphery rounded; last whorl slightly axially deflected. Aperture subcircular; peristome continuous, expanded, slightly reflected, and very short sinulus. Apertural dentition with one strong parietal, one palatal, and one strong columella lamella. Umbilicus open and deep (Fig. 7C, D).
Distribution. This species is only known from the type locality, the southern part of Myanmar (Stoliczka 1871).
Remarks. No new specimens were collected in this survey; however, authenticated museum specimens were examined. Regarding genitalia, Oophana obtusus and Haploptychius burmanicus were the first two species anatomically examined and illustrated among several streptaxids in Myanmar by Stoliczka (1871), who noted that there was no noticeable difference in reproductive forms between these two species. Based on the genitalia drawing, O. obtusus has a thick penial sheath covering almost the entire penis, and vas deferens not inserted into the penial sheath, but the lengths of vagina and atrium are unclear. Thus, the description and drawing remain insufficient to confirm the distinguishing characters of this species. Diagnosis. Oophana laevis differs from O. mouhoti and O. obtusus by having a rounded penultimate whorl, convex spire, and apertural dentition with parietal and basal lamellae. Although O. mouhoti and O. obtusus have a slightly angular penultimate whorl and elevated spire, O. mouhoti usually has only a parietal lamella (sometimes with basal lamella). In contrast, O. obtusus has parietal, palatal, and columellar lamellae.
Distribution. This species is known only from the type locality, which was mentioned only as 'Tenasserim' (Blandford 1899). This locality possibly refers to the Tanintharyi Region, southeastern Myanmar.
Remarks. No new specimens were collected in this study. However, we compared the possible type specimen with the other congeners. Blanford (1899) clearly stated that the type series was collected by Beddome and consisted of three specimens. However, the NHM, London holds a lot of only a single specimen from the Beddome collection, with the word India, probably added at a later date, on the label. Therefore, we consider this lot to be a possible syntype.
Type species. Helix perrotteti Petit, 1841 by subsequent designation by Forcart (1946: 215). Diagnosis. Shell oblique-heliciform, and translucent. Longitudinal furrows present behind apertural lip. Apertural dentition usually consists of two parietal, one palatal, one basal and one columellar lamella, and upper palatal and supracolumellar lamellae may be present. Genitalia with long and slender penis, penial sheath thin and not extending the entire penis length. Penial hooks dense, pale brown, expanded at base, with pointed tips, located on penial papillae, and curved towards genital orifice. Vaginal hooks may be present.
Remarks. Perrotettia and Discartemon are generally similar in having complex apertural dentition; however, their shell morphology is obviously different. Perrottetia has a sub-heliciform shell, smaller size, last whorl rounded and more or less deflected, and mostly with two parietal lamellae. Although parietal, palatal, basal and columellar lamellae are always present in Perrottetia, possession of second parietal, upper palatal and supracolumellar lamellae is variable, as is the presence of bifid lamellae (Siriboon et al. 2013;Inkhavilay et al. 2016;Bui et al. 2019). In contrast, Discartemon exhibits flattened to globose-heliciform shells, last whorl rounded to angular and less deflected with, usually, one parietal lamella.
At present, the genus Perrottetia is comprised of about 30 nominal species distributed from India and Sri Lanka to Indochina and southern China (Kobelt 1906;Richardson 1988;Schileyko 2011;Siriboon et al. 2013;Inkhavilay et al. 2016). So far, P. theobaldi Benson, 1859 is the only species known from Myanmar. Diagnosis. Perrottetia theobaldi is similar to P. dugasti (Morlet, 1892) from Vietnam; however, the former species can be distinguished by having a second parietal lamella running to the main parietal lamella, thicker and less reflected peristome, subquadrangular aperture, and shallow suture. In contrast, P. dugasti has a weak second parietal lamella running to the sinulus, thinner and more reflected peristome, semi-ovate aperture, and a deeper suture with a clear bifid columellar lamella. Similarly, P. mabillei (Bavay & Dautzenberg, 1903) from Vietnam can be separated from P. theobaldi by its strong radial ridges, wide and short sinulus, basal lamella absent, bifid columellar lamellae, and deep umbilicus, while P. theobaldi has a smooth shell surface, long and narrow sinulus, strong basal lamella, columellar lamellae separated, and shallow umbilicus. Furthermore, P. theobaldi differs from the Thai species P. aquilonaria Siriboon & Panha, 2013 by having a shallow suture, narrow and long sinulus, rounded last whorl, peristome thicker and less reflected, aperture subquadrangular and columellar lamellae are separated. In contrast, P. aquilonaria possesses deep suture, shorter and wider sinulus, the last whorl shouldered, aperture subcircular, more expanded peristome, and bifid columellar lamella.
Description. Shell sub-oblique heliciform, white, and translucent; whorls 5-5½; spire convex with distinct suture. Shell surface glossy with transverse ridges that diminish below periphery. Embryonic shell ~ 2½ whorls with smooth surface; following whorls regularly coiled. Shell periphery rounded; last whorl axially deflected; two deep and short longitudinal furrows present. Aperture triangular with sinulus; peristome continuous, thickened, expanded, and reflected. Apertural dentition with one large and strong parietal, nearly adjoined small second parietal lamella; adjoined at right angles, one small upper palatal, one strong palatal, one strong basal, and bifid columellar lamella. Columellar lamella is sometimes absent. Umbilicus narrow (Fig. 8). Distribution. This species has been widely recorded from India to Bhutan and Myanmar (Blanford and Godwin-Austen 1908;Ramakrishna et al. 2010;Gittenberger et al. 2021). In Myanmar, the previous record was from Bhamo, Kachin State (Blanford and Godwin-Austin 1908) and the empty shells together with H. thebawi (Godwin-Austin, 1888) were found from Shan State in this sampling.
Remarks. All the specimens of P. theobaldi (Fig. 8) showed slight differences in the apertural dentition and peristome positions, particularly the columellar and supracolumellar lamellae that are closer or almost united compared to the specimens from the Aik Kham Cave, Shan State (Fig. 8D). However, all were collected from the same range; we place them as the same species.

Genus Haploptychius von Möllendorff, 1906
Haploptychius von Möllendorff in Kobelt, 1906: 127. Zilch 1960: 562. Richardson 1988 Diagnosis. Shell oblique-heliciform to ovate and last whorl deflected. Penultimate whorl round to bluntly angular and extended beyond last whorl. Apertural dentition includes only one parietal lamella. Genitalia with penial sheath thin to thick and extending ~ 1/2 to entire penis length. Penial hooks dense, slightly expanded at base, tips pointed, located on low to high conical papillae and vaginal hooks absent.
Remarks. Haploptychius is almost identical with Carinartemis in having a deflected last whorl, extended penultimate whorl, and bearing a single parietal lamella. However, Haploptychius can be recognized by its oblique-ovate shell and rounded to angular penultimate whorl, while Carinartemis possesses an oblique-heliciform shell with sharply keeled penultimate whorl. In genitalia, Haploptychius has long and slender penial hooks, without vaginal hooks, while Carinartemis possesses shorter and blunt penial hooks, and sometimes transparent vaginal hooks may be present (Siriboon et al. 2014b;Inkhavilay et al. 2016).
A recent molecular phylogeny revealed that Haploptychius is polyphyletic, and the traditional genus concept using shell shape and apertural dentition seems unreliable (Siriboon et al. 2020). However, further intensive genital examination and molecular analysis of the type species are necessary to restrict the Haploptychius s.s., and generic revision absolutely requires both forms of evidence. Therefore, since the morphological and molecular evidence have never been evaluated, we follow the traditional genus concept in recognizing the streptaxids with oblique-heliciform shells and only one parietal lamella as members of the genus Haploptychius s.l.
Currently, the genus Haploptychius is comprised of about 40 nominal species distributed from India to Indochina, southern and central China, and Sulawesi of Indonesia (Kobelt 1906;Blanford and Godwin-Austen 1908;Zilch 1961;Richardson 1988;Schileyko 2000;Do and Do 2015;Inkhavilay et al. 2016). In addition, five species of Haploptychius s.l. have been documented mainly in southeastern Myanmar (Blanford and Godwin-Austen 1908), and three new species are added in this study. Fig. 9 Helix bombax Benson, 1859b: 186. Fig. 9C). Diagnosis. Haploptychius bombax can be differentiated from H. burmanicus by having a large oblique-ovate shell, without sinulus, and larger or wider last whorl. In contrast, H. burmanicus possesses a small sub-oblique heliciform shell, wide sinulus, and compressed last whorl. Compared with H. pellucens (Pfeiffer, 1863) from Laos, H. bombax differs by having strong radial ridges, convex spire, and narrow umbilicus, while H. pellucens exhibits a nearly smooth surface, more ovate shape, elevated spire, and umbilicus widely open.
Distribution. Haploptychius bombax is only known from the type locality in southeastern Myanmar (Benson 1859b). Remarks. The original description mentioned only 5½ whorls, but the museum specimen (Fig. 9C, D) had 7 whorls. This study collected no specimens, but authenticated museum specimens (juveniles and adults) were examined. Fig. 10A Diagnosis. Haploptychius fischeri (Morlet, 1887) almost shares the same shell form as H. blanfordi, but the latter possesses a more depressed shell, penultimate whorl more bulging, aperture wider, longer and subquadrangular shape.
Distribution. This species has been recorded with a wide distribution range from Arakan [Rakhine State], Pegu [Bago Region], and Shan State in Myanmar. However, the record from Cocos Islands in the southern Indian Ocean by Blanford and Godwin-Austen (1908) needs to be verified with modern evidence rather than by shell morphology alone.
Remarks. The taxonomic status of this species is still ambiguous because it is identical in shell morphology to Streptaxis birmanica. Theobald (1864)  scribed Streptaxis blanfordi and Streptaxis birmanica based on specimens from the same geographical area as Pegu. These two nominal species resemble each other in having one parietal and one palatal lamella, whereas they differ in only minor characters of shell shape and size. In this revision, we consider these two nominal species as synonyms. Only the type specimens of H. blanfordi could be located and examined; we therefore consider Streptaxis birmanica as the junior synonym.
The original spelling of the species was blanfordi, which was intentionally modified to blanfordianus by Stoliczka (1871) but for an unclear reason. This subsequent spelling of blanfordianus is an unjustified emendation made available with its own authorship and date, and so became a junior objective synonym (ICZN 1999: Arts 32.3, 33.2.3, 50.5).
Theobald (1864) clearly stated that Streptaxis birmanica W. Blanford, (in MSS.) was described based on a single specimen received from W.T. Blanford. However, we could not locate this single shell as the holotype fixed by monotypy. Theobald (1864) also stated that the other two shells lacked the palatal lamella and were of a relatively smaller size, which are recognized as distinct varietal entities. Therefore, these two specimens are excluded from the type series of Streptaxis birmanica. The authorship was originally attributed to W.T. Blanford as the manuscript name. However, since Blanford did not write the description or credit the description to W.T. Blanford, the taxon is attributed to Theobald only (ICZN 1999: Art. 50.1.1). ( Description. Shell oblique-heliciform, white, and translucent; whorls 6; spire convex with distinct suture. Shell surface glossy with fine transverse ridges that diminish below periphery. Embryonic shell ~ 2½ whorls with smooth surface; following whorls regularly coiled. Shell periphery rounded; last whorl axially deflected. Aperture semiovate; peristome continuous; sometimes discontinuous, thin, expanded, and slightly reflected. Apertural dentition with one strong parietal lamella. Umbilicus open and deep (Fig. 10D). (Blanford 1865). Outside Myanmar, it is also reported from Mizoram in India (Ramakrishna et al. 2010); however, this record needs to be verified.

Distribution. Haploptychius burmanicus is still known only from the type locality in southern Myanmar
Remarks. This species highly resembles H. blanfordi in shell form, but H. burmanicus is more globosely heliciform, with a higher spire and only one parietal lamella. Without anatomical information, the generic placement of this species is still tentative, and we retain this as Blanford and Godwin-Austen (1908). In addition, H. perlissus Vermeulen et al. 2019 from Vietnam (Vermeulen et al. 2019: figs 49-51) can be distinguished from H. burmanicus by having an oblique-ovate shell, less extended penultimate whorl from the last whorl, lower to nearly flattened spire, the palatal side is almost straight, basal side rounded, and columellar side broadly rounded, whereas H. burmanicus has a higher spire, more compressed shell, and the last whorl is more axially deflected.

Haploptychius solidulus (Stoliczka, 1871) Figs 1, 11
Streptaxis solidulus Stoliczka, 1871: 166, pl. 7, fig. 10  Diagnosis. Among the Haploptychius species from Myanmar, this species is distinctly large with an oblique-ovate shell, and less deflected last whorl. Haploptychius solidulus has almost the same shell form as Oophana mouhoti. However, it differs from O. mouhoti by having somewhat enlarged last whorl, more deflected last whorl, and a conical spire with only one parietal lamella. In contrast, O. mouhoti shows a depressed and obtuse conical spire, with one parietal and small basal lamellae.
Description. Shell oblique-ovate, white, and opaque; whorls 6½-7; spire elevated conical with distinct suture. Shell surface glossy with fine transverse ridges that diminish below periphery. Embryonic shell ~ 2½ whorls with smooth surface; following whorls regularly coiled. Shell periphery rounded; last whorl axially deflected. Aperture semi-ovate; peristome discontinuous, thickened, expanded, and slightly reflected. Apertural dentition with one strong parietal lamella. Umbilicus open and deep (Fig. 11). Distribution. This species appears to be restricted to limestone karsts and is only recorded from southern Myanmar.
Remarks. Stoliczka (1871) mentioned the specimens received from Theobald, who collected at Yethebiankoo [Rathe Pyan Cave] on the Attaran river, south-east of Moulmein [Mawlamyine]. Therefore, the exact type locality is assumed to be Rathe Pyan Cave, but it is located southwest of Hpa-an, Kayin State. Unfortunately, no living specimens could be examined.  Fig. 12D, E). Diagnosis. Haploptychius thebawi is similar to H. solidulus in having a high conical spire and globosely ovate shell. The former species can be discriminated by its smoother shell surface and narrower aperture, more rounded and extended penultimate whorl, and less inflated last whorl. Additionally, H. thebawi resembles H. porrectus (Pfeiffer, 1863) from Laos in having strong radial ridges, conical spire, and an inflated and deflected last whorl, whereas H. thebawi exhibits a larger shell, less depressed and deflected last whorl, fine radial ridges, and higher spire.
Distribution. This species occurs in central-eastern Myanmar, based on the type locality and two localities in Shan State, one locality in Mandalay Region, and it is relatively low in population density.
Remarks. Originally, H. thebawi was described based on specimens from Pingoung, Shan Hills, which is probably now referred to as Pinlaung Township, Taunggyi District, Shan State. Unfortunately, the type specimens of H. thebawi could not be located in the NHM, London collection. However, the specimens examined herein match well with the original description and the syntype illustrated in Gude (1903: figs 11-13). Despite that, the specimens from Mandalay Region tend to have a more ovate shell and elongated last whorl, and their smooth shell surface, narrow umbilicus, and conical spire make them most similar to this nominal species. Therefore, we treat this population as an intraspecific variation. Examination of genitalia of specimens from this population is necessary to clarify their taxonomic status.
Blanford and Godwin-Austen (1908) treated this nominal species as a junior synonym of H. burmanicus. However, the recently collected specimens of H. thebawi can be distinguished from H. burmanicus and H. blanfordi by having an oblique-ovate to oblique-heliciform shell, elevated and conical spire, nearly smooth shell surface, penultimate whorl extended beyond last whorl, only one parietal lamella, and narrow umbilicus. Conversely, the two latter species have sub-oblique heliciform shells, depressed spire, prominent radial ridges on the shell surface, penultimate whorl slightly extended beyond the last whorl, with one parietal and one palatal lamella, and a wide umbilicus. Therefore, we consider H. thebawi to stand as a separate species.
Among three populations of H. thebawi (Table 1), Aik Kham Cave specimens have the smallest size with a more depressed shell, followed by Ywangan Village; Apache Cement Factory specimens have the largest shell with more conical spire and rounded last whorl. Type locality. This new species was found from the limestone karsts near Lampane Village, Tanintharyi Region, Myanmar (11°40'18.1"N, 99°13'30.1"E).

Haploptychius tenasserimicus
Etymology. The specific name tenasserimicus refers to the type locality of this new species located on the Tenasserim Mountain Range, which forms the backbone of Indochina.
Diagnosis. This species is distinguishable by its small size, angular penultimate whorl, low convex spire, and aperture that elongates and grows almost horizontally. Haploptychius tenasserimicus sp. nov. differs from H. burmanicus and H. blanfordi species by having oblique-ovate shells, prominent transverse ridges, higher spire, rounded penultimate whorl, and less deflected last whorl. This new species also differs from H. blaisei (Dautzenberg & Fischer, 1905) from Laos and Vietnam by having a relatively smaller shell (width ~ 8 mm), nearly flattened spire, angular penultimate whorl and rounded last whorl. In contrast, H. blaisei possesses a relatively larger shell (width Figure 13. A-C Haploptychius tenasserimicus sp. nov. A holotype CUMZ 13011 with apertural dentition B, C paratypes CUMZ 13012 from the type locality D Haploptychius heliakosus sp. nov. holotype CUMZ 13013 with apertural dentition. 10 mm), higher spire, rounded penultimate whorl, and compressed last whorl. In addition, H. tenasserimicus sp. nov. can be distinguished from H. dorri (Dautzenberg, 1894) from Vietnam (see Inkhavilay et al. 2016) by having a more depressed and larger shell (width ~ 8 mm), angular penultimate whorl, aperture longer and more axially deflected last whorl. Haplotychius dorri exhibits a depressed and smaller shell (width ~ 5 mm), smooth shell surface, rounded penultimate whorl, shorter aperture and last whorl less axially deflected from the vertical axis.
Distribution. This species was only collected from the type locality; limestone hills in primary forest in the Tanintharyi Region, Myanmar.
Remarks. The genitalia information is not known. Diagnosis. Haplotychius heliakosus sp. nov. differs from H. bombax by having a deeper suture, higher spire, rounded penultimate whorl, and subquadrangular aperture. In contrast, H. bombax possesses a relatively shallower suture, lower spire, angular penultimate whorl, and semi-ovate aperture. Haplotychius heliakosus sp. nov. also differs from H. burmanicus and H. blanfordi by having an oblique ovate shell, higher spire, and less axially deflected last whorl. In contrast, the two latter species exhibit a depressed heliciform shell and lower spire, and more axially deflected last whorl. Although H. heliakosus sp. nov. has a shell similar to H. pellucens from Laos, this new species has a less axially reflected last whorl, subquadrangular aperture, and more ridges on the shell surface. Additionally, the genitalia of H. heliakosus sp. nov. has a thickened penial sheath covering almost the entire penis, and short and stout penial hooks on papillae, while H. pellucens has a thin penial sheath covering ~ 1/2 of the penis, and long and slender penial hooks without papillae. This new species differs from C. exacutus (Gould, 1856) by having penial sheath retractor muscle originating at atrium, vas deferens passing through a short section of thin penial sheath before extending ~ 1/3 of the penial sheath length to the curved portion, shorter free oviduct, seminal vesicle ca. twice the length from talon to branching point of seminal vesicle, thickened atrial folds with sparse atrial pores, and stout distal penial hooks.
Genital organs. Atrium (at) short. Penis (p) very thin, and long tube. Penial sheath (ps) muscularly enlarged, very thickened, and extending entire penis length; penial sheath retractor muscle (psr) thin, originating at atrium, and inserting distally on penial sheath (Fig. 15A). Vas deferens (vd) passes through a short section of thin penial sheath then extends ~ 1/3 of the penial sheath length to a curved portion before entering penis distally. Curved portion with very thin connective tissue attached between vas deferens and penial sheath wall (Fig. 15B). Penial retractor muscle (pr) thin, very long, inserting at junction of penis and vas deferens.
Vagina very short, stout, and ~ 1/10 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) enlarged, tapering to a smaller tube in the middle part, then enlarged distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short, and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) of about twice the length from talon to branching point of seminal vesicle (Fig. 15A).
Vaginal wall with longitudinal vaginal folds (Fig. 16I), folds with nearly smooth surface, and vaginal hook absent.
Radula. Each row consists of ~ 35 teeth with formula (17)-1-(17). Central tooth very small with pointed cusp. Lateral and marginal teeth undifferentiated, lanceolate, unicuspid, and lanceolate. Latero-marginal teeth gradually reduced in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 24C). Etymology. The specific name heliakosus is derived from the Greek word heliakos meaning of the sun. It honors our colleague, Dr. Arthit Pholyotha, who collected the specimens and took the photos of the living snails used in this study. His first name Arthit means the Sun.
Distribution. This new species is currently known from two localities in the limestone karsts near Salween (Thanlwin) Basin, Kayin State, southeastern Myanmar.
Remarks. Shell variations of H. heliakosus sp. nov. were found between two populations. Specimens from the Kyonknow population (Fig. 14B) have a straighter periphery or nearly cylindrical last whorl compared to those from the type locality, Bardai Mountain (Fig. 13D, 14A). As no living specimens from the Kyonknow Cave were collected, we considered the Kyonknow population as an intraspecific variation of H. heliakosus sp. nov. because this locality is very close to the type locality. Living specimens from the Kyonknow population and genital examination are necessary to resolve these systematic issues.
Diagnosis. Haploptychius karenorum sp. nov. can be differentiated from H. heliakosus sp. nov. by having a convex spire, penultimate whorl angular and extended well beyond the diameter of the last whorl, and more axially deflected last whorl. In contrast, H. heliakosus sp. nov. possesses an elevated spire, penultimate whorl rounded, less extended beyond the diameter of the last whorl, and less axially deflected last whorl. This new species differs from H. bombax by having an angular penultimate whorl, more axially deflected last whorl, subcircular aperture, and broadly expanded lip. In comparison, H. bombax has a rounded penultimate whorl, less axially deflected last whorl, semi-ovate aperture, with thickened and slightly expanded lip. For further comparison, H. karenorum sp. nov. differs from H. burmanicus, H. blanfordi, and H. thebawi in having a more axially deflected last whorl, lower spire, penultimate whorl angular and strongly extended beyond the diameter of the last whorl, and without sinulus. The three latter species have an elevated spire, penultimate whorl rounded and slightly extended beyond the diameter of the last whorl, and less axially deflected last whorl.
Description. Shell oblique-ovate, solid and translucent; whorls 6-7½; spire depressed convex and with distinct suture. Embryonic shell ~ 2½ whorls with smooth surface; following whorls growing regularly and last whorl intermediately expanded. Shell surface has moderately strong radial ridges that diminish below periphery of last whorl and around umbilicus. Penultimate whorl bluntly angular and extended beyond last whorl. Last whorl compressed to flattened, axially deflected from columellar axis. Aperture subcircular; peristome thickened, expanded, and slightly reflected. Apertural dentition with one strong parietal lamella. Umbilicus widely open and deep (Fig. 14C-E).
Etymology. The specific name karenorum refers to the Karen people, the major ethnicity in Kayin State, Myanmar.
Distribution. This species is known from two localities in the limestone karts of Kayin State, southern Myanmar.
Remarks. Comparing populations from the two localities, shells of H. karenorum sp. nov. from the Taung Lay population (Fig. 14E) have a more elevated spire and weaker parietal lamella. However, the bluntly angular penultimate whorl and oblique ovate shells are identical to the type specimens, which we consider an intraspecific shell variation. However, these two localities are quite distant from each other, and on opposite sides of the Attaran River (Fig. 1). Thus further, genitalia information will help determine whether they are just geographical variations.

Type species. Carinartemis vesperus Siriboon & Panha, 2014 by original designation.
Diagnosis. Shell obliquely heliciform and with conical spire. Penultimate whorl keeled and extended beyond the diameter of the last whorl. Last whorl rounded to shouldered and strongly axially deflected. Aperture semi-ovate to subcircular; apertural dentition with or without one or two parietal lamellae. Genitalia with thin to thick penial sheath that covers entire penis length; penial hooks and vaginal hooks may be present.
Remarks. The genus is comprised of two endemic species occurring in limestone outcrops in western Thailand. A recent phylogenetic study revealed that the previously recognized Haploptychius petitii (Gould, 1844) and Indoartemon medius Siriboon & Panha, 2014 are clustered with members of the Carinartemis (see Siriboon et al. 2020) with strong support. Siriboon et al. (2020) suggested reassigning these two species into Carinartemis. Therefore, based on this phylogenetic result, the previously recognized H. petitii is relocated here under the genus Carinartemis. Fig. 17A, B

Material examined. Syntype
Diagnosis. Carinartemis petitii can be distinguished from C. sankeyi (Benson, 1859) by having a fine transverse ridge on the upper periphery, penultimate whorl keeled and little extended beyond the diameter of last whorl, and a subcircular aperture. In addition, C. petitii differs from I. medius from Thailand by having a more axially deflected last whorl, and only one parietal lamella present, while I. medius has a less axially deflected last whorl, and with one additional small palatal lamella. Carinartemis petitii is superficially similar to H. blaisei but it has an elevated spire, keeled penultimate whorl, subcircular aperture, and thicker lip.
Distribution. This species is known from the type locality in Myanmar (Gould 1844) and Kanchanaburi Province in Thailand (Siriboon et al. 2020).
Remarks. No new specimens were collected in this survey. However, the syntype (Fig. 17A) and the museum specimens (Fig. 17B) show slightly different shell forms. Carinartemis petitii is similar in shell form to the genus Haplotychius in having one parietal lamella and a deflected last whorl. However, an initial molecular analysis placed this species within the Carinartemis clade (Siriboon et al. 2020). This species is clearly distinct from other recognized Carinartemis species by its oblique-heliciform shell, translucence and a high to low conical spire with a distinct suture. Moreover, the shell surface has fine transverse ridges that diminish below periphery, whorls regularly coiled, shell periphery is keeled; umbilicus open and deep. Aperture is semi-ovate, peristome thickened, expanded, reflected, and apertural dentition with one strong parietal lamella.  Streptaxis exacutus -Pfeiffer 1871: 30, 31, pl. 115, figs 13, 14. Hanley and Theobald 1874: 40, pl. 98, figs 8-10. Nevill 1878: 3. Tryon 1885: 72, pl. 14, figs 11, 12. Blandford and Godwin-Austin 1908: 8. Haploptychius exacutus -Kobelt 1906: 142, 143, pl. 57, figs 16-18. Richardson 1988: 215. Siriboon et al. 2014b.  Panha, 2014, andC. striatus Siriboon &Panha, 2014 from western Thailand, but it has a larger shell, convex spire, immediately expanded penultimate whorl, semi-ovate aperture, two parietal lamellae, very thickened penial sheath, vas deferens passes through penial sheath, curved portion of vas deferens with very thin connective tissue, and hooks located on irregular trapezoidal penial papillae separated by longitudinal folds. In comparison, C. sankeyi, C. vesperus, and C. striatus have an elevated spire, regularly expanded penultimate whorl, but C. sankeyi has fine transverse ridges on the entire shell, subquadrangular aperture, one parietal lamella, slender atrium, thin penial sheath, vas deferens does not pass through a penial sheath, curved portion of vas deferens is without connective tissue, proximal penial hook located on laterallyflattened penial papillae, and distal penial hooks located on laterally compressed penial papillae separated by reticulated folds. In contrast, C. vesperus has a subcircular aperture, lacks parietal lamellae, has a less axially deflected last whorl, vas deferens passes through the penial sheath, curved portion of vas deferens is without connective tissue, and penial papillae absent. Meanwhile, C. striatus has strong transverse ridges over the entire shell, a semi-ovate aperture, one parietal lamella, vas deferens is attached to the distal end of the penial sheath with very thin connective tissue, and hooks are located on papillae without connected longitudinal folds.
Description. Shell oblique-heliciform, white, and translucent; whorls 6-6½; spire convex with distinct suture. Shell surface glossy with fine transverse ridges, nearly smooth with few transverse ridges near peristome; varices present. Embryonic shell ~ 2½ whorls with smooth surface; following whorls intermediately coiled. Shell periphery wide and sharply keeled along nearly the entire penultimate whorl; last whorl axially deflected. Aperture semi-ovate; peristome discontinuous, thickened, expanded, and slightly reflected. Apertural dentition with one strong parietal lamella and sometimes with a second parietal lamella adjoined at a right angle. Umbilicus open and deep (Figs 17C,D,18).
Genital organs. Atrium (at) short. Penis (p) a very thin, and long tube. Penial sheath (ps) muscularly enlarged, very thickened and extending entire length of penis; penial sheath retractor muscle (psr) thin, originating near genital orifice, attached to atrium with short and thin connective tissue, and inserting distally on penial sheath (Fig. 21A). Vas deferens (vd) passes through a short portion of penial sheath, then extends to curved portion at ~ 1/11 of the penial sheath length before entering penis distally. Curved portion of vas deferens with very thin connective tissue originating at penial sheath (Fig. 21B). Penial retractor muscle (pr) thin, very long, inserting at penis and vas deferens junction.
Vagina (v) very short and ~ 1/12 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) enlarged then tapering to smaller diameter distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) ~ 1/2 the length from talon to branching point of seminal vesicle (Fig. 21A).
Vaginal wall with longitudinal oblique vaginal folds, folds with nearly smooth surface and vaginal hook absent (Fig. 22G).
Distribution. This species was collected from five limestone hills in Kayin State, southern Myanmar, in this survey.
Remarks. This species appears at a high abundance among the limestone karsts in Hpa-an, Kayin State. All the specimens examined from the populations from Lun Nga Mountain and Bayin Nyi Cave have a very small to indistinct upper parietal lamella, and some specimens from Bayin Nyi Cave have strong transverse ridges on almost the entire whorl. Moreover, the Lun Nga Mountain population have a last whorl that is more extended anteriorly and an elongated semi-ovate aperture (Fig. 18C). However, the genitalia in all localities show no difference from this locality; thus, we consider them as intraspecific variations within C. exacutus. Some specimens from Bayin Nyi Cave have strong transverse ridges on almost the entire whorl.
Genital organs. Atrium (at) short, thin and slender. Penis (p) very thin and long. Penial sheath (ps) thin and extending nearly entire length of penis; penial sheath   retractor muscle (psr) thin, originating near genital orifice and attached to atrium with short and thin connective tissue, and inserting distally on penial sheath (Fig. 21C). Vas deferens (vd) runs downwards to curved portion, ~ 1/3 of the penial sheath length, without insertion before entering penis distally (Fig. 21D). Penial retractor muscle (pr) thin, very long, inserting at penis and vas deferens junction.
Vagina (v) short, stout and ~ 1/5 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) enlarged then tapering to smaller diameter in middle section, and slightly enlarged distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) ca. the same length as from talon to branching point of seminal vesicle (Fig. 21C).
Vaginal wall generally smooth with vaginal pores, and vaginal hook absent (Fig. 23H).
Distribution. This species occurs from three localities in Mon State, southern Myanmar and is likely to be endemic to this area.
Remarks. Benson (1859a) introduced C. sankeyi based on a single specimen from 'Moulmein'. Later, Stoliczka (1871) provided some diagnostic characters with a description of the soft body color and suggested that the Farm-Cave is possibly the correct type locality. This historical locality name refers to a group of caves located on a karst ridge, namely Kayon Hill, situated on the west bank of the Attaran River. At the same time, Stoliczka (1871) proposed Streptaxis hanleyanus based on a single specimen with a small and depressed shell, wide umbilicus, and almost rectangular aperture. However, this holotype specimen was collected from the same geographical area as C. sankeyi. Therefore, we consider this nominal species as a smaller shell form and so treat it as a junior synonym with C. sankeyi.
The original spelling of this nominal species was sankeyi, which was intentionally modified to sankeyanus by Stoliczka (1871) without a clear reason. Therefore, this unjustified emendation name was made available with its authorship and date and became a junior objective synonym (ICZN 1999: Arts 32.3, 33.2.3, 50.5).
Recently, the population collected from Dhammatat Cave showed a more rectangular aperture, slightly compact penultimate whorl, and larger parietal lamella (Fig. 20C), but this species could only be examined from the empty shells. Therefore, we have to conclude that these differences are an intraspecific variation until more specimens are available, or at least the genitalia.

Discussion
This research presents all known Streptaxidae in Myanmar, comprising eighteen species belonging to five genera (Carinartemis, Discartemon, Haploptychius, Oophana, and Perrottetia), including fourteen formerly known species and four new species (Table 2). In addition, this study has added the first anatomical information for three formerly known species (D. tonywhitteni, C. exacutus, and C. sankeyi) and one new species (H. heliakosus sp. nov.). The diversity yielded from the southern part of Myanmar (four genera with nine species) was higher than in the central-northeast part (two genera with two species). However, the number of streptaxid taxa found in the central-northeast part of Myanmar are believed to be low because sampling could only be conducted in a few areas. Further land snail surveys should also focus on areas we could not cover in this expedition, such as Rakhine State and Bago Region, areas that contain many of the formerly known species (Theobald 1864;Blanford 1865).
Most reported streptaxids in Myanmar occupy a narrow distribution, and some species were found in only a single area, such as one species of Perrottetia in Shan State, two species of Discartemon in the Tanintharyi Region, and two species of Carinartemis in Kayin and Mon States, which are adjacent regions. In contrast, Haploptychius has a wide distribution, ranging from central-northeastern to southern Myanmar, including previously recorded localities, such as Rakhine State and the Bago Region (Theobald 1864;Blanford 1865). Notably, the shell size of streptaxids from the northern part of Myanmar is smaller than those from the southern part, and the population density is also lower. In southern regions, geomorphological and climatic conditions seem to offer more favorable habitats for snails (Siriboon et al. 2020;Sutcharit et al. 2020). On the other hand, this may reflect very narrow distribution ranges, naturally low population levels, or difficulty in finding the northern species due to their smaller size. The two species from the genus Discartemon are clearly different in shell morphology, genital structure, and geographic distribution. Discartemon tonywhitteni is distributed on the mainland, while D. paurodeviatus sp. nov. occurs on an isolated island. Discartemon species are mainly localized in southern Thailand and Peninsular Malaysia (Siriboon et al. 2014a(Siriboon et al. , 2020. Herein, all previously documented species of Oophana have been redescribed, based on original descriptions compared with historical museum specimens except for O. mouhoti, a new record in Myanmar but based on only a single shell. Siriboon et al. (2020) reported this species from several localities in western Thailand, adjacent to Mon State and Kayin State, but it seems rare in Myanmar even though most the historical materials are recorded from Mawlamyine and Tanintharyi. A phylogenetic analysis revealed that O. mouhoti and O. strangulatus (von Möllendorff, 1894) were members of the same clade, and were distinct from other congeners in having a more cylindrical shell. In comparison to the Thailand species, most Oophana species from Myanmar show a more elongated globose-ovate shell form and weaker apertural dentition (see Siriboon et al. 2020), but O. elisa is still ambiguous. Genetically, Oophana from Myanmar appear to be closer to the O. mouhoti clade and have a similar shell shape and apertural dentition; however, the genital anatomy of the Oophana species remains largely unknown.
The most dominant genus, Haploptychius, are found mainly in Hpa-an, in the southern part of Myanmar. This genus also shows variability in its shell shape related to their geographic distribution. For example, snails from the (i) Kayin State have more nov. from the type population has an extra small tubercle next to the parietal lamella, and similarly, H. blanfordi has a small palatal lamella. While the male reproductive organ of the Haploptychius species in Laos shows a relatively thin penial sheath with slender, elongate penial hooks (Inkhavilay et al. 2016), surprisingly, H. heliakosus sp. nov. and C. exacutus superficially share a lack of differentiation in their external genitalia features by having a very thickened penial sheath that covers the entire penis, with broader basal penial hooks, and obvious penial papillae (Table 2). Further molecular analysis may suggest the possible cause of these shared characteristics among the streptaxids.
So far, five species in the genus Carinartemis have been recorded from Thailand and Myanmar (Siriboon et al. 2014b), of which four species have been investigated in terms of their genitalia. The distinctive traits of the male organs of Carinartemis from Myanmar are the possession of penial hooks with reticulated folds that are covered with penial papillae ( Table 2). The internal sculpture of the genitalia of C. exacutus and C. sankeyi could be useful in discriminating the species, although their shell morphology is highly similar, but distinct from the Thai species (Siriboon et al. 2014b). In addition, the shell shape shared among Carinartemis species was observed in H. karenorum sp. nov. and H. tenasserimicus sp. nov., which tend to have an angular penultimate whorl that extends beyond the last whorl. This angular or slightly keeled penultimate whorl also occurs in some species of Oophana and Indoartemon (Siriboon et al. 2020). As Siriboon et al. (2020) suggested, to stabilize the traditional taxonomic boundary in these groups, more information on at least the genitalia is required. Furthermore, these records of new biological diversity in Myanmar indicate the uniqueness of its ecosystems and should promote more discussion concerning conservation efforts in Myanmar.