226 



Key to the Indo-Australian species. 



A. Head very small; neck very slender. 



I. Two superposed anterior temporals. 



a. Praefrontals separated by the frontal I. 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 2 9 33 scales round body ; ventrals 



225298 3. H. gradlis p. 228. 



XX 37 scales round body; ventrals 298 321. 4. H. foweri p. 229. 



2. Scales in 40 50 rows round body. 



aa. 31 40 scales round the neck; 40 5 



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

 bb. 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 7. H. brookei p. 230. 



b. Frontal shorter than its distance from the rostral. 8. H. torqitatns p. 231. 

 . Head moderately small ; neck not very slender. 

 I. Anterior ventrals three or four times as broad 

 as the last row of scales 9. H. viper inus 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. 



f Ventrals 159 n. H. mertoni p. 233. 



ft Ventrals 270 354. 



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

 bb. Scales round body in 32 40 rows. 



X Head yellow 13. H. brugmansi p. 233. 



XX Head black with a curved yellow 



marking 14. H. spiralis p. 234. 



tft Ventrals 372400 15. H. grandls 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. 



aa. One postocular 16. H. hybridns p. 235. 



/V^.Two or three postoculars 17. H. ornatus p. 236. 



