THE OPHIDIA IN THE MONNOW VALLEY. 205 
this theory; aud the fact that the adder is so often 
restricted to a particular locality in many counties, in 
addition to what we have seen to account for its 
presence here, leads rather to the conclusion that it is 
a case simply of a suitable environment. 
The result of this investigation into the distribution 
of the Ophidia in the valley of the Monnow in its 
course on the South Herefordshire boundary may be 
summed up thus :— 
1. That the adder (Vipera berus) is here relatively 
common. 
2. That the average length is 24 inches in the adult 
male, 252 
o 
in the adult female — being much 
above the averave of most localities. 
3. That the ring snake (Tvopidonotus natrix) is not 
found, except probably when artificially con- 
veyed thither, and certainly does not breed there. 
4. That the smooth snake does not occur, 
5, The small red viper has been taken once (by the 
author), and seen on two other occasions.? 
Some such factors as the foregoing must be held to 
be mainly responsible for the striking ophidian char- 
acteristics of this and other localities which present 
similar peculiarities. There may, of course, be other 
modifying influences at work, which have either in 
past times contributed to, or even now are maintain- 
ing, the existing state of affairs. 
‘Cf. “The Reptilia of the Monnow Valley,” Woolhope Club 
Transactions, 1898-99.—Author. 
