PREFACE. 



cannot be satisfactorily indicated by any method of con- 

 secutive linear arrangement ; in any such system this imper- 

 fection seems to me to be unavoidable, but on that account 

 it is the more important, in selecting from amongst various 

 allied forms the two which shall serve as connecting links 

 between any given genus or species and the portions of the 

 series immediately preceding and succeeding it, to take into 

 consideration every description of characteristic peculiarity, 

 whether external or internal, and thus to secure a nearer 

 approach to a natural sequence than could result from any 

 arrangement based on one class of characters only, to the 

 exclusion, more or less complete, of all others. 



I am well aware that the method which I have here indi- 

 cated is but imperfectly carried out in the following pages ; 

 but I have endeavoured to keep it in view to the best of my 

 ability, and in doing so I have not always thought it desir- 

 able to place at the head of each subfamily that which may 

 be considered as the typical genus, nor at the head of each 

 genus the typical species, but rather to place in these 

 positions the genus or the species which appears to me to 

 approach the most nearly to that which immediately pre- 

 cedes it, 



I may here mention a few matters which have come under 

 my notice since my list of species was placed in the hands of 

 the printers, one of these being that I have recently had 

 an opportunity of examining the plates of Raptorial birds 

 appended to Dr. Menzbier^s ' Ornithological Geography of 

 Russia,^ and also his pamphlet (in French) on the ' Orni- 

 thology of the Governments of Moscow and Toula/ the 

 latter having been kindly presented to me by the author. I 

 confess that I am sceptical as to the validity of some newly- 

 described species and subspecies of Birds of Prey referred to 

 in these works ; but 1 have no definite information to offer on 



