vill PREFACE. 
I have divided the book into two parts. Part I. 
deals with the three species in turn, with some ad- 
ditional chapters on special points connected with 
them. Part II. consists of the result of my en- 
deavour to ascertain the average length and relative 
frequency of the various species in all the counties. 
This inquiry has involved an immense correspond- 
ence, and I cannot sufficiently express my gratitude to 
those who have assisted in it. Every effort has been 
made to verify the reports, and I have no reason 
to doubt their accuracy: at the same time, of course, 
each observer is responsible for his own statements. 
The source of these local observations is acknow- 
ledged at the end of each report, and I have given 
the addresses of the various writers in the hope that 
they may thus be encouraged to communicate with 
each other, having found from experience that the 
great difficulty in getting local information is know- 
ing where to apply for it. I am very grateful to all 
these correspondents for the trouble they have taken 
in sending me their own notes, or in getting the in- 
formation from others for me. Without their cordial 
help my effort to compare our Ophidia in various 
localities must necessarily have been barren of re- 
sults. Many of these observers have written books, 
or contributed papers on their county fauna, and 
