262 viperim: 



28. Ancistrodon halys, Pallas 

 Pallas's Pit-Viper 



Form. — Moderately elongate. Head subtriangular, 

 flat or slightly concave above, swollen in the tem- 

 poral region, very distinct from neck ; snout rounded 

 or obtusely pointed, slightly turned up at the end, 

 with obtuse canthus and vertical or slightly oblique 

 loreal region ; eye rather small. Tail seven to eight 

 and a half times in the total length. 



Fig. 42 



Head-Shields. — Rostral as deep as broad or slightly 

 broader than deep, just visible from above. A pair 

 of internasals and a pair of larger prefrontals. 

 Frontal as broad as the supraocular, as long as or 

 a little longer than its distance from the end of the 

 snout, as long as or a little shorter than the rather 

 short parietals. Supraocular extending beyond the 

 vertical of the posterior border of the eye. Loreal 

 pit between three shields, separated from the labials. 

 Nostril between two nasals, the posterior of which 



