Dixonius siamensis, (Boulenger, 1899) (Boulenger, 1899)

Pauwels, Olivier S. G., Das, Sunandan, Brecko, Jonathan, Bringsøe, Henrik & Sumontha, Montri, 2024, Rediscovery and redescription of Dixonius siamensis (Boulenger, 1899) (Squamata: Gekkonidae), type species of the genus, with lectotype designation, Zootaxa 5543 (3), pp. 301-328 : 304-319

Results

Description of the syntypes. Four specimens collected by Stanley Smyth Flower (1871–1946) preserved in ethanol, housed in the herpetological collections of the Natural History Museum, London, UK (NHMUK, previously known as the British Museum of Natural History, BMNH): one juvenile male (BMNH 97.3.31.1) and three subadult females (BMNH 97.3.31.2 and BMNH 1946.8.24.40–41) ( Figures 2–7 ). BMNH 1946.8.24.40–41 were previously registered as BMNH 98.4.2.3–4 (P. Campbell, pers. comm. to OSGP, 2024). Measurements and scale counts for each specimen are provided in Table 1 . Individual morphometric ratios are given in the following order: BMNH 97.3.31.1–2, BMNH 1946.8.24.40–41.

SVL 26.8 mm, 30.6 mm, 39.7 mm and 36.4 mm. Flower (1899a: 628), based on the four specimens then known, gave the maximum total length as ‘’ 86 mm (snout to vent 42; tail 44)’’. One can assume that this corresponds to an approximate measurement of the SVL of the female type BMNH 1946.8.24.40, and that part of its tail was lost after its examination by Flower.

Head relatively long (HL/SVL ratios 0.34, 0.30, 0.32, 0.31), wide (HW/HL ratios 0.59, 0.67, 0.63, 0.68), not markedly depressed (HD/HL ratios 0.43, 0.42, 0.40, 0.49), distinct from neck. Lores and interorbital region weakly inflated. Canthus rostralis relatively prominent. Snout moderately short (SnOrb/HL ratios 0.34, 0.35, 0.35, 0.42), rounded, slightly longer than orbit diameter (OrbD/SnOrb ratios 0.61, 0.67, 0.59, 0.53). Scales on snout and forehead small, hexagonal to rounded, flattened, with smooth or slightly rugose surface. Scales on snout larger than those on occipital region. Eye of moderate size (OrbD/HL ratios 0.21, 0.24, 0.21, 0.22). Pupil vertical with crenelated margins. Supraciliaries short, without spines. Ear opening oval, moderate (EarL/HL ratios 0.04, 0.06, 0.06, 0.06); orbit to ear distance distinctly greater than orbit diameter (OrbEar/OrbD ratios 1.37, 1.36, 1.46, 1.44). Rostral distinctly wider than high (RosW/RosH ratios 1.56, 2.00, 1.62, 1.40), dorsally incompletely divided (about 50%) by a median cleft. Two enlarged supranasals in broad contact on their whole length (BMNH 97.3.31.2), for half their length (BMNH 1946.8.24.41), or totally separated by a smaller one (BMNH 97.3.31.1 and BMNH 1946.8.24.40). Rostral in contact with supralabial I on each side, nostrils and two (BMNH 97.3.31.2 and BMNH 1946.8.24.41) or three (BMNH 97.3.31.1 and BMNH 1946.8.24.40) supranasals. Nostrils round, each surrounded by supranasal, rostral, supralabial I, and two (BMNH 97.3.31.1–2 and BMNH 1946.8.24.40) or three (BMNH 1946.8.24.41) postnasals. Mental triangular, broader than long (MenL/MenW ratios 0.73, 0.81, 0.76, 0.85). Two pairs of enlarged postmentals, anteriormost approximately three times larger than posterior. Each anterior postmental bordered anteriorly by mental, medially by the other anterior postmental, anterolaterally by infralabial I, posterolaterally by the second postmental (in BMNH 97.3.31.2 the left postmental also in contact by a point with infralabial II; in BMNH 1946.8.24.40 the left anterior postmental is also bordered by an additional granular scale located between the anterior and posterior postmentals and the 1 st and 2 nd IL); the pair collectively bordered posteromedially by a row of four (BMNH 1946.8.24.40–41) or five (BMNH 97.3.31.1–2) throat scales. Supralabials to mid-orbital position 6/6 (except for BMNH 97.3.31.2, which shows 6/5); enlarged supralabials to angle of jaws 7 (BMNH 97.3.31.2), 8 (BMNH 1946.8.24.40–41) or 9 (BMNH 97.3.31.1). Infralabials 6/6 (BMNH 97.3.31.2), 6/7 (BMNH 97.3.31.1) or 7/7 (BMNH 1946.8.24.40–41). Interorbital scales 10 (BMNH 97.3.31.1 and BMNH 1946.8.24.40–41) or 11 (BMNH 97.3.31.2); interciliary scales 19 (BMNH 97.3.31.1 and BMNH 1946.8.24.40–41) or 20 (BMNH 97.3.31.2).

Body slender, elongate (TrunkL/SVL ratios 0.40, 0.40, 0.37, 0.42), without ventrolateral folds. Dorsal scales heterogeneous, small, irregular, flattened to conical, distributed among large, strongly keeled tubercles arranged in 12 (BMNH 97.3.31.2) or 14 (BMNH 97.3.31.1 and BMNH 1946.8.24.40–41) regular longitudinal rows at midbody. PV 33 (BMNH 1946.8.24.41), 35 (BMNH 97.3.31.2) or 38 (BMNH 97.3.31.1 and BMNH 1946.8.24.40); PV’ 23 (BMNH 97.3.31.1–2) or 24 (BMNH 1946.8.24.40–41). Paravertebral rows of tubercles separated by four dorsal scales in BMNH 97.3.31.1–2 or two or three in BMNH 1946.8.24.40–41. Flanks covered with irregular, smooth to slightly conical scales. Gular region with relatively homogeneous, granular scales. Ventral scales smooth, imbricate, their free margin rounded. Ventrals increasing in size from throat to chest to abdomen. Midbody scale rows across belly to lowest rows of tubercles 20 (BMNH 1946.8.24.41), 25 (BMNH 97.3.31.1 and BMNH 1946.8.24.40) or 26 (BMNH 97.3.31.2). Six poorly developed precloacal pores in a continuous series in the male (difficult to see to the naked eye and possibly overlooked by Boulenger, they appear clearly under a careful examination through the binocular). Pore-bearing scales not enlarged relative to adjacent scale rows. No pits or pores in the females. No femoral pores or enlarged femoral scales.

Fore- and hind limbs short, slender (FaL/SVL ratios 0.14, 0.12, 0.14, 0.13; TibL/SVL ratios 0.15, 0.16, 0.18, 0.17). Digits slender, dilated distally, all bearing robust, slightly recurved claws. Basal subdigital lamellae narrow, without scansorial surfaces (8-10-10-10-8 on right manus and 7-10-13-14-11 on right pes of BMNH 97.3.31.1; 8- 9-9-8-8 on right manus and 7-9-11-12-11 on right pes of BMNH 97.3.31.2; 6-9-10-10-9 on right manus and 8-10- 12-15-13 on right pes of BMNH 1946.8.24.40; and 7-9-10-9-9 on right manus and 8-10-12-14-13 on right pes of BMNH 1946.8.24.41); setae-bearing lamellae restricted to enlarged, distal, ‘‘leaf-like’’ scansors. Scales on palm and sole small, smooth, rounded to oval. Interdigital webbing absent. Relative length of digits (manus): III≈IV>V≈II>I (BMNH 97.3.31.1), III≈IV>II>V>I (BMNH 97.3.31.2) or III≈IV>II>V>I (BMNH 1946.8.24.40–41). Relative length of toes (pes): IV>V>III>II>I (BMNH 97.3.31.1 and BMNH 1946.8.24.40–41) or III>IV>V>II>I (BMNH 97.3.31.2). Tail complete and original only in the male, BMNH 97.3.31.1 (TailL 30.5 mm; TailL/SVL ratio 1.14), showing 57 subcaudals enlarged into transverse plates (counted from the first widened at the base of the tail). In the three other types a part of the tail is missing, and the part remaining is original, not healed or regenerated. Supracaudals markedly keeled in the anterior portion of the tail.

Coloration in preservative: In the female BMNH 97.3.31.2 the pattern has totally faded or was already poorly contrasted or absent in life; the whole dorsal surface is light brown, except the tubercles which are beige, and a discontinuous series of white tubercles on the upper flanks from the nape to the anterior part of the tail; the throat and belly are uniformly beige, and the underside of the tail is light brown. In the three other types, the dorsal surface of the head is light brown with irregular dark brown blotches (nearly faded away in BMNH 97.3.31.1 or already poorly contrasted when it was alive). On each side of the head of BMNH 1946.8.24.40–41 a dark brown canthal stripe runs from the nostril through the eye and extends to the level of the occiput; this stripe is not visible in BMNH 97.3.31.1–2. The supralabials and infralabials are light brown, strongly barred vertically with dark brown in all four specimens. In BMNH 1946.8.24.40–41, similarly to the dorsal surface of the head, the neck and the dorsum show a light brown background color with irregularly disposed dark brown spots, roundish in BMNH 1946.8.24.41 or more transversely elongate in BMNH 1946.8.24.40 ( Figures 4–5 ); the remaining part of the tail of BMNH 1946.8.24.40 shows more or less regularly disposed dark and light rings. Poorly contrasted dorsal spots and well contrasted tail rings are visible in BMNH 97.3.31.1. A discontinuous series of white tubercles is perceptible on the upper flanks and from nape to tail in BMNH 97.3.31.1–2 and, with less contrast, in BMNH 1946.8.24.40; these white tubercles are not visible in BMNH 1946.8.24.41. Dorsal surfaces of members light brown with dark brown spots, well visible in BMNH 1946.8.24.40–41, poorly contrasted in BMNH 97.3.31.1 and absent or no longer visible in BMNH 97.3.31.2. The tail of BMNH 97.3.31.1, complete and original, shows ten light rights irregularly disposed along the entire length of the tail, the anterior ones poorly contrasted. Infralabials colored as supralabials. Throat of BMNH 1946.8.24.40–41, which is more contrasted than in the two other specimens, light brown, mottled with dark brown. Ventral surfaces of body, members and tail light brown, punctuated with dark brown dots in BMNH 1946.8.24.40–41 (dots not visible in BMNH 97.3.31.1–2).

Flower (1899a: 628) gave a brief description of the coloration in life of the types: ‘‘Above brown, spotted very strongly with black. Below grey, mottled with purple. Underneath of head brown. Labials marked with dark purplish brown and pale yellowish brown.’’ It is, however, not clear on which specimens Flower’s description is based.

Cranial osteology. Based on the subadult female BMNH 1946.8.24.40.

Snout and palatomaxillary bones.— The premaxilla is single ( Figure 7A–B ). The alveolar shelf bears 11 pleurodont teeth. The posterior margin of the alveolar shelf projects out caudally into two triangular palatal processes. The ascending process runs posterodorsally and articulates with the nasals.

Nasals are paired and parallelogram-shaped, with an anterior process from the anteromedial end and a posterior process jutting out from the posterolateral end ( Figure 7A ). Though there is a slight embayment medial to the anterior process, there is no anterolateral process as seen in some gekkonids ( Evans 2008; Villa et al. 2018). The nasal articulates with the maxillary facial process laterally and with the frontal posteriorly in a semilunar arc.

The paired vomers constitute the ventral part of the encasing for the vomeronasal organ ( Figure 7C ). There is a shallow lateral embayment for the vomeronasal organ in the anterior half of the vomer. Rostrad to this embayment, vomer extends into a small process that articulates with the maxillary palatal shelf. This process, however, does not reach the premaxilla. There is a teardrop-shaped fontanelle between the anterior processes of the paired vomers. A posterodorsal process from the posterior lateral margin of the vomer articulates with the palatine.

The paired septomaxillae have a marked medial ridge, a ventrally lamina roofing the vomeronasal organ and lateral ridge. The posterolateral edge of the septomaxilla has a hook-shaped, elongated process. The posteromedial margin gives rise to another small, triangular, caudally directed process.

The maxillae are paired and consist of a premaxillary process, a well-developed facial process, the tooth-bearing alveolar border, a medial palatal shelf and a posterior or orbital process ( Figure 7A–B ). The premaxillary process is divided into an obtuse anterolateral and a tapering, elongated anteromedial process. The anteromedial process articulates with the premaxilla and vomer. The alveolar border bears 32-33 pleurodont teeth. The facial process is broad-based and has an embayment in its anteroventral border. The dorsal and the posterior borders articulate with the nasal and the prefrontal respectively. The posterodorsal corner of the facial process is projected caudad into a wedge between the frontal and prefrontal. The orbital process articulates with the ectopterygoid, prefrontal base and the jugal.

The palatines are paired, edentulous laminar bones ( Figure 7C ). They articulate posteriorly with the pterygoid. Anteriorly the palatine possesses an anteromedial vomerine process articulating with the vomer and an anterolateral maxillary process that contacts the maxilla.

The pterygoids are paired and edentulous ( Figure 7C ). The triradiate pterygoid comprises of an anteromedial palatine process, an anterolateral ectopterygoid process and a posterolaterally directed quadrate process. The ectopterygoid process has a lateral ridge articulating with the ectopterygoid. The palatine process, articulating with the palatine bone, has a broad base that tapers into a medial process. At the base of the quadrate process, there is a ventral basipterygoid fossa and a dorsal columellar fossa (for the epipterygoid).

The ectopterygoids are a pair of edentulous, crescentic bones with tapering anterior and posterior ends. These bones articulate to the maxillary orbital process and the pterygoid. It contacts the jugal laterally.

Chondrocranial braincase bones.— The prootics are paired bones that house the anterior semicircular and part of the horizontal semicircular canals ( Figure 7B ). The alar process is well developed and projects anterodorsally. The crista prootica is drawn into a lateral spina prootica. The trigeminal foramen is located medial to the crista prootica. There is no prominent incisura prootica. There is an elongated bulge on the lateral surface of the prootic corresponding to the horizontal semicircular canal. The prootic articulates with the otoccipital dorsal and ventral to the fenestra ovalis. Ventrally the prootic articulates with the parabasisphenoid and the basioccipital while dorsally it articulates with the supraoccipital.

The otoccipitals are paired, bulbous bones housing parts of the posterior and the horizontal semicircular canals and other parts of the inner ear. Dorsally the otoccipitals articulate to the supraoccipital. Anteriorly, otoccipitals contact the prootics and bear a deep embayment for the fenestra ovalis. Ventrad to the fenestra ovalis, there is a crista interfenestralis. Medial and ventrad to the crista interfenestralis, opens the lateral opening of the recessus scalae tympani. Right above the fenestra ovalis, a prominent paroccipital process projects laterally. Ventrally the otoccipital articulates with the basioccipital with which it forms the occipital condyle.

The supraoccipital is an unpaired bone that forms the dorsal margin of the foramen magnum. The medial part of this bone is narrow ( Figure 7A ). This part is flanked on both sides by expanded lateral wings.Anteromedially directed bulging ridges on the lateral wings correspond to the posterior semicircular canals. Anteriorly the supraoccipital is partly overlapped by the parietal. There is no processus ascendens. Laterally the supraoccipital articulates with the prootic and otoccipital.

The parabasisphenoid is a single, ventral element of the chondrocranial braincase ( Figure 7C ). Anteriorly it projects into a parasphenoid rostrum. Lateral to the parasphenoid rostrum, the parabasisphenoid projects anterolaterally into a basipterygoid process. These processes are wider in their anterior end and bear an articulatory facet. The dorsal surface of the parabasisphenoid bears the sella turcica. A transverse crista sellaris is present caudad to the sella turcica.

The basioccipital is a single, shield like, dorsally concave bone that forms the medial part of the occipital condyle ( Figure 7C ). It articulates with the parabasisphenoid along its frontal border and the prootic and the otoccipital laterally.

Dermal skull-roofing bones.— The frontal is a single dermatocranial element in the skull roof ( Figure 7A ). In dorsal view, the frontal is a T-shaped bone, with its widest part being along its articulation to the parietal. The anterior part, articulating with the nasal and maxillary facial process, has a rounded rostral end. The cristae cranii fuse along the ventral midline. Posterolaterally the frontal articulates with the postorbitofrontal whereas caudally it articulates with the parietals.

The parietals are a pair of flat bones that contact each other along a straight medial suture ( Figure 7A ). Laterally the parietals articulate with the postorbitofrontal. There is a posteromedial process that overlaps the supraoccipital to form a syndesmotic connection. Posterolaterally postparietal processes project out from the parietals. These processes contact the squamosal laterally.

Circumorbital bones.— The prefrontals are paired, crescentic bones ( Figure 7A–B ). The orbitonasal flange contacts the frontal crista cranii medially. The dorsal end of the orbitonasal flange projects caudad along the lateral margin of the frontal dorsal lamina. Ventrally there is a small process from this flange that rests upon the frontal.

The postorbital and the postfrontal are fused into one postorbitofrontal on both sides, as is typical of the gekkotans ( Evans 2008) ( Figure 7A ). This bone is Y-shaped in Dixonius siamensis and articulates medially to the frontal and the parietal.

The paired jugals are reduced to a small splint of bone articulated to the frontal and the ectopterygoid ( Figure 7A ). There is no lacrimal. A prominent, large scleral ring is present ( Figure 7A–B ).

Suspensorial and palatoquadrate derived bones.— The squamosal is a J-shaped paired bone ( Figure 7B ). It articulates with the postparietal process and the paroccipital process. It does not appear to have any real role in suspending the quadrate.

The quadrates are paired bones suspending the mandibles from the upper part of the cranium ( Figure 7A–B ). There is a cephalic condyle that contacts the paroccipital process. Along the medial margin is the central column of the quadrate. Lateral to this there is the posteriorly concave conch and the tympanic crest. The mandibular condyle is bicephalic and articulates with the compound bone.

The epipterygoid is a rod that articulates ventrally to the columellar fossa on the quadrate and dorsal is proximal to the prootic alar process ( Figure 7B ). The stapes is present and consists of a stapedial footplate and a shaft.

Mandible.— The dentaries are paired dentigerous bones bearing 32-34 teeth ( Figure 7B ). The Meckelian fossa is closed. The dentary is bifurcated posteriorly, with the posterodorsal process articulating to the coronoid and the much longer posteroventral process articulating to the surangular and the prearticular.

The splenial is a paired bone. It is a rather reduced element that is located medial to the trijunction between the dentary, the coronoid and the compound bone.

The coronoid is a paired, tetraradiate bone ( Figure 7B ). This bone consists of a dorsal, triangular coronoid process, an anterolateral labial process, an anteromedial process and a posteromedial process. There is a depression between the coronoid and the posteromedial processes. This bone articulates to the dentary, splenial, surangular and the prearticular.

The compound bone is a paired element formed of the surangular, prearticular and the articular ( Figure 7B–C ). The lateral surangular and the ventromedial prearticular enclose an adductor fossa. The surangular is expanded just rostrad to the articular facet for the quadratic mandibular condyle. The articular, confluent with the prearticular, forms the articular facet and projects caudally into a retroarticular process with an expanded end.

Geographical origin of the syntypes. Boulenger (1899) did not specify how many specimens he used for the description of Phyllodactylus siamensis , but certainly at least two, because he wrote “Specimens were obtained by Mr. S. S. Flower at Dung Phaya Fai, Siam, at an altitude of 700 feet.” Dong Phaya Fai, currently often called Dong Phaya Yen, is a mountain range separating central from eastern Thailand, parallel to the Phetchabun Range. It was nearly unexplored until the late 19 th century ( Terwiel 2017). A large part of the Dong Phaya Yen lies today within Khao Yai National Park . The type series was collected by Flower at a period when this mountain range had just been made more accessible through forest clearing and the construction of the first roads linking central to eastern Thailand, with the prospect to build a railroad through Dong Phaya Yen .

In an account on the mammals of Thailand, Flower (1900: 309) gave the following definition for ‘‘Dong Phya Fai’’ [sic], the ‘‘Forest of the Lord of Fire’ ’: ‘‘a hilly tract covered with jungle, about 50 miles across, between Ayuthia and Korat in Siam, abounding in animal life’’. On the Dong Phaya Yen range, Flower collected at ‘‘Muok Lek, elevation 900 feet above the sea’’ (now Muak Lek, ca. 14° 39′ 20″ N, 101° 11′ 54″ E, in Saraburi Province, along the border with Nakhon Ratchasima Province) and ‘‘ Hinlap’ ’ (now Hin Lap , ca. 14°39’47.3”N 101°07’59.3”E, about seven airline km W-NW from Muak Lek, in Saraburi province) ( Flower 1899a: 617, 628, 640, etc.; 1899b: 896; 1900: 311; Figure 8 ). Muak Lek and Hin Lap are located on the first and once only road linking Saraburi to Khorat ( Bamrungkhul & Tanaka 2022), where it is easiest to cross the Dong Phaya Yen range. The collecting localities of Flower (1899a) in Dong Phaya Yen are joined by the railroad for which exploratory roads were being built in the late 19th century ( Kakizaki 2012), during the travels of Flower. Flower (1900: 336) even met some European engineers involved in the construction of the railway through the Dong Phaya Yen.

Flower (1899a: 627–628) gave more information than Boulenger about the precise localities where the types of Phyllodactylus siamensis were caught: ‘‘ The first two specimens of this little Gecko were from M. Pran and Hinlap: subsequently, in Nov. 1897, I caught two more under stones in the jungle near Hinlap ( Dong Phya Fai ), elevation about 700 feet’’. There is no other mention of ‘‘ M. Pran’ ’ by Flower (1899a), but it is written in extenso as ‘‘ Muang Pran’ ’ by Flower (1900: 310, 359) and located ‘‘in Siam’ ’. Muang Pran is currently located in Pranburi District , in the northern part of Prachuap Khiri Khan Province, in peninsular Thailand. It lies at about 300 airline km S-SW of Hin Lap , across the Gulf of Thailand, in an ecologically and zoogeographically very distinct zone. There is hence an obvious high risk that more than one species is represented by the type series. The page of the NHMUK entry catalogue for Phyllodactylus siamensis indicates that BMNH 1946.8.24.40–41 originate from “Dong Phya Fai, 700 ft., Siam”, and BMNH 97.3.31.1–2 from “ Siam ” ( Das 2004; P. Campbell, pers. comm. to OSGP, February 2024).

In their catalogue of the recent species of Gekkota, de Lisle et al. (2013) erroneously listed five syntypes for Dixonius siamensis : “BMNH 1946.8.24.40–41, 1897.3.31. 1–2, 1948.8.24.51”. The latter one is a mistyping for 1946.8.24.51, which is actually a “cotype of P. burmanicus ”, collected in “Tavoy, Tenasserim” and originating from the “Indian Museum” according to what is written on the NHMUK entry catalogue (P. Campbell, pers. comm. to OSGP, February 2024; see also Das et al. 1998).

Lectotype designation. Because the type series of Phyllodactylus siamensis most probably contains two species, a diagnosis based on all four type specimens would be composite and artificial, and prevent valid interspecific comparisons in future taxonomic works. Only two specimens originate with certainty from the type locality stated in the original description, i.e. BMNH 1946.8.24.40–41. Relying on the above information provided by the collector himself, the type locality can be more precisely stated as Hin Lap within the Dong Phaya Yen range. Based on the dorsal patterns still visible in the specimens of the type series, in particular the width of caudal annuli and the presence of transversely elongate dark spots on the dorsum, the type which is most similar to the specimen illustrated in the original description is BMNH 1946.8.24.40 (compare Figures 1A and 4 ). In order to enhance nomenclatural stability, we here formally designate this latter specimen as the lectotype, in agreement with Article 74 of the International Code of Zoological Nomenclature ( Anonymous 1999). All three other syntypes become de facto paralectotypes.

Revised diagnosis. The lectotype BMNH 1946.8.24.40 and paralectotype BMNH 1946.8.24.41, both subadult females, show SVL of 39.7 mm and 36.4 mm, respectively; eight supralabials with the 6 th in midorbital position; seven infralabials; three and two supranasals, respectively; 10 interorbital scales; 14 longitudinal rows of dorsal tubercles; 38 and 33 paravertebral tubercles, respectively, among which 24 between limb insertions; 25 and 20 longitudinal rows of ventrals across the abdomen, respectively; no pores; ten and nine subdigital lamellae beneath 4 th finger, respectively; 15 and 14 subdigital lamellae beneath 4 th toe, respectively; a canthal stripe continuing posteriorly until the level of the occiput; dark barred supralabials; dorsal pattern with irregularly disposed, round or transversely elongate spots; tail showing relatively regularly spaced dark and light rings. No additional or distinct pattern appears under UV light ( Figure 6 ). Additional morphometric ratios for each of these two types are provided above in the description of the syntypes.

In order to add, refine or confirm diagnostic characters for Dixonius siamensis sensu stricto, one of us (MS) travelled in February 2024 to Dong Phaya Yen to photograph live specimens and encountered an adult male and an adult female in Hin Lap (see Figures 9–11 and 14 , the first published photographs of live, topotypical individuals), and one male and two females from Muak Lek ( Figures 12–13 ). We provide hereafter measurements and scale counts which were possible to take directly on these live individuals or on photographs we made of them. The male and the female from Hin Lap show respectively: SVL 48.3 mm and 49.4 mm, TailL 58.0 mm (tail original and complete) and 47.7 mm (of which the last 34.5 mm regenerated); HL 13.9 mm and 13.7 mm; 7/8 and 7/7 SL, with the 6 th /6 th and 5 th /5 th in midorbital position; 6/6 and 6/7 IL; 11 and 10 interorbital scales; 14 longitudinal rows of dorsal tubercles; 38 and 34 paravertebral tubercles, respectively, among which 25 between limb insertions; paravertebral rows of tubercles separated by three dorsal scales. The Hin Lap male shows two enlarged supranasals totally separated by a smaller one ( Figure 10 ); the female shows two enlarged supranasals in broad contact ( Figure 11 ). The female from Hin Lap laid two eggs a few days before being photographed; their size was 10.1 x 7.2 mm and 9.8 x 7.1 mm, respectively. The male and the two females (the first being pregnant) from Muak Lek show respectively: SVL 50.5 mm, 47.3 mm and 47.1 mm; TailL 51.4 mm (of which the last 22.2 mm regenerated), 55.4 mm and 55.3 mm (tail original and complete in both females); HL 14.8 mm, 14.4 mm and 13.7 mm; 11, 10 and 11 interorbital scales; 37, 33 and 33 paravertebral tubercles, among which 25, 24 and 24 between limb insertions; paravertebral rows of tubercles separated by three or four dorsal scales; all three show two enlarged supranasals in broad contact. Both males have seven precloacal pores in a continuous row ( Figure 10 ); the females have no pore. Their dorsal and supracaudal pattern is similar to the one of the two types from Hin Lap.

Combining the four known specimens from the type locality Hin Lap (including the lectotype and the paralectotype BMNH 1946.8.24.40–41) and the three specimens from the nearby locality Muak Lek, we propose the following updated diagnosis for Dixonius siamensis :

maximum known SVL 50.5 mm; HL/SVL ratio in adults 0.28–0.30; TailL/SVL (original and complete tails) in adult male 1.20 (n = 1), in adult females 1.17 (n = 2); seven or eight supralabials with the 5 th or the 6 th in midorbital position; six or seven infralabials; two or three supranasals; 10 or 11 interorbital scales; 14 longitudinal rows of dorsal tubercles; 33–38 paravertebral tubercles, respectively, among which 24 or 25 between limb insertions; paravertebral rows of tubercles separated by two to four dorsal scales; 20–25 longitudinal rows of ventrals across the abdomen; seven precloacal pores, in a continuous series, in males; no precloacal pores in females; no femoral pores in both sexes; nine or ten subdigital lamellae beneath 4 th finger; 14 or 15 subdigital lamellae beneath 4 th toe; a black canthal stripe continuing posteriorly until the level of the occiput; black barred supralabials; dorsal surface of head brown with irregular black spots; dorsum brown with round or transversely elongate black spots; tail brown with relatively regularly spaced black and light brown rings; venter white with a few light gray punctuations on the posterior part of each ventral scale.

Figures

FIGURE 1. Drawings of general dorsal views of Phyllodactylus siamensis originally published by Boulenger (1899) (A), of P. burmanicus by Annandale (1905b) (B) and of P. paviei by Mocquard (1904) (C).

FIGURE 2. Preserved juvenile male syntype (BMNH 97.3.31.1) of Phyllodactylus siamensis. A. General dorsal view. B. General ventral view. C. Dorsal view of head. D. Ventral view of head. E. Right profile of head. F. Left profile of head. Photos by J. Venderickx.

FIGURE 3. Preserved subadult female syntype (BMNH 97.3.31.2) of Phyllodactylus siamensis. A. General dorsal view. B. General ventral view. C. Dorsal view of head. D. Ventral view of head. E. Right profile of head. F. Left profile of head. Photos by J. Venderickx.

FIGURE 4. Preserved subadult female syntype (BMNH 1946.8.24.40) of Phyllodactylus siamensis, presently designated as lectotype. A. General dorsal view. B. General ventral view. C. Dorsal view of head. D. Ventral view of head. E. Right profile of head. F. Left profile of head. Photos by J. Venderickx.

FIGURE 5. Preserved subadult female syntype (BMNH 1946.8.24.41) of Phyllodactylus siamensis. A. General dorsal view. B. General ventral view. C. Dorsal view of head. D. Ventral view of head. E. Right profile of head. F. Left profile of head. Photos by J. Venderickx.

FIGURE 6. Preserved subadult female syntype (BMNH 1946.8.24.40) of Phyllodactylus siamensis under UV light. Photo. by J. Brecko.

FIGURE 7. Cranium of a subadult female Dixonius siamensis (BMNH 1946.8.24.40). A. Dorsal view. B. Lateral view. C. Ventral view. Scans and plate by S. Das and J. Brecko.

FIGURE 8. Map of Thailand showing the type localities of Dixonius siamensis, D. burmanicus and Phyllodactylus paviei, and of the other Dixonius species described from Thailand. Map by W. Sodob.

FIGURE 9. Live adult male (above) and female (below) Dixonius siamensis from Hin Lap, Saraburi Province, Thailand, in dorsal view. Note the partly regenerated tail of the female. Specimens not preserved. Photo. by M. Sumontha.

FIGURE 10. Live adult male Dixonius siamensis from Hin Lap, Saraburi Province, Thailand. Same specimen as on Figure 9. A. Right profile of the head. B. Head in frontal view. C. Ventral view of the head. D. Cloacal area. Photos by M. Sumontha.

FIGURE 11. Live adult female Dixonius siamensis from Hin Lap, Saraburi Province, Thailand. Same specimen as on Figure 9. A. Right profile of the head. B. Head in frontal view. C. Right flank. Photos by M. Sumontha.

FIGURE 12. Live adult male Dixonius siamensis from Muak Lek, Saraburi Province, Thailand. Photo. by M. Sumontha.

FIGURE 13. Live adult pregnant female Dixonius siamensis from Muak Lek, Saraburi Province, Thailand. Photo. by M. Sumontha.

FIGURE 14. Biotope of Dixonius siamensis at Hin Lap train station, Saraburi Province, Thailand. Photo. by M. Sumontha.