Vlll 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 



