90 THE ZOOLOGIST. 



labial shields border the upper lip ; a series of scales borders the 

 eye in front (praeoculars), below (suboculars), and behind (post- 

 oculars) ; and two or three scales separate the prseoculars from 

 the nasal. In the following paragraphs we shall examine how 

 far these characters are constant. 



a. The Syncipital shields. — In British specimens they are 

 nearly always well developed. In one specimen only (from 

 Hampshire) I find the frontal much reduced and the parietals 

 broken up into scales, the specimen in this respect agreeing with 

 V. aspis. In two specimens (from Eeigate) the parietals are very 

 small. In five specimens (from Reigate, Hampshire, Somerset, 

 and Morayshire), on the other hand, the frontal shield is so large 

 as to be entirely, or nearly entirely, in contact with the supra- 

 ocular on each side ; and in others (from Hampshire) these 

 shields are in contact posteriorly, or on one side only. The 

 specimen from Morayshire, in which the frontal is not separated 

 from the supraocular, is further remarkable in having the scales 

 on the upper surface of the snout between the canthals fused to 

 a single large shield, thus being the opposite extreme to the 

 specimen from Hampshire in which the disintegration of the 

 shields into small scales has reached its highest point. Any such 

 extreme specimens, either in one or the other direction, are worth 

 recording and preserving. 



b. The Rostral shield is either as deep as broad, or its depth 

 exceeds its width by one-third at the most. 



c. Two is the normal number of Canthal shields on each side. 

 I have, however, examined one specimen (from Sutherlandshire) 

 in which they are fused to a single shield. 



d. The number of Labial shields y not being always the same, 

 has to be counted on both sides of the animal. In 35 out of 74 

 cases I find 8 shields, in 30 cases 9, in 4 cases 10, in 4 cases 7, 

 in i case 6. Continental specimens have much more frequently 

 9 than 8 shields. V. aspis has from 9 to 11. Usually the fourth 

 and fifth labials are situated below the eye, but in 15 out of 74 

 cases I find only the fourth below the eye, a character which has 

 been given as distinctive of the Spanish form, in which, however, 

 I have shown it is not constant. 



It would be interesting to know whether specimens occur with 

 as many as eleven upper labials. 



e. The number of scales round the eye (prse-, sub- and post- 

 oculars) varies between 6 and 11 in British specimens, the two 

 extreme numbers occurring only once in my lists, 8 or 9 being 

 the usual number. In continental specimens I note 7 to 11 scales, 

 usually 9 or 10, In V. aspis the number varies between 10 and 13. 



