Streptaxis discus Pfeiffer, 1851, by subsequent designation by Ancey (1884: 399).

The genus was recently revised. For complete illustrations, species descriptions and dichotomous key see Siriboon et al. (2014a).

Lectotype of Streptaxis discus Pfeiffer, 1853 NHMUK 20130684. Lectotype of Streptaxis paradiscus Möllendorff, 1900 SMF 108534 and paralectotypes SMF 108535 (5 shells).

Discartemon discus has been recently re-described from the shell, genitalia and radula, and type specimens were re-investigated and illustrated (see Siriboon et al. 2014a).

All previous records of this species were all from “Annam” (Siriboon et al. 2014a). This term is a historical political division during the colonial period, with an uncertain boundary. The distribution of D. discus (=D. paradiscus) in Laos was reported by Schileyko (2000: 784, 2011: 23). However, no specimens were found by the present study and the records from Laos remain to be confirmed.

Streptaxis sinensis Gould, 1859, by original designation.

Shell depressed to very distorted, mostly white-hyaline or transparent. Shell surface smooth and glossy or with fine radial ridges. Embryonic shell smooth; following whorls increasing regularly; penultimate whorls slightly to strongly extended beyond body whorl. Last whorl rounded and more or less deviated from the vertical axis. Umbilicus narrowly open and deep. Aperture sub-circular to semi-ovate. Peristome expanded and reflected. Apertural dentition always consisting of a single parietal lamella. Schileyko (2000) includes species with a “smooth” parietal wall, i.e. without a lamella in Haploptychius, but whether such taxa belong in this genus requires further investigation.

Live specimens exhibit a semi-transparent bright yellow body, sometimes with brownish spots; skin reticulated. Upper tentacles yellow to orange, long, with black eye-spot on tip; lower tentacles short. Brownish digestive gland and black kidney may be visible through transparent shell. Foot narrow, undivided and with short tail.

Genitalia with long and slender penis; penial sheath long, about a half to whole length of penis. Internal wall of penis with numerous long and slender penial hooks in longitudinal arrangement. Vas deferens passes under penial sheath before connecting apically to penis. Vagina and free oviduct short. Seminal vesicle present, convoluted and short. Vaginal hooks not found.

Currently, the genus Haploptychius consists of about 40 nominal species distributed from India to Indochina, south of China and Greater Sunda Islands (Kobelt 1906, Zilch 1961, Richardson 1988, Schileyko 2000). Fifteen species were reported from Indochina, of which only three species: H. pellucens (Pfeiffer, 1863), H. porrectus (Pfeiffer, 1863) and H. fischeri (Morlet, 1887) were recorded from Laos (see Gude 1903, Kobelt 1906, Schileyko 2011).

General shell morphology of Haploptychius is quite similar to Oophana Ancey, 1884 and Indoartemon Forcast, 1946. However, it differs in having only a parietal lamella; while Oophana usually has parietal, palatal, columellar and basal lamellae, and Indoartemon always has parietal and basal lamellae. In addition, the genitalia of Haploptychius have a penial sheath extends about a half to entire the penis length, vas deferens passes through penial sheath, and long slender penial hooks. In Oophana, the vas deferens enter the penial sheath apically with very short vagina (Berry 1963, Schileyko 2000); and Indoartemon, the vas deferens attached (not pass through) the penial sheath, with small and short penial hooks (Siriboon et al. 2013).

Carinartemis Siriboon & Panha, 2013 resembles Haploptychius in having only a parietal lamella. However, it differs from Haploptychius in its very sharp peripheral keel and having the last whorl more deviated from the vertical axis. In addition, the genitalia has thick or thin penial sheath, penial hook short and stout, and vaginal hooks present (Siriboon et al. 2014b).

The relatively large, distorted heliciform shell and dentition restricted to a parietal lamella clearly differentiate Haploptychius from Discartemon Pfeiffer, 1856 and Perrottetia Kobelt, 1905 (Schileyko 2000, Siriboon et al. 2013, 2014a, b).

This species was described from the H. Cuming collection. An illustration of the shell and one set of measurements were given in the original description. Three specimens from the Cuming collection at NHM have Pfeiffer’s handwritten label stating the species name and locality. In order to stabilise the name, an identical specimen matching with the illustration and measurements given in the original description is designated here as lectotype NHMUK 20160249.1 (Fig. 3A; H = 11.7, W = 11.2). The other two remaining shells from the same lot then became paralectotypes NHMUK 20160249.2 (2 shells; Fig. 3B; H = 11.1, W = 10.6 and H = 13.1, W = 13.4).

Figure 1. 

Approximate locations of the type localities of Haploptychius spp., Perrottetia spp., and Indoartemon spp. in Laos. Described species (●) Haploptychius pellucens, (○) Haploptychius porrectus, (★) Haploptychius blaisei, (△) Perrotettia aquilonaria, (▲) Perrottetia unidentata sp. n., (□) Perrottetia megadentata sp. n. and (■) Indoartemon diodonta sp. n. The numbered localities are detailed in Table 1, except locality no. 6 is from Tam Kao Rao, Vieng Phoukha, Luang Namtha, Laos, and no. 11 from Ban Bo Khoun, Boun Neua, Phongsaly, Laos.

Figure 2. 

Living snails of A Haploptychius pellucensCUMZ 6265, from Xayabouly (shell width about 11 mm) and B Haploptychius porrectusCUMZ 6273, from Xieng Khuang (shell width about 7 mm).

Figure 3. 

Shells of Haploptychius spp. A–C Haploptychius pellucens A lectotype NHMUK 20160249.1 with apertural dentition B paralectotype NHMUK 20160249.2, and C specimen CUMZ 6264, from Xayabouly D–F Haploptychius porrectus D lectotype NHMUK 20140750.1 E paralectotype NHMUK 20140750.2, and F specimen CUMZ 6273, from Xieng Khuang. G Haploptychius fischeri, lectotype MNHN-IM 200030873.

Cambodia: NHMUK MacAndrew coll. (4 shells). Ban Namone, Xayabouly, Laos (about 40 Km. from Ngeun District, Lao-Thai border to Xayabouly District): CUMZ6264 (Fig. 3C; 8 shells), 6265 (4 specimens in ethanol). Tam Phatok, Ngoi, Luang Phrabang, Laos: CUMZ 6267 (7 shells). Ngoi, Luang Phrabang, Laos: CUMZ 6268 (7 shells). Nam Ork Roo, Nathong, Namor, Oudomxay, Laos: CUMZ 6269 (29 shells), 2670 (6 specimens in ethanol; Figs 3A, B, 8A, 9A–F, 10G). Ban Oudom, Pak Beng, Oudomxay, Laos: CUMZ 6271 (15 shells). Tam Kao Rao, Vieng Phoukha, Luang Namtha, Laos: CUMZ 2672 (2 shells). Tam Mung Korn, Khamkeurt, Bolikhamxay, Laos: CUMZ 6266 (4 shells).

Shell. Shell oblique-ovate, white and translucent. Whorls 6½, spire conical with distinct suture. Shell surface glossy with thin transverse ridges which diminish below periphery. Embryonic shell about 2½ whorls, with smooth surface; following whorls regularly coiled. Penultimate whorl and last whorl rounded, axially deflected. Aperture subcircular; peristome thin, little expanded and reflected. Apertural dentition with one more or less strong parietal lamella. Umbilicus open and deep (Fig. 3A–C).

Radula. Each row consists of 77–85 teeth with formula (38-42)-1-(38-42). Central tooth very small, triangular, with a pointed cusp. Lateral and marginal teeth undifferentiated, lanceolate, unicuspid. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 10G).

Genital organs. Atrium (at) short. Proximal penis (p) stout about one-thirds of penis length; distal penis slender. Penial sheath (ps) thin, extending about half of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserted apically at penial sheath (Fig. 6A). Vas deferens (vd) passes through about one-third of penial sheath length before entering into penis apically. Penial retractor muscle (pr) very thick and connected at penis apically (Fig. 7A, B).

Internal wall of atrium generally corrugated with numerous atrial pores (Fig. 9A). Penial wall densely covered in light brown penial hooks, about 6 hooks/200 μm². Hooks located on low conical penial papillae, separated by thin reticulated folds. Penial hooks small (< 0.1 mm in length), long, slender, slightly expanded at base, tips pointed and curved towards genital orifice (Fig. 9B–E).

Vagina (v) short, about one-third of penis length. Gametolytic duct (gd) long tube extending to albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) proximally large with almost equal diameter to vagina, becoming narrower 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 and thin seminal vesicle. Seminal vesicle (sv) about three times longer than the length from talon to branching point of seminal vesicle (Fig. 7A).

Vaginal wall with series of transverse and undulated parallel vaginal folds; vaginal hooks absent (Fig. 9F).

This species is known from several limestone areas from central to northern part of Laos. The animals can be found at altitudes from 150-300 meters above mean sea level.

This species can be distinguished from H. porrectus by having a larger shell, more elevated spire elevated and less oblique aperture. The vas deferens passes through a shorter part of the penial sheath length, and the vagina wall has undulated transverse ridges rather than papillae. Haploptychius pellucens can be distinguished from H. costulatus (Möllendorff, 1881) from China by having a larger and thinner shell, narrower umbilicus andhaving the left periphery of the penultimate whorl extending beyond the diameter of the last whorl. Haploptychius fischeri differs from this species by having a larger, more depressed and thicker shell, with a more obtuse spire, and subquadrangular aperture (Fig. 3G).

All live adult specimens were dissected and the genitalia have been examined, and three different types of genitalia are observed. There are six fully adult specimens collected from Nam Ork Roo, Oudomxay with ‘normal’ genitalia (Fig. 8A). Two specimens from Ban Namone, Xayabouly have no male genital organs (penis, retractor muscle, vas deferens and prostate gland), while female genital organs are well developed and fully function (Fig. 8D). This is apparently the first report of aphallic animals in Streptaxidae. The other two specimens from Ban Namone, have a ‘normal’ penis, but have an enlarged and curved “vaginal caecum (vc)” near the penis and atrium junction (Fig. 8B, C). This too is an unusual or unique structure in Streptaxidae. Nevertheless, all these animals appear conspecific based on their shells and the causes of this variation are unknown.

This species was described from the H. Cuming collection. The number of specimens was not indicated, but only one set of measurements was given in the original description. The NHM collection contains two specimens from the Cuming collection that has Pfeiffer’s handwritten label stating the species name and collection locality. In order to stabilize the name, a specimen matching with the measurements given in the original description is designated here as lectotype NHMUK 20140750.1 (Fig. 3D; H = 8.0, W = 9.0). The other specimen from the same lot becomes a paralectotype NHMUK 20140750.2 (1 shell; Fig. 3E; H = 8.0, W = 8.2).

Laos: NHMUK 1906.1.1.770 (4 shells), NHMUK MacAndrew coll. (2 shells). Ban Nong Tang, Phoukood, Xieng Khuang, Laos: CUMZ 6273 (18 shells; Fig. 3F), 6274 (1 specimen in ethanol; Figs 2B, 7C, D). Tam Pew, Kham, Xieng Khuang, Laos: CUMZ 6275 (4 specimens in ethanol; Figs 9G–M, 10H).

Shell. Shell oblique-heliciform, white and translucent. Whorls 6½, spire conical, suture distinct. Shell surface glossy, with transverse ridges that diminish below the periphery. Embryonic shell smooth with 2½ whorls; following whorls regularly coiled. Penultimate whorl rounded; last whorls rounded and axially deflected. Aperture subcircular; peristome thickened and reflected. Aperture dentition with one parietal lamella. Umbilicus open and deep (Fig. 3D–F).

Radula. Each row consists of 46–58 teeth with formula (23-29)-1-(23-29). Central tooth very small and triangular, with a pointed cusp. Lateral and marginal teeth undifferentiated, lanceolate, unicuspid. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 10H).

Genital organs. Atrium (at) short. Proximal penis (p) stout about one-fifth of penis length; distal penis slender. Penial sheath (ps) thin, extending about two thirds of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting distally on penial sheath (Fig. 7C). Vas deferens (vd) passes through about a quarter of the penial sheath length before entering into penis apically (Fig. 7D). Penial retractor muscle (pr) thick, short and connected with penis apically.

Internal wall of atrium generally smooth (Fig. 9G). Proximal penial wall densely covered with brownish penial hooks, about 10 hooks/200 μm². Hooks located on low conical penial papillae, separated by very thin reticulated folds. Proximal penial hooks small and short (< 0.04 mm in length), slightly expanded at base, tip sharp and directed towards genital orifice (Fig. 9H, I). Distal penial wall less densely scattered with brownish penial hooks, about 4 hooks/200 μm²; penial papillae absent. Distal hooks very large, long and slender (< 0.5 mm in length), expanded at base, tip obtuse and directed towards genital orifice (Fig. 9J, K).

Vagina (v) short, about half of penis length. Gametolytic duct (gd) long tube extending as far as albumin gland; gametolytic sac (gs) small. Free oviduct (fo) short with almost the same diameter as vagina. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small and club shape. Hermaphroditic duct (hd) bearing very long and enlarged seminal vesicle (sv) about ten times longer than the length from talon to branching point of seminal vesicle (Fig. 7C).

Vaginal wall generally corrugated with irregular vaginal papillae (Fig. 9L, M). Vaginal hooks absent.

This species is known from the limestone outcrops in northeastern and central parts of Laos. The animals can be found at altitudes from 150-300 meters above mean sea level.

This species can be distinguished from H. dorri (Dautzenberg, 1894) and H. blaisei (Dautzenberg & Fischer, 1905) in having a less depressed shell and less deviated last whorl. In addition, H. blaisei possesses a solid shell with an angular penultimate whorl, and H. dorri has a smaller and smooth shell with an angular penultimate whorl. Haploptychius anceyi (Mabille, 1887) is similar to H. porrectus, however it differs in its smaller shell, circular aperture, and nearly smooth shell surface.

The species was described based on material from Jourdy’s collection and an illustration was included in the original description (Morlet 1887: 259, pl. 12, fig. 1, 1a). There is a single specimen from L. Morlet in the MNHN collections with an original label stating “Type”. In order to stabilize the name, a shell that matched well with the illustration and measurements given in the original description is designated here as lectotype MNHN-IM 200030873 (Fig. 3G).

Haploptychius fischeri is currently known only from the north of Vietnam (Schileyko 2011, Do and Do 2015). The type specimen was examined. Shell thickened, oblique-heliciform with depressed spire. Shell surface with strong radial ridges; penultimate whorl rounded; last whorl axially deflected. Aperture subquadrangular, parietal lamella strong and parietal callus thickened. Peristome wide; lip thickened and reflected. Umbilicus narrowly open.

Compared with H. pellucens and H. porrectus, this species differs in its larger and thicker shell, depressed spire, prominent transverse ridges, subquadrangular aperture, thicker parietal lamella, and narrower umbilicus.

The original description was based on single specimen since stated “un seul examplaire” (a single example). The specimen of M. Blaise in the MNHN collections is considered as holotype MNHN-IM 200030866 (Fig. 4D).

Figure 4. 

Shells of Haploptychius spp. A Haploptychius anceyi lectotype MNHN-IM 200030868 B Haploptychius diespiter syntype MNHN-IM 200030870 C Haploptychius dorri syntype MNHN-IM 200030869 D–F Haploptychius blaisei D holotype MNHN-IM 200030866 and E, F specimens from Luang Phrabang CUMZ 6257.

Phu Ly, Dongson, Ha Nam, Vietnam: NHMUK Vermeulen coll. (4 shells). Tam Phatok, Ngoi, Luang Phrabang, Laos: CUMZ 6276 (1 shell; Fig. 4E), 6257 (15 shells; Fig. 4F).

Shell oblique-heliciform, white and translucent. Whorls 6½; spire depressed to slightly convex, with distinct suture. Shell surface glossy, with thin transverse ridges that diminish below periphery and around umbilicus. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly expanded. Penultimate whorl rounded; last whorl axially deflected. Aperture semi-ovate; peristome discontinuous, parietal callus thin; lip thickened and slightly expanded. Apertural dentition with one strong parietal lamella. Umbilicus widely open and shallow.

Haploptychius blaisei is superficially similar to H. diespiter (Mabille, 1887) and H. dorri from north Vietnam, but it has a larger shell, more depressed spire, rounded penultimate whorl, a wide and deep umbilicus, and thin transverse ridges on the upper periphery. For comparison, H. diespiter (Fig. 4B) has the last whorl less deviated from the vertical axis, and H. dorri (Fig. 4C) has a more depressed suture.

Helix peroteti Petit, 1841, by subsequent designation of Forcart (1946: 215).

The genus Perrottetia differs from all other Southeast Asian streptaxid genera in having two longitudinal furrows outside the aperture. Apertural dentition usually comprises one or two parietal lamellae, plus, palatal, basal and columellar lamellae. Genitalia with long penis, penial hooks present, and vaginal hooks sometimes present (Zilch 1960, Schileyko 2000, Siriboon et al. 2013).

Currently, 29 Perrottetia species are recognized, from India and Sri Lanka to Indochina and southern China (Kobelt 1906, Richardson 1988, Schileyko 2011, Siriboon et al. 2013). Two species have been reported from Laos, P. dugasti (Morlet, 1892) and P. daedaleus (Bavay & Dautzenberg, 1908) (see Schileyko 2011).

The species was described based on material from L. Dugast collection but no illustration was given. Morlet (1893: 315, 316, pl. 7, fig. 5, 5a, 5b) subsequently published the description and illustrated a single specimen. There is a specimen of L. Morlet in the MNHN collections with an original label stating “Type”. In order to stabilise the name, the shell that closely matched with the measurements given in the original description and illustration in Morlet (1893: pl. 7, fig. 5, 5a, 5b) is here designated as lectotype MNHN-IM 200030867 (Fig. 4A).

Shell sub-oblique heliciform with depressed spire and 6 whorls. Shell surface smooth, glossy and with a distinct suture. Embryonic shell smooth, following whorl regularly expanded. Last whorl rounded, axially deflected, with longitudinal furrows present. Aperture narrow; peristome discontinuous, thick and expanded, and short sinulus present. Aperture dentition consisting of two parietal lamellae (lower one large; upper one small and close to sinulus), one palatal lamella, one basal lamella and one bifid columellar lamella.

Compared with P. messageri (Bavay & Dautzenberg, 1908), this species differs in having a strong lower parietal lamella, a bifid columellar lamella, and the left periphery of penultimate whorl not extended beyond the diameter of the last whorl. In contrast, P. messageri has a strong columellar lamella, a supracolumellar lamella is present, and the left periphery of the penultimate whorl extended beyond the diameter of the last whorl (Fig. 5D).

Figure 5. 

Shells of Perrottetia spp. A Perrottetia dugasti lectotype MNHN-IM 200030867 B Perrottetia mabillei syntype MNHN-IM 200030874 CPerrottetia daedaleus var. major syntype MNHN-IM 200030871 D Perrottetia messageri syntype MNHN-IM 200030875 E Perrottetia aquilonaria specimen CUMZ 6278 from Xayabouly with apertural dentition F, G Perrottetia unidentata sp. n. F holotype CUMZ 6281 with apertural dentition and G paratype CUMZ 6282 H, I Perrottetia unidentata sp. n. specimens from Tam Than Kaisone H specimen with upper palatal CUMZ 6284 and I specimen without upper palatal CUMZ 6285.

Syntype of Streptaxis daedaleus var. majorMNHN-IM 200030871 (Fig. 5B). Tonkin: NHMUK 1909.6.9.118-9 (2 shells). Pac-Kha, Tonkin: NHMUK 1909.7.9.15-6 (2 shells), NHMUK Preston coll. date 7.4.09 (2 shells), Rolle coll. date 27.11.09 (3 shells). Long Ping, Tonkin: NHMUK Rolle coll. date 27.1.09 (2 shells).

Shell suboblique-heliciform with a convex spire and 6 whorls. Shell surface with strong transverse ridges running continuously to umbilicus. Embryonic shell with thin transverse ridges and following whorl regularly expanded. Last whorl rounded, axially deflected, longitudinal furrows present. Aperture triangular; peristome discontinuous, thickened, broadly expanded and sinulus absent. Apertural dentition with two parietal lamellae (lower one small; upper one large and close to sinulus), one angular lamella, one palatal lamella (located far inside aperture) and one columellar lamella.

This species is superficially similar to P. mabillei (Bavay & Dautzenberg, 1903) in having strong transverse ridge over the entire shell, but P. daedaleus has a large upper parietal lamella, a palatal lamella located inside the aperture, and strong columellar lamellae, while P. mabillei (Fig. 5B) has a large lower parietal lamella and bifid columellar lamellae.

Holotype CUMZ 5003, paratypes CUMZ 5004 (4 shells). Ban Namone, Xayabouly, Laos: CUMZ 6278 (2 shells; Fig. 5E), CUMZ 6279 (1 specimen in ethanol). Ban Bo Khoun, Boun Neua, Phongsaly, Laos: CUMZ 6280 (1 shell).

Perrottetia aquilonaria was described from several localities in the northern part of Thailand with a complete information on shell, radula and genitalia. The specimens collected from limestone outcrops in Borkeo and Phongsaly of Laos have both shells and genitalia that match very well with this species. Laos specimens seem to differ only in the slightly smaller shell, therefore we treated them as the same species.

Perrottetia aquilonaria can be distinguished from P. dugasti and P. messageri from Vietnam by having a depressed spire, shouldered last whorl, thin parietal callus and upper-parietal lamella separated at a right angle. In contrast, P. dugasti has a rounded last whorl and a small upper-parietal lamella located deeper inside the aperture, and P. messageri has paralleled parietal lamellae, a small supercolumellar lamella is present, and the left side of the penultimate whorl extended beyond the diameter of the last whorl (Fig. 5A, D).

Holotype CUMZ 6281 (Fig. 5F). Measurement: shell height 5.3 mm, shell width 9.7 mm and 6½ whorls. Paratypes CUMZ 6282 (4 shells; Fig. 5G), CUMZ 6283 (1 specimen in ethanol; Figs 7E, F, 9A–F, I), NHMUK 20160250 (2 shells).

Figure 6. 

Shells of Perrottetia and Indoartemon spp. A, B Perrottetia megadentata sp. n. A holotype CUMZ 6286 with apertural dentition, and B paratype CUMZ 6287. C Indoartemon tridens holotype SMF 108507/1 with apertural dentition D–F Indoartemon diodonta sp. n. D holotype CUMZ 6289 with apertural dentition E paratypes CUMZ 6290, and F specimen from Tam Nang Ann, Tha Khek, Khammouan CUMZ 2691.

Figure 7. 

Genitalia of Haploptychius and Perrottetia species. A, B Haploptychius pellucensCUMZ 2670 A reproductive system, and B insertion of vas deferens into penial sheath C, D Haploptychius porrectusCUMZ 6274 C reproductive system, and D insertion of vas deferens into penial sheath E, F Perrottetia unidentata sp. n. CUMZ 6283 E reproductive system, and F insertion of vas deferens into penial sheath.

Figure 8. 

Genitalia of Haploptychius pellucens A completed reproductive system CUMZ 2670 B, C completed reproductive system with “vaginal caecum” CUMZ 6265, and D aphallic reproductive system CUMZ 6265.

Figure 9. 

Internal sculpture of genitalia of Haploptychius spp. A–F Haploptychius pellucens, CUMZ 2670 A details of atrium surface B arrangement of penial hooks C top view of penial hook (from white square in B) D arrangement of penial hooks E lateral view of penial hook, and F arrangement of undulated parallel vaginal folds. G–M Haploptychius porrectus specimen CUMZ 6275 G details of atrium surface H arrangement of penial hooks in distal area I lateral view of penial hook in distal area J arrangement of penial hooks in proximal area K lateral view of penial hook in proximal area L arrangement of papillae and vaginal folds, and M arrangement of vaginal folds.

Tam Than Kaisone, Viengxay, Houaphanh, Laos: CUMZ 6284 (5 shell; Fig. 5I), CUMZ 6285 (2 shells; Fig. 5H).

The limestone outcrop at Ban Nawit, Viengxay, Houaphanh, Laos (20°22'37.3"N, 104°16'43.2"E) about 700 meters above mean sea level.

This new species differs from P. daedaleus, P. aquilonaria, P. dugasti and P. messageri from Vietnam in having an oblique shell, a single parietal lamella, widely expanded lip, the last whorl strongly axially deflected, the left side of penultimate whorl well extended beyond the diameter of last whorl, and the distal end of penis with a wing-like structure. The other four species have two parietal lamellae, the last whorl little axially deflected and the left side of penultimate whorl not extended beyond the diameter of the last whorl. For further comparison, P. daedaleus has an elevated spire, transverse ridges over the entire shell and a basal lamella located deep inside aperture (Fig. 5C); P. aquilonaria has a smaller shell, elevated spire, bifid columellar lamella, and genitalia with atrial pores and vaginal hooks absent (Fig. 5E); P. dugasti and P. messageri have a smooth shell surface, a bifid collumella lamella and a supracolumellar lamella (Fig. 5A, D). Perrottetia gudei from north Vietnam differs from the new species in having an elevated spire, in being less deviated from the vertical axis, and in having thin transverse ridges (see Siriboon et al. 2013).

Shell. Shell oblique-heliciform, semi-transparent; whorls 6½, spire weakly convex with distinct suture. Shell surface glossy with strong transverse ridges on upper shell surface. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Shell periphery shouldered; last whorl axially deflected; two deep longitudinal furrows present. Aperture semi-ovate; peristome discontinuous; parietal callus thin; lip thickened, broadly expanded and slightly reflected. Apertural dentition with one large, strong and sinuous parietal lamella, one small upper palatal lamella, one palatal lamella, one large basal lamella, one strong columellar lamella, and one small supracolumellar lamella. Umbilicus widely open and shallow (Fig. 5F–I).

Radula. Each row consists of 26–38 teeth with formula (13-19)-1-(13-19). Central tooth small and triangular, with pointed cusp. Lateral and marginal teeth undifferentiated, lanceolate, unicuspid. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 10I).

Figure 10. 

Internal sculpture of genitalia of A–F Perrottetia unidentata sp. n. paratype CUMZ 6283 A details of atrium surface B arrangement of penial hooks C top view of penial hook D lateral view of penial hooks E arrangement of vaginal hooks, and F top view of vaginal hook. Radula morphology of G Haploptychius pellucens specimen CUMZ 2670 H Haploptychius porrectus specimen CUMZ 6275, and I Perrottetia unidentata sp. n. paratype CUMZ 6283.

Genital organs. Atrium (at) short. Proximal penis (p) long and slender; distal part near retractor muscle with an expanded wing-like structure (a flat blade on either side of the penis, each about one-tenth of penis length). Penial sheath (ps) thin and extending about one-third of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting distally on penial sheath (Fig. 7E). Vas deferens (vd) passes through about one-third of penial sheath length before entering into penis apically (Fig. 7F). Penial retractor muscle (pr) thin and long, inserted at penis and vas deferens junction.

Internal wall of atrium generally smooth (Fig. 10A). Penial wall densely covered with light brown penial hooks, about 20 hooks/200 μm²; hooks located on low elliptical penial papillae. Penial hooks small (< 0.1 mm in length), slender, expanded at base, tips pointed and curved towards genital orifice (Fig. 10B–D).

Vagina (v) short, about one-tenth of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) long and cylindrical with equivalent diameter to vagina, tapering distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) very small, short and club shape. Hermaphroditic duct (hd) bearing very short and thin seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 7E).

Vaginal wall with transparent vaginal hooks (about 10 hooks/200 μm²). Hooks located on low conical vaginal papillae. Vaginal hooks small (< 0.1 mm in length), short and expanded at base; tips pointed and straight to slightly curving away from genital orifice (Fig. 10E, F).

The specific epithet “unidentata” derived from the Latin words “unus” meaning “one” and “dens” meaning “tooth”. It referred to a single parietal lamella (or teeth) of the new species.

This species is known only from the type locality, Houaphanh, a limestone karst area.

Shell variation is evident from specimens from Tam Than Kaisone, about 20 km west of the type locality (Fig. 5H, I; CUMZ 6284, 6285). They are smaller, with a sinuous parietal lamella, and sometimes lack the upper palatal lamella (Table 1). However, only five shells and no living specimens were collected, so we provisionally identifying them as the same species.

Holotype CUMZ 6286 (Fig. 6A). Measurement: shell height 7.1 mm, shell width 8.2 mm, and with 6 whorls. Paratypes: CUMZ 6287 (31 shells; Fig. 6B), CUMZ 6288 (2 shells), NHMUK (2 shells), NUOL 20160251 (2 shells), SMF (2 shells).

The limestone outcrop at Ban Phone Can, Yommalat, Khammouan, Laos (17°31'35.6"N, 105°9'40.7"E)

The characters distinguishing Perrottetia megadentata sp. n. from P. daedaleus, P. aquilonaria, P. dugasti and P. mabillei are a single large parietal lamella, the absence of a palatal lamella absent and the presence of an infra-columellar lamella. The other four species have two parietal lamellae and a palatal lamella. Furthermore, P. dugasti and P. aquilonaria have a smooth shell, slightly depressed spire, and a bifid columellar lamella (Fig. 5A, E). Perrottetia daedaleus and P. mabillei have strong transverse ridges over the entire shell, a palatal lamella, and a bifid basal lamella, a columellar lamella is absent in P. mabillei (Fig. 5B), while one basal and one columellar lamella are present in P. daedaleus (Fig. 5C). The new species differs from P. unidentata sp. n. in its ovate shape, smooth shell surface, thicker shell, in the absence of a palatal lamella, and in having infra- and supra-columellar lamellae. The new species is superficially similar to P. dermapyrrhosa Siriboon & Panha, 2013, but is distinguished by having a single and large parietal lamella, and in the absence of a palatal lamella.

Shell oblique-ovate, white and translucent; whorls 6, spire conical, with distinct suture. Shell surface glossy with transverse ridges near suture. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Shell periphery rounded; last whorl axially deflected; two shallow and short longitudinal furrows present. Aperture subcircular, peristome continuous; parietal callus thickened; lip thickened, expanded and reflected; short sinulus present. Apertural dentition with very large and strong sinuous parietal, one large basal lamella located deep inside aperture, one small infracolumellar lamella, one large columellar lamella, and one small supracolumellar lamella. Umbilicus widely open and deep (Fig. 6A, B)

The specific epithet “megadentata” is derived from the Greek word “mega” meaning “large” and the Latin word “dens” meaning “tooth”. It referred to the single large parietal lamella of the new species.

This species is known only from the type locality in central Laos.

To date no living specimens have been collected.

Streptaxis eburnea Pfeiffer, 1861, by original designation.

The genus Indoartemon can be recognized by the dentition, which consists of one parietal and one palatal lamella (a basal lamella is also present in some species). The penis is long, with a thin penial sheath extending about half of the penis length, through which the vas deferens does not pass. Penial hooks are present (Siriboon et al. 2014b).

Currently, ten species are recognized, of which seven were reported from Indochina south of China and Hainan. Only one species, I. tridens (Möllendorff, 1898) has previously been recorded from Laos (Richardson 1988, Schileyko 2000, Siriboon et al. 2014b); here we describe another.

Holotype SMF 108507 (Fig. 6C).

Shell oblique-ovate with 5½ whorls, semi-transparent, spire slightly convex, with distinct sutures. Shell surface glossy white with thin growth lines; following whorls regularly coiled. Last whorl axially deflected. Aperture triangular; peristome continuous; lip thickened, little expanded and slightly reflected. Apertural dentition with one large parietal lamella, one palatal lamella, and one small bifid columellar lamella.

Only the type specimen was examined. Indoartemon tridens differs from I. eburneus, I. prestoni (Gude, 1903) and I. medius Siriboon & Panha, 2014 from Thailand by having a bifid columellar lamella, an ovate-heliciform shape, its smooth shell surface, narrow umbilicus, and having the left side of penultimate whorl extended beyond the diameter of last whorl. For comparison, I. eburneus and I. prestoni have a less deviated last whorl, transverse ridges on the shell, and a widely open umbilicus; I. medius has an angular penultimate whorl and strong transverse ridges.

Holotype CUMZ 6289 (Fig. 6D). Measurement: shell height 7.5 mm, shell width 8.3 mm, and with 7 whorls. Paratypes: CUMZ 6290 (44 shells; Fig. 6E), NHMUK 20160252 (2 shells), NUOL (2 shells), SMF (2 shells).

Tam Nang Ann, Tha Khek, Khammouan, Laos: CUMZ 6291 (7 shells, Fig. 6F). Tam Xieng Lieb, Tha Khek, Khammouan, Laos: CUMZ 6292 (15 shells).

Tam Xang, Tha Khek, Khammouan, Laos, 17°25'44.0"N, 104°51'49.1"E.

This new species superficially resembles I. eburneus and I. prestoni from Thailand, but it differs in having a much smaller shell, an oblique-heliciform shape, open umbilicus, and the last whorl is strongly deviated from the vertical axis. This species differs from I. medius from Thailand in its smaller shells, angular penultimate whorl and thin transverse ridges. Indoartemon diodonta sp. n. differs from I. bidens (Möllendorff, 1883) from Hainan and I. tridens by having fine transverse ridges on the upper periphery, and the last whorl is less deviated from the vertical axis. These two species also have a smooth shell surface and a more strongly deviated last whorl, and a bifid columellar lamella is present in I. tridens.

Shell. Shell oblique-heliciform, white and translucent; whorls 6½–7, spire conical, with distinct suture. Shell surface dull, with fine transverse ridges that diminish below the periphery. Embryonic shell large, about 2½ whorls, with smooth surface; following whorls regularly coiled. Last whorl shouldered, axially deflected, and not expanded. Aperture subcircular; peristome continuous, parietal callus thickened; lip thickened, expanded and little reflected. Apertural dentition with one large and strong parietal and one small palatal lamellae. Umbilicus narrow and deep (Fig. 6D–F).

The specific epithet “diodonta” is derived from the Greek words “di” meaning “two” and “odontos” meaning “tooth”, referring to the dentition of the new species.

This species is known from limestone karst in Khammouan Province, central Laos. The animals can be found at altitudes up to 140 meters above mean sea level.

To date no living specimens have been collected.