Review of the genus Endothyrella Zilch, 1960 with description of five new species (Gastropoda, Pulmonata, Plectopylidae)

Abstract All known taxa of the genus Endothyrella Zilch, 1960 (family Plectopylidae) are reviewed. Altogether 23 Endothyrella species are recognized. All species are illustrated and whenever possible, photographs of the available type specimens are provided. Five new species are described: Endothyrella angulata Budha & Páll-Gergely, sp. n., Endothyrella dolakhaensis Budha & Páll-Gergely, sp. n. and Endothyrella nepalica Budha & Páll-Gergely, sp. n. from Nepal, Endothyrella robustistriata Páll-Gergely, sp. n. from the Naga Hills, India, and Endothyrella inexpectata Páll-Gergely, sp. n. from Sichuan, China. Helix (Plectopylis) munipurensis Godwin-Austen, 1875 is synonymized with Helix (Plectopylis) serica Godwin-Austen, 1875, and Plectopylis (Endothyra) gregorsoni Gude, 1915 is synonymized with Helix (Plectopylis) macromphalus W. Blanford, 1870. Plectopylis plectostoma var. exerta Gude, 1901 is a synonym of Plectopylis plectostoma var. tricarinata Gude, 1896, which is a species in its own right. Five species of the genus Chersaecia viz. Plectopylis (Chersaecia) bedfordi Gude, 1915, Helix (Plectopylis) brahma Godwin-Austen, 1879, Helix (Plectopylis) Oglei Godwin-Austen, 1879, Helix (Plectopylis) serica Godwin-Austen, 1875, and Plectopylis (Endothyra) williamsoni Gude, 1915 are moved to Endothyrella. The holotype of Plectopylis hanleyi Godwin-Austen, 1879 seems to be lost; therefore, Plectopylis hanleyi is considered to be a nomen dubium.


Introduction
The Plectopylidae Möllendorff, 1898 are a land snail family of the superfamily Plectopyloidea that ranges across large parts of southeast Asia from Nepal to southern Japan (Gude 1899d, Páll-Gergely andHunyadi 2013). Schileyko (1999) classified two families in the Plectopyloidea: the Plectopylidae and the mainly Sri Lankan Corillidae Pilsbry, 1905. Other authors (Zilch 1960, Bouchet andRocroi 2005) also included the African Sculptariidae Degner, 1923 in the superfamily. Historically, the family name Corillidae (e.g. Yen 1939 andZilch 1960) or the helicid subfamily Corillinae (in Gude 1914b) have been applied to the current concept of Plectopyloidea. The Chinese Amphicoelina Haas, 1933 has been included in the Corillidae or the Plectopylidae by Yen (1939), Zilch (1960) and Schileyko (1999). That genus, however, likely belongs to the Camaenidae (see Páll-Gergely and Asami 2014), as originally proposed by Haas (1933). The Plectopylidae differ from the Corillidae by the presence of one or two vertical (= perpendicular to the suture) lamellae on the parietal wall, approximately a quarter to a half whorl behind the aperture. In contrast, the Corillidae have only horizontal (= parallel with the suture) parietal plicae (in Corilla all plicae may be absent).
Gude revised every known taxon of Plectopylis Benson, 1860 at the end of the 19 th century, and published drawings of their shells and armature (lamella complex) (see citations in Richardson 1986). He subdivided Plectopylis into seven "sections" (Gude 1899c): Endothyra Gude, 1899c, Chersaecia Gude, 1899c, Endoplon Gude, 1899c, Plectopylis, Sinicola Gude, 1899c, Enteroplax Gude, 1899d and Sykesia Gude, 1897f. Enteroplax was transferred to the Strobilopsidae Wenz, 1915(Solem 1968, Schileyko 1998, and Ruthvenia Gude, 1911 (replacement name for Sykesia which itself was a replacement name for Austenia Gude, 1897e) to the Endodontidae Pilsbry, 1895 (Gude 1914b, Schileyko 2001 or to the Charopidae Hutton, 1884 (Schileyko 2010, Raheem et al. 2014). The name Endothyrella was established by Zilch (1960) to replace Endothyra Gude, 1899, a junior homonym of Endothyra Phillips, 1845 (Foraminifera). Gude's (1899c) diagnoses of his sections are based on the direction of the coiling of the shell, the depth of the umbilicus, and the morphology and direction of the palatal folds. Most of his diagnoses are not mutually exclusive. Recent revisions of the genera Endoplon and Sinicola (Páll-Gergely and Hunyadi 2013, Páll-Gergely and Asami 2014, and Páll-Gergely et al. 2015 showed that the species assigned to these two genera should be classified within multiple genera and the genera should be rediagnosed. Moreover, several species were misassigned by Gude (1899c), which was probably the result of focusing exclusively on the morphology of the parietal plicae.
The aim of this paper is to review and diagnose all Endothyrella species, publish images of the type specimens where possible, provide a diagnosis of Endothyrella, and delimit it from other plectopylid genera. Ongoing revision of the genera Chersaecia and Plectopylis revealed that Chersaecia sensu Gude (1899cGude ( , 1915 worked as a "garbage can" including species that could not be classified within other sections. Revising the validity of Chersaecia species is beyond the scope of the present paper. However, three sinistral (bedfordi, brahma, williamsoni) and two dextral (oglei, serica) species are moved from Chersaecia to Endothyrella, mainly based on the sculpture of the embryonic whorls and the absence of the apertural fold. Additionally, five new Endothyrella species are described from Nepal, India, and China.

Taxonomic history of Endothyrella and Chersaecia species
Endothyrella plectostoma was the first described species that is currently placed in the Plectopylidae. It was introduced as Helix plectostoma by Benson (1836), who classified it within the subgenus Helicodonta and who mentioned that because of its angulated periphery it shows connection towards the subgenus Helicigona. In modern classifications Helicodonta and Helicigona belong to the families Helicodontidae and Helicidae, respectively, and both are the members of the superfamily Helicoidea (Schileyko 2006a(Schileyko , 2006b. Benson (1836) compared Helix plectostoma with H. personata, (= Isognomostoma isognomostomos [Schröter, 1784], family Helicidae) and H. corcyrensis (= Lindholmiola corcyrensis [Rossmässler, 1838], family Helicodontidae).
For the nomenclature of lamellae (vertical parietal folds) and plicae (horizontal parietal folds and palatal folds) see Figure 1. Whenever possible, the internal lamellae and plicae have been exposed by removing the shell wall at the appropriate part of the shells (inner view). Yet, if damaging the shells was not an option (because too few shells available), the plicae were figured on the basis of their visibility through the shell wall (outer view). "Anterior" refers to the part or side of the armature in direction of the aperture, "posterior" refers to the other side of the armature.
For each taxon, the specimens studied are listed separately as types, museum material and new material. Geographic names mentioned in the literature and on labels (Table 1) were searched using Google, Google Earth and Lozupone et al. (2004). Locality names are copies from the labels and from the literature with original spelling. Therefore the same locality might present with more than one spelling (e.g. Sikkim/ Sikhim, Sadia/Sadiya, Khasi/Khasia).
Ethanol-preserved specimens were dissected under a Leica stereomicroscope, equipped with a photographic camera. In description of the reproductive system, we used the terms "proximal" and "distal" relative to the centre of the body.
Individual buccal masses was removed and soaked in 2 M KOH solution for 5 h before extracting the radula, which was preserved in 70% ethanol. Radulae and shells were directly observed without coating under a low vacuum SEM (Miniscope TM-1000, Hitachi High-Technologies, Tokyo).
The dates of publication of the Proceedings of the Zoological Society of London follows Duncan (1937). and palatal (C) plicae and lamellae. A shows a "Gudeodiscus-type" plication with two lamellae B shows a usual Endothyrella lamellation D shows a "Chersaeciatype" lamellation with long lower plica and middle plica not connected to the apertural fold (in most species however, they are connected forming a continuous plica). Small arrows under the letters show the direction of the aperture (A shows dextral, B and D sinistral specimen). Large arrow next to C shows the direction of counting of palatal plicae (first above, last below). Abbreviations: af: apertural fold; al: anterior lamella; am: apertural margin (peristome); ip: intermediate plica; l: lamella; lp: lower plica; mp: main plica; pl: posterior lamella; pd: posterior denticles; pl: posterior lamella; up: upper plica. Note that there are upper and lower plicae on both (palatal and parietal) walls.

Taxonomic treatment
All available type material of each Chersaecia taxon deposited in the MCZ, NHMUK, SMF and ZMUC have been examined. The type specimens of Endothyrella taxa examined are mentioned under each species.
The following shell characters of species formerly classified in Chersaecia and Endothyrella were examined in order to revise the generic assignment and diagnose genera: (1) coiling direction; (2) sculpture of the protoconch; (3) presence or absence of the apertural fold; morphology of the parietal plicae and lamellae, namely (4) the presence/ absence/length of a horizontal main plica, (5) the presence/absence/length of a the lower plica, and (6) the presence or absence of additional denticles behind the lamella; (7) morphology of middle palatal plicae (the first and last are straight in almost all cases); and the (8) presence/absence/morphology of hairs. This taxonomic revision of Endothyrella species is based on morphology by examination of specimens and literature. The present species are defined based on unique combinations of morphological traits, some of which are discrete in nature (e.g. presence or absence of periostracal filaments) or continuous but with distinct gaps (e.g. height of the spire). No specimens were found that show transitional characters between probably sympatric morphospecies (Table 2). Although we have no, or too little, information on the genetic, physiological and/or ecological basis of the phenotypic characters used to describe the species in this work, we putatively interpret the diagnostic phenotypic differences under the biological species concept (Mayr 1942), i.e. as markers of reproductive isolation. However, the biological species concept is not   Figure 2) by original designation. Diagnosis. Shell sinistral or dextral, flat, widely umbilicated; in most cases protoconch seemingly "smooth" to the naked eye, but not glossy, rather matt; under the microscope usually tubercles of various size are visible ( Figure 2B); sometimes the tuberculated protoconch is irregularly wrinkled; flat periostracal filaments are visible on the body whorl or on the dorsal surface in only a few species; aperture always with a fold; parietal wall with one vertical lamella and usually one or two long horizontal plicae (main plica and lower plica) reaching the callus; palatal plicae horizontal, sometimes divided in the middle, in some species with several additional denticles posteriorly, in some species similar to that of Plectopylis (three horizontal plicae above and one below the vertical plate formed by the accretion of two plicae).
Only one Chersaecia species is known anatomically (Ch. simplex in the original description: Solem 1966). Penis internally with approximately eight longitudinal rows, those situated next to the vas deferens are distinctly larger; vas deferens becomes a part of the penis wall at the penioviducal angle; no epiphallic differentiation observed; retractor muscle inserts on the dorsal surface of the penis and attaches to the diaphragm; diverticulum absent, gametolytic sac long and thickened.
Differential diagnosis. Chersaecia differs from Endothyrella, Gudeodiscus Páll-Gergely, 2013, Halongella Páll-Gergely, 2013, Sicradiscus Páll-Gergely, 2013 and Sinicola by the usually tuberculated (not regularly ribbed) protoconch. The presence of long parietal plicae (main and lower) distinguishes most Chersaecia species from most Endothyrella, Gudeodiscus, Halongella, Sicradiscus and Sinicola species. The delimitation of Chersaecia from Plectopylis and Endoplon needs further investigation. Among all plectopylids examined to date Chersaecia simplex is the only species found to lack an epiphallus. The anatomy of more Chersaecia species should be studied to check the taxonomic value of the lack of the epiphallus.
Content. austeni, brachydiscus, degerbolae, dextrorsa, kengtungensis, leiophis (pseudophis is probably a synonym, see Gude 1908a), muspratti, nagaensis, perarcta, perrierae, refuga, shanensis, shiroiensis, simplex. Distribution. The genus is known to inhabit northeastern India, eastern and southern Myanmar (Burma) and northern Thailand.  Figures 6A-F); periostracal folds usually present on the body whorl; they are arranged in 3-7 lines; folds hair-like in most species, resulting from the rolling of flat folds; folds flat (not rolled) in some species only (see Figures 8D, 20A-F); dorsal sculpture strong, usually reticulated (both radial and spiral lines present, see Figure 8A); umbilicus wide to narrow; body whorl rounded in some species but rather bluntly shouldered (keeled) in others; apertural fold always absent; main plica usually absent (present in a few species only); low plica (if present) runs close to and parallel with the lower suture, it is usually very short (present only under the lamella), but in some species it reaches the callus; parietal wall with a single lamella with denticles posteriorly (probably homologous with the posterior lamella); two lamellae were reported in one species (E. aborensis) only; palatal plicae complicated in most species with many small denticles at their posterior ends; in many species they are at least party divided in the middle.
Genitalia (see Figures 18,21,25,26): The left ommatophoral retractor passes between penis and vagina (in sinistral species). Penis internally with hollows (small pocket-like structures) having calcareous granules inside; penial papilla absent; epiphallus may be longer than penis and enters penis laterally; epiphallus with longitudinal folds internally; small penial caecum usually present at the penis-epiphallus boundary; retractor muscle inserts on the caecum and attaches to the diaphragm; diverticulum (if present) and gametolytic sac are of the same size.
Radula (see Figures 19A-F): Central tooth larger than the ectocones of the first laterals; marginals tricuspid (= ectocones are divided) or even quadricuspid (both the endocones and ectocones are divided); the incision between the ectocones and endocones usually deep (E. fultoni has rhomboid marginals which are unique in the whole family).
Differential diagnosis. All known species of the genera Sinicola, Gudeodiscus, Halongella and Sicradiscus are dextral. Regardless of the coiling direction, most Endothyrella species differ from Sinicola by the presence of usually hair-like periostracal folds standing in multiple lines. Deciduous periostracal folds in Sinicola are present only along the keel and the folds are always flat. Most Sinicola species (especially the large species) have a sharp keel, whereas Endothyrella species usually have a rounded or slightly keeled, shouldered body whorl. The palatal plicae of Sinicola are usually simple, horizontal, straight and parallel, but in Endothyrella they are often oblique to vertical, divided and ornamented with minute denticles at their posterior ends. In Sinicola the posterior lamella is present on the parietal wall, with two horizontal plicae anteriorly above and below, whereas in most Endothyrella species (probably except for E. aborensis) the anterior lamella is present and the posterior is missing or reduced to one or two short vertical plicae.
Some Gudeodiscus and Halongella species possess low, radial periostracal folds (e.g. Páll-Gergely et al. 2015, fig. 10e-f), similar to those of E. nepalica sp. n. (see there). The radial folds have serrated edges in Gudeodiscus phlyarius (Mabille, 1887). The tiny tips of the serrated folds seem to occur in a spiralling pattern (see Hunyadi 2013, fig. 113 andPáll-Gergely et al. 2015, fig. 10c-d). All of these periostracal features of Gudeodiscus and Halongella are, however, easily distinguishable from the long, hair-like folds of the genus Endothyrella.
Some Gudeodiscus species possess a fold in the aperture, which is always missing in Endothyrella. The palatal plicae in Gudeodiscus are usually depressed Z-or L-shaped and posterior small denticles are very rare (except for one denticle above the posterior end of the last plica), whereas the palatal plicae of Endothyrella are frequently divided in the middle and posterior small denticles are usually present. In Endothyrella the anterior lamella is present, and often the upper horizontal plica is missing, whereas in Gudeodiscus both lamellae, or only the posterior one, are visible and the upper horizontal plica (above the lamella) is almost always present. Additionally, Gudeodiscus species have a rounded body whorl, while in many Endothyrella species the body whorl is angled or shouldered. Our limited knowledge on the anatomy of Endothyrella species shows that the entire inner penial wall of Endothyrella is covered by pits, whereas in Gudeodiscus these pocketlike structures are restricted to the a certain (usually apical) portion of the penis.
Sicradiscus is similar to Endothyrella in possessing a weak or reduced posterior lamella. Long periostracal folds standing in more than one row have also been found in one Sicradiscus species, namely in juveniles of Sicradiscus transitus Páll-Gergely, 2013. This species, however, has hairs standing in two spiral lines on the body whorl, whereas in Endothyrella the hairs are arranged in 3-7 spiral lines. This trait seems to be absent in adult S. transitus shells and all other species of Sicradiscus, but is common in fully grown Endothyrella shells (i.e. most species possess them). The two genera (i.e. Endothyrella and Sicradiscus) differ in the short, straight palatal plicae, which are usually connected in Sicradiscus vs. longer, more complex palatal plicae sometimes having additional denticles in Endothyrella. In both genera divided plicae may occur, but in the case of Sicradiscus the posterior fourth and fifth plicae seem to be always connected, whereas in Endothyrella all plicae are free. Moreover, western Sicradiscus species (feheri Páll-Gergely, 2013, invius [Heude, 1885], mansuyi [Gude, 1908b], securus [Heude, 1885] and transitus) differ from Endothyrella by the presence of a strong apertural fold.
Plectopylis and Endoplon species have a granulated or smooth protoconch, whereas it is usually finely ribbed in Endothyrella. Moreover, Plectopylis and Endoplon usually have a strong apertural fold which is often connected to a long main plica. In contrast, although some Endothyrella species have a main plica, they all lack an apertural fold. See also under Chersaecia and Table 3.
Distribution. The distribution of this genus is restricted to Nepal, northeastern India and the province Sichuan in China. One species (E. plectostoma) was reported from Myanmar ( Figure 3).
Distribution. Only known from the type locality ( Figure 7).  Diagnosis. Shell very small, dextral, almost flat, relatively widely umbilicated with elevated callus; hairs standing in three lines on the body whorl; parietal wall with a single, curved lamella; palatal wall with six short plicae.

Endothyrella inexpectata
Description. Shell dextral, with almost flat, very slightly domed dorsal side (protoconch slightly elevates from the dorsal surface); brownish or slightly reddish in colour; protoconch consists of 1.5-1.75 whorls, first whorls rather smooth, last 0.25-0.5 whorl regularly ribbed ( Figure 6F); teleoconch with irregular, rough growth lines and spiral structure; sculpture stronger on the dorsal surface but still well-visible on the ventral surface; deciduous, slim and flat folds standing in three lines on the body whorl ( Figure  8D); whorls 4.75, very much bulging, separated by deep suture; umbilicus moderately wide and deep; apertural lip whitish, thickened and slightly reflexed; callus strong, elevated, sharp and slightly S-shaped; with canals at both ends; no fold in the aperture.
One specimen (the holotype) was opened. The armature is situated very close to the aperture, palatal plicae visible from oblique view through the aperture. Parietal wall with a single curved lamella without additional denticles; arms of the lamella pointing posteriorly; palatal wall with six very short plicae becoming narrower posteriorly; the last one with an additional denticle posteriorly ( Figures 9A-B).
Measurements (in mm): D: 6.6-6.7, H: 3.0-3.1 (n = 2, from different localities). Differential diagnosis. Endothyrella babbagei is much larger than E. inexpectata sp. n., and it has flatter whorls and has a weaker callus than the new species. Sinicola species of the same size have a keeled or shouldered body whorl and have two parallel parietal plicae anterior to or above the lamella (one near the upper, the other near the lower suture). Sicradiscus invius also occurs in Sichuan, but it is smooth (glossy) and has a strong apertural fold. See also under Endothyrella oglei and E. serica and Table 5.
Etymology. The name inexpectata (meaning unexpected in Latin) refers to the surprizing new, especially dextral Endothyrella species in China. Measurements (in mm): D: 16.8-16.9, H: 7.7-8.1 (n = 2, type series). Differential diagnosis. Endothyrella babbagei and E. inexpectata sp. n. differ from the E. oglei by the flat dorsal surface of the shell and the presence of hairs arranged in three rows on the body whorl. See also under E. serica and Table 5.

Endothyrella serica (Godwin-Austen, 1875)
wall with a single curved lamella with denticles near the upper and lower ends posteriorly, which occasionally fuse with the lamella.
Differential diagnosis. Endothyrella babbagei and E. inexpectata sp. n. differ from E. serica by the flat dorsal surface of the shell and the presence of three rows of hairs on the body whorl. Endothyrella oglei differs from the also dextral E. serica by the much larger size, the absence of the groove on the protoconch, which runs parallel with the suture in E. serica, and the morphology of the lamella which has only posteriorly elongated ends. See also Table 5.
Distribution. The species is recorded from the Naga Hills (see also remarks). "Plectopylis munipurensis" was described from "end of the Ihang valley" (Figure 11).
Remarks. Godwin-Austen (1875) described Helix (Plectopylis) serica and Helix (Plectopylis) munipurensis in the same publication. He did not mention the differences between the two species. According to the illustrations and the identification key in the original description, the upper end of the lamella in munipurensis is more elongated anteriorly than that of H. serica. Two shells of E. serica were opened from the Hengdan sample, and both had an anteriorly elongated plica. In this respect, and also in shell shape, these shells were more similar to E. munipurensis specimens. In the Khunho sample four shells were opened, three having no or very slight upper elongation, but one had an as long plica as in typical munipurensis shells. Examining the type specimens of the two species we have not found significant differences. The width of the umbilicus and the height of the spire showed some variability. Therefore we synonymize munipurensis with serica. We choose Helix (Plectopylis) serica to be the valid specific name.
In the original description Godwin-Austen (1875) reported the species from the "peak of Henozdan" and from the "Kopamedza ridge". The second sample is probably identical with the one from Khunho in the type collection of the NHM. Gude (1897h) mentions that according to Godwin-Austen, the correct names for "Henozdan" and "Kopameda" in Gude (1897a) are "Hengdan" and "Kopamedza", respectively. According to the same erratum, Godwin-Austen also mentioned that the locality of Ponsonby's shell (Sylhet) is probably incorrect, because Plectopylis serica is a very local species, inhabiting altitudes higher than 5000 feet.

Sinistral species
Endothyrella aborensis (Gude, 1915)   Types. According to the original description, two shells, an adult and a juvenile were collected and finally deposited in the Indian Museum (inventory numbers: 5998 and 6135). Specimen reference collections in the Indian Museum were transferred to the ZSI following foundation of the ZSI in 1916. The ZSI supplied us with two photos of an adult shell under the name of Plectopylis aborensis, which they considered as one of the type specimens. These photos, however, clearly showed a different specimen than the one figured in Gude (1915). No other information could be obtained from the ZSI.
Diagnosis. Shell small, sinistral, almost flat, widely umbilicated; callus strong; palatal plicae Z or L-shaped; there are two parietal lamellae, a short upper plica which is in contact with the posterior lamella, and a long lower plica which reaches the peristome.
Measurements (in mm): D: 14, H: 6.5 (according to the original description). Differential diagnosis. The species was not examined by us, but according to the original description the species differs from all congeners by the short and uniquely shaped palatal plicae, which are depressed Z-shaped, or the lower branch of the "Z" is elongated. See also Table 5.
Remarks. So far, this is the only Endothyrella species with two well-developed lamellae. The parietal lamellae show a very unusual arrangement which has not been ob-  (Gude, 1915), (syntype, photos published in Gude 1915) C Endothyrella miriensis (Gude, 1915), NHMUK 1903. Photos A and C by H. Taylor. Scale represent 5 mm. served in any other species of Plectopylidae. The two parietal plicae can be the result of teratological duplication which has been reported for some species (Gude 1908b: 347).  Types. India, Khasia Hills, ex Fulton, NHMUK 1922.8.29.36 (syntype, Figure 13G); Khasia Hills, NHMUK 1901.4.25.41-43 (3 syntypes Diagnosis. Shell small, sinistral, yellowish, with narrow umbilicus, conical dorsal surface and shouldered body whorl; hairs are arranged in four rows on the body whorl; callus strong, middle palatal plicae usually divided in the middle; the posterior fragments are oblique, the anterior ones are rather straight; parietal wall with a single, slightly curved lamella with short denticles posteriorly, one above and one below, and a horizontal lower plica which may be divided in the middle.
One specimen was opened. Palatal wall with a single, straight lamella, with two short denticles on the posterior side of the lamella, both are in contact with the lamella; a short, free horizontal plica is visible under the lamella; palatal wall with six plicae, first straight, last slightly curved, the middle plicae are divided in the middle, the fragments are horizontal, oblique or Z-shaped ( Figure 9I-J).
Etymology. The Latin angulatus (cornered, angular) refers to the shouldered/angulated body whorl of the new species.
Distribution. Endothyrella angulata sp. n. is known only from the type locality ( Figure 15). Figure 16C 1915 Plectopylis (Chersaecia) Figure 16C). Diagnosis. Shell very small, sinistral, brownish, with moderately wide umbilicus, almost flat dorsal surface (only the apex is elevated slightly), and rounded body whorl; callus strong, palatal plicae long, more or less straight horizontal, with dichotomously divided posterior ends and many small denticles at their posterior ends; lamella single, curved, in contact with a lower plica, which runs until the peristome.

Endothyrella bedfordi (Gude, 1915)
Measurements (in mm): D: 9.1, H: 4.9 (n = 1, type series). Differential diagnosis. Endothyrella bedfordi has a single curved parietal lamella with a long lower plica (which reaches the peristome) attached to it, and at the posterior ends of palatal plicae there are several small denticles. These features distinguish E. bedfordi from all congeners. See also Table 5.
The left ommatophoral retractor passes between penis and vagina. Atrium short, penis long, rather cylindrical, but slowly tapers towards the proximal end; opening the penis was very difficult, not only because of its size, but also due to the age of the speci- men; the internal morphology could hardly be seen, although parallel folds forming "pockets" were visible; a little thickening was found near the posterior end of the penis, this could be interpreted as a penial caecum. The slender and relatively long retractor muscle inserts on the proximal end of the penis, slightly in proximal direction from the caecum; epiphallus also slender, slightly longer than the penis; vas deferens long and slim; vagina shorter than the penis and epiphallus combined, it is very thick, with a well-developed vaginal bulb; several short muscle fibres attach the vagina to the body wall and diaphragm; both the gametolytic sac and the diverticulum are very long and slim, although the gametolytic sac is somewhat thickened.
Radula (Figures 19A-B): Radula elongated, but not very slender, central tooth present, laterals approximately 6, standing in straight lines (perpendicular to the central column); marginals approximately 14, although it is difficult to distinguish which are laterals and which are marginals; marginals are placed in oblique rows; central tooth wide-based triangular, smaller than the endocone of the first lateral, but much larger than the ectocone; laterals bicuspid, endo-and ectocones are triangular; marginals usually tricuspid (the endocone has two cusps), but some of the marginals are  (Gude, 1898). For locality see Fig. 17C. Abbreviations: A atrium AG albumen gland D diverticulum E epiphallus EM embryos GS gametolytic sac P penis RM retractor muscle V vagina VD vas deferens. tetracuspid (both the endocone and the ectocone have two cusps); all cusps pointed, the incision between the innermost two cusps is deep.
Distribution. Most museum samples have been collected in the Sikkim area. Gude received the holotype from Godwin-Austen, and it was said to be collected in the Naga Hills, approximately 600 km from Sikkim. The anatomically examined specimens have been collected from Silchar Cachar, which is located at least 500 km from Sikkim, but not far from the Naga Hills. If the samples from the Naga Hills and from Silchar are correctly labelled, we may expect that the species is widely distributed throughout north-eastern India (see also Figure 11).   Figure 16B 1879a Helix (Plectopylis) brahma Godwin-Austen: Journal of the Asiatic Society of Bengal,48 (2) Diagnosis. Shell very small, sinistral, with narrow umbilicus, depressed conical dorsally, conspicuous radial sculpture without hairs; callus very strong; palatal plicae short, straight, with many small denticles at their posterior ends, standing along a vertical line; lamella oblique, with three horizontal plicae anteriorly, the lowermost is in contact with the lower end of the lamella; besides these anterior plicae, there is a short upper plica above the lamella, and long lower plica close to the lower suture, which runs until the aperture.

Endothyrella dolakhaensis
Diagnosis. Shell small with rather conical dorsal surface; body whorl slightly angulated with five rows of hairs; parietal lamella simple with one or two denticles posteriorly and a plica below; middle palatal plicae divided or almost divided.
Description. Shell very small, sinistral, with somewhat elevated spire and rather conical apex; protoconch elevated from the dorsal surface; colour brownish or greyish; protoconch conspicuously large, consists of 2.25-2.5 whorls (n = 2), very finely, regularly ribbed; teleoconch with clearly visible reticulated sculpture dominated by radial growth lines; sculpture somewhat weaker on the ventral surface; very slender, long periostracal folds (hairs) standing in five spiral lines along the body whorl; whorls 5.25-5.5 (n = 3) moderately bulging, separated by relatively deep suture; umbilicus wide and deep; apertural lip whitish, thin, slightly reflexed; callus also very weak, slightly S-shaped; no fold in the aperture.
One specimen from the type locality was opened. Parietal wall with one rather straight lamella with slight lower arms pointing in both directions; small denticle near the upper end posteriorly, connected to the lamella; two short horizontal plicae under the lamella; palatal wall with six plicae; first slim and short, the second-fifth plicae are divided in the middle and are of the same length; last plica also short, rather straight ( Figures 9G-H).
Description of the genitalia (Figures 21, 22B-C): A single specimen was anatomically examined. Collection data: Khasi, leg. Godwin-Austen, NHMUK 1903.7.1.598. The specimen had some embryos developing in the uterus. The whole body was very fragile, therefore the gametolytic sac and the diverticulum could not be dissected out.
The left ommatophoral retractor passes between penis and vagina. Atrium relatively long; penis long, consists of a longer, slimmer distal and a shorter, more thickened proximal part; at the proximal end of the penis there is a rounded bulb-like thickening (similar to that of some Gudeodiscus species, see Asami 2014 andPáll-Gergely et al. 2015); penis internally with honey-comb-like tubercles without calcareous granules ( Figure 22C); the somewhat slimmer penial caecum has some (approximately 8) parallel folds inside, which also form minute hollows standing in lines between the folds ( Figure 22B); these small pockets may serve for small calcareous granules, although no granules were found; epiphallus enters penis at the basis of the rounded penial thickening; epiphallus relatively short, approximately as long as the proximal, thickened part of the penis; retractor muscle inserts on the proximal end of the penial caecum, it is approximately as long as the proximal part of the penis; vas deferens long and thick, it becomes curly near its insertion to the spermoviductus; vagina shorter than the the half of the penis; it has a vaginal bulb at the middle; two batch of fibres attach the proximal and distal part of the vaginal bulb to the body wall; there are also some longer and more slender muscle fibres attached to the vagina; between the atrium and the vaginal bulb there is a slender, longitudinal thickening on the inner  (Benson, 1836), For locality, see Fig. 19 B-C Endothyrella fultoni (Godwin-Austen, 1892), for locality see Fig. 21. D-F Endothyrella plectostoma, for locality, see Fig. 19. Arrow on D shows the entering point of the vas deferens to the penis. Arrow on E shows rounded calcareous granules. All photos by B. Páll-Gergely. vaginal wall; vaginal bulb internally with fine, irregularly reticulated sculpture; the area of the inner vaginal wall between the bulb and the spermoviductus is roughly reticulated; gametolytic sac relatively thick, the diverticulum is more slender.
Radula ( Figure 19C-D): The radula of the only available specimen was very fragile, probably because of the age of the sample; only a fragment of the middle part of the radula could be examined; central tooth present, laterals 14, marginals at least 8; central tooth very long, but somewhat shorter than the endocone of the first lateral, although larger than the ectocones; central tooth elongated triangular with slightly concave marginal line; endocone of the laterals are rather rhomboid, blunt, ectocone pointed triangular; endocones of marginals deformed rhomboid, sometimes oval, showing the sign of becoming bicuspid; ectocones of marginals blunt or pointed triangular.
Diagnosis. Shell very small, sinistral with relatively wide umbilicus, reticulated, almost flat spire (only the apex is elevated) and smooth umbilical side; callus weak, only very slight whitish lime layer is visible; palatal plicae straight, divided or not, lamella with short upper and lower plicae and two posterior denticles, one above and one below; the lower plica might be long (see under Additional material examined).
Measurements (in mm): D: 5.5-8.2.2, H: 2.7-4.2 (n = 13, shells from different samples); the holotype of Plectopylis gregorsoni is 7.5 × 3.7 mm. Differential diagnosis. Endothyrella macromphalus has more depressed shells than E. blanda. Moreover, E. macromphalus shells are smooth on the ventral side, whereas most blanda shells have hairs, or in case of corroded E. blanda specimens, holes which indicate the hairs' positions. Endothyrella dolakhaensis sp. n. is hairy, has weaker sculpture, and its spire is more elevated than in E. macromphalus. Endothyrella robustistriata sp. n. is smaller, has a narrower umbilicus and stronger dorsal sculpture. See also under E. williamsoni and Table 5.
Distribution. Endothyrella macromphalus seems to have a wide range including Assam and the Dafla and Khasi Hills. It has been reported from the Naga Hills, but those samples are probably misidentified. Plectopylis gregorsoni (treated here as a synonym of E. macromphalus) is recorded from the type locality only (approximately: 28°13.4'N, 95°13.3'E) (Figure 11).
Remarks. The type specimen of Plectopylis gregorsoni is very similar to typical E. macromphalus specimens. The main difference is that the palatal plicae are not divided in gregorsoni, and the base is less glossy (rather weakly ribbed). In our view these minor difference are not sufficient for species level distinction, especially because E. macromphalus is a relatively variable species inhabiting wide geographical range. Very little is known about the distribution of specimens having divided or undivided palatal plicae. Therefore, until more information becomes available, Plectopylis gregorsoni is synonymised with Endothyrella macromphalus. Types. Darjiling, leg. Stoliczka, coll. Godwin-Austen, NHMUK 1903.07.01.768/10 syntypes. See also remarks.
Diagnosis. Shell tiny, sinistral, with relatively narrow umbilicus, flat dorsal surface and four rows of hairs; callus strong; palatal plicae divided; lamella straight or slightly curved, with two denticles posteriorly, one above and one below; lower plica can be short and in some specimens reaching the peristome.
Differential diagnosis. Endothyrella minor is smaller and has weaker keeled body whorl than E. angulata sp. n. Moreover, the first and second rows of the periostracal folds are comparatively at larger distance from each other in E. minor than in E. angulata sp. n. Endothyrella blanda has more elevated spire and more hair rows than E. minor. Endothyrella robustistriata sp. n. has more elevate spire than E. minor and lacks the hairs on its ventral surface. Endothyrella macromphalus is hairless and larger than E. minor, it has a comparatively larger protoconch and a lower (or missing) parietal callus. Endothyrella minor is smaller and flatter than E. dolakhaensis sp. n. Moreover, it has a more elevated parietal callus, and has only four rows of hairs (E. dolakhaensis sp. n. has five). See also under E. williamsoni and Table 5.
Distribution. Originally the species was recorded from Darjeeling, Sikkim area. Very similar specimens were found from Central Nepal in the surroundings of Kathmandu (Shivapuri-Nagarjun National Park and Phulchowki hill) and Langtang National Park. Some literature records (Laisen Peak, Naga Hills) are based on misidentified specimens (see Figure 11 and 15).
Remarks. W. Blanford (1870) described Helix (Plectopylis) macromphalus, and while giving information on its locality, he mentioned that "varietas minor" inhabits the Rungun valley near Darjeeling. No description or illustration of "varietas minor" was provided in the paper, therefore the name is not available. Later, Godwin-Austen (1879b) described Helix (Plectopylis) minor from "Darjiling hills" and mentioned those shell "no doubt are referable to P. macromphalus W. Blf., var. minor". Blanford's specimens labelled as macromphalus minor have not been found in the collection of the NHM, but the type sample examined and described by Godwin-Austen (NHMUK 1903.07.01.768) was found.
Recent fieldwork in Nepal yielded a few populations in the surroundings of Kathmandu which can be assigned to E. minor. "Typical" specimens of E. minor and Nepalese shells are very similar in terms of size, shell and aperture shape and the morphology of the plicae and lamellae. The only notable difference between these shells is the position of the hair rows on the body whorl. The first row is situated more upper in position (on the upper angle of the body whorl) in the Nepalese shells, whereas in typical shells the first row runs under the angle. Additionally, the distance between the third and fourth rows is smaller in the Nepalese populations. Figure 12C 1915 Plectopylis (Endothyra) Figure 12C) Diagnosis. Shell small, sinistral, with very slightly elevated spire, relatively wide umbilicus, and conspicuous spiral sculpture; callus moderately strong, palatal plicae slightly oblique, connected by a vertical ridge; lamella almost straight, with anteriorly elongated upper and lower ends and small denticles on the posterior side, one above and one below.
Distribution. The species is known from the type locality only ( Figure 10).   Figure 24C). Diagnosis. A small to middle-sized, hairless species with domed dorsal surface and rounded body whorl; parietal lamella simple with one or two denticles posteriorly and sometimes a plica below the lamella, middle palatal plicae divided or almost divided.

Endothyrella nepalica
Description. Shell very small to small, sinistral, with somewhat elevated spire and domed dorsal surface; protoconch slightly elevates from the dorsal surface; usually brownish but sometimes turns into yellowish; protoconch consists of 1.5-1.75 whorls, very finely, regularly ribbed; teleoconch with very weak, irregular growth lines on the ventral surface and fine reticulated sculpture on the dorsal surface; in high magnification the surface is covered by flat periostracal folds; no spirally arranged large deciduous folds found; whorls 5.5-6.25, moderately bulging, separated by relatively deep suture; umbilicus wide and deep, whorls almost flat inside, resulting in an funnel-like shape, apertural lip whitish, rather thin, slightly reflexed; callus inconspicuous, but present, slightly S-shaped; no fold in the aperture.
Ten specimens were opened from different populations. Parietal wall with one slightly curved lamella with arms pointing in the direction of the aperture; lower end on the lamella more conspicuously curved than the upper end; two small denticles above and below posteriorly of the lamella (exceptionally, the lower one is missing); in some populations (e.g. Majhbeni -Parbat District, Champadevi -Kathmandu District and Siddha Cave -Tanahu District) with short plica under the lamella; palatal wall with six plicae; first slim and short, parallel with the suture; second plica is the longest, it shows a tendency towards dividing in the middle, but the two parts always fused; third, fourth and fifth plicae usually divided (third one sometimes not); last plica short, slightly curved with arms pointing in the direction of the lower suture ( Figures 9C-F).
Differential diagnosis. Endothyrella nepalica sp. n. is usually larger than E. angulata sp. n., it has a domed dorsal surface, rounded body whorl and lacks hairs standing in spiral rows, whereas E. angulata sp. n. has a flat dorsal surface, shouldered body whorl and has hairs which are arranged in spiral rows. Endothyrella dolakhaensis sp. n. differs from E. nepalica sp. n. by the usually smaller size, fewer whorls, stronger sculpture, comparatively larger protoconch, conical dorsal surface, slightly angulated body whorl and the presence of hairs standing in five spiral lines. For comparison with E. oakesi and E. pinacis, see under those species. See also Table 5.
Description of the genitalia (Figures 25A-C): Three specimens from three populations were anatomically examined (Champadevi, Balaju of Kathmandu District and Godawari Botanical Garden, Lalitpur District). Penis short, narrow distally and slowly tapers toward the proximal end; internal surface with several tubercles including minute calcareous hooks; epiphallus slender, cylindrical, longer than the penis, it enters penis laterally; penial caecum very short, blunt, cylindrical, with a short retractor muscle attached at its proximal end; vas deferens thin and nearly 1.5 times longer than epiphallus, convoluted before connection to prostate; vagina shorter than the penis with well-developed vaginal bulb; gametolytic sac very thin throughout and ends into a small rounded sac; there is a slender diverticulum running parallel with the gametolytic sac; it is as long as the gametolytic sac.
Etymology. The name nepalica refers to the country (Nepal) where the new species lives.
Remarks. Schileyko (1999) figured a shell from the "SW slope of Swayambhunat (= Swoyambhunath) hill, Kathmandu valley, Nepal" (Fig. 594.). The figured specimen is probably Endothyrella nepalica sp. n., but the drawing is not sufficient for identification. (Gude, 1915) Figure 16A 1915 Plectopylis (Endothyra) Figure 16A). clearly visible in E. pinacis. The most similar species is Endothyrella nepalica sp. n., which nevertheless has a higher spire and rounded whorls, whereas E. pinacis has shouldered whorls and nearly flat dorsal surface. The ventral surface of the two species is similar, but E. pinacis has slender hairs standing in 3 lines, which is missing in E. nepalica sp. n. According to previous studies (Godwin-Austen 1889-1914, Schileyko 1999) E. pinacis has no diverticulum, but in all E. nepalica sp. n. we dissected that organ was present. Endothyrella oakesi is similar to E. pinacis, but has much more complicated palatal plicae, more descending aperture, differently shaped umbilicus and rounded body whorl. See also Table 5.   (Benson, 1836

Diagnosis.
A very small, sinistral species with very narrow umbilicus, conical dorsal surface, and hairs standing in five rows on the body whorl; palatal plicae more or less straight, the 4th and 5th divided; lamella slightly curved, with short lower and long upper elongation in anterior direction; there are two denticles posteriorly, one above and one below.
Measurements (in mm): D: 8.1-9, H: 4.6-5.1 (n = 3, SMF 172072). Differential diagnosis. Endothyrella plectostoma is similar to E. affinis and E. tricarinata in the narrow umbilicus. All other Endothyrella species of similar size have wider umbilicus. Endothyrella plectostoma is usually smaller, darker than E. affinis, it has a horizontal, relatively long plica anterior to the lamella, and has the periostracal folds arranged on five spiral line. In contrast, E. affinis lacks the horizontal parietal plica and has four hair rows. Moreover, E. plectostoma has a narrower umbilicus and more elevated spire than E. affinis. See also under E. sowerbyi and E. tricarinata and Table 5.
The left ommatophoral retractor passes between penis and vagina. Atrium short; penis relatively short, internally with holes of various sizes; some tiny, rounded calcareous crystals were found in the penis lumen, not directly associated with the holes; this inner structure continued in the epiphallus; penial caecum short, with central thickening; retractor muscle short, it inserts on the proximal end of the penial caecum; epiphallus slightly longer than penis, it enters the proximal penial portion laterally; vas deferens long and slender; vagina approximately as long as the penis, but thicker, curved centrally; vagina with several thick and relatively long muscle fibres attaching it to the body wall and to the diaphragm, especially at its curved portion; vagina internally with longitudinal folds, which are rather sharp, elevated at the curved area of the vagina, and low elsewhere; the gametolytic sac and the diverticulum are aligned in parallel ; the gametolytic sac is slightly thicker and shorter; a relatively long part of the spermoviduct was visible distal to the thickened uterus with the developing embryos; the embryo sac contained no visible calcareous granules, which were reported in other plectopylid species (Páll-Gergely and Hunyadi 2013, Páll-Gergely and Asami 2014); albumen gland conspicuously small. The latter trait is largely dependent on the period of the life cycle of the dissected specimen. In the present case, however, three specimens were anatomically examined and all specimens had a small albumen gland.
Radula ( Figure 19E-F): Radula elongated, but not very slender, central tooth present, laterals 8, standing in straight lines (perpendicular to the central column); marginals at least 14, staying in oblique rows; central tooth relatively narrow-based triangular, smaller than the endocone of the first lateral, but much larger than the ectocone; laterals bicuspid, endocone oval or narrow-based triangular; marginals tricuspid (the endocone has two cusps); all cusps pointed, the incision between the innermost two cusps is deep; in some cases the three cusps are almost of the same size.
Distribution. Museum samples are labelled from several locations. This species is probably widely distributed in north-eastern India through south-eastern Bangladesh to Bago, the Arakan Hills and in the Kayah State in Burma (Myanmar) (Figure 7). A sample (ZMH 45910) was collected in "Siam" (= Thailand), which is possible because other samples were collected in Myanmar not far from the Thai Border.

Endothyrella robustistriata
Description. Shell tiny, sinistral, with slightly elevated spire and conical/domed dorsal surface; colour light brown, greenish or yellowish; protoconch consists of approx. 2 whorls, glossy, in some populations (NHMUK 1903.7.1.767, NHMUK 1903.7.1.770, NHMUK 1903) only the last half whorl has a somewhat ribbed surface, whereas in another population (NHMUK 1903.7.1.765) nearly the whole protoconch is ribbed; dorsal surface of the teleoconch with clearly visible reticulated sculpture dominated by spiral lines; ventral side hairless, smooth, glossy, sometimes with radial growth lines; the ventral and dorsal surface change relatively abruptly above the middle line of the body whorls (from apertural = frontal view); inside the umbilicus there are sharp periostracal folds corresponding with radial ribs; whorls 4.5-4.75 (n = 3), slowly growing, separated by relatively deep suture; umbilicus narrow and deep; apertural lip whitish, thickened, normally not reflexed, or reflexed only near the umbilicus; callus very weak, nearly invisible in case of fresh shells, in case of old, corroded shells it becomes white; aperture without entering fold.
Two opened specimens were observed (NHMUK 1903.7.1.767 andNHMUK 1903.7.1.765). Parietal wall with one rather straight lamella which bends anteriorly; it has both the upper and lower ends elongated anteriorly; two small denticles visible at the posterior side of the lamella, one above and one below; lower plica very long, reaches the peristome; palatal wall with six plicae; first slim and short, the second-fifth plicae horizontal; they do not seem to be divided if we observe through the translucent shell wall, but their middle portion (where the lamella is present on the parietal wall) is much lower; the posterior ends of the middle plicae slightly bent downwards, whereas the anterior parts are straight and horizontal; the last plica is short and slightly curved ( Figure 9K-L).
Measurements (in mm): D: 4.1-4.6, H: 2.3-3.5 (n = 2 NHMUK 1903.7.1.765). Differential diagnosis. Endothyrella blanda is similar in shell shape to E. robustistriata sp. n., but is larger, has hairy ventral surface (or if hairs are missing, than hollows are visible indicating the hairs' positions), and on its dorsal surface the radial lines are dominant. See also under E. macromphalus and E. williamsoni and Table 5.
Etymology. The word robustistriata means strongly striated (Latin) which refers to the prominent spiral striae of the new species on the dorsal side of its shell.
Type locality. Munipur, Laisen Peak. Distribution. The new species is known only from the Naga Hills and Manipur ( Figure 11). Figure 13C-D Types. Khasia Hills, India, NHMUK 1922.8.29.48. (holotype, Figure 13C). Diagnosis. A very small, sinistral species with narrow umbilicus (but wider than in the three similar species; affinis, plectostoma, tricarinata), rather domed dorsal surface, and hairs standing in five rows on the body whorl; the hairs are usually missing and the ventral side is with relatively strong radial lines; plication similar to E. plectostoma, but the main anterior parietal plica is missing or weak.

Endothyrella sowerbyi (Gude, 1899)
Measurements (in mm): D: 7.8-8.6, H: 4.3-5.0 (n = 3, SMF 346408). Differential diagnosis. Endothyrella affinis is larger, has lighter shell with narrower umbilicus and a weaker sculpture. Endothyrella sowerbyi has a wider umbilicus and a thinner peristome than E. plectostoma. Moreover, the spire is lower and the dorsal side is rather domed in E. sowerbyi (conical in plectostoma), and the main parietal plica is weaker or missing. See also under E. tricarinata and Table 5.
Distribution. Museum specimens are collected from the Khasi Hills, Darjeeling, and Burma.
Remarks. During the preparation of this revision, Endothyrella sowerbyi was handled as the synonym of E. plectostoma, because the only known specimen (the holo-type) looked like a juvenile shell of E. plectostoma. The first author recognized that E. sowerbyi is a valid species in the Senckenberg Museum in August, 2015, because of several mixed samples deposited there. Thus, the Endothyrella plectostoma/sowerbyi sample of the SMF were identified and the E. sowerbyi shells were separated by B. Páll-Gergely. The E. plectostoma samples in the NHM were checked by Jonathan Ablett, whereas those in the NHMW were examined by Zoltán Fehér. Figure 13E-F rows on the body whorl; palatal plicae more or less straight, they are more or less divided; lamella slightly curved, with small denticles on the posterior side (they might fuse to the lamella), and a long upper plica on the anterior side of the lamella.
Distribution. All museum samples were collected from the Khasi Hills and Assam ( Figure 11).
Remarks. Two varieties of Plectopylis plectostoma have been described under the names Plectopylis plectostoma var. tricarinata and P. plectostoma var. exerta. Both of them differ from typical Endothyrella plectostoma specimens by the more shouldered whorls, and the more conical dorsal side of the shell having stronger spiral lines. No difference between the type specimens of these forms have been found except for the presence (exerta) and the absence (tricarinata) of hairs. The absence of hairs might be due to the corroded state of the syntypes of tricarinata. Although the difference between typical E. plectostoma and typical tricarinata/exerta shells seem to be minor, we found no intermediate forms, and in some cases we found mixed museum samples which indicate that the shells might have been collected from the same site. This suggest that Endothyrella plectostoma and E. tricarinata are distinct species. (Gude, 1915) Figure 17A 1915 Plectopylis (Endothyra) Figure 17A) Diagnosis. Shell very small, sinistral with narrow umbilicus and conical dorsal surface; shell hairless but densely, finely ribbed and ornamented with low radial periostracal lamellae on the whole shell; callus strong; palatal plicae horizontal, almost straight and thin at their middle; lamella slightly curved; there is long, horizontal plica anteriorly to the lamella, and a short horizontal plica above the long one; additionally, there is a very short upper plica above the lamella, a small denticle posteriorly above, and a long lower plica near the suture which reaches the aperture.

Endothyrella williamsoni
Measurements (in mm): D: 6, H: 3.6-3.7 (n = 2, type series). Differential diagnosis. Endothyrella williamsoni has a more elevated spire than E. macromphalus and E. minor, and has two horizontal parietal plicae anterior to the lamella which are missing in the other two species. The most similar species in terms of shell shape and size to E. williamsoni is E. blanda. The latter species, on the other hand, lacks the two horizontal parietal plicae anterior to the lamella which area characteristic for E. williamsoni. Moreover, E. blanda specimens have seven rows of hairs, whereas E. williamsoni is hairless. Endothyrella robustistriata sp. n. is smaller, has stronger dorsal sculpture and lack the main plica which is characteristic for E. williamsoni. See also Table 5.
Distribution. This species is known from the type locality only (Figure 10).

Species with uncertain identity
Plectopylis hanleyi Godwin-Austen, 1879b Original description. "Shell sinistral, depressedly conoid, openly umbilicated, probably hirsute when young. Sculpture coarse, irregular, transverse ridges. Colour uniform ochraceous. Spire conoidal; apex blunt, smooth. Suture well marked. Whorls six, close-wound, convex. Aperture semicircular, diagonal; peristome somewhat thickened, white, with a thin callus on the parietal margin, not to the extent of a ridge. Sizemajor diam. 5.5, minor diam. 5.0, alt. 3.0 millims. Parietal vertical lamina simple; palatal plicae in two rows, four long in front, four short behind, and one basal long. The shell is very distinct; it has somewhat the form of P. plectostoma, but is not so angular on the periphery, while the internal plication is quite different, besides being so very much smaller in size." Remarks. In the original description Godwin-Austen (1879b) wrote that the holotype is "in the collection of Mr. Sylvanus Hanley". In Godwin-Austen's copy of Gude (1914, page 77), Godwin-Austen has written "In my collection". The holotype, however, was not found in the collection of the NHM. Only one NHM specimen was found labelled Plectopylis hanleyi, and this is annotated with a question mark ("Sikkim, Rarhichu, H. H. Godwin-Austen colln."). However, this specimen is very similar to the type specimen of Plectopylis blanda, and is not identical with the single shell in Godwin-Austen's (1879b) description, because it has only 4.75 whorls (the holotype of P. hanleyi has six). Moreover, Godwin-Austen (1879b) described the palatal lamellation, whereas the above mentioned specimen is intact, therefore the inner lamellae and plicae could not be observed. Some parts of Hanley's collection are housed in the Leeds Museum and in the Manchester Museum. The former were contacted and confirmed that the holotype was not deposited there. The catalogue of the type specimens of the Manchester Museum (McGhee 2008) did not list Plectopylis hanleyi. Since the holotype of Plectopylis hanleyi seems to be lost, and the description is not sufficient to diagnose the species (although it matches with E. blanda), P. hanleyi is considered to be a nomen dubium.

Results and discussion
Examining all species assigned to Chersaecia and Endothyrella by Gude (1899cGude ( , 1915 revealed that all species formerly assigned to Endothyrella by Gude (1899cGude ( , 1915 were correctly placed in that genus. The genus Chersaecia is, on the other hand, very diverse in terms of shell characters. The type species of Chersaecia, Plectopylis leiophis, has a finely tuberculated protoconch and an apertural fold ( Figure 2). We suggest retaining only those species in Chersaecia which share the same features. Consequently, some former Chersaecia species (aborensis, andersoni, babbagei, bedfordi, brahma, laomontana, oglei, serica, williamsoni) are excluded from that genus. Most of these species (aborensis, babbagei, bedfordi, brahma, oglei, serica, williamsoni) are classified in Endothyrella on the basis of the absence of an apertural fold, the ribbed protoconch, the hairs standing in multiple spiral lines and the characters of the armature. Plectopylis andersoni and P. laomontana are not assigned to either genus because of the large, keeled shell of andersoni with reticulated protoconch and the unique anatomical features of laomontana (unpublished information). The systematic position of these two species and the species remained in genus Chersaecia will be discussed in separate publications.
The finely ribbed protoconch is considered to be one of the key characters allowing separation of Chersaecia and Endothyrella species. Dextral Endothyrella species however, have "no typical" protoconch: (1) E. babbagei has slightly waved ribs ( Figure 6C); (2) E. inexpectata sp. n. has a rather smooth protoconch, some ribbing is only visible on the last half/quarter of whorl ( Figure 6F); (3) E. serica has a very finely granulated protoconch with rather irregular ribs/ridges and there is an additional spiral line running close to and parallel with the suture ( Figures 6B). However, we see no justification for erecting new (sub) genera for these dextral species yet. Information on their anatomy and molecular evidence may shed light on the importance of these differences as well as the relationship with sinistral Endothyrella species.