VIPERA 



231 



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

 broader than deep, rarely once and one-third as deep 

 as broad, not or but scarcely visible from above. In 

 addition to the supraoculars, three large shields, the 

 frontal and the parietals, are as a rule present on 

 the top of the head. Frontal as long as broad or a 

 little longer than broad, rarely much longer than 

 broad, once and a half to twice and a half as broad 

 as the supraocular, from which it is as a rule separated 

 by one to four 

 shields, as long 

 as or a little 

 shorter than its 

 distance from the 

 rostral, as long as 

 or a little shorter 

 than the parietals. 

 Parietals usually 

 in contact with 



Fig. 35 (after Sordelli) 



the frontal and separated from the supraoculars 

 by small shields, but sometimes in contact with 

 both, or separated from the frontal. Exception- 

 ally, in specimens from Great Britain, Germany, 

 and Austria, the parietals, or the frontal and the 

 parietals, are broken up into scales, and this is more 

 frequently the case in specimens from North-Western 

 Spain (var. seoanei). Upper surface of snout bor- 

 dered by six (rarely by five or four) small shields, viz., 

 two apicals (rarely one), and on each side two can- 



