(Fig. 8).ZMKU R 00984, adult male from Thailand, Phang-nga Province, Thai Mueang District, Lam Kaen Subdistrict, Mu Ko Similan National Park, Ko Similan, Ao Nguang Chang Bay (8°64.840'N, 97°64.834'E; 13 m a.s.l.), collected on 5 March 2018 by Natee Ampai, Attapol Rujirawan, Siriporn Yodthong and Piyawan Puanprapai.

(Fig. 9). Three adult females paratypes. ZMKU R 00985–00986 (two adult females), same data as holotype. ZMKU R 00987 (one adult female), same data as holotype except collected on 6 March 2018 by Natee Ampai, Attapol Rujirawan, Siriporn Yodthong and Piyawan Puanprapai.

Cnemaspissimilan sp. nov. can be distinguished from all other members of the C.siamensis group by having the following combination of characters: (1) SVL of 47.6 mm in adult male and 38.6–48.1 mm (mean 43.6 ± 4.8 mm, N = 3) in adult females; (2) eight or nine supralabial and seven or eight infralabial scales; (3) ventral scales keeled (4) one pore-bearing precloacal scale, pore rounded in male; (5) 24 or 25 paravertebral tubercles, arranged randomly; (6) five small, elongated, spine-like tubercles on lower flanks; (7) 23 or 24 subdigital lamellae under the 4^th toe; (8) no enlarged median subcaudal scale row; (9) ventrolateral caudal tubercles anteriorly present; (10) two postcloacal tubercles on lateral surface of hemipenial swellings at tail base in male; (11) sexual dimorphism in dorsal and ventral patterns; and (12) pale yellow reticulum on head, neck, flanks, belly and limbs only in male.

An adult male in good state of preservation; 47.6 mm SVL; head moderate in size (HL/SVL 0.26), narrow (HW/SVL 0.16), flattened (HD/HL 0.39) and head distinct from neck; snout moderate (ES/HL 0.43), in lateral profile concave; loreal region marginally inflated, canthus rostralis nearly absent; postnasal region concave medially; scales of rostrum smooth, raised, larger than conical scales on occiput; weak and faint supraorbital ridges; gular scales granular, keeled, rounded, juxtaposed; throat scales granular, keeled, flat, subimbricate; shallow frontonasal sulcus; eye large (ED/HL 0.19); pupil round; extra-brillar fringe scales small in general but slightly larger anteriorly; scales on interorbitals and supercilium keeled; eye to ear distance greater than eyes diameter (EE/ED 1.50); ear opening elongate, much taller than wide (EL/HL 0.08); rostral concave dorsally; rostral bordered posteriorly by supranasals and laterally by first supralabials; 8R,L supralabials decreasing in size posteriorly; 7R,L infralabials decreasing in size posteriorly; nostril small, elliptical, oriented dorsoposteriorly, bordered posteriorly by small postnasal scales; mental scales large, triangular, flat, extending to level of second infralabial scales, bordered posteriorly by three large postmental scales.

Body robust, not elongate (AG/SVL 0.41); small, raised, keeled, dorsal scales equal in size throughout body intermixed with numerous large, keeled, multicarinate tubercles; 24 paravertebral tubercles randomly arranged; five small, elongated, spine-like tubercles on flanks; tubercles present on lower flanks; tubercles extend from occiput to tail; pectoral and abdominal scales keeled, round, flat, imbricate; abdominal scales larger than pectoral and dorsal scales; ventral scales of brachia smooth, raised and juxtaposed; one pore-bearing precloacal scale, with rounded pore; precloacal depression absent; femoral pores absent.

Fore and hind limbs moderately long, slender; scales beneath forearm slightly raised, smooth and subimbricate; subtibial scales keeled; palmar scales keeled, flat and subimbricate; digits long, slender with inflected joint; claws slightly recurved; subdigital lamellae unnotched; lamellae beneath first phalanges wide; lamellae beneath phalanx immediately following inflection granular; lamellae of distal phalanges wide; lamellae beneath inflection large; interdigital webbing generally absent; enlarged submetatarsal scales on 1^st toe present; total subdigital lamellae on fingers I–V: 15-21-22-24-23 (right manus), 15-21-23-24-23 (left manus); fingers increase in length from first to fourth with fifth nearly equal in length as fourth; relative length of fingers IV>V>III>II>I; total subdigital lamellae on toes I–V: 17-20-22-24-23 (right pes), 17-19-22-24-23 (left pes); toes increase in length from first to fourth with fifth nearly equal in length as fourth; relative length of toes IV>V>III>II>I.

Tail regenerated, subcylindrical, relatively swollen at the base; tail length (TL) 49.6 mm; tail length longer than head and body (TL/SVL 1.04); dorsal and ventral scales at the tail base similar in size on mid-body dorsum; subcaudal scales keeled, juxtaposed, larger than dorsal scale of the tail size; shallow, middorsal furrow; lateral caudal furrow present; enlarged, transverse caudal tubercles arranged in segmented whorls, encircling tail; enlarged median subcaudal scale row absent; caudal tubercles present between upper and lower of lateral furrow; rest of the tail regenerated, slightly keeled, imbricate scales with no enlarged tubercles; scales on ventral aspect of the regenerated tail marginally larger in size than mid-body ventrals; 2R,L enlarge postcloacal tubercle at lateral surface of hemipenial swellings at the tail base.

(in mm; Table 7). SVL 47.6; TL (regenerated tail) 49.6; TW 4.6; FL 6.8; TBL 8.6; AG 19.6; HL 12.4; HW 7.8; HD 4.8; ED 2.4; EE 3.6; ES 5.3; EN 4.0; EL 1.0; IN 1.1; IO 3.1.

(Figs 8, 9). Dorsal ground color of head brown, top of head and snout bearing diffuse, mottled with smaller yellowish markings; 3R,L vertical, thin and fine dark stripes extending from postorbital to neck; 1R,L indistinct darker stripes runs from preorbital to supranasal; pupil black with orange streak; irregular, faint pale yellow reticulum on lateral surface of head, neck and flanks; 1R,L light-colored prescapular crescent on shoulder, located at forelimb insertion dorsoanteriorly; two dark streaks form a bipartite pattern on neck; dorsal ground color of body and tail brown with irregular black blotches except much paler brown on limbs; pale sage vertebral blotches run from the nape to tail; flanks with smaller dark and larger pale yellow streaks; enlarged conical spine-like yellowish tubercles on lower flanks; tubercles on the whole body pale sage and pale yellow; digits with distinct dark and pale bands; dorsum of limbs pale brown with dark blotches randomly arranged; ventral surfaces pale greyish intermixed with pale yellowish blotches on gular, neck, limbs and belly; no markings on gular and belly regions; original part of the tail brown with dark streaks form a bipartite pattern; regenerated part of the tail brown without bands; ventral side of tail pale greyish with no markings.

(Figs 10, 11). Overall coloration of head, body, limbs, flanks and tail about the same as in life. Dorsal ground color of the whole-body became faded. The pale tones of limbs and tail darker than in life. Vertebral blotches run from the nape to tail became paler than in life. All pale yellowish coloration on head, limbs, flanks fade to creamy white. Ventral region of the whole-body homogenously tan colored.

Due to having only a single adult male (N = 1), variation in adult males is currently unknown. Most paratypes approximate the holotype in general features of body pattern and coloration. Adult females lack pore-bearing precloacal scale. Pale yellowish markings in head, neck, limbs, flanks and caudal regions were also absent in adult females. Three adult females have paler dorsal markings than the holotype. ZMKU R 00985 and ZMKU R 00986 have regenerated tails of uniform tan colored. ZMKU R 00985 has a large calcium sac on each side of the neck. ZMKU R 00985 has also broken left 4^th pes.

Cnemaspissimilan sp. nov. is known only from the type locality at Ao Nguang Chang Bay (8°64.840'N, 97°64.834'E; 13 m a.s.l.; Fig. 12), Ko Similan, Lam Kaen Subdistrict, Thai Mueang District, Phang-nga Province, Thailand, approximately 65 km off the mainland of Thai Mueang District, Phang-nga Province in the Andaman Sea.

The type locality is dominated by mixed evergreen forest with shrub and beach forests. Ao Nguang Chang Bay is located at the southern part of the largest island, Ko Similan (= Ko Pad). All specimens of C.similan sp. nov. were found in granitic rocky outcrops near Ao Nguang Chang Bay during the day (1542 h) and night (2023–2049 h) with an air temperature of 28.4 °C and relative humidity of 86%. Granitic boulder surfaces appeared to be relatively dry and cool. The male holotype was found during the night (2023 h) on a tree near a boulder. Most paratypes (ZMKU R 00985–00986) were found during the day time on vegetation (tree trunks, roots, or vines) except ZMKU R 00987, which was perched on a rock wall. Cnemaspissimilan sp. nov. seems to be a diurnal rock-dwelling species. During the day, geckos were generally active, quite wary and quickly retreated when approached or disturbed. At night, geckos were found inactive or sleeping on vegetation near crevices or cracks of rock boulder as high as 2 m above the ground. They were often found clinging upside down to the underside of rock boulder overhang. During field surveys, the larger, nocturnal gekkonid Cyrtodactylusoldhami (Theobald, 1876) was found in sympatry on the ground and vegetation near boulders.

The specific epithet similan is a noun in apposition and refers to the type locality of Ko Similan.

Cnemaspissimilan sp. nov. can be distinguished from 13 congeners of the siamensis group (C.adangrawi, C.chanardi, C.huaseesom, C.kamolnorranathi, C.lineatubercularis, C.omari, C.phangngaensis, C.punctatonuchalis, C.samui sp. nov., C.selenolagus, C.siamensis, C.thachanaensis, and C.vandeventeri) by having a unique combination of morphological characters (Table 6) and uncorrected pairwise sequence divergences in mtDNA (ND2) of 8.16–27.11% (Table 2).

Cnemaspissimilan sp. nov. is distinguished from C.adangrawiAmpai et al. 2019 by having maximum SVL 48.1 mm (vs. 44.9 mm); seven or eight infralabial scales (vs. nine scales); one pore-bearing precloacal scale (vs. 6–8 scales); eight or nine supralabial scales (vs. 10 scales); tubercles on lower flanks present (vs. absent); 23 or 24 lamellae under 4^th toe (vs. 26–28 lamellae); and two postcloacal tubercles in males (vs. one tubercle).

Cnemaspissimilan sp. nov. is distinguished from C.chanardiGrismer et al. 2010 by having maximum SVL 48.1 mm (vs. 40.9 mm); one pore-bearing precloacal scale (vs. 6–8 scales); 23 or 24 lamellae under 4^th toe (vs. 26–29 lamellae); single median row of subcaudal keeled (vs. smooth); enlarged median subcaudal scales row absent (vs. present); ventrolateral caudal tubercles anteriorly present (vs. absent); two postcloacal tubercles in males (vs. one tubercle); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.huaseesomGrismer et al. 2010 by having maximum SVL 48.1 mm (vs. 43.5 mm); one pore-bearing precloacal scale (vs. 5–8 scales); ventral and subcaudal scales keeled (vs. smooth); single median row of subcaudal keeled (vs. smooth); ventrolateral caudal tubercles anteriorly present (vs. absent); subtibial scales keeled (vs. smooth); yellow coloration in the subcaudal region absent (vs. present); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.kamolnorranathiGrismer et al. 2010 by having maximum SVL 48.1 mm (vs. 37.8 mm); one pore-bearing precloacal scale (vs. six or seven scales); pore-bearing precloacal scale row absent (vs. continuous); pore-bearing precloacal scale rounded (vs. elongated); ventrolateral caudal tubercles anteriorly present (vs. absent); and ventral pattern sexually dimorphic present (vs. absent).

Cnemaspissimilan sp. nov. is distinguished from C.lineatubercularisAmpai et al. 2020 by having maximum SVL 48.1 mm (vs. 41.8 mm); seven or eight infralabial scales (vs. nine scales); one pore-bearing precloacal scale (vs. 4–7 scales); 24 or 25 paravertebral tubercles (vs. 19–21 tubercles); paravertebral tubercles randomly arranged (vs. linearly arranged); 23 or 24 lamellae under 4^th toe (vs. 27–29 lamellae); caudal tubercles restricted to a single paravertebral row on each side absent (vs. present); two postcloacal tubercles in males (vs. one tubercle); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.omariGrismer et al. 2014 by having maximum SVL 48.1 mm (vs. 41.3 mm); one pore-bearing precloacal scale (vs. 3–6 scales); 23 or 24 lamellae under 4^th toe (vs. 25–28 lamellae); single median row of subcaudal keeled (vs. smooth); ventrolateral caudal tubercles anteriorly present (vs. absent); two postcloacal tubercles in males (vs. one tubercle); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.phangngaensisWood et al. 2017 by having maximum SVL 48.1 mm (vs. 42.0 mm); eight or nine supralabial scales (vs. 10 scales); seven or eight infralabial scales (vs. 10 scales); one pore-bearing precloacal scale (vs. four scales); 24 or 25 paravertebral tubercles (vs. 22 tubercles); paravertebral tubercles randomly arranged (vs. linearly arranged); tubercles on lower flanks present (vs. absent); 23 or 24 lamellae under 4^th toe (vs. 29 lamellae); caudal tubercles restricted to a single paravertebral row on each side absent (vs. present); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.punctatonuchalisGrismer et al. 2010 by having maximum SVL of 48.1 mm (vs. 49.6 mm); one pore-bearing precloacal scale (vs. absent); 23 or 24 lamellae under 4^th toe (vs. 29–31 lamellae); ventral and subcaudal scales keeled (vs. smooth); single median row of subcaudal keeled (vs. smooth); and enlarged median subcaudal scales row absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.samui sp. nov. by having maximum SVL 48.1 mm (vs. 42.3 mm); one pore-bearing precloacal scale (vs. 5–8 scales); enlarged median subcaudal scales row absent (vs. present); and yellow coloration in the subcaudal region absent (vs. present).

Cnemaspissimilan sp. nov. is distinguished from C.selenolagusGrismer et al. 2020 by having maximum SVL 48.1 mm (vs. 36.2 mm); eight or nine supralabial scales (vs. 10 or 11 scales); seven or eight infralabial scales (vs. 10 scales); one pore-bearing precloacal scale (vs. six or seven scales); pore-bearing precloacal scale shape rounded (vs. elongated); 24 or 25 paravertebral tubercles (vs. 16–18 tubercles); tubercles on lower flanks present (vs. absent); ventral and subcaudal scales keeled (vs. smooth); ventrolateral caudal tubercles anteriorly present (vs. absent); and subtibial scales keeled (vs. smooth).

Cnemaspissimilan sp. nov. is distinguished from C.siamensis (Smith, 1925) by having maximum SVL 48.1 mm (vs. 39.7 mm); one pore-bearing precloacal scale (vs. absent); single median row of subcaudal keeled (vs. smooth); enlarged median subcaudal scales row absent (vs. present); and ventrolateral caudal tubercles anteriorly present (vs. absent).

Cnemaspissimilan sp. nov. is distinguished from C.thachanaensisWood et al. 2017 by having maximum SVL 48.1 mm (vs. 39.0 mm); eight or nine supralabial scales (vs. 10 or 11 scales); seven or eight infralabial scales (vs. 9–11 scales); pore-bearing precloacal scale present (vs. absent); 24 or 25 paravertebral tubercles (vs. 15–19 tubercles); paravertebral tubercles randomly arranged (vs. linearly arranged); caudal tubercles restricted to a single paravertebral row on each side absent (vs. present); and two postcloacal tubercles in males (vs. absent).

Cnemaspissimilan sp. nov. is distinguished from C.vandeventeriGrismer et al. 2010 by having maximum SVL 48.1 mm (vs. 44.7 mm); one pore-bearing precloacal scale (vs. four scales); enlarged median subcaudal scales row absent (vs. present); and ventrolateral caudal tubercles anteriorly present (vs. absent).