Xenochrophis tytleri ( Blyth, 1863 )

Published, First, 2012, 3473, Zootaxa 3473, pp. 1-60 : 30-32

Xenochrophis tytleri ( Blyth, 1863)

Figs. 25–26

Tropidonotus tytleri Blyth, 1863: 88 .—Type locality. “Andaman”, now Andaman Islands, India.— Holotype. ZSI 7402. Tropidonotus striolatus Theobald, 1868 .

Taxonomic comments. This species has variously been cited as X. piscator melanzostus (e.g. Smith 1943; Biswas & Sanyal 1977) or X. melanzostus ( Das 1999; Whitaker & Captain 2004; Vijayakumar & David 2006). Our data show that this taxon is different from populations living on Java, the genuine X. melanzostus , and deserves a specific status, for which the binomen Tropidonotus tytleri Blyth, 1863 is the oldest available name. It is not sympatric with any other species of this group but with Xenochrophis trianguligerus (Boie, 1827) which ist known from the Nicobar islands.

Identification. Body rather stout; tail length moderate. Maximum total length 920 mm for female BMNH 1940.3.7.5. Examined males only a little shorter than females (maximum length females / males 1.11); longest male 827 mm (FMNH 134925). Relative tail length sexually dimorphic: tail 30.8–32.4 % of total length in 3 males, 27.0–27.9 % in 3 females. Head distinct from neck; eye average, diameter nearly equal to distance between eye and lip. Dorsal scales in 19–19–17 rows, rather strongly keeled. Vertebral scales not enlarged. Ventral scales: 131–138 in males, 140–145 in females, unkeeled; subcaudals: 79–86 in 3 males, 76–77 in 3 females, unkeeled, paired. Anal plate divided. Head scalation includes: 1 loreal, 1 preocular, 3 (rarely 4) postoculars, 2 anterior temporals (in one case 1), 2 (less commonly 3) posterior temporals, 9 supralabials with 4 th and 5 th contacting eye, 10 (in one specimen 9) infralabials with anteriormost 5 first touching anterior chin shields. Body pattern variable, pale brown with either black stripes or blotches, or both. There are three common forms ( Whitaker & Captain 2004): (1) Cream or enamel white with a series of large, subrectangular, dark brown, black-edged blotches on either side of the vertebral line. Blotches entirely black, paired or alternate; sometimes an additional series of smaller, subrectangular spots on lower side of body. Underside cream, some belly scales have black outer margins. Tail is dotted. (2). Pale brown or buff, striped from neck to midbody. There may be two broad, black dorsolateral stripes separated by thin pale brown vertebral line; or “stripe” may consist of irregular fusion of thick black bars, separated by pale brown lines. Posterior part of body and tail have large, black (sometimes pale-centred) spots, those on sides of tail may join to form a line. Underside cream, some ventral scales have black outer edges. (3). Pale brown or buff, with 4–5 black or dark brown dorsolateral stripes along entire length of body and tail. Stripes narrower and less distinct on posterior part of body; lateral stripes often broken into a dotted line on each side of tail. Supralabials and underside cream. Juveniles have additional narrower, pinkish-brown stripes, only on scale edges. In morphs 2 and 3, the nuchal markings form a wide “V” ( Whitaker & Captain 2004; own observations).

Distribution. India. This species is endemic to Andaman Islands (South Andaman, North Andaman, Ross Island [Mount Blair], Baratang). However, it may be present on the Nicobar Islands. Whereas former authors considered this species to be endemic to the Andamans and not the Nicobars (de Rooij 1917; Smith 1943), Biswas (1984) reported two specimens from Great Nicobar as well as a specimen from South Andaman Island. We have no explanation Biswas (1984) being the sole author to have reported specimens of this species from the Nicobar Islands. At the present time, we regard as doubtful the occurrence of X. tytleri on Great Nicobar.

Material examined (11 specimens). India. Andaman Islands . FMNH 134922–5 , North Andaman Island ; FMNH 134926 , Port Blair , South Andaman Island ; BMNH 1940.3.4.9–10, Fischers Laboratory , Port Blair ; BMNH 1940.3.7.5–8, “ Andaman Islands ” .