ZMB 5004, from “Calcutta” [in error], purchased from J. G. W. Brandt; Figure 6.

The type specimen, whose origin was given as “Calcutta”, was acquired by the Zoologisches Museum Berlin in the middle of the 19th century from Johann Georg Wilhelm Brandt (1794–1856), a dealer in natural history objects in Hamburg, Germany. The two additional specimens in the Museum für Naturkunde Berlin (ZMB 31134–31135) are non-types collected from “Margherita, in the Patkai Hills, Upper Assam” by Ernst Hartert in the fall of 1888. The Reptile Database (Uetz et al. 2025) lists these specimens under “Types” as “additional material” along with the holotype and refer to Ananjeva and Stuart (2001) even though Denzer et al (1997) did not list these two specimens as types. However, these two specimens are not linked to the type in any way. Given the absence of Ptyctolaemus from Kolkata (Calcutta) and the morphological similarity of the type specimen to specimens from Meghalaya, we suspect that type could have been collected from Shillong, Meghalaya.

Three adult females (WII-ADR3479, WII-ADR3480 and WII-ADR3481) collected from Risa forest (25.55615°N 91.89389°E, elevation 1670 m a.s.l.), Shillong, East Khasi Hills district, Meghalaya, India collected on 30 June 2016 by Abhijit Das, Bitupan Boruah and V. Deepak; one adult female (ZSI-R-29477) collected from Narpuh Wildlife Sanctuary (25.11062°N 92.37215°E, elevation 70 m a.s.l.), East Jaintia Hills district, Meghalaya, India, collected on 30 May 2022 by Abhijit Das and Bitupan Boruah; one adult male (WII-ADR3180) from Risa Forest (25.55615°N 91.89389°E, elevation 1670 m a.s.l.), Shillong, East Khasi hills District, Meghalaya, India, collected on 23 May 2022 by Abhijit Das and Bitupan Boruah; one adult male (WII-ADR1436) from Daribokgre (25.49675°N 90.32742°E, elevation 1120 m a.s.l.), Nokrek, Meghalaya, India, collected on 25 May 2022 by Abhijit Das, Bitupan Boruah and Vijayan Jithin; one adult male (WII-ADR108) from Tyrna (25.24052°N, 91.68183°E, elevation 750 m a.sl.), East Khasi Hills district, Meghalaya, India, collected on 17 September 2017 by Vivek Sarkar; one adult male (ZSI-R-29478) from Malki forest (25.55602°N, 91.88678°E, elevation 1705 m a.s.l.), Shillong, East Khasi Hills district, Meghalaya, India, collected on 5 June 2024 by Abhijit Das, Isaac Rayen and Asim Bashir; one adult female (WII-ADR1054) from Ngengpui Wildlife Sanctuary, (22.49004°N, 92.75874°E, elevation 220 m a.s.l.) Lawngtlai district, Mizoram, India, collected on 7 September 2021 by Abhijit Das and Bitupan Boruah; one adult female (WII-ADR1152) from Teirei, Dampa Tiger Reserve, Mamit district, Mizoram, India, collected on 16 September 2021 by Abhijit Das and Bitupan Boruah; one adult male (WII-ADR3477) and one adult female (WII-ADR3478) from Darlawn (24.01611°N, 92.92905°E, elevation 1071 m a.s.l.), Aizawl district, Mizoram, India, collected on 24 August 2021 by Samuel Lalronunga, Isaac Zosangliana and Malsawmdawngliana; one adult male (WII-ADR3482) and three adult females (WII-ADR3483–WII-ADR3485) from Reiek (23.69319°N, 92.60626°E, elevation 1255 m a.s.l.), Aizawl district, Mizoram, India, collected on 25 September 2018 by Samuel Lalronunga and Lalhmangaiha Khiangte; one adult female (WII-ADR3018) from Kalai (27.72294°N, 96.4346°E, elevation 1110 m a.s.l.), Kamlang Tiger Reserve, Lohit district, Arunachal Pradesh, India, collected on 3 October 2022 by Abhijit Das, Bitupan Boruah and Naitik G. Patel; one adult female (WII-ADR3473) from Kalai (27.72294°N, 96.4346°E, elevation 1110 m a.s.l.), Kamlang Tiger Reserve, Lohit district, Arunachal Pradesh, India, collected on 20 July 2023 by Abhijit Das, Rajiv N.V. and Jason D. Gerard; one adult female (WII-ADR1450) from 18 Mile (27.49548°N, 96.3919°E, elevation 440 m a.s.l.), Namdapha Tiger Reserve, Changlang district, Arunachal Pradesh, India, collected on 20 May 2022 by Abhijit Das and Bitupan Boruah; one adult female (WII-ADR1782) from Sally Lake (28.16814°N, 95.83751°E, elevation 520 m a.s.l.), Mehao Wildlife Sanctuary, Lower Dibang valley district, Arunachal Pradesh, India, collected on 12 August 2022 by Bitupan Boruah; one adult female (WII-ADR3292) from 40 Mile (27.48789°N, 96.54165°E, elevation 470 m a.s.l.), Namdapha Tiger Reserve, Changlang district, Arunachal Pradesh, India, collected on 27 May 2023 by Abhijit Das, Rajiv N.V. and Sourav Dutta; one adult female (WII-ADR1407) from Deban (27.49445°N 96.39022°E, elevation 460 m a.s.l.), Namdapha TR, Changlang district, Arunachal Pradesh, India, collected on 12 May 2022 by Abhijit Das and Bitupan Boruah; one adult female (WII-ADR1406) from Motijheel Trail (27.49624°N 96.33304°E, elevation 405 m a.s.l.), Namdapha Tiger Reserve, Changlang district, Arunachal Pradesh, India, collected on 13 May 2022 by Abhijit Das and Bitupan Boruah.

ZMB 5004 (Fig. 6), an adult male with SVL 65.7 mm and TAL 153 mm; tail length more than twice of snout-vent length (TAL/SVL = 2.33). Head distinct from neck, head longer than wide (HW/HL = 0.59), slightly concave on top; rostral scale crescent, snout rounded; pupil rounded, scales on loreal region slightly keeled, surrounded by heterogeneous scales; nasal separated from rostral by one scale; canthus rostralis sharp, strongly keeled with 14 enlarged scales on each side; the keels gradually reduces towards snout; nostrils rounded, positioned slightly towards lateral side, in contact with first supralabials; snout scales irregular in shape and size, series of seven enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly; head height 11.04 mm; scales on head, snout and interorbital region heterogenous in size and shape; tympanum hidden and covered with smooth scales; neck region with overlapping small scales interspersed with enlarged scales and are large towards the trunk; in the temporal region three enlarged, keeled, and elevated scales positioned posterior; scales around orbital region small and irregular in shape; parietal eye not distinct; scales on anterior region of gular pouch smaller than the middle region, heterogeneous in size feebly keeled and mucronate, the scales in middle region are larger than those of anterior and posterior region; three distinct raised gular folds on either side of midline; folds curved towards midline posteriorly, scales on the inner folds are granular; nine supralabials on both sides; ten infralabials on left and nine on right; nuchal crest poorly developed with 25 conical scales (Tables S4, S5).

Mental scale triangular, broader than long, and slightly narrower than the rostral; bordered posteriorly by one infralabial on each side and two enlarged postmentals in contact with the first infralabials; postmentals medially separated by a single small gular scale; four chin shields present on each side, positioned parallel to the infralabials; the anterior portion of the first chin shield contacts the first infralabial, while the remaining part of the first and second chin shields separated from infralabial by one intervening scale row, while subsequent two chin shields separated from the infralabials by two intervening scale row; scales in the anterior region of gular feebly keeled.

Habitus slender, slightly compressed, dorsal scales keeled, imbricate, posteriorly pointed; mid-dorsal scale row strongly keeled, enlarged scales appearing discontinuously; lateral scales heterogeneous in size, mostly smaller than the dorsal, slightly keeled, imbricate, and interspersed with enlarged, strongly keeled scales; 99 vertebral scales (VTSR), 93 rows of scales around the midbody; ventral scales 135, larger than the lateral scales and approximately equal to the enlarged dorsal scales, strongly keeled, imbricate, and pointed backward.

Limbs slender, moderate sized, scales on dorsal surface strongly keeled, imbricate scales, lower arm slightly longer than the upper arm (UAL/LAL = 1.11); thigh length approximately equal to crus length (femur/crus = 1.22); scales on dorsal surface of the forelimbs strongly keeled, uniform and imbricate; scales on dorsal side of the hindlimb slightly enlarged, keeled and imbricate; scales on ventral side of the hindlimb smaller than the dorsal, slightly keeled and imbricate; relative length of digits: IV>III>II>V>I; relative length of toes: IV>III>V>II>I; 33/34 bicarinate subdigital lamellae under fourth toe.

Tail rounded in cross section, slightly compressed laterally, thick at the base, covered with homogeneous scales on the dorsal and ventral surface arranged regularly, strongly keeled and imbricate.

Dorsal surface of head brown; lateral side of head light-brown; lips pale-brown coloured; paravertebral region with feeble irregular shaped greyish patches; feeble greyish indistinct patch on lateral region; limbs brown with dark brown or greyish patches; radial stripes around the eye indistinct except for two below the eye; inner folds of gular black; ventral side of body light-brown with light-greyish spots; forelimb and hindlimbs slightly darker than the rest of the ventral region with brown light-grey; digits with indistinct bands; tail brown with indistinct greyish cross bands.

Morphometric and meristic characters are provided in Tables 3 and 4. Moderate-sized lizard, SVL 62.7–79.2 mm (male) and 46.7–76.3 mm (female); TAL 131.3–181.2 mm (male) and 101.3–166.2 mm (female); tail length more than twice the of snout-vent length (TAL/SVL = 2.0–2.4). Head distinct from neck, head longer than wide (HW/HL = 0.43–0.59), slightly concave on top; rostral scale crescent, snout rounded; pupil rounded, scales on loreal region slightly keeled, surrounded by heterogeneous scales; nasal separated from rostral by one scale; canthus rostralis sharp, strongly keeled with 12–15 enlarged scales on each side; the keels gradually reduces towards snout; nostrils rounded, positioned slightly towards lateral side, in contact with first supralabials; snout scales irregular in shape and size, series of 5–7 enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly; head height 7. 4–11. 7 mm; scales on head, snout and interorbital region heterogenous; tympanum hidden and covered with smooth scales; neck region with overlapping small scales interspersed with enlarged scales and are large towards the trunk; three enlarged, keeled, and elevated scales positioned posterior and horizontal to orbit; scales around orbital region small and irregular in shape; parietal eye not distinct; gular in males distinct; scales on gular region smaller than the surrounding scales slightly heterogeneous in size feebly keeled and mucronate, the scales in middle region are larger than those of anterior and posterior region; three distinct raised gular folds on either side of midline; folds curved towards midline posteriorly (Fig. 7), scales on the inner folds are granular; 6–10 supralabials on left and 6–10 on right side; 7–10 infralabials on left and 6–10 on right side; nuchal crest poorly developed with 14–29 conical scales.

Mental scale triangular, broader than long, and slightly narrower than the rostral; bordered posteriorly by one infralabial on each side and two enlarged postmentals in contact with the first infralabials; postmentals followed by 1–3 small gular scale; four chin shields present on each side, positioned parallel to the infralabials; the anterior portion of the first chin shield contacts the first infralabial, while the remaining part of the first and second chin shields separated from infralabial by one intervening scale row, while subsequent two chin shields separated from the infralabials by two intervening scale row; scales in the anterior region of gular feebly keeled.

Habitus slender, slightly compressed, dorsal scales keeled, imbricate, posteriorly pointed; mid-dorsal scale row strongly keeled, enlarged scales appearing discontinuously; lateral scales heterogeneous in size, mostly smaller than the dorsal, slightly keeled, imbricate, and interspersed with enlarged, strongly keeled scales; 79–114 dorsal scales (VTSR), 71–101 rows of scales around the midbody; ventral scales 114–142, larger than the lateral scales and approximately equal to the enlarged dorsal scales, strongly keeled, imbricate, and pointed backward.

Limbs slender, moderate sized, scales on dorsal surface strongly keeled, imbricate scales, lower arm slightly longer than the upper arm (UAL/LAL = 0.84–1.01); femur length approximately equal to crus length (femur/crus = 0.95–1.08); scales on dorsal surface of the forelimbs strongly keeled, uniform and imbricate; scales on dorsal side of the hindlimb slightly enlarged, keeled and imbricate; scales on ventral side of the hindlimb smaller than the dorsal, slightly keeled and imbricate; relative length of digits: IV>III>II>V>I; relative length of toes: IV>III>V>II>I; 29–40/27–36 bicarinate subdigital lamellae under fourth toe.

Tail rounded in cross section, slightly compressed laterally, thick at the base, covered with homogeneous scales on the dorsal and ventral surface arranged regularly, strongly keeled and imbricate.

Dorsal head golden brown; greyish-white blotch on the parietal region; lateral head light brown; nostril light-greyish; enlarged keeled scales on the posterior mandibular region light coloured; lips pale greyish coloured; body golden brown coloured; paravertebral region with scattered greyish patches; greyish indistinct patch on lateral region; limbs light brown with greyish patch; radial stripes around the eye indistinct; mental white to light golden brown; inner folds of gular dark coloured, midline of gular light golden brown coloured; ventral side of forelimb and body light yellow with light greyish patch, ventral side of hindlimb light grey coloured; digits with indistinct bands; tail golden brown with indistinct greyish cross bands; scales on gular region smaller than the surrounding scales slightly heterogenous in size and mucronate, the scales in middle region are larger than those of anterior and posterior region; three distinct raised gular folds on either side of midline; folds curved towards midline posteriorly, scales on the inner folds are granular (Fig. 6).

A medium-sized agamid lizard, SVL 46.67–79.24 mm (n = 22), TAL 101.32–181.23 mm (n = 22). Nuchal crest is poorly developed, consisting of 14–29 nuchal scales. Supratympanic spines absent. Body laterally compressed, scales at the trunk heterogeneous in size, larger than ventrals, dorsally and posteriorly oriented, 79–114 dorsal scales (VTSR), 71–101 rows of scales at midbody, 114–142 ventrals. Mental smaller than chin shields, first pair of chin shields elongated and in midline contact, the gular scales at the midline are smaller than the adjacent scales away from the midline.

Colouration in life variable (Figs 8–10). Head primarily brown to dark brown intermixed with pale-brown scales, or intermixed with pale-green or yellowish green scales in some individuals; three pale-brown or pale-greenish brown bands on dorsal surface of head, first one concaved on snout followed by one diffused in front of the orbital region, third one broad, nearly bow shaped on interorbital region connecting the supraciliary scales; occipital region paler; supralabials and infralabials uniform brown or with dark-brown patches or anteriorly dark-brown and gradually paler towards angle of jaw forming a pale stripe, in some individuals this stripe colour pale-greenish; alternative dark-brown and pale-brown streaks radiating from eyes; these streaks may be diffused, or dark stripes may represent only by dark edges; one similar streak radiating from eye to angle of jaw; lateral side of neck pale-brown or pale-greenish or pale-yellowish green with dark-brown oblique streaks on neck and dark-brown reticulation on trunk; paravertebral region with irregular shaped enlarged dark-brown patches separated by pale-brown/pale-green narrow lines or rusty brown patches separated by greyish brown narrow patches; pale-yellow/greenish stripe may be present running parallel along the paravertebral region starting at neck and posteriorly diffused on trunk; dorsal surface of the limbs brown or dark-brown or greyish brown with irregular pale-brown lines; dorsally tail with alternative broad dark-brown and comparatively narrow pale-brown patches; lateral sides of tail base pale-brown or rusty brown; on ventral side, lower jaw pale brown with or without dark-brown lines; ground colour of gular region pale-brown or pale-bluish green or pale-yellowish green; three to four broad dark-blue stripes with lighter edge and separated by narrow light lines; edge of the dark-blue stripes irregular; belly pale-brown.

Ptyctolaemus gularis is a widely distributed agamid lizard inhabiting forested landscape of northeast India (Fig. 8). In Meghalaya, where it has been recorded from Khasi, Garo and Jaintia Hills from low lying areas (50 m) of Jaintia hills to ~1600 m in Shillong plateau (Fig. 11A, B). On 30 June 2016, we surveyed for agamid lizards in the areas adjoining Malki forest in Shillong between 10:00–13:00 hrs. We found six individuals of P. gularis, all were females and five were gravid females. The smallest female individual measured was 61.1 mm (SVL) and the largest was 79.9 mm (SVL). We caught and gently pressed the belly to find out the number of eggs in these individuals. The number of eggs in these individuals varied between 2, 5 and 7. During June 2016, in Malki forest we observed a gravid female making a pit on loose soil using its snout probably for laying eggs. In the Barail hills of southern Assam, it is found as low as 30 m to 900 m elevation. Subadult individuals were often recorded along the forest edges during May. One large male was detected on the trunk of a tree growing on a forested hill slope. During September two females were recorded along riparian vegetation showing dark crypsis. In Dampa Tiger Reserve, one Individual was seen in a bamboo dominated patch during 15 September 2021. This species is widely distributed in the mountains of northeast India across south of Brahmaputra valley and to the eastern part of the valley. The westernmost distribution limit of the species we recorded was the Garo hills and are distributed in the Mehao Wildlife Sanctuary, Arunachal Pradesh in the east (Fig. 1), and in the Ngengpui Wildlife Sanctuary, Mizoram in the south.

WII-ADR1176, adult female, from Rottung (28.14114°N, 95.1562°E, elevation 390 m a.s.l.), East Siang district, Arunachal Pradesh, India, collected on 22 October 2021 by Bitupan Boruah.

WII-ADR1210, adult male, from Pittung (28.67146°N, 94.96159°E, elevation 415 m a.s.l.), Upper Siang district, Arunachal Pradesh, India, on 28 October 2021 by Bitupan Boruah; ZSI-R-29479, adult male, from Jengging (28.53543°N, 95.03106°E, elevation 945 m a.s.l.), Upper Siang district, Arunachal Pradesh, India, on 5 October 2018 by Abhijit Das; Figure S2.

WII-ADR2542, adult female, from Khellong (27.0035°N, 92.24502°E, elevation 2955 m a.s.l.), Eaglenest Wildlife Sanctuary, West Kameng district, Arunachal Pradesh, India, on 29 August 2022 by Krishnendu Banerjee; WII-ADR465, adult female, from Potin (27.34786°N, 93.8497°E, 580 m a.s.l.), Lower Subansiri district, Arunachal Pradesh, India, on 19 October 2019 by Abhijit Das and Bitupan Boruah.

An adult female, SVL 63.65 mm and TAL 153.95 mm; TAL/SVL ratio 2.42; head distinct from neck, longer than wide (HW/HL = 0.48), slightly concave on top; rostral scale crescent; snout rounded, longer than orbital diameter (OD/EN = 0.65); pupil round, scales on the loreal region slightly keeled, surrounded by scales of irregular size and shape; nasal separated from rostral by one scale; canthus rostralis sharp, strongly keeled and consists 13 enlarged scales on each side; keels weak towards the snout; nostrils rounded, slightly laterally positioned, in contact with first supralabials; snout scales irregular in shape and size, series of six enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scale on either side is oriented diagonally towards the superciliary ridge; head height at occipital region 9.89 mm; scales on head, snout and interorbital region heterogenous in shape and size; tympanum hidden and covered with smooth scales; neck region with small overlapping scales interspersed with enlarged scales that increase in size towards trunk; three enlarged, keeled, and elevated scales located posterior and horizontal to orbit; scales around orbital region small and irregular in shape; parietal eye is not distinct; gular in males distinct; scales on gular heterogeneous in size and mucronate, feebly keeled, scales in middle region larger than those on anterior and posterior region; three distinct raised gular folds on either side of midline; folds curved towards midline posteriorly (Fig. 7); nine supralabials on both sides; seven infralabials on left and eight on right; nuchal crest poorly developed, consisting of 14 conical scales (Tables S4, S5).

Mental scale triangular, broader than long, and slightly narrower than the rostral, bordered posteriorly by one infralabial on each side and two enlarged postmentals in contact with the first infralabials; postmentals followed by two small gular scale; four chin shields present on each side, positioned parallel to the infralabials; the anterior portion of the first chin shield contacts the first infralabial, while the remaining part of the first and the subsequent two chin shields separated from the infralabials by one intervening scale row; scales in the anterior gular region feebly keeled.

Habitus slender, slightly compressed, dorsal scales keeled, imbricate, and posteriorly pointed; mid-dorsal scale row strongly keeled, enlarged scales appearing discontinuously; lateral scales heterogeneous, mostly smaller than the dorsal, feebly keeled, imbricate, and interspersed with enlarged, strongly keeled scales; 89 dorsal scales (VTSR); 87 scales around midbody; 132 ventral scales, larger than lateral scales and approximately equal to the enlarged dorsal scales, strongly keeled, imbricate, posteriorly pointed.

Limbs are slender, moderate sized, dorsal surface covered in strongly keeled, imbricate scales; lower arm length slightly longer than the upper arm length (UAL/LAL = 0.94); femur length slightly longer than the crus length (femur/crus = 1.03); scales on dorsal surface of the forelimbs strongly keeled, uniform and imbricate; scales on ventral side of the forelimbs relatively smaller, feebly keeled; relative length of digits: IV > III > II > V > I; scales on dorsal side of the hindlimb slightly enlarged, keeled and imbricate; scales on ventral side of the hindlimb smaller than the dorsal, slightly keeled and imbricate; relative length of toes: IV > III > V > II > I; 30/30 subdigital lamellae under fourth toe and bicarinate.

Tail length more than twice of SVL, rounded, slightly compressed laterally, broader at the base, gradually tapering towards tip, covered with regularly arranged strongly keeled, imbricate and homogeneous scales.

A moderate-sized lizard, SVL 66.90–77.68 mm in male (n = 2) and SVL 58.03–66.62 mm in female (n = 3), TAL 157.56–189.96 mm in male (n = 2) and 140.75–153.95 mm in female (n = 3). Snout scales irregular in shape and size with an inverted Y-shaped pattern. Nuchal crest poorly developed with 14–24 conical scales. Body slightly compressed, scales at the trunk heterogeneous in size, smaller than the dorsal, slightly keeled, oriented backwards, 89–114 dorsal scales (VTSR), 86–105 rows of scales around midbody and 132–148 ventrals. Mental broader than long, postmentals medially separated by a single small gular scale, anterior region of the first chin shield contacts the first infralabial, gular with three distinct raised gular folds on either side of midline excluding the base, gular scales heterogeneous in size, feebly keeled, scales in middle region larger than those on anterior and posterior region.

Ptyctolaemus siangensissp. nov. can be distinguished from Ptyctolaemus collicristatus by having relatively smaller SVL/TAL ratio 0.41–0.45 (vs. 0.47–0.56; Table 3), gular region with dark blue with white lines vs bright yellow medially with greenish-yellow and dark brown laterally; differs from Ptyctolaemus gularis by gular region with dark blue with white lines (vs. pale-brown or pale-bluish green or pale-yellowish green; three to four broad dark-blue stripes; Fig. 13); differs from Ptyctolaemus chindwinensis by relatively fewer scales on the nuchal crest 18–24 (vs. 26–29), gular region with dark blue with white lines vs bright yellow with two horizontal parallel black stripes (Fig. 13).

Details of morphometric and meristic variation among the type series are presented in Table S3–S4. The paratypes (WII ADR 1210, ZSI-R-29479) closely resemble the holotype in overall morphology, with the following distinctions. Paratype WII ADR 1210 has three scales posteriorly connected to the first pair of chin shield; series of seven enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scale on either side is oriented diagonally towards the superciliary ridge; paravertebral region rusty brown coloured varied from that of holotype in preservation; ventral region with dark creamish brown to dark brown colours bordering the flank region; scattered dark brown spots on the mental region. Paratype ZSI-R-29479 has two scales posteriorly attached to the first pair of chin shield; scattered dark brown spots on the mental region; series of seven enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scales on either side is oriented diagonally towards the superciliary ridge; ventral part of the thigh and tail with distinct brown patch scattered.

Dorsal and lateral colour variable (Fig. 13). Head pale-brown or dark-brown with intermixed pale-yellow scales, some scales with golden yellow keel; three light bands on dorsal surface of head, first concaved, second one diffused and third on interorbital space continuing to supraciliary scales; these bands varies from pale-brown to pale-greenish; lateral sides of head brown to dark-brown, paler towards lips; alternative dark-brown and pale-brown/pale-green streaks radiating from eyes; a dark streak from eye directing towards angle of jaw; lateral side of neck and trunk pale-yellowish brown to pale-green with dark-brown reticulation; lateral side of trunk may be rusty brown without reticulation in some individuals; dorsal surface of back brown with enlarged dark-brown or rusty brown patches; limbs on top dark-brown with pale-brown narrow irregular lines; tail with alternative broad dark-brown and comparatively pale-brown patches on dorsal surface; mental and ventral region creamish brown with ground colour on gular very pale-brownish white or bluish white with three broad dark-blue stripes separated by narrow light lines.

Dorsal and lateral head light rusty brown; greyish cross band on interorbital region; nostril and labials greyish speckled; radiating lines around the orbit dark greyish; an oblique streak from posterior margin of orbit indistinct greyish color; lateral region of neck and body greyish colored; paravertebral region same as head; thigh and upper arm rusty brown; crus and lower arm with greyish blotches; digits with dark bands; mental light brownish cream to cream towards the gular with speckles; gular on the midline creamish white with dark streaks on the inner side of folds; ventral side of forelimb, hindlimb and body brownish cream with speckles throughout; tail rusty brown with greyish patch and indistinct light bands (Fig. 12).

Ptyctolaemus siangensissp. nov. has high genetic divergence with its sister species P. gularis 13.9–16.0%. With other members of the genus, P. siangensissp. nov. has 23.8–26.3% genetic difference (Table 5).

The specific epithet is a toponym derived from the name of the river “Siang” in the state of Arunachal Pradesh.

Siang green fan-throated lizard

The holotype was found roosting on a branch of a small tree around two metres above the ground, alongside a fast-flowing hill stream at Rottung. One individual was recorded along roadside vegetation in Potin (Fig. 11C). This species is currently known from west of Siang River and north of Brahmaputra valley in Arunachal Pradesh. We recorded the species at Rottung, Mouling National Park to Tuting in Adi hills, Potin to Eaglenest Wildlife Sanctuary in the western Arunachal Pradesh, Nameri Tiger Reserve in Assam. In addition, the published sequence from Medog, China is nested within P. siangensis samples. Thus, this species also occurs in Medog, China. The report of P. gularis from Royal Manas National Park, Bhutan (Das et al. 2016) is most likely of P. siangensissp. nov. but requires further verification.

WII-ADR3178, adult male, from Gandhigram (27.26515°N, 96.93878°E, elevation 1135 m a.s.l.), Changlang district, Arunachal Pradesh India, collected on 17 September 2022 by Abhijit Das and Bitupan Boruah.

an adult female (WII-ADR3179), collected with the holotype from the same locality as of the holotype by Abhijit Das and Bitupan Boruah; an adult female (ZSI-R-29480), collected from Kamala valley, Namdapha TR, Changlang district, Arunachal Pradesh India, collected on 18 May 2022 by Abhijit Das and Bitupan Boruah; Figure S3.

one adult male (WII-ADR1409) and three adult females (WII-ADR1410–WII-ADR1412) collected from 18–19 Mile (27.48404°N, 96.40473°E, elevation 495 m a.s.l.) on 12 May 2022 by Abhijit Das and Bitupan Boruah; one adult male (WII-ADR1427) from Kamala valley (27.45808°N, 96.42804°E, elevation 730 m a.s.l.) on 18 May 2022 by Abhijit Das, Bitupan Boruah and Vijayan Jithin; one adult male (ZSI-R-29481) from Kamala valley (27.46457°N, 96.43790°E, elevation 540 m a.s.l.) on 3 June 2023 by Abhijit Das, Rajiv N.V., Jason D. Gerard and Sourav Dutta; one adult male (WII-ADR3061) and one adult female (WII-ADR3062) from 17–19 Mile (27.49338°N, 96.39535°E, elevation 450 m a.s.l.) on 8 September 2022 by Abhijit Das, Bitupan Boruah and Naitik G. Patel; one adult male (WII-ADR1403) from 14–15 Mile (27.49689°N, 96.35438°E, elevation 430 m a.s.l.) on 9 May 2022 by Abhijit Das and Bitupan Boruah; one adult male (WII-ADR3283) from Haldibari (27.52453°N, 96.39913°E, elevation 500 m a.s.l.) on 9 May 2023 by Rajiv N.V. and Sourav Dutta; one adult male (WII-ADR1440) from Motijheel trail (27.49624°N, 96.33304°E, elevation 400 m a.s.l.) on 20 May 2022 by Abhijit Das, Bitupan Boruah and Vijayan Jithin; one adult female (WII-ADR3070) from Motijheel (27.48644°N, 96.33136°E, elevation 640 m a.s.l.) on 11 September 2022 by Abhijit Das and Bitupan Boruah. All these localities fall in the Namdapha Tiger Reserve, Changlang district, Arunachal Pradesh, India.

An adult male, SVL 81.22 mm and TAL 123.8 mm (incomplete), with a TAL/SVL ratio 1.52; head distinct from the neck, head longer than wide (HW/HL = 0.54), slightly concave on top; rostral scale crescent; snout rounded, longer than orbit (OD/EN = 0.79); scales on loreal region slightly keeled, surrounded by heterogenous scales; nasal separated from rostral by one scale; canthus rostralis sharp with 13 enlarged scales on each side; keels on canthal scales weak towards snout; nostril rounded, in contact with first supralabials; snout scales irregular in shape and size, with inverted Y-shaped pattern at the centre; head height at occipital region 12.89 mm; scales on head, snout and interorbital region heterogeneous; pupil round, horizontal orbital diameter 5.58 mm; tympanum concealed and covered with smooth scales; scales on neck overlapping and small interspersed with enlarged scales, size increases towards the trunk; three enlarged, keeled, and elevated scales behind the orbit; scales around the orbit small and irregular in shape; parietal eye is not distinct; gular distinct; scales on gular heterogeneous in size and mucronate, scales anterior to the gular pouch small, rounded, imbricate, and feebly keeled, larger in the middle; two distinct raised gular folds on either side of midline; folds curved towards midline posteriorly (Fig. 7); eight supralabials on left and nine on right; nine infralabials on both sides; nuchal crest poorly developed, consisting of 21 conical scales (Tables S4, S5).

Mental scale triangular, broader than long, and slightly narrower than the rostral; bordered posteriorly by one infralabial on each side, two enlarged postmentals in contact with the first infralabials; postmentals followed by a three small gular scale; four chin shields present on each side, positioned parallel to the infralabials; the anterior portion of the first chin shield contacts the first infralabial, while the remaining part of the first chin shield are separated from the infralabials by one intervening scale row and the other subsequent three chin shields are separated from the infralabials by two intervening scale rows.

Habitus slender, slightly compressed laterally, dorsal scales keeled, imbricate, and posteriorly pointed; mid-dorsal scale row strongly keeled, interspersed with enlarged scale, no enlarged keeled scales on flank; lateral scales heterogeneous, mostly smaller than the dorsals, slightly keeled, imbricate; 104 dorsal scales (VTSR); 106 rows of scales around the midbody; 126 ventral scales, larger than lateral scales and approximately equal to the enlarged dorsal scales, strongly keeled, imbricate, posteriorly pointed.

Limbs slender, moderate sized, lower arm length slightly longer than upper arm length (UAL/LAL = 0.91); femur length equal to crus length (femur/crus = 1.01); scales on dorsal surface of forelimbs strongly keeled, uniform and imbricate; scales on ventral side of the forelimbs relatively smaller, feebly keeled; relative length of digits: IV > III > II > V > I; scales on ventral side of hindlimb smaller than dorsal side, slightly keeled and imbricate; relative length of toes: IV > III > V > II > I; 36/35 sub digital lamellae under fourth toe, bicarinate.

Tail rounded, slightly compressed laterally, thick at the base, gradually tapering towards tip; covered with homogeneous scales; scales on the dorsal and ventral surface arranged regularly, strongly keeled, and imbricate.

A moderate-sized lizard, SVL 45.9–81.2 mm in male (n = 8) and SVL 55.4–72.9 mm in female (n = 7), TAL 115.6–184.5 mm in male (n = 8) and 131.8–181 mm in female (n = 7). Snout scales irregular in shape and size with an inverted Y-shaped pattern. Nuchal crest poorly developed with 12–20 conical scales. Body slightly compressed, scales at the trunk heterogeneous in size, smaller than the dorsal, slightly keeled, oriented backwards, no enlarged keeled scales on flank region, 73–110 dorsal scales (VTSR), 90–106 rows of scales around midbody, 116–138 ventrals. Mental broader than long, two enlarged postmental in contact with the first infralabials, anterior region of the first chin shield contacts the first infralabial, gular with two distinct raised gular folds on either side of midline, gular scales heterogeneous in size, feebly keeled, scales in middle region larger than those on anterior and posterior region.

Ptyctolaemus namdaphaensissp. nov. looks similar to P. chindwinensis, as they are sister species. Ptyctolaemus namdaphaensissp. nov. differs from P. chindwinensis by fewer nuchal crest NC 13–25 (vs. 26–29); P. namdaphaensissp. nov. can be distinguished from P. collicristatus by relatively larger FLL/SVL 0.50–0.58 (vs. 0.40–0.45), by relatively larger HLL/SVL 0.87–0.99 (vs. 0.64–0.73), by higher number of midbody scales MBS 90–106 (vs. 75–87). Ptyctolaemus namdaphaensissp. nov. differs from P. gularis by gular region pale-brownish white or bluish white with three broad dark-blue stripes (vs. pale-brown or pale-bluish green or pale-yellowish green; three to four broad dark-blue stripes; Fig. 15). Ptyctolaemus namdaphaensissp. nov. differs from P. gularis and P. siangensissp. nov. by absence of enlarged keeled scales on flank (vs. enlarged keeled scales scattered on flank).

In addition, the colouration on the gular region of P. namdaphaensissp. nov. differs from P. siangensissp. nov. in having light grass green gular in males (vs. gular with dark blue stripes separated by narrow white lines; Fig. 15). Ptyctolaemus namdaphaensissp. nov. differs from P. chindwinensis in having a gular with light grass green (vs. bright yellow with two horizontal parallel black stripes). Ptyctolaemus namdaphaensissp. nov. differs from P. collicristatus in having a gular region yellowish green with black spots (vs. bright yellow medially with greenish-yellow and dark brown laterally).

Details of morphometric and meristic variation among the type series are presented in Tables S4 and S5. The paratypes (WII ADR 3179) closely resemble the holotype in overall morphology, with the following distinctions. Each side of the lower jaw bears three chin shields posterior to the postmentals, arranged parallel to the infralabials; a series of six enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first four anterior scales aligned along the midline and pointed posteriorly, posterior to the fourth scale, one scale on either side is oriented diagonally towards the superciliary ridge; paravertebral region rusty brown coloured varied from that of holotype in preservation; nuchal crest composed of enlarged scales in the paratype varied from that of triangular scales in the holotype; the paratype exhibits two enlarged temporal scales that are comparatively smaller than those of the holotype; additionally, the paratype has a moderately distinct gular fold bearing medium-sized, triangular scales, which differ slightly in size and prominence from those observed in the holotype; tail prominent white colouration with distinct brown bands scattered; dark spots on head and reticulation on flank in female paratypes barely visible. Paratype (ZSI-R-29480) shows the following distinctions, a series of six enlarged, keeled scales on the snout form an inverted “Y”-shaped pattern, with the first four anterior scales aligned along the midline and pointed posteriorly, posterior to the fourth scale, two scale on either side is oriented diagonally towards the superciliary ridge; paravertebral region rusty brown coloured varied from that of holotype in preservation; the paratype has a moderately distinct gular with medium-sized, triangular scales, which differ slightly in size and prominence from those observed in the holotype; scattered dark brown spots on the mental region is less distinct (Fig. S3).

Adult males have a nuchal crest; gular in males green while the females have pale-yellow gular without any spots (Fig. 16).

Head brown or greyish brown or pale-yellowish brown with dark-brown spots; scales with golden yellow keels; pale bands on dorsal surface of head indistinct; dark edged light short streaks radiating from eye; an oblique streak extends from the posterior margin of eye to angle of jaw; lips pale-brown; paravertebral uniform light brown; lateral and dorsal side of neck pale-yellowish brown with irregular dark-brown spots; gular region light grass green with black spots (Fig. 15D); flank pale-yellowish with brown reticulation; reticulation diffused; dorsal surface of limbs brown with pale-yellow and dark-brown spots; tail light brown on the base to reddish brown towards the middle and paler towards tip, dark edged light cross bands and blackish patches irregularly placed; on ventral side, with black spot scattered on the anterior region; mental region creamish yellow with black spot forming irregular line towards the gular.

Dorsal head light brown with darks tiny spots; light greyish cross band between interorbital region; lateral head light brown with light greyish patch; nostril greyish with tiny black spots; lateral head light brown with greyish patch; enlarged keeled scales on the posterior mandibular region light coloured; few scales on the neck and lateral body with black tips; body light brown to rusty brown coloured; paravertebral region bluish grey coloured; greyish indistinct patch on lateral region; limbs light brown with greyish patch; dark brown patch on the limbs are visible; radial stripes around the eye visible; mantle creamish white with series of black spots forming irregular line; gular region pale bluish coloured; ventral side of forelimb, hindlimb and body creamish with greyish patch, black spots scattered throughout; tail dark brown with indistinct light bands; light bands on the digits visible (Fig. 14).

Ptyctolaemus namdaphaensissp. nov. has high genetic divergence to its sister species P. chindwinensis 8.2–9.5%. With other members of the genus, P. siangensissp. nov. has 8.9–26.7% genetic difference (Table 5).

The specific epithet is a toponym derived from the name of the place “Namdapha Tiger Reserve” in the state of Arunachal Pradesh, India.

Namdapha green fan-throated lizard.

We recorded individuals of this species in the following locations: Deban, Motijheel, Gibbon’s Land and Kamala valley in the Namdapha Tiger Reserve (Fig. 11D), and Gandhigram. During the day, we found individuals active along the roadside vegetation and forest trails in May and June of 2022 and 2023. We observed them perching on twigs and ferns at heights of around 1–2 metres above the ground. This species is sympatric with P. gularis in the Namdapha Tiger Reserve. Currently, this species is only known from Gandhigram and the Namdapha Tiger Reserve in Arunachal Pradesh, India.