282 



Key to the Indo-Australian species. 



A. Scales between the eyes smooth or obtusely « 

 keeled; gular scales smooth. 



I. Snout not prominent, not raised above the 

 nostrils. 



a. Supraoculars large. 



1. Supraoculars separated by 5 — 8 

 scales; scales smooth or feebly keeled, 

 in 21 — 25 (27) rows; ventrals 132 — 



158; tail not prehensile i. L. monticola p. 282. 



2. Supraoculars separated by 4 — 9 

 scales; scales feebly keeled, in 21 

 rows; ventrals 180 — 191; tail pre- 

 hensile 2. Z. suniatranus p. 283. 



3. Supraoculars separated by 6 scales; 

 scales feebly keeled, in 21 rows; 



ventrals 162; tail feebly prehensile. 3. Z. fasciatus p. 284. 



b. Supraoculars narrow if distinct. 



aa. Supraoculars separated by 12 — 15 

 scales; scales strongly keeled, in 25 

 or 27 rows; ventrals 160 — 182; tail 



slightly prehensile 4. Z. piirpurcoindculatus p. 284. 



bb. Supraoculars separated by 8 — 13 

 scales; scales almost smooth or dis- 

 tinctly keeled, in 19 — 23 rows ; ven- 

 trals 145 — 175; tail prehensile. . . 5. Z. graininciis p. 285. 

 II. Snout prominent, the upper edge raised 



above the nostrils 6. Z. puiiiceus p. 286. 



B. Scales between the eyes strongly keeled; 



gular scales keeled . . 7. Z. wagleri p. 286. 



I. Lachesis monticola (Gthr.). 



Trimcresitrus monticola^ Giinther, Rept. Brit. Ind. 1864, p. 388, pi. XXIV, fig. B. 

 Lachesis monticola^ Boulenger, Cat. Sn. Ill 1896, p. 548 (s. syn.). 



Snout very short; eye small. Rostral as broad as deep or 

 a little more broad; nasal divided or partly divided; scales on 

 the head small, smooth; supraocular large; i — 3 scales between 

 the internasals, which are sometimes in contact; 5 — 8 scales 

 between the supraoculars; eight or nine upper labials, sepa- 

 rated from the eye by 3 or 4 rows of scales; second labial 

 usually bordering the loreal pit anteriorly; temporal scales 



