2 Proceedings of the Royal Physical Society. 



the observance, and so we find that in a series of adders 

 hardly two can be found which are what is called " typical '* 

 in their specific scaling arrangements. And so it comes to 

 pass that there is a variety of snake in these Isles which does 

 not grow to the size of the average adder, is of the same 

 colour in the two sexes, and is very limited in its distribu- 

 tion, but which, because its scales happen to be arranged in 

 the way authorities have decided is that of the adder, is 

 likewise classed as Vipera hems. I refer to the small red 

 viper. Even in its temper and disposition this snake is 

 unlike the adder, a fact with which country folks, where the 

 red viper occurs, are quite familiar with, but which system- 

 atists consider of no importance, if they are aware of it. 

 Anyone who has seen specimens of the two reptiles together, 

 is strongly tempted to think that those who are responsible 

 for classing them as the same species never had a similar 

 opportunity. But their scales are similarly arranged; that 

 is quite sufficient. 



During the time I have been working on this subject, 

 I have obtained several specimens of the small red viper, 

 which are now in the University Zoology Museum, where 

 the two reptiles can be compared. In the last five years I 

 have taken or examined about five hundred British adders, 

 but I have only seen four of these red vipers, a fact which 

 in itself is strongly against them being of the same species. 

 Their very rarity is the difficulty in investigating them ; they 

 have not been observed with their young, nor have they 

 been known to pair with the common adder. So, as they 

 conform to the adder scaUng, adders they must be under 

 present arrangements. What follows will, I think, show 

 how extremely variable this scaling is, and to what extent 

 its limits have to be stretched to include all adders within 

 its range. 



G. A. Boulenger, the distinguished ophiologist of the 

 British Museum, is the only person who has paid much 

 attention to the variations of the adder in Great Britain. 

 He has laid down the limits of scaling recorded, in the 

 following paragraphs, which it is necessary to quote to show 

 the great variation which obtains. 



