132 Proceedings of the Royal Physical Society, 



The extent of colour variation on the helly is as follows — 



Black. 



Dark Indigo Blue. 

 Bluish Grey. 



Mottled Grey or Eeddish Grey. 

 White, with the external edges of the ventral scales 

 of a blackish or brown colour. 



In the caudal region the ventral aspect of the tail is 

 generally of some bright colour, yellow or orange-red, or 

 occasionally white, while on its dorsal aspect the zig-zag 

 line is frequently merged in a general dark brown colour 

 over the whole surface. 



On the dorsal and lateral aspects of the body, an immense 

 range of colour variation is noticed, affecting both the 

 markings and the ground colour. The former vary from 

 pitch black to light brown, while the ground colour may be 

 grey, light brown, light green, dark green, or of any inter- 

 mediate shade. Moreover, while as a rule the dorsal zig-zag 

 line stands out fairly prominently, the lateral line of dark 

 spots frequently merges into the surrounding body colour to 

 some extent. 



This completes the bare catalogue of colours and combina- 

 tions of colours in the multi-coloured common adder. 



One Coloured Adders. 



It is very exceptional to find an adder which is of uniform 

 colour all over. When they do occur, they are either — 



1. Black. 



2. Some dark shade of green, olive-green, or 



brownish green (now recorded for the first 

 time, as far as I know). 



3. Eed. 



4. White. 



Consider these four varieties seriatim, always bearing in 

 mind that they are rarities in Great Britain. 



