Key to the species of Oligodon in the Sumatra region

In the region of Sumatra, nine species of Oligodon are now recognized: O. bitorquatus Boie, 1827, O. octolineatus (Schneider, 1801), O. petronellae Roux in De Rooij, 1917, O. praefrontalis Werner, 1913, O. pulcherrimus Werner, 1909, O. purpurascens (Schlegel, 1837), O. signatus (Günther, 1864), O. trilineatus (Duméril, Bibron & Duméril, 1854), and O. wagneri sp. nov. On the basis of Tillack & Günther (2010) and of our material, these species can be identified with the following key (adapted from David & Vogel 1996 and Tillack & Günther 2010).

1. Anal plate divided..................................................................................... 2

- Anal plate entire...................................................................................... 3

2. 15 DSR at midbody; no internasals, no loreals................................................... O. praefrontalis

- 17 DSR at midbody; internasals present (exceptionally absent); loreals present......................... O. pulcherrimus

3. 19 or 21 DSR at neck and at midbody......................................................... O. purpurascens

- No more than 17 DSR at neck and midbody................................................................. 4

4. Dorsal pattern distinctly striped with 3 to 8 stripes............................................................ 5

- Dorsal pattern blotched or with crossbars, only a blotched vertebral stripe possible.................................. 6

5. Dorsal pattern made of 6, 7 or 8 dark stripes; usually 6 supralabials................................... O. octolineatus

- Dorsal pattern made of 3 narrow dark stripes; 7 supralabials.......................................... O. trilineatus

6. 15 DSR around the neck and at midbody................................................................... 7

- 17 DSR around the neck, most usually 17 (exceptionally 15) DSR at midbody..................................... 9

7. Dorsal pattern made of a series of 20–25 elongate vertebral blotches, connected by a stripe anteriorly, turning to dark-edged rhombic blotches posteriorly.................................................................. O. petronellae

- Dorsal pattern made of widely separated vertebral blotches or crossbars.......................................... 8

8. Anterior vertebral blotches chevron-shaped on the sides of the neck; body not dotted with pale spots; 144–150 ventrals in males....................................................................................... O. signatus

- Anterior vertebral blotches short, not chevron shaped; body heavily dotted with pale spots; 156 ventrals… O. wagneri sp. nov.

9. Pattern made of large, broad vertebral blotches, the 2 or 3 anterior ones chevron-shaped on the sides of the neck; body not dot- ted with pale spots; 44–59 SC; loreal always present.................................................. O. signatus

- Pattern made of a mixture of small vertebral blotches, the anterior ones not chevron-shaped on the sides of the neck, and of numerous narrow crossbars; body heavily dotted with pale spots forming vertical bars; 29–44 SC; loreal present or absent............................................................................................ O. bitorquatus