of the European Ornis, and its Causes. 297 



ornithologists to Brehm's position since the year 1855 : between 

 Thienemann and Bonaparte there is a difference of 100 ; between 

 Thienemann and Brehm of 540 species. The gap between these 

 numbers must have its origin in principles, or in a diversity of 

 views as to the separation of species. 



If we examine the group of smaller numbers, we find that it 

 contains essentially four different sections : — 



1. Thienemann, with 401 species as the minimum. 



2. KeyserUng, Blasius, Schlegel, and De Selys, with 424-430 species. 



3. Bonaparte, 1850, and Des Murs, with 463-466 species. 



4. Bonaparte, 1856, with 500 species. 



Amongst the species cited by Thienemann there are but few 

 that are open to doubt, — such, for example, as Sitta uralensis, 

 Licht.; Sylvia sarda, ^larm. ; Anthus cervinus, Pall.; Glareola 

 melanoptera, Nordm.; Podiceps arcticus, Hoie ; and Uria hring- 

 via, Briinnich, — in respect of the determination of the species, 

 and Ixos obscurus, T., and Lanius tschagra, Vieill., with regard 

 to the domicile. In the union of the Crossbills he goes very 

 sharply to work, but not entirely without reason. In other 

 unions he is decidedly wrong, — for example, in that of Circus 

 cineraceus, Mont., and C. pallidus, Sykes. Numerous new dis- 

 coveries since the year 1816 would have brought his list pretty 

 accurately to the position of those under No. 2. This position 

 is exceeded by the lists under No. 3 by about 40 species, and by 

 that under No. 4 by about 80 species. 



Afier carefully comparing all known facts, I find that the 

 European Oruis consists, in round numbers, of 425 indubitable 

 species of birds breeding in Europe {Brdtvogeln), besides 60 

 varieties or races, which are frequently regarded as species, and 

 about 100 exotic species. These 60 varieties, which are some- 

 what increased in Bonaparte's Catalogue, form the still doubtful 

 specific element in the European fauna, if we follow the majority 

 of ornithologists. They constitute almost exactly the eighth part 

 of the total valuation. By the application of rigorous principles 

 the number may be still greatly reduced. 



Up to the year 1820, and, with few exceptions, even up to 

 the year 1840, ornithology, in its conception of species, was 

 developed exactly in analogy with the rules followed in other 



VOL. III. X 



