Hebius khasiensis ( Boulenger, 1890 )

Hebius khasiensis ( Boulenger, 1890) View in CoL

( Fig. 4 View FIGURE 4 , 5 View FIGURE 5 , 6 View FIGURE 6 , 9 View FIGURE 9 , 10A and 10B View FIGURE 10 ; Table 3 View TABLE 3 )

Tropidonotus khasiensis Boulenger 1890: 344 View in CoL — Type Locality. Khasi Hills (25°34N, 91°53E; 1,525 m asl approx), Meghalaya, northeast India — Lectotype (by present designation) (Formerly syntypes): BMNH 1946.1 .12.80, an adult female collected by T. C. Jerdon from Khasi Hills (25°34N, 91°53E; 1525 m asl approx), Meghalaya, northeast India; Paralectotypes: BMNH 1946.1 .12.81 and BMNH 1946.1.12.82, two adult males bear the same collection details as the lectotype and BMNH 1946.1 .13.45, a juvenile female collected by Sir J. Hooker from the same locality as the lectotype.

Chresonyms

Tropidonotus khasiensis — Boulenger 1893a: 322, 1893b: 223: Plate 13: Fig. 3 View FIGURE 3 ; Annandale 1905:210, 1912: 49 & 53; Wall 1908: 316, 317: Fig. 2 View FIGURE 2 .

Natrix khasiensis — Wall 1923: 601; Wall 1926:559 (Wall himself synonymized his described species gilhodesi with khasiensis ); Bourret 1936 a, b; Smith 1943: 289.

Amphiesma khasiensis — Malnate 1960; Das 1996: 53; Sharma 2004.

Paranatrix modesta (non Tropidonotus modestus Günther, 1875 )— Mahendra 1984:247 (The consideration of H. khasiensis as a synonym of H. modestus was erroneous; see David et al. 2013:8).

Amphiesma khasiense — Whitaker & Captain 2004: 25, 218 & 219; Ziegler et al. 2006; Ahmed et al. 2009: 19; Wallach et al. 2014: 30; Chan-ard et al. 2015: 233.

Amphiesma cf. khasiense — Grismer et al. 2007.

Hebius khasiense — Guo et al. 2014 (implicitly).

Hebius khasiensis — Zhou et al. 2019; David et al. 2021.

Materials examined: Syntypes — BMNH 1946.1.12.80 , an adult female collected by T.C. Jerdon from Khasi Hills (25°34N, 91°53E; 1525 m asl approx), Meghalaya, northeast India; GoogleMaps BMNH 1946.1.12.81 and GoogleMaps BMNH 1946.1.12.82 , two adult males bear the same collection details as the above female syntype; GoogleMaps BMNH 1946.1.13.45 , a juvenile female by Sir J. Hooker from Khasi Hills (25°34N, 91°53E; 1525 m asl approx), Meghalaya, northeast India. GoogleMaps

Lectotype ( Fig. 4 View FIGURE 4 .) (By present designation)— BMNH 1946.1.12.80 , an adult female collected by T.C. Jerdon from Khasi Hills (25°34N, 91°53E; 1525 m asl approx), Meghalaya, northeast India GoogleMaps .

Paralectotypes ( Fig. 5 View FIGURE 5 )— BMNH 1946.1.12.81 and GoogleMaps BMNH 1946.1.12.82 , two adult males bear the same collection details as the lectotype; GoogleMaps BMNH 1946.1.13.45 , a juvenile female collected by Sir J. Hooker from the same locality as the lectotype GoogleMaps .

Additional topotypic and referred materials: MZMU 3526 ( Fig. 6 View FIGURE 6 ), an adult female collected by Sanath Chandra Bohra and Holiness Warjri on 12 th April 2024 at around 21:45 h from Mairang, Eastern West Khasi Hills district (25.559415°N, 91.635047° E; 1564 m asl), Meghalaya, India; MZMU2810, MZMU2973, MZMU3239, all adult females collected by H. T. Lalremsanga, Lal Biakzuala and others from Tamdil National Wetland (23.728665°N, 92.956578°E), Aizawl district, Mizoram, India; MZMU2706, a juvenile female collected by H. T. Lalremsanga, Lal Biakzuala and others from Theiriat (22.868358°N, 92.788137°E), Lunglei district, Mizoram, India; MZMU2540, an adult female collected by H. T. Lalremsanga, Lal Biakzuala and others from Sailam (23.350624°N, 92.797968°E), Aizawl district, Mizoram, India; MZMU2096, an adult female collected by H. T. Lalremsanga, Lal Biakzuala and others from Durtlang (23.795506°N, 92.726469°E), Aizawl district, Mizoram, India; MZMU1304, an adult female collected by H. T. Lalremsanga, Lal Biakzuala and others from Reiek (23.677444°N, 92.603713°E), Aizawl district, Mizoram, India; MZMU1531, an adult female collected by H. T. Lalremsanga, Lal Biakzuala and others from Sawleng (23.981553°N, 92.930910°E), Aizawl district, Mizoram, India; MZMU923, an adult male by H. T. Lalremsanga, Lal Biakzuala and others from Durtlang (23.795506°N, 92.726469°E), Aizawl district, Mizoram, India.

Notes: Since Tropidonotus (Hebius) khasiensis was described based on four syntypes, the species would be taxonomically stable after designating a lectotype. Herein, we have designated BMNH 1946.1.12.80, an adult female as the lectotype for the given species as it appears to be more morphologically pronounced and is the only specimen with a complete (though broken) tail amongst our syntypes. In the literature alongside the description, Boulenger (1893) stated that he had a total of three adult females and an unsexed juvenile specimen (four syntypes formerly) in the original type series but upon examination it was observed that the type series comprises of one adult female (designated as the lectotype herein), two adult males and a juvenile female (see David et al. 2013).

Diagnosis and Description: A medium sized natricid snake growing upto a maximum SVL of 412 mm and is diagnosed from all other congeners based on the combination of the following characters: (1) cylindrical body with 19 (OSR):19 (MSR):17 (PSR) dorsal scale rows, all of which are strongly keeled except for the OSR and the outermost row close to ventral edges that are usually very feebly keeled, rarely moderately keeled. Posterior region close to the base of the tail are always strongly keeled (2) ventrals 145–157 (plus 1 or 2 preventrals) (3) subcaudals 91–103, all paired or divided (4) anal plate divided or paired (5) tail relatively long with a Tal/TL ratio of 0.275 –0.341 (6) 8–9 supralabials or upper labials out of which 3 rd, 4 th and 5 th or 4 th, 5 th and 6 th (rarely 4 th and 5 th) are touching the orbit and the last three supralabials are comparatively much larger (7) 10–11 infralabials or lower labials out of which the first five are touching the first pair of anterior chin shields; First pair of infralabials are the longest and are in contact with each other behind mentals (8) nasal scale distinct and divided, nostril lies laterally in the center of the nasal scale (9) internasals divided or paired (10) a single loreal scale dorso-laterally present on either side of the head (11) 17–21 maxillary teeth on both sides, slightly getting enlarged posteriorly including the last two to three posterior teeth without proper diastema that are moderately enlarged as compared to the anterior ones (12) dorsal body coloration in life mostly ranges from chocolate brown to sepia or blackish brown along with two thin and parallel rusty brown or burnt sienna dorso-lateral stripes that are properly visible from above, each stripe running just from behind the nape till the base of the tail dorsally on either side. The thin rusty brown dorso-lateral stripes are at times slightly faded and frequently interrupted as well as intermixed with a continuous series of distinct ochre yellowish spots of nearly equal width (13) upper lips or supralabials are usually off white in coloration intermixed with distinct black markings that are usually present in and around the marginal edges of each supralabial scale, the black markings become comparatively much larger in the last three supralabials (14) nape with a short but continuous, distinct off whitish or creamish streak which begins just behind the last supralabial scale, thereby covering a length of 5–8 continuous scales and nearly touches the anterior portion of rusty-brown dorso-lateral stripe in the neck (15) upper portion of the head mainly has two shades of coloration ranging from chocolate brown to sap greenish intermixed with irregular creamy yellowish spots (16) ventral region is completely off-white in coloration along with the presence of distinct black spots on the ventral edges of each ventral, anal and each subcaudal scale throughout, thereby forming a somewhat thin, distinct and dark ventro-lateral line like appearance.

Description of the lectotype ( Fig. 4 View FIGURE 4 )—An adult female with a cylindrical as well as a slender body having a TL (total length) of 604 mm, SVL 412 mm, Tal 192 mm and a Tal/TL ratio of 0.318.

Head is elongated and moderately large, somewhat distinct from neck (HL/SVL 0.04); Snout is rather large, sub-equally as long as broad and semi-oval in shape as seen from above. Eye is moderately large (ED1 3.0 mm; ED2 2.9 mm) and pupils are round. Rostral is partially visible from above, much wider than high and is in broad contact with 1 st supralabial, anterior portion of nasal as well as inter-nasals; nasal scale on either dorso-lateral side of the head, irregularly pentagonal and somewhat elongated; the nasals are completely divided sub-equally into anterior and posterior portions by a somewhat perpendicular suture above and below the crescentic nostril; the nostril lies right in the center of the nasal scale laterally; a pair of internasals clearly visible from above, slightly longer than broad (L–INas 2.0 mm; W–INas 1.8; W–INas/L–INas 0.9) and are in broad contact with each other; each internasal is irregularly sub-triangular in shape and is in contact with rostral, nasal and prefrontal scales, but the portion of internasals broadly contacting nasals on the lateral sides of the head are somewhat semicircular in shape; a pair of pre-frontals that are irregularly hexagonal in shape and are somewhat sub-equal in length and width and are broadly connected with each other; prefrontal larger than internasal in terms of both length as well as width (L–INas/LPreFro 0.8; W–INas/W–PreFro 0.8) and prefrontal sutures slightly longer than internasal sutures; prefrontal is in contact with internasal, nasal, loreal, preocular, supraocular and frontal; frontal pentagonal, elongated, longer than broad (FL 4.4 mm, FW 3.2 mm; FW/FL 0.7), about twice longer than prefrontal length (L–PreFro/ FL 0.5) and is in contact with prefrontal, supraocular as well as parietal; one elongated supraocular above the eyeball on either side that is anteriorly narrowed, irregularly rectangular and is in contact with prefrontal, preocular, frontal, parietal as well as postocular; a pair of parietals that are large, much longer than broad (L–Par 6.4mm, W–Par 3.1mm;W–Par/L–Par 0.5), broadly in contact with each other and are also in contact with the dorsal scales on the occiput, temporals (anterior as well as posterior), postocular, supraocular as well as frontal; one small loreal scale on either dorso-lateral side of the head, slightly longer in length to depth (L–Lor 1.6 mm, H–Lor 1.5 mm; H–Lor/L–Lor 0.9), in contact with 2 nd and 3 rd supralabials on both the sides; a small preocular on either dorso-lateral side of the head; 3 postoculars on either dorso-lateral side of the head, size somewhat decreasing from top to bottom; 9 supralabials on the left out of which 1 st and 2 nd are touching the nasals, 2 nd and 3 rd are touching the loreals and 4 th, 5 th, 6 th are touching the orbit whereas 8 supralabials on the left side out of which 1 st and 2 nd are touching the nasals, 2 nd and 3 rd are touching the loreals and 3 rd, 4 th, 5 th, are touching the orbit. Temporals 1+1 (anterior + posterior) on either side; 10 infralabials on both the sides out of which the first pair is the longest and are in broad contact with each other behind the mental; the first five infralabials are in contact with the anterior pair of chin shields and 5 th, 6 th, 7 th are in contact with the posterior pair of chin shields. Mental roughly triangular, wider than high; two pairs of chin shields, posterior chin shields are longer than the anterior ones, separated from each other by a row of two to three medium sized, elongated scales and mental groove is apparent.

Dorsal scales somewhat rhomboid in shape, arranged in 19 (OSR):19 (MSR):17 (PSR) rows, all of which are strongly keeled except for the OSR and the outermost row close to ventral edges that are very feebly keeled; dorsal region behind the neck begins with very feebly keeled scales.

Dorsal scale reduction formula:

4+5 → 4 (92) (left)

19 ———————————17

4+5 → 4 (97) (right)

Ventrals are 148 (plus 2 preventrals); anal plate is divided; and subcaudals are 95, all of which are paired or divided. Tail is long, complete but broken at 13 th subcaudal, having a length of 192 mm, Tal/TL ratio of 0.318 and is gradually tapering posteriorly. Maxillary dentition is 21 (18+3) in number, becoming slightly enlarged posteriorly with the last three posterior teeth being un-grooved, distinct and moderately enlarged, nearly sub-equal with the anterior ones. Furthermore, there is no proper diastema separating the last three enlarged posterior teeth with the anterior ones.

Coloration in preservative: The overall coloration of the specimen looks faded. Doral region including the head appears to have various shades of brown, mostly golden or yellowish brown. Upper lips or supralabials are usually off white in coloration intermixed with distinct faded dark markings, somewhat burnt sienna in coloration that are usually present in and around the marginal edges of each supralabial scale, the dark markings become comparatively much larger in the last three supralabials. Infralabials are mostly creamish in coloration intermixed with certain faded shades of brown i.e. burnt sienna. Nape with a short but continuous, distinct creamish streak which begins just behind the last supralabial scale and covers a length of 8 continuous scales. The entire ventral region appears to be creamish in colour with the presence of faded but somewhat distinct dark spots on the ventral edges of each ventral scale throughout the forebody after which the spots eventually disappear, indicating the presence of a thin, dark, distinct ventro-lateral line like appearance in life.

Variation: For variation within the species, refer to Table 3 View TABLE 3 . Among the examined type series, all specimens agree with the general morphology of the lectotype, and no major variations were observed except for a single female specimen (MZMU 3526) which bears a notably lower number of maxillary teeth i.e. 17 (15+2) including the last two moderately enlarged posterior ones.

Sexual dimorphism: Due to lack of further male specimens, no major sexual dimorphism could be observed among both the sexes.

Comparisons ( Fig 7 View FIGURE 7 , 8 View FIGURE 8 ; Table 4 View TABLE 4 ): Genetically, H. khasiensis is sister to H. gilhodesi comb. nov. and can be differentiated from each other by an un-corrected p-distance of 6.0 to 6.5 % in the mitochondrial cytochrome b gene and certain morphological parameters (see Table 2 View TABLE 2 , Table 4 View TABLE 4 ).

Morphologically H. khasiensis can be easily diagnosed from all other congeners by the combination of following characters:

(1) Dorsum mostly chocolate brown to sepia or blackish brown in life (versus brownish olive dorsum with black edged whitish or creamish crossbars on the forebody of H. andreae ; dorsal background dark brown, dark greyish brown or dark brownish-grey, becoming more or less distinctly darker on the back than on sides in H. clerki ; dorsum with irregular, blackish-brown or dark grey blotches in H. deschauenseei ; dorsum mostly olive green intermixed with blackish and whitish spots in H. flavifrons ; dorsum with dark brown, dark chestnut-brown or blackish-brown in H. igneus ; dorsum with sandy beige with the sides yellowish-brown in H. jingdongensis ; dorsum with blackish brown, somewhat checkered in H. johannis ; dorsum with dark grey or blackish brown in H. leucomystax ; dorsum reddish brown or grayish brown in H. maximus ; dorsum blackish brown or chocolate brown in H. miyajimae ; dorsum dark greyish-brown, brown or dark brown, scattered with blackish-brown or black spots or blotches in H. modestus ; dorsum with shades of mixed yellow along with distinct black lines in H. octolineatus ; dorsum very dark, somewhat blackish brown with whitish or yellowish crossbars edged with black in H. optatus ; dorsum dark reddish-brown or probably dark chestnut-brown, turning to cream, grey, pinkish-grey, tan, more or less dark greyish-brown in H. parallelus ; dorsum mostly dark, greyish black or brownish black in H. popei ; dorsum blackish or chocolate brown mostly along with whitish or yellowish crossbars which fades into small spots towards the posterior half in H. pryeri ; top of dorsum parmasean yellow intermixed with continuous black blotches and flanks are covered with a broad and a continuous pinkish line in H. sanguineus ; dorsum dark slate-gray, with most scales densely speckled with dark grey, minute dots intermixed with large, diffuse dark brown blotches in H. sangzhiensis ; dorsum mostly dark intermixed with shades of mixed yellow such as ochre and dark on the flanks in H. septemlineatus ; dorsum mostly brown ground color, darker on the top in H. terrakarenorum ; dorsum olive brown, olive-grey, dark grey, brown to dark brown or sometimes blackish-brown checkered by the presence on sides intermixed with elongate or rectangular blackish-brown or very dark grey blotches in H. venningi ; dorsum reddish-brown or chocolate brown, somewhat darker medially in H. vibakari ; dorsal region towards midbody reddish brown, forebody and posterior body blackish or greyish brown in H. viperinus ; dorsum mostly greyish black in H. weixiensis ; dorsum greyish black intermixed with yellowish markings in H. yanbianensis ; dorsum mostly dark, brownish black in H. youjiangensis ).

(2) A distinct dorso-lateral line present on both the sides, somewhat rusty brown or burnt sienna intermixed with distinct ochre yellowish spots throughout (versus absent in H. andreae , H. concelarus , H. flavifrons , H. ishigakiensis , H. lacrima , H. optatus and H. pryeri ; present on both sides that are creamish and are edged with black in H. bitaeniatus ; present, one weak yellow stripe marked with a series of rusty spots in H. craspedogaster ; large, elongate blotches, yellow-ochre, rusty red or yellowish-brown in H. deschauenseei ; present, at times continuous and at times yellowish ochre spots forming lines in H. igneus ; present, two brick-red stripes on the dorsolateral scale rows in H. jingdongensis ; usually a lighter spots series or ill-defined lighter-spots made stripe in H. johannis ; present, one well defined greyish-pink strip at first, gradually diffused at back in H. kerinciensis ; somewhat present, vertically elongated or divided dorsolateral spots, salmon or rusty red on a dark grey background in H. leucomystax ; present, one khaki stripe inset by a bold pattern of alternating rows of black squares in H. metusia ; present, three stripes, one yellow, one black, one red stripe in H. miyajimae ; somewhat present, a more or less conspicuous, ochre-yellow, ochre-red, orange-brown or reddish-brown stripe, often reduced to a succession of elongate blotches on the anterior part of the body in H. modestus ; four dorsal stripes on each side, two yellow and two grayish-black in H. octolinatus ; very ill defined, instead a lateral series of black spots in H. petersii ; very ill defined, instead a lateral series of whitish spots which becomes indistinct in the posterior half in H. popei ; not a stripe but a broad pinkish or reddish band on the flanks in H. sanguineus ; Present, a pale brown or beige dorsolateral stripe in H. sangzhiensis ; present, four dorsal stripes on each side, all dark in H. septemlineatus ; very ill defined in H. vibakari ; present, uniform and continuous beige stripe in H. youjiangensis ).

(3) Ventrals off white along with dark spots on ventral edges forming a distinct ventrolateral line like appearance (versus ventrals yellowish with small dark spots close to edges, ventral edges with zig zag dark line in H. bitaeniatus ; very discontinuous zigzag ventrolateral stripe in H. clerki ; ventrals overall dark, i.e., dark brown, blackish-brown or black in H. igneus ; ventrals light yellow with the outer part of each scale brick-red in H. jingdongensis ; ventrals purple greyish-brown at their outer border, with a row of well-defined dark brown blotches in H. kerinciensis ; ventrals pale ochre-brown or pale brown on a wide central area, broadly edged with dark brown or blackish in H. modestus ; ventrals immaculate pinkish-cream except for the pale salmon corners of the ventral in H. terrakarenorum ; ventral edges in forebody with large, distinct blackish bars in H. viperinus ).

(4) Dorsal scale rows are strongly keeled except for OSR and the outermost row close to ventral edges that are usually very feebly keeled, rarely moderately keeled (versus outer dorsal scale rows keeled in H. craspedogaster and dorsal scale rows barely or weakly keeled at midbody in H. modestus ).

(5) A Tal/TL ratio of 0.275 –0.341 (versus 0.245 –0.266 in H. bitaeniatus ; 0.235 –0.243 in H. jingdongensis ; 0.231 in H. johannis ; 0.238 –0.289 in H. metusia ; 0.28 in H. modestus ; 0.207 –0.274 in H. octolineatus ; 0.221 –0.252 in H. parallelus ; 0.24–0.27 in H. sangzhiensis ; 0.247 –0.281 in H. septemlineatus ; 0.235 –0.256 in H. weixiensis ; 0.256 in H. yanbianensis ).

(6) 145–157 ventrals (versus 179–180 in H. andreae ; 153–177 in H. bitaeniatus ; 162–173 in H. clerkii ; 157– 169 in H. concelarus ; 159–169 in H. igneus ; 164–178 in H. ishigakiensis ; 163–166 in H. jingdongensis ; 165–170 in H. johannis ; 138–140 in H. kerinciensis ; 154–166 in H. leucomystax ; 159–176 in H. metusia ; 156–169 in H. optatus ; 160–173 in H. parallelus ; 130–142 in H. popei ; 166–183 in H. pryeri ; 160–164 in H. sangzhiensis ; 164– 175 in H. septemlineatus ; 159–171 in H. terrakarenorum ; 101 in H. viperinus ; 171–182 in H. weixiensis ; 172 in H. yanbianensis ; 160 in H. youjiangensis ).

(7) 91–103 paired subcaudals and a divided cloacal plate (versus 76–86 in H. bitaeniatus ; 115–141 in H. deschauenseei ; 115–129 in H. igneus ; 71–74 in H. jingdongensis ; 85–89 in H. johannis ; 64–92 in H. maximus ; 72–93 in H. metusia ; 104–122 in H. modestus ; 70–80 in H. octolineatus ; 63–77 in H. parallelus ; 65–78 in H. petersii ; 66–88 in H. popei ; 112–130 in H. pryeri ; 81–82 in H. sangzhiensis ; 80–96 in H. septemlineatus ; 107–130 in H. terrakarenorum ; 115–129 in H. venningi ; 54–89 in H. vibakari ; 59 in H. viperinus ; 74–88 in H. weixiensis and 112 in H. youjiangensis ).

(8) Presence of 17–21 teeth in the maxilla including the moderately enlarged posterior ones (versus 34, last 2 enlarged ones in H. andreae ; 25–26 in H. concelarus ; 29–30, last 2 moderately enlarged in H. deschauenseei and H. igneus ; 27, last 3 enlarged posteriorly in H. lacrima ; 28–30, last 2 enlarged posteriorly in H. leucomystax ; 24, last 2 distinctly enlarged in H. maximus ; 27–30, last 2 moderately enlarged in H. modestus ; 25, last 2 slightly enlarged (only from lectotype) in H. pryeri ; 23–25, last 2 distinctly enlarged in H. yanbianensis ; 30, the last 3 enlarged in H. youjiangensis ).

Hebius khasiensis is somewhat similar to H. boulengeri and H. inas but can be morphologically diagnosed from the latter two species based on the combination of following characters: (1) Nape with a short but distinct, continuous off whitish or creamish streak originating just behind the last supralabial scale, eventually touching the rusty-brown dorso-lateral stripe on the neck anteriorly and never touches the anterior dorsal scale rows (versus nape with a distinct, continuous ochre or creamish streak which begins just behind the last supralabial scale, continues as a single lateral line beyond anterior dorsal scale rows, thereby breaking up into continuous series of large lateral spots towards midbody in H. inas ; A distinct whitish or creamish streak originating from the back of the eye extending till the nape which touches the continuous dorso-lateral reddish or reddish brown stripe in H. boulengeri ); (2) Ventrals off white in life with dark spots on the ventral edges (versus ventrals ivory or cream, with the outer quarter or third of each ventral dark reddish-brown in H. inas ); (3) Dorsal scales in the midbody strongly keeled (versus dorsal scales in the midbody weakly or moderately keeled in H. boulengeri ); (4) Presence of 17–21 teeth in the maxilla including the moderately enlarged posterior ones (versus 25–28, last 2 or 3 moderately enlarged in H. boulengeri ).

Hebius khasiensis (n=14) is morphologically very similar to H. gilhodesi comb. nov. (n=15) but differs mainly from the latter species based on: (1) dorsal coloration in life ranges from chocolate brown to sepia or blackish brown (versus dorsum mostly with a reddish tinge, somewhat rusty brown in life in H. gilhodesi comb. nov.); (2) a distinct, thin rusty brown or burnt sienna dorso-lateral stripe in life on either side running just from behind the nape till the base of the tail dorsally intermixed with distinct ochre yellowish spots (versus dorso-lateral stripe on the dorsum is absent and is instead replaced by a series of small, indistinct, very obscure faded or ochre spots which properly continues till the midbody in H. gilhodesi comb. nov.); (3) nape usually with a short but continuous, distinct off whitish or creamish streak which begins just behind the last supralabial scale, thereby covering a length of at least 5–8 continuous scales and nearly touches the anterior portion of rusty-brown dorso-lateral stripe in the neck (versus nape with an indistinct, discontinuous off whitish or creamish streak which breaks up into whitish spots and each whitish spot are separated from each other by an interval of atleast 2 to 5 scales usually in H. gilhodesi comb. nov. except for a single specimen where the elongated spots are separated from each other by an interval of only one scale); (4) 17–21 maxillary teeth including the last 2 or 3 moderately enlarged ones (versus 21–23 maxillary teeth including the last 2 or 3 moderately enlarged posterior ones in H. gilhodesi comb. nov.); (5) the outer dorsal scale row i.e. OSR is usually very feebly keeled, rarely moderately keeled (versus presence of a strongly keeled OSR i.e. outer dorsal scale row usually in H. gilhodesi comb. nov.); (6) supralabials 3 rd to 5 th or 4 th to 6 th usually are touching the orbit (versus only 4 th to 6 th supralabials are touching the orbit in H. gilhodesi comb. nov.).

Etymology: The specific epithet “ khasiensis ” is derived from the Khasi Hills, Meghalaya from where the species was collected and described.

Natural history and biology: Hebius khasiensis is a terrestrial species which mainly prefers to live in close proximity to streams and other water bodies surrounded by the forest type of tropical semi-evergreen to evergreen, tropical moist deciduous, tropical montane and at times even moderately disturbed hilly forested areas ( Fig. 14 View FIGURE 14 ). Based on our specimens, the species were found in areas of higher elevation ranging from 600–1,700 m asl. All the newly collected specimens from Mizoram and Meghalaya were found nearby streams, boulders with or without mosses, loose soils or roadside edges within tropical wet montane or tropical wet semi evergreen forests ( Fig. 14 View FIGURE 14 ). Based on our observations, we consider this species as “cathemeral” since two specimens in Meghalaya were found to be actively moving at night and most of the specimens were collected during the day. Wall (1908) stated that he obtained two young specimens (possibly hatchlings) during the month of October suggesting that breeding occurs during peak monsoon season. Just like other members of the genus, this species might primarily feed on frogs, toads, lizards and perhaps smaller mammals.

Distribution: This species is currently confined to the hills of northeast India but based on our genetic data it is very likely that H. khasiensis occurs on the states lying towards the southern bank of Brahmaputra River. Hence, we agree with the current and literature records reporting H. khasiensis from the Khasi Hills and Garo Hills of Meghalaya; Tamdil National Wetland, Dampa Tiger Reserve, Durtlang, Sailam, Lunglei, Sawleng and Reiek regions of Mizoram and Kohima as well as Wokha districts of Nagaland ( Wall 1923; Smith 1943; Ao et al. 2004; Malsawmdawngliana et al. 2022; This study) (see Fig. 1 View FIGURE 1 ). Furthermore, it is very likely that H. khasiensis might occur in Chin State of Myanmar as well since the hills of Mizoram forms contiguous ranges with the hills in Chin State, Myanmar. However, due to the lack of specimens and genetic data, literature records of this species from Arunachal Pradesh which lies in the northern bank cannot be currently considered as H. khasiensis sensu stricto as Brahmaputra River might act as a potential barrier to gene flow.

Conservation status: Based on our current data, we consider this species Data Deficient (DD) as per the IUCN.