Opisthotropis

David, Patrick, Pham, Cuong The, Nguyen, Truong Quang & Ziegler, Thomas, 2011, A new species of the genus Opisthotropis Günther, 1872 (Squamata: Natricidae) from the highlands of Kon Tum Province, Vietnam, Zootaxa 2758, pp. 43-56 : 52-53

Key to the species of Opisthotropis and related genera

On the basis of recent taxonomic modifications and of new material available subsequent to Ziegler et al. (2008), we provide a new key to the genus Opisthotropis and related genera. This key, as well as Table 1 above, are based on specimens examined by us and the references listed in the Materials and Methods.

1 Posterior upper maxillary teeth distinctly enlarged; nostrils rounded, dorsolateral, laterally directed; first supralabials distinctly longer than high................................................................... Parahelicops annamensis

- Upper maxillary teeth subequal; nostrils crescentic, in dorsal position, directed upwards; first supralabials distinctly higher than long............................................................................................ 2

2 15 or 17 scale rows at midbody and on neck............................................................... 3

- 19 rows at midbody, 19–23 rows on neck.................................................................. 16

3 15 scale rows at midbody, 15–17 scale rows on neck.......................................................... 4

- 17 rows at midbody.................................................................................... 7

4 Internasal in contact with loreal................................................................... O. jacobi

- Internasal not in contact with loreal....................................................................... 5

5 1 preocular; 1 anterior temporal; dorsal scales entirely smooth.................................................. 6

- 2 preoculars; 2 anterior temporals; dorsal scales keeled posteriorly...................................... O. kikuzatoi

6 9 SL; body dark with pale crossbars.......................................................... O. guangxiensis

- 8 SL; body black with a tallow spot on each dorsal scale............................................. O. maculosa

7 Dorsal scales strongly keeled (endemic to Sumatra).................................................. O. rugosa

- Dorsal scales smooth or weakly keeled on posterior part of body................................................ 8

8 No preocular; elongate loreal entering orbit....................................................... O. latouchii

- At least 1 preocular................................................................................... 9

9 Internasal in contact with loreal......................................................................... 10

- Internasal not in contact with loreal...................................................................... 12

10 Dorsal pattern uniformly blackish-brown; dorsal scales keeled posteriorly.................................... O. atra

- Dorsal pattern uniformly greyish-brown; dorsal scales smooth................................................. 11

11 Greyish-olive above; 189–194 VEN; endemic to southern Vietnam................................... O. daovantieni

- Greyish-brown above; 183 VEN; endemic to northern Thailand....................................... O. spenceri

12 Dorsal scales entirely smooth; dorsum with pale crossbars............................................... O. cheni

- Dorsal scales at least keeled on posterior part of body; dorsal pattern not mainly made of crossbars.................... 13

13 2 anterior temporals........................................................................ O. tamdaoensis

- 1 anterior temporal................................................................................... 14

14 Body uniformly dark with pale-edged scales; 2 suboculars........................................... O. andersonii

- Body pattern not as such; no suboculars................................................................. 15

15 A black lateral stripe separating abruptly pale colour of venter from dark dorsum colour; 159–173 VEN; 9–11 SL; 1 preocular; dorsal scales keeled throughout body............................................................. O. lateralis

- No black lateral stripe separating pale colour of venter from dark dorsum colour; 147–155 VEN; 6–8 SL; 2 preoculars; dorsal scales smooth on anterior part of body............................................................ O. maxwelli

16 Internasal in contact with loreal......................................................................... 17

- Internasal not in contact with loreal..................................................................... 19

17 1 prefrontal................................................................... Opisthotropis cucae sp. nov.

- 2 prefrontals......................................................................................... 18

18 Dorsal scales smooth; 195 VEN; endemic to the Philippines............................................ O. alcalai

- Dorsal scales keeled; 160–176 VEN; endemic to Borneo............................................... O. typica

19 Dorsal scales strongly keeled........................................................................... 20

- Dorsal scales smooth or only weakly keeled posteriorly...................................................... 21

20 Dorsal scales with strong, thick keels; 136–140 VEN; 8–9 SL; dorsal pattern uniform..................... O. boonsongi

- Dorsal scales with strong but narrow keels; 146–154 VEN; 13–16 SL; body with black stripes............. O. kuatunensis

21 Dorsal scales keeled on posterior part of body; 190–205 VEN; strong dorsal pattern made of broad, black, pale-centred cross- bars........................................................................................ O. balteata

- Dorsal scales entirely smooth; 145–155 VEN; subdued pattern with faint dark crossbands or dark, large blotches.......... Paratapinophis praemaxillaris