226 



Key to the Indo-Australian species. 



.-<. Head very small; neck very slender. 

 I. Two superposed anterior temporals. 



a. Praefrontals separated by the frontal \. H. frontalis p. 227. 



b. Praefrontals in contact 2. H. nigrocinctus p. 227. 



II. A single anterior temporal. 



a. Frontal as long as its distance from the rostral. 



1. Scales in 29 — 37 rows round the body. 



X 29 — 33 scales round body ; ventrals 



225 — 298 3- A^. gracilis p. 228. 



XX 37 scales round bodyj ventrals 298 — 321. 4. H. Jloiveri p. 229. 



2. Scales in 40 — 50 rows round body. 



aa. 31 — 40 scales round the neck; 40 — 50 



round the body; ventrals 310 — 438 . . 5. //. diadema p. 229. 

 hi'. 25 — 31 scales round the neck; 40 — 48 



round the body; ventrals 345 — 500. . . 6. H. fasciatus p. 230. 

 cc. 30 scales round the neck; 42 round the 



body; ventrals 416 "]. H. broohei p. 230. 



(!'. Frontal shorter than its distance from the rostral. 8. H. torqnatus p. 231. 

 B. Head moderately small; neck not very slender. 

 I. Anterior ventrals three or four times as broad 



as the last row of scales <^. H. viperintts p. 231. 



II. Anterior ventrals not more than twice as broad 

 as the last row of scales. 

 a. One anterior temporal. 



1. 19 — 21 scales round the body 10. H. jerdoni p. 232. 



2. Scales round the body in more than 21 rows. 



t Ventrals 159 \\. H. inerloni p. 233. 



tt Ventrals 270 — 354. 



aa. Scales round body in 45 rows . . . . 12. H. polyodontus p. 233. 

 hb. Scales round body in 32 — 40 rows. 



X Head yellow it,. H. bntgnia/isi p. 233. 



XX Head black with a curved yellow 



marking 14. //. spiralis p. 234. 



ttt Ventrals 372 — 400 15. //. gra/idis p. 235. 



b. Two or three superposed anterior temporals. 

 I. Scales round body in 34 — 50 rows; ventrals 

 squarish. 



X Second pair of chin-shields, if distinct, 

 separated by several scales. 



rtfl. One postocular 16. H. hybridus p. 235. 



/V'. Two or three postoculars 17. //. ornaltis p. 236. 



