Xenochrophis trianguligerus (H. Boie in F. Boie, 1827)— Native; Indeterminate.

Tropidonotus Trianguligerus H. Boie in F. Boie, 1827: 535. Lectotype: RMNH.RENA.1102, designated by R.F. Inger in 1959, according to R. de Ruiter pers. comm. in Koch (2012: 284). Type locality: “ Java ”, Indonesia.

Triangle Keelback

(Figures 20G & 20H)

Singapore records.

Tropidonotus trianguligerus — Ģnther, 1858b: 70.— Dennys, 1880a:3.— Blanford, 1881: 215.— Boulenger, 1893: 224.— Flower, 1896: 879.— Hanitsch, 1898: 19.— Flower, 1899: 659.—Ridley, 1899: 207.— Hanitsch, 1912b: 16.— de Rooij, 1917: 84.

Natrix trianguligera —Sworder, 1923: 61.— de Haas, 1949: 84 (Bukit Timah [BTNR]; Holland Road).— de Haas, 1950: 544.— Grandison, 1972: 84.—K.P. Lim & F.L.K. Lim, 1988d: 87.—K.K.P. Lim & L.M. Chou, 1990: 54.—L.M. Chou et al., 1994: 105.

Xenochrophis trianguligerus —K.K.P. Lim & F.L.K. Lim, 1992: 80, 147.—R. Subaraj et al., 1995: 16 (Upper Peirce Service Road).— David & Vogel, 1996: 134.—R.C.H. Teo & Rajathurai, 1997: 384 (Lower Peirce West Forest [LPF]).—Chan-ard et al., 1999: 36.— Iskandar & Colijn, 2001: 110.—K.P. Lim & F.L.K. Lim, 2002: 147.— de Lang & Vogel, 2005: 178.—N. Baker & K.P. Lim, 2008: 161.—K.K.P. Lim et al., 2008: 166, 265.— Das, 2010: 343.—N. Baker & K.P. Lim, 2012: 161.— Das, 2012a: 129.—Wallach et al., 2014: 799.—Chan-ard et al., 2015: 223.— de Lang, 2017: 216.— Das, 2018: 100.— Charlton, 2020: 218.

Remarks. A common snake elsewhere throughout its range (Tweedie 1983; Stuebing et al. 2014; de Lang 2017), X. trianguligerus is exceedingly rare in Singapore (Baker & Lim 2012). Xenochrophis trianguligerus was first reported in Singapore by Ģnther (1858b) who examined a specimen from Hardwicke’s collection. Blanford (1881) included X. trianguligerus in his list from Dennys (Dennys 1880a), and Boulenger (1893) reported three specimens from Hardwicke and one by Dennys deposited at NHMUK. Subsequent to de Haas (1949) report of two specimens stored at the Raffles Museum that were collected in 1894 at BTNR and 1909 at Holland Road, X. trianguligerus was not recorded again until 86 years later (Table 2) on 20 May 1995 when a roadkill was found along UPRR (Lim et al. 1995) that Teo & Rajathurai (1997) reported as a moult of X. trianguligerus . Three specimens of H. petersii were misidentified as X. trianguligerus (see account of H. petersii above).

Occurrence. Known only from a few specimens predating 1909 and one from 1995. Rare.

Singapore conservation status. Critically Endangered.

Conservation priority. Highest.

IUCN conservation status. Least Concern [2021].

LKCNHM & NHMUK Museum specimens. Singapore (no locality): BMNH 1880.9.10.38 (no date), BMNH 1963.962 – 963 (no date); Bukit Timah Nature Reserve: ZRC.2.2493 (26-May-1894); Holland Road: ZRC.2.2494 (31-May-1909) .

Additional Singapore museum specimens. Singapore (no locality): BPBM; Bukit Timah Nature Reserve: BPBM.

Singapore localities. Bukit Timah Nature Reserve—Holland Road*—Lower Peirce Forest—Upper Peirce Reservoir Road.