Boiga dightoni ( Boulenger, 1894 )

Ganesh, S. R., Achyuthan, N. S., Chandramouli, S. R. & Vogel, Gernot, 2020, Taxonomic revision of the Boiga ceylonensis group (Serpentes: Colubridae): reexamination of type specimens, redefinition of nominate taxa and an updated key, Zootaxa 4779 (3), pp. 301-332 : 314-315

Boiga dightoni ( Boulenger, 1894)

( Tables 3–4; Fig.7 )

Dipsas dightoni Boulenger, 1894

Dipsadomorphus dightoni — Wall 1909

Boiga dightoni — Smith 1943; Inger et al. 1984

Specimens examined. Females (n=4). Holotype (by monotypy): India. Kerala. BMNH 1946.1 .1.32 Peermad, Travancore.

Other specimens: FMNH 217699 Ponmundi, Trivandrum; BNHS 1839 and BNHS 2813 from Peermade, Travancore State.

Taxonomic history. Boiga dightoni was described as Dipsas dightoni by Boulenger (1894), based on a specimen presented by H.S. Ferguson from “Pirmeed” in Travancore. Since then this species has not been collected despite several surveys, until Inger et al. (1984) reported it from the Ponmudi Hills further south. Though recognized by subsequent workers, almost nothing is known about this species ( Das 2002; Whitaker & Captain 2004; Wallach et al. 2014).

Etymology. Patronym, named in genitive singular case, after S.M. Dighton, the collector of the type specimen; he was a tea planter who worked in the Ghats ( Boulenger 1894).

Diagnosis (redefined herein). A species of Boiga endemic to the Southern Western Ghats of India, characterised by the following combination of characters: 21–23 midbody scale rows (vs. 19 in B. ceylonensis , B. thackerayi , B. beddomei , B. flaviviridis ); vertebral scales strongly enlarged (vs. mildly enlarged in B. barnesii ); venter with salmon pink spots in life (vs. yellowish in B. thackerayi , B. flaviviridis ; variable in B. andamanensis ; dorsum predominantly uniform brown (vs. green in B. flaviviridis ; variable in B. andamanensis ); ventrolateral pattern with salmon pinkish markings (vs. with alternate white and black blotches in B. barnesii , B. thackerayi ; without any pattern in B. andamanensis , B. flaviviridis ); temporal subequal to coastal body scale (vs. larger than coastal body scale in B. nuchalis ).

Redescription of the holotype. A medium-sized snake reaching 1,083 mm total length, snout-vent length: 858 mm, tail length: 225 mm; with fairly slender habitus, narrower neck, wider head; long tail (relative tail length 20.8%); 23–23–15 scale rows; rostral scarcely visible from above; preocular 1, larger than loreal; postoculars 2; loreal 1; supralabials 8, with 3 rd– 5 th touching eye; infralabials 13/14, with 1–5 touching chin shields; temporals 18/17; preventrals 2; ventrals 242, angulate laterally; cloacal 1; subcaudals 99 pairs. Dorsal colour brownish-grey, with traces of obscure transverse markings across; no markings on top of head; head with a few minute dark dots on labia, loreal and near parietals; labials, chin and venter ashy brown, finely spotted with darker shade along both sides.

Variation. Other specimens agreeing with holotype in most aspects and showing the following variation: snout to vent length 352–908 mm; tail length 194 (incomplete in other specimens); anterior scale rows 21–21–15(16) scale rows; temporals 17–19; infralabials 11–12; ventrals 235–248; subcaudals 102–112 pairs (incomplete in the rest); number of cross bars 0–66 on body.

Distribution and natural history. This species has rarely, if ever, been collected and properly identified. Apart from the original description the only known subsequent collection and description of this species is from Ponmudi Hills ( Inger et al. 1984) (Fig. 13). Animals were seen actively foraging at night on plants and bushes and one was recorded having eaten a Calotes . There have been a few reports of this species from the Anaimalais, but these lack morphological or taxonomical data (Vijayakumar et al. 2001) to permit unambiguous verification.

Figures

FIGURE 7. Holotype of Boiga dightoni BMNH 1946.1.1.32 from Peermad, Travancore. (A) entire—dorsal, (B) entire—ventral, (C) ventral pattern close-up, (D) head—ventral, (E) head—lateral, (F) head—dorsal views.