V "s93 X ] ALLEN, Origin and Distribution of ' N. A. Birds. I "2 T 



Cvpseloides Amphispiza Chamaea 



Aeronautes Calamospiza Psaltriparus 



Selasphorus Phainopepla Auriparus 



Xanthocephalus Salpinctes Mviadestes 



Calcarius Catherpes 



Rhvncophanes Oroscoptes 



Were we to include in this connection some 3S additional 

 tropical genera which range only a short distance into the Warm 

 Temperate, as here defined, we should have to add 7 genera to the 

 eastern list and about 30 to the western list. In other words, out 

 of a total of about 150 genera distinctive of the Warm Temper- 

 ate, 1 about 65, or 43 per cent., have a transcontinental distribu- 

 tion, and about 85, or 57 per cent., are either eastern or western. 



The higher ratio of peculiar types in the Arid Province as 

 compared with the Humid Province is obviously due to ■ geo- 

 graphic conditions, the Arid Province adjoining at the southward 

 a broad tropical land area, while the southern boundary of the 

 Humid Province is formed by the Gulf of Mexico. A large pro- 

 portion of the genera peculiar to either the Humid or Arid 

 Provinces range across the whole north and south breadth of the 

 Warm Temperate Subregion. 



The northern half of the Warm Temperate, however, also 

 differs faunally quite markedly from the southern half, in conse- 

 quence of the extension southward of a few northern genera over 

 most of its northern half, and the extension northward of many 

 tropical genera over a portion of its southern half. As regards 

 birds, while a considerable list of species would fall respectively 

 into one or the other of these two categories, the number of 

 genera is small, owing to the fact that if we take them on the 

 basis of their transcontinental range their representation is often 

 very different in the two provinces, as regards both their geo 

 graphical distribution and the species which represent them. The 

 northern list would include perhaps such genera as Botau- 

 rus (excluding Btitor ides) , Bonasa, Passerculns (subgenus), 

 and perhaps Tachycineta and Amflelt's, and in the East Carpo- 

 dacus and Merula; although most of these are really Cold 



1 Cosmopolitan.and other wide-ranging genera are not included in this connection, 

 but only such as are distinctively'American. 



