VARIATIONS OF THE VIPER IN GREAT BRITAIN. 89 



South Coast of England. It is very common in Surrey, Hamp- 

 shire, and Dorsetshire, but rare in Cornwall. It has long been 

 on record from the Isle of Arran, and, as my friend Mr. W. 

 Eagle Clarke kindly informs me, from Skye and Lewis (Martin, 

 'Description of the Western Islands' [1695], pp. 37, 159); 

 specimens from Islay and Mull, I am told by the same gentleman, 

 are preserved in the Edinburgh Museum. 



Are there any districts in Great Britain from which the Viper 

 is absent ? 



2. Sexual Differences. — It is of primary importance, when 

 dealing with the varieties of this species, to discriminate the 

 sexes, and nothing is easier. The males have the tail thicker, 

 less gradually attenuate, and longer; its length is contained in 

 the total from 5J- to 7f times in the males, 8 to 9f times in the 

 females. We shall see further on that the number of subcaudal 

 shields is greater in males than in females. 



3. Shape of the Head. — The head is always distinct from 

 the neck, though often not more so than in the Common Snake, 

 Tropidonotus natrix. This character is therefore worthless as a 

 criterion for distinguishing the Viper from the harmless snakes. 

 The snout is rounded, with obtuse angle all round, and never 

 turned up at the end as is normally the case in Vipera aspis. In 

 some specimens, however, from Spain and Central Asia, the 

 upper edge of the snout, or canthus rostralis, is somewhat raised, 

 the upper surface being slightly concave. I have not yet observed 

 anything of the kind in British specimens. 



4. Scaling of the Head. — Atypical V. berus may be described 

 as with three enlarged symmetrical shields on the crown, the 

 syncipital shields, in addition to the supraocular shield, situated 

 above the eye ; these three shields are termed the frontal (the 

 azygous anterior shield) and the parietals ; between the frontal 

 and the supraocular two or three scales form a longitudinal series. 

 The rostral shield covers the vertical border of the end of the 

 snout, and is just visible from above ; it is followed by one or two 

 small shields on the top of the snout, and separated from the 

 nasal by a vertically elongated shield, the naso-rostral. The 

 canthus rostralis is occupied by two shields, the canthal shields, 

 the posterior of which is in contact with the supraocular. The 

 space left between the shields above mentioned is covered by 

 four to seven scales. On each side of the head eight or nine 



