Trimeresurus popeiorum Smith, 1937

Idiiatullina, Sabira S., Nguyen, Tan Van, Pawangkhanant, Parinya, Suwannapoom, Chatmongkon, Chanhome, Lawan, Mirza, Zeeshan A., David, Patrick, Vogel, Gernot & Poyarkov, Nikolay A., 2024, An integrative taxonomic revision of the Trimeresurus popeiorum group of pitvipers (Reptilia: Serpentes: Viperidae) with descriptions of two new species from the Indo-Burma Biodiversity Hotspot, Vertebrate Zoology 74, pp. 303-342 : 303

Trimeresurus popeiorum Smith, 1937

Figs 4 , 5 , 6 , 7A-E; Tables S3, S4

Trimesurus Synonymy.

Trimesurus [sic] Trimeresurus elegans Gray, 1853: 391. - Holotype: NHMUK 1946.1.19.20, a subadult female from “Sikkim”, India, donated by Joseph D. Hooker. A nomen dubium based on its original description, but here considered both a senior subjective synonym of T. popeiorum Smith, 1937 and a nomen oblitum after examination of the holotype (see below.)

Trimeresurus popeiorum Smith, 1937: 730. - Lectotype: NHMUK 1872.4.17.137A, an adult male from "Khasi Hills" [Meghalaya State, India; ca. 25.60°N, 91.65°E], donated by Thomas C. Jerdon; designated by Taylor and Elbel (1958: 1174).

Trimeresurus yingjiangensis Chen et al., 2019: 9. - Holotype: CIB DL2017070101, an adult male from Heihe Village, Kachang Town, Yingjiang County, Yunnan Province, China (24.782°N, 97.878°E; elevation 1112 m). According to Mirza et al. (2023), a subjective junior synonym of T. popeiorum Smith, 1937.

Etymology.

The species name is a patronym, in genitive plural, created in honour of Clifford H. Pope (1899-1974) and his wife Sarah H. Pope (1901-1995); see below for a discussion of the correct spelling. We recommend the following common names for this species: "Pō pǔ zhú yè qīng” (坡普竹叶青) (in Chinese), “Pope’s green pitviper" (in English), "Ngu Khiew Hang Mai Thong Khiew Assam" (งูเขียวหางไหม้ท้องเขียวอัสสัม) (in Thai), “Trimérésure vert des Pope" (in French), "Popes Bambusotter" (in German), and "Bambukovaya kufiya Poupov" (in Russian).

Systematics and nomenclature.

Before Smith (1937), the species Trimeresurus popeiorum s. str. was widely mentioned in the literature under the combinations T. gramineus or Lachesis gramineus (non Coluber gramineus Shaw, 1802, a distinct, valid species from Peninsular India; see, for example, Pope and Pope 1933: 9). As explained above, Regenass and Kramer (1981) divided this species into three subspecies, retaining the nominative one, T. p. popeiorum , for populations of the Asian mainland. Currently, following Vogel et al. (2004), Wostl et al. (2016), and the present work, Trimeresurus popeiorum s. str. is monotypic.

We take this opportunity to mention the taxon Coluber viridicaeruleus La Cépède, 1789, which Wallach et al. (2014: 575) placed in the synonymy of T. popeiorum . La Cepède (1789: 122 and 306) erected this taxon as a replacement name for Coluber cyaneus Linnaeus, 1758. Based on its scalation characters, such as a head covered with large plates and 110 subcaudals, this taxon is obviously not a pitviper, but may represent a nearctic or neotropical colubrid species, as it was stated to have originated from "Les Amériques”. Therefore, we formally remove Coluber viridicaeruleus from the synonymy of Trimeresurus popeiorum , while the taxonomic identity of Coluber viridicaeruleus La Cépède, 1789 remains unclear.

The species nomen Trimeresurus popeiorum .

A nomenclatural problem arose when Smith (1943: 518) stated in a footnote that the spelling Trimeresurus popeiorum in his earlier paper was a clerical error and, on the same page, corrected it into Popeia popeorum . As a result, the spelling Popeia popeorum has been widely used in the literature, for example by Haas (1950), Taylor and Elbel (1958), Klemmer (1963), Werler and Keegan (1963), Taylor (1965), Leviton (1968), Harding and Welch (1980), and Regenass and Kramer (1981). David and Vogel (1996: 163) were the first authors to discuss the spelling problem and pointed out that, based on Art. 32 (c) (ii) of the Code (ICZN 1985), the original spelling had to be retained even though Smith (1943) tried to correct the original spelling. According to Art. 32.5.1 of the Code (ICZN 1999), the initial spelling was an incorrect transliteration or Latinization and does not allow for "correction of an incorrect original spelling". According to the Art. 33.4, the use of a termination - orum in a subsequent spelling of a species-group name that is a genitive based upon a personal name in which the correct original spelling terminates with - iorum, is an incorrect subsequent spelling, even if the change is deliberate. The original spelling, Trimeresurus popeiorum , must therefore be conserved. McDiarmid et al. (1999) and Orlov et al. (2002a, 2002b) challenged this interpretation and argued that the spelling Popeia popeorum was the correct one. However, these authors have not been followed.

The status of Trimesurus Trimeresurus elegans Gray, 1853.

This taxon has long been forgotten or considered a synonym of Trimeresurus gramineus . For example, Uetz et al. (2024) currently list this taxon in the synonymy of Craspedocephalus gramineus (Shaw, 1802) based on Stejneger (1907, 1927). These authors apparently overlooked the fact that Stejeneger confused several green pitvipers under the combination Trimeresurus gramineus . The type locality of Trimesurus elegans makes clear that it cannot be a synonym of T. gramineus , as currently defined, a species endemic to southeastern Peninsular India (see Mallik et al. 2021).

The brief original description of Trimesurus elegans does not allow a formal identification of the species. However, its holotype (NHMUK 1946.1.19.20), which we examined, is indeed a subadult female referable to Trimeresurus popeiorum s. str. as defined here. On this basis, Trimesurus elegans Gray, 1853 should be considered a senior subjective synonym of T. popeiorum . Such a conclusion would be problematic in terms of nomenclatural stability, as the species name Trimeresurus elegans has seemingly never been used as valid after its establishment by Gray (1853), while the Trimeresurus popeiorum has been used as valid in dozens of publications since 1937 in the genera Trimeresurus or Popeia .

For this reason, in order to protect the binomen Trimeresurus popeiorum Smith, 1937, we here make use of Art. 23.9 of the Code to reverse precedence (ICZN 1999). In order to apply this Article, two conditions must be fulfilled: Art. 23.9.1.1 states that the senior synonym must not have been used as a valid nomen after 1899; and Article 23.9.1.2 states that the junior synonym must have been used for a particular taxon, as its presumed valid nomen, "in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years" (ICZN 1999).

In the present case, the first condition is met because to the best of our knowledge, the specific epithet Trimeresurus elegans , as proposed by Gray (1853), has never been used as valid for any pitviper after 1853. It should be noted that Craspedocephalus elegans Gray, 1849, now Protobothrops elegans , a valid species inhabiting Japan, was placed in the genus Trimeresurus by Stejneger (1907). In this case, Trimesurus elegans Gray, 1853 also becomes a secondary homonym of Craspedocephalus elegans Gray, 1849 in the genus Trimeresurus .

In order to fulfil the second condition, the epithet Trimeresurus popeiorum should have been used as valid in the genus Trimeresurus , even if under the erroneous spelling Popeia popeorum , by at least 25 authors since 1972. We provide below a list of 25 works published from 1972 onwards in which the epithet Trimeresurus popeiorum (or Popeia popeorum ) has been used as valid: Harding and Welch (1980: 74); Regenass and Kramer (1981: 186; as T. p. popeorum ); Tweedie (1983: 139, 158); Toriba in Golay et al. (1993: 103; as T. popeorum ); David and Ineich (1999: 288); Leviton et al. (2003: 446); Gumprecht et al. (2004: 37, 256; as Trimeresurus popeiorum popeiorum ); Malhotra and Thorpe (2004: 97); Sanders et al. (2004: 183); Vogel et al. (2004: 19); Castoe and Parkinson (2006: 105); Sanders et al. (2006: 361); Vogel (2006: 107); Leviton et al. (2008: 80); Das (2010: 307); Malhotra et al. (2010: 175); Teynié and David (2010: 268); Wallach et al. (2014: 575); Visser (2015: 387); Guo et al. (2015: 267); Chan-ard et al. (2015: 345); Das et al. (2016: 275-276); Wostl et al. (2016: 637); Chen et al. (2019: 20); Nguyen et al. (2020: 239); Liu et al. (2022: 86); and Rathee et al. (2022: 3)

The foregoing sources allow to conclude that Art. 23.9 can be applied to Trimesurus elegans and precedence can be reversed. We therefore declare Trimesurus elegans Gray, 1853 to be a subjective senior synonym of Trimeresurus popeiorum Smith, 1937 and a nomen oblitum. In so doing, Trimeresurus popeiorum Smith, 1937, and also becomes a nomen protectum and the binomen can be used for green pitvipers from Southeast Asia.

Referred specimens

(n = 15). Nepal. NHMUK 1874.4.29.881 (adult female), “Himalayas”. - India. Meghalaya State: NHMUK 1872.4.17.137A (lectotype of Trimeresurus popeiorum , adult male), from Khasi Hillis; Sikkim State: NHMUK 1946.1.19.20 (holotype of Trimesurus elegans Gray, 1853, subadult female); West Bengal State: NHMUK 1872.4.17.377 (paralectotype of Trimeresurus popeiorum , adult male), NHMUK 1872.4.17.378 and NHMUK 1891.9.11.28-29 (three adult females) from Darjeeling District; Mizoram State: MZMU ZOO-GV 001 (adult male); Arunachal Pradesh: NCBS NRC-AA-4548 (adult male) from Kamlang WS., NCBS NRC-AA-4549 (adult male) and NCBS NRC-AA-4534 (adult female) from Eaglenest WS. China. Yunnan Province: CIB DL201070102 and CIB DL201070103 (paratypes of T. yingjiangensis , two adult males) from Heihe Village, Kachang Town, Yingjiang Country. - Myanmar. Kachin State: ZMMU NAP-09445 (adult male) from Inn Gyin Taung Mt., Indawgyi NR., Mohnyin Township; Sagaing Region: ZMMU NAP-09522 (subadult male) from Zalon Taung Mt., Ban Mau District.

Diagnosis.

Trimeresurus popeiorum differs from all other members of the subgenus Trimesurus Popeia by the combination of the following morphological characters: (1) dorsal surfaces in various shades of green, bluish-green or even turquoise blue; (2) in males, a vivid, wide bicolored ventrolateral stripe, bright and deep red below, white above; in females, stripe thin, white or yellow; (3) males with a conspicuous, bicolored postocular streak, thin and white ventrally, wide and bright red dorsally; streak absent in females; (4) eyes red to deep red in both males and females; (5) 21 dorsal scale rows at midbody, more or less strongly keeled in males, weakly keeled in females, scales of the first dorsal scale row always smooth; (6) first supralabial entirely separated from nasal scale by a distinct suture; (7) supraoculars much narrower than internasals; (8) internasals never in contact, separated by one or two scales; (9) 159-173 ventrals; 55-76 subcaudals, all paired; (10) hemipenes long and forked, reaching at least to the 25th subcaudal, without spines; (11) 11-13 cephalic scales between the supraoculars in males, 10-12 in females; (12) relative tail length 0.18-0.21 in males, 0.14-0.19 in females.

Description of the holotype

(NHMUK 1946.1.19.20) of Trimesurus elegans Gray, 1853 (Fig. 4 ). A subadult female in a relatively good state of preservation after more than 150 years in preservative.

Morphology.

Body cylindrical, long, and laterally compressed (SVL 322 mm, TaL 62 mm, TL 384 mm, TaL/TL 0.161). Head triangular in dorsal view, elongate, clearly distinct from the neck (HL 18.4 mm, HL/SVL 0.06), snout elongate, flattened, and rounded when seen from above, rather rectangular when seen from lateral side, with a very distinct and sharp canthus rostralis; loreal pit present, triangular in shape. Eye average (ED 3.1 mm, SnL 5.2 mm, ED/SnL 0.58); pupil vertical, elliptic.

Body scalation.

Dorsal scales in 25-21-15 rows; dorsal scales all moderately keeled, except the first row, the scales of which are smooth; 167 ventrals (plus single preventral); cloacal plate single; 61 subcaudals, all divided.

Head scalation.

Rostral slightly visible from above, triangular; one large pair of enlarged internasals, separated by a one small scale; nostril completely included in nasal scale; nasal scale completely separated from the first supralabial; 1/2 small scales between nasal and second supralabial; scales on the upper snout surface and in the interorbital region smooth, irregular, barely imbricate; temporal and occipital scales strongly keeled; two elongate upper preoculars above the loreal pit; lower preocular forming the lower margin of the loreal pit; one supraocular on each side, large, broader than the internasals; 13 irregular cephalic scales between the supraoculars; one long, thin, crescent-like subocular scale (Fig. 4C ); 9/9 supralabials, third largest and separated from the subocular by one scale on each side, fourth and fifth supralabials separated from subocular by one scale on each side; 2/2 postoculars (Fig. 4E, F ); 13/12 infralabials, those of the first pair in contact with each other behind the mental, the first three pairs in contact with the single pair of chin shields. Five pairs of gulars aligned between the chin shields and the first preventral (Fig. 4D ).

Coloration and pattern.

Body green, beneath paler, whitish; scales of the back moderate, smooth, not keeled, the lateral series rather broader, the first lateral series green, with a small white spot on the hind part of the upper edge forming an interrupted lateral line.

Description of the lectotype

(NHMUK 1872.4.17.137A) of Trimeresurus popeiorum Smith, 1937 (Fig. 5 ). An adult male in a relatively good state of preservation after more than 150 years in preservative.

Morphology.

Body cylindrical, long, and laterally compressed (SVL 758 mm, TaL 167 mm, TL 925 mm, TaL/TL 0.181). Head triangular in dorsal view, elongate, clearly distinct from the neck, snout elongate, flattened, and rounded when seen from above (Fig. 5C ), rather rectangular when seen from lateral side, with a very distinct and sharp canthus rostralis; loreal pit present, triangular in shape (Fig. 5E ). Eye average; pupil vertically elliptic (Fig. 5E ).

Body scalation.

Dorsal scales in 23-21-15 rows; dorsal scales all moderately keeled, except the first row, the scales of which are smooth; 165 ventrals (plus single preventral); cloacal plate single; 70 subcaudals, all divided.

Head scalation.

Rostral slightly visible from above, triangular; one large pair of enlarged internasals, separated by one small scale (Fig. 5C ); nostril completely included in an entire nasal scale; nasal scale completely separated from the first supralabial; 1/2 small scales between nasal and the second supralabial; scales on the upper snout surface and in the interorbital region smooth, irregular, barely imbricate; temporal and occipital scales strongly keeled; two elongate upper preoculars above the loreal pit; lower preocular forming the lower margin of the loreal pit (Fig. 5E ); one supraocular on each side, large, broader than the internasals; ten irregular cephalic scales on a line between the supraoculars (Fig. 5C ); one long, thin, crescent-like subocular scale; 9/10 supralabials, third largest and separated from the subocular by one scale on each side; fourth and fifth supralabials separated from subocular by one or two scales on each side; 2/2 postoculars (Fig. 5E ); 12/12 infralabials, those of the first pair in contact with each other behind the mental, the first three pairs in contact with the single pair of chin shields. Five pairs of gulars aligned between the chin shields and the first preventral (Fig. 5D ).

Coloration and pattern.

Color uniform green above; paler green below. First row of scales on each side brown with yellow tip, second row yellow below the median keel. The narrow bicolor lateral stripe thus formed ending just behind head anteriorly and at vent posteriorly, incompletely developed on tail. Tip of tail pale reddish. Head without pattern or postocular stripe (Fig. 5A, B, F ).

Redescription of the paratype

(CIB DL201070102) of Trimeresurus yingjiangensis Chen et al. (Fig. 6 ). Below we provide a brief redescription of the paratype of T. yingjiangensis (CIB DL201070102), examined by one of us (GV), in order to provide a detailed morphological data justifying the synonymy of this taxon with T. popeiorum , as proposed based on molecular data by Mirza et al. (2023).

An adult male in a very good state of preservation.

Morphology.

Body cylindrical, long, and laterally compressed; SVL 594 mm, TaL 148 mm, TL 742 mm, TaL/TL 0.199. Head triangular in dorsal view, elongate, clearly distinct from the neck (HL 29.8 mm, HW 18.1 mm, HL/SVL 0.05); snout elongate, flattened, and rounded when seen from above, rather rectangular when seen from lateral side, with a very distinct and sharp canthus rostralis; loreal pit present, triangular in shape. Eye average (ED 12.9 mm); pupil vertically elliptic.

Body scalation.

Dorsal scales in 21-21-15 rows; dorsal scales all moderately keeled, except the first row the scales of which are smooth; 164 ventrals (plus single preventral); cloacal plate single; 76 subcaudals, all divided. Hemipenes long, reaching to 23-24 SC, forked opposite fifth to sixth subcaudal scale, no spines (Fig. 6H ).

Head scalation.

Rostral slightly visible from above, triangular, broader than high; one enlarged internasal on each side, internasals separated by one small scale behind the top of rostral (Fig. 6E ); nostril completely included in the entire nasal scale, pentagonal, not divided, elongate, as long as high; nasal scale completely separated from the first supralabial (Fig. 6C, D ); one internasal on each side, pentagonal, curved, wide, transversely elongate, separated by one small scale; two small scales between the nasal and the second supralabial; scales on the upper snout surface and in the interorbital region smooth, irregular, barely imbricate; 3/3 canthal scales, slightly larger than adjacent snout scales, bordering the canthus rostralis between the internasal and corresponding supraocular; temporal and occipital scales obtusely keeled; one relatively large triangular loreal between the upper preocular and the nasal; two elongate upper preoculars above loreal pit, lower one bordering the upper margin of loreal pit, upper one visible from above, both elongate and in contact with loreal; lower preocular forming lower margin of loreal pit; one supraocular on each side, long, much longer than wide, cephalic scales relatively small, irregular or slightly rounded, juxtaposed, flat and smooth; 11 irregular cephalic scales between the supraoculars; one long, thin, crescent-like subocular scale; occipital scales rhombohedral, distinctly but obtusely keeled; 2/2 small postoculars; 10/11 supralabials, first supralabial short, entirely separated from the nasal by a distinct suture; second supralabial tall, forming the anterior border of loreal pit; third supralabial largest and in contact with the subocular on each side; fourth and fifth supralabials much lower than the third one, separated from the subocular by one scale on each side (Fig. 6C, D ); 12/12 infralabials, those of the first pair in contact with each other behind the mental, the first three pairs in contact with the single pair of chin shields. Five pairs of gulars aligned between the chin shields and the first preventral (Fig. 6F ).

Coloration in preservative

(Fig. 6 and Fig. 1D in Chen et al. 2019). The body is uniform deep bluish-green (bright grass-green in life), without darker areas or crossbands; a conspicuous, bicolored ventrolateral stripe extends from the beginning of the neck to the vent, pinkish-brown (bright deep red in life) ventrally, this color covering nearly the whole surface of scales of the first dorsal scale row except their upper posterior corner that is cream (white in life), same as the lower half of scales of the second row. The tail is bluish-green like the dorsum; the ventrolateral stripe extends up to the first third of the tail; near its end, the dorsal surface of the tail is irregularly mottled with pinkish-orange (rusty-red in life).

The dorsal surface of the head and temporal region are bluish-green like the body; the side of the head below the eye, i.e., the sides of the snout, nasal scale, anterior supralabials and lower temporals, is distinctly paler than the dorsal surface of the head, namely pale bluish-green (pale green in life); thin and short bicoloured postocular strip (red and white), runs from the posterior part of the subocular to the angle of the jaw. The chin and throat are pale sea-green (yellow green in life), uniform but with few faint darker areas on infralabials sometimes. The eye is grey but it was deep fire-red in life. The venter is uniform pale sea-green (yellow green in life); dorsal tail heavily mottled with dark red blotches, the dark red blotches contiguous posteriorly; the ventral surface of the tail is as the venter anteriorly, tip of tail red on dorsal while dark salmon on ventral.

Variation.

This description is based on the ten specimens examined by us, supplemented by data from 15 specimens published by Das et al. (2016), Chen et al. (2019), Liu et al. (2022), and Mirza et al. (2023) (see Table S3).

Morphology.

The maximum known total length is 925 mm in males (NHMUK 1872.4.17.137), 848 mm in females (NHMUK 1891.9.11.28). The body is robust but relatively slender in males, thicker in large females, laterally compressed; head triangular, elongate, wide posteriorly, flattened in males, moderately thick in females, clearly distinct from the neck; snout elongate, distinctly flattened, rounded seen from above, angular and obliquely truncated in profile view, with a distinct canthus rostralis; nostril piercing in the middle of nasal scale; eye average, amounting for 0.9-1.2 times in males and 0.7-1.1 times in females the distance between the lower margin of eye and upper lip border; tail average to long, progressively tapering and distinctly prehensile; ratio TaL/TL 0.140-0.219, with a weak sexual dimorphism (males: 0.179-0.219; females: 0.140-0.191).

Body scalation.

Dorsal scales rhombohedral, more or less strongly keeled in males, weakly keeled in females, in 21-21-15 (73%) or 23-21-15 (23%) rows (exceptionally in 25-21-15 rows; 4%); scales of the first dorsal scale row smooth and not enlarged; 159-173 ventrals (plus one or two preventrals), rounded; 57-76 paired subcaudal scales with overlapping sexual dimorphism (64-76 in males, 57-70 in females); cloacal plate entire.

Head scalation.

Rostral much broader than high, triangular, well visible from above; nasal subrectangular, entire, elongate, longer than high; one internasal on each side, pentagonal, curved, wide, transversely elongate, separated by one (90%) or rarely two (10%) small scales; four or five canthal scales, slightly larger than adjacent snout scales, bordering the canthus rostralis between the internasal and corresponding supraocular; one relatively large triangular loreal between the upper preocular and nasal; two upper preoculars above loreal pit, lower one bordering the upper margin of loreal pit, upper one visible from above, both elongate and in contact with loreal; lower preocular forming lower margin of loreal pit; one supraocular on each side, entire, elongate and rather narrow, about 2.7-3.3 times longer than wide, about 0.5-0.9 times as wide as the internasals, indented on their inner margins by the upper head scales; cephalic scales relatively small, irregular or slightly rounded, juxtaposed, flat and smooth; 10-13 cephalic scales on a line between supraoculars; occipital scales rhombohedral, moderately or more frequently distinctly keeled in males, smooth or weakly keeled in females; temporals rhombohedral, distinctly keeled or less frequently smooth in males, always smooth in females; on each side, one thin, elongate, subocular scale, crescent-shaped; 2-3 small postoculars; 9-13 (usually 10-12) supralabials; first supralabial short, entirely separated from the nasal by a distinct suture; second supralabial tall, always forming the anterior border of loreal pit, separated from the nasal by one or two small scales; third supralabial the longest and highest, rather tall, usually separated from the subocular by one scale on each side (77.8%), rarely in contact (22.2%); fourth supralabial as long as high, lower than third supralabial, separated from subocular by one scale; fifth supralabial smaller than the fourth one, separated from the subocular by one or two scales of similar size; 10-15 (generally 12 or 13) infralabials, those of the first pair in contact with each other, the first three pairs in contact with the chin shields.

Coloration and pattern.

In life, the body is uniform bright green, grass-green, deep green, bluish-green or even turquoise blue ( Wall 1909). In preservative, the general background color remains green or turns to bluish-green, reddish-brown, brown or even black. Generally, numerous faint, dark transversal bands due to the dark brown or dark grey skin between the dorsal scales; in males, a broad and conspicuous, bicolored ventrolateral stripe, bright red, deep red or rusty brown on its lower part covering the lower half of the scales of the first dorsal scale row, white or whitish-yellow above on the upper posterior half of scales of the first row and on the lower part of scales of the second row, extends from the angle of the mouth to the base of the tail; in females, the ventrolateral stripe is thinner, white or creamish-yellow anteriorly, white or cream posteriorly, conspicuous and extends from the neck to the base of the tail on the first dorsal scale row. The tail is of the same green color than the dorsum, irregularly mottled with reddish-brown or rusty brown, without a clear demarcation between the red and green colors, entirely reddish-brown posteriorly; the ventrolateral stripe extends up to the first third to half-length of the tail.

The dorsal surface of the head and temporal region are uniform green or bluish-green like the body; the side of the head below the eye, i.e., the lower sides of the snout, nasal scale, and anterior supralabials and lower temporals, is distinctly paler than the dorsal surface of the head, generally pale green, yellowish-green or pale bluish-green; in males, a vivid, broad, bicolored postocular streak, the lower part narrow and white, the upper part broad and bright red, rusty-red or brownish-red, present at any age, extends from the postoculars obliquely towards the angle of the mouth then to the lower side of the neck where it connects to the ventrolateral stripe; in females, the postocular streak is usually absent, or present as a white and thin line. The chin and throat are generally pale yellowish-green, with infralabials sometimes bright yellow or marked with green. The eye is bright red, fire-red or deep red in life in adult specimens of both sexes (Fig. 7A-E ).

The venter is uniform yellowish-green or pale green; tips of ventrals red as the lower part of the ventrolateral stripe. The ventral surface of the tail is as the venter anteriorly, becoming rusty-red on its posterior half to third.

Hemipenis.

The organ is long and thin, deeply forked, extending to the 25th or 26th subcaudal scale in situ, forked opposite at the level of the sixth to eighth subcaudal scales; the base of the organ, up to the point of bifurcation, is entirely smooth with longitudinal folds, except for the sulcus spermaticus; from the point of bifurcation up to the tip of the organ, each fork is finely calyculate. The sulcus is prominent; it divides near the base of the organ and ends near the tip of the fork (based on Smith 1937; Chen et al. 2019; Mirza et al. 2023; our data).

Dentition.

Maxilla with one functional and 5-6 replacement fangs; palatine with four teeth, pterygoid with eight teeth, 10-12 dentary teeth (based on Mirza et al. 2023; and our data).

Distribution

(Fig. 1 ). Based on our definition of T. popeiorum , we establish its range as follows: India (northeasternern part of the country, in the states of Sikkim, West Bengal, Meghalaya, Assam, Arunachal Pradesh, and Mizoram); Bhutan (south); Nepal (east); Bangladesh (southeast: Chittagong Province), China (western Yunnan Province: Dehong Dai and Jingpo Autonomous Prefecture), and Myanmar (northern and southwestern parts of the country, in Kachin and Chin States, and Sagaing Region). The southernmost record for this species is from Ngape Township, Rakhine Yoma, Rakhine State, Myanmar (our data). The occurrence of this species in the states of Nagaland and Manipur, India, is expected.

Natural history notes.

Trimeresurus popeiorum inhabits hilly and montane regions covered with humid tropical and subtropical submontane and montane evergreen forests and semi-evergreen forests. Chen et al. (2019) stated that at the type locality of T. yingjiangensis in Yunnan Province this species prefers to inhabit sites near streams at an elevation of about 1000 m, and can be found perched on branches waiting for prey in ambush. In contrast, in Myanmar, Liu et al. (2022) found individuals perched on small or big trees at elevations of only 155-176 m, and no rivers or streams were nearby. In the Dampa Tiger Reserve, Mizoram State, India, Malsawmdawngliana et al. (2022) noted that this species was quite common in their study area. These authors encountered more than ten individuals among roadside vegetation and along forest trails, and a female perched in ambush position on a small guava tree near the guest house. In Mizoram State, one of the authors of the present paper (GV) found a large female, on a tree trunk at about 1.7 m above the ground, in a secondary forest at an elevation of about 800 m. Moreover, T. popeiorum appears to be common across lower-elevation forests of Arunachal Pradesh State. Most individuals were observed perched on vegetation along roads, but we observed a higher number of individuals along streams. The species is found in sympatry with T. salazar Mirza, Bhosale, Phansalkar, Sawant, Gowande & Patel in Arunachal Pradesh and Assam states and T. erythrurus (Cantor) in Meghalaya and Mizoram states.

Figures

Figure 1. Distribution of the species and subspecies of the subgenus Trimesurus Popeia. Base map created using simplemappr. net. A dot in the center of a colored circle denotes type locality. Colors of circles and locality numbers correspond to those in Figures 2 - 3 and Appendix II; for locality information see Appendix VIII. Type localities of the included taxa are shown in colored clouds; taxon names that are not valid nomina of recognized taxa are shown in quotes.

Figure 4. Trimeresurus popeiorum in preservative - specimen NHMUK 1946.1.19.20 (holotype of Trimesurus elegans, subadult female) A General dorsal view; B General ventral view; C Dorsal view of the head; D Ventral view of the head; E Lateral view of the head, right side; F Lateral view of the head, left side. Photos by P. D. Campbell.

Figure 5. Trimeresurus popeiorum in preservative - specimen NHMUK 1872.4.17.137 (Lectotype, adult male) A General dorsal view; B General ventral view; C Dorsal view of the head; D Ventral view of the head; E Lateral view of the head, right side; F Latero-ventral view of the tail. Photos by P. D. Campbell.

Figure 6. Trimeresurus popeiorum in preservative - specimen CIB DL 201070102 (Paratype of T. yingjiangensis, adult male) A General dorsal view; B General ventral view; C Lateral view of the head, right side; D Lateral view of the head, left side; E Dorsal view of the head; F Ventral view of the head; G Latero-ventral aspect of the body; H Latero-ventral aspect of the tail. Photos by G. Vogel.

Figure 7. Trimeresurus popeiorum, T. nebularis, and T. phuketensis in life. - Trimeresurus popeiorum: A Buxa Tiger Reserve, West Bengal, India (adult male); B Karimganj, Assam, India (adult female); C Aizawl, Mizoram, India (adult female); D Inn Gyin Taung Mt., Kachin, Myanmar (male); E Yingjiang, Yunnan, China (adult male); T. nebularis: F, G Cameron Highlands, Pahang, Malaysia (adult male and adult female, respectively); T. phuketensis: H Phuket Is., Phuket, Thailand (adult male); I Sri Phang Nga NP, Phang Nga, Thailand (adult male). Photos by: P. Ray (A), R. Gassah (B), G. Vogel (C, E-G), N. A. Poyarkov (D), R. Grassby-Lewis (H), and S. Plongnui (I)