76 BRITISH SERPENTS. 



is absent from Ireland. It is frequently seen in the 

 islands of Mull and Jura. 



Description. 1. Size. — Some confusion has arisen 

 in the minds of some as to the size of the adder, from 

 the fact of the small red viper not being regarded as a 

 distinct species, a most excellent work on Natural His- 

 tory thus making the statement that the " average size 

 of the common viper is 10 inches." The fact of the 

 matter is that the small red viper averages this figure, 

 but the common adder has a very different measurement. 

 A reference to the fisures in the various counties will 

 show that the average size of the adult adder in this 

 country varies from 18 inches to 25 inches, accord- 

 ing to the locality. When I was working up the 

 Ophidia of the Monnow Valley I was very much 

 struck with the large size of the adders there, and 

 wrote to G. A. Boulenger on the subject. I had 

 then recently obtained a specimen measuring 28 \ 

 inches, and was anxious to know what this authority 

 thought of it. His opinion on this matter is prob- 

 ably of more value than any other that could be 

 obtained, as many of the interesting specimens taken 

 in this country go to him at the British Museum. 

 Mr Boulenger says : — 



" The usual size of adult vipers in this country is 

 from 20 to 25 inches, specimens of 26 inches being 

 very rare. I have no British example measuring as 

 much as 28 inches. The largest specimens in the 

 British Museum measure — 



