IXTRODrCTIOX. vn 



I also received great assistance from my friends the late Mr. IIo« ard 

 Saunders and the late Prof. Dr. Oustalet. 



In any future edition of the ' Hand-list ' I should divide the Cla>3 

 Aves into the two Sub-Classes, Palcvognathce and Neognathce, since I 

 consider this arrangement, proposed by Mr. Pycraft, more natural than 

 the old division into Ratitce and Oarinatce. 



It will be of interest to tabulate the number of species of Birds, fossil 

 and recent, now known to science, and the following is an attempt to 

 arrive at something like an estimate. I have been at some trouble to 

 make this computation, which I believe to be fairly comijlete, but at the 

 time of writing, the ' Zoological Record ' for 1908 has not yet been 

 printed, and I may not have included some of the species described 

 in recent years. The same can be said of those described during the 

 present year, 1909 ; but the totals may be considered fairly accurate, 

 and we may conclude that the number of known species of birds is about 

 18,937, distributed under 2310 genera. 



lu 'The Ibis' for January 1900 (p. 2! 5) the Editoi's gave an estimate 

 of the number of genera and species enumerated in the first volume of 

 tlie ' Hand-list ' as follows : — • 



Genera 851 ; Species 3727. 



Sir Eay Lankester, in his " Preface" to Yol. II. (June 1900), gives a 

 slightly smaller estimate : — 



Genera 830 ; Species 3626. 



The Editors of ' The Ibis ' have probably included additional species 

 which, to their knowledge, had been described since the publication of 

 Vol. I. of the 'Hand-list.' 



My present computation tor Vol. I. is as follows : — 

 Genera 865 ; Species 4261 , 



