258 



VIPERID.E 



vertical diameter less than its distance from the 

 mouth in the adult. Nostril large and directed 

 backwards. Length of tail six (males) to ten times 

 (females) in the total length. 



Head-Shields. — Rostral as deep as broad, a little 

 broader than deep, or slightly deeper than broad, 

 reaching or nearly reaching the upper surface of 

 the snout, and in contact with two or three apical 

 shields. Upper surface of head covered with small 



sub imbricate 

 scales, which 

 are all more 

 or less dis- 

 tinctly keeled, 

 or, rarely, 

 smooth on the 

 snout and 



forehead; 



Fig. 41 (after Sordelli) 



^ v J sevento 



twelve longitudinal series of scales between the 

 eyes (supraoculars included) ; two to four canthal 

 shields, of which the anterior is the largest, and 

 may be regarded as a supranasal. Supraocular 

 narrow, usually broken up into two or more small 

 shields. Twelve to eighteen scales round the eye ; 

 two or three series of scales between the eye 

 and the labials ; two or three vertical series of 

 scales separate the preoculars from the nasal, 

 which is single and often strongly hollowed out, 



