1894- PAL^ARCTIC AND NEARCTIC REGIONS. 445 



Ethiopian ; showing that, by this test of the number of families which 

 are not found in both regions, the Palaearctic and Nearctic are three 

 times as distinct as are the Ethiopian and Oriental Regions. 



If we now consider the genera which are characteristic of the 

 one region as compared with the other, we shall find equally strong 

 evidence of their diversity. In the Palaearctic Region we have 

 120 genera which are not Nearctic, out of a total of 174 ; so that a 

 little more than two-tllirds of the Palaearctic genera of land-birds 

 are quite unknown in the Nearctic Region ; and these genera contain 

 472 species out of a total of 767- In other words, out of every 5 

 land-birds in the Palaearctic Region, 3 belong to genera which are 

 not Nearctic. 



Looking at the came problem from the other side of the Atlantic, 

 the results are even more striking. Out of a total of 167 genera of 

 Nearctic land-birds no less than 113 are not Palaearctic, the propor- 

 tion being almost exactly twO- thirds. These 113 genera comprise 

 282 species out of a total of 417 species ; so that again almost 

 exactly tWO-thirdS of the Nearctic land-birds belong to genera 

 which are not Palaearctic. This is a larger proportion than in the 

 case of the Palaearctic Region ; and nothing can more forcibly bring 

 before us the fundamental diversity of the two areas than the fact 

 that, almost everywhere in the Nearctic Region, out of every three 

 birds we might meet with, tWO would be generically unknown to the 

 student of the Palaearctic avifauna. There is probably no such 

 amount of difference as this between any two adjacent regions, except 

 perhaps between the Oriental and Australian, the latter admittedly 

 the most isolated on the globe. 



I have now shown, by a careful comparison of their mammalia 

 and birds, that the Palaearctic and Nearctic Regions, instead of being 

 so much alike that they should be united to form a single region, are 

 really exceptionally distinct. They are certainly much more distinct" 

 than are the Oriental and Ethiopian Regions, and are probably quite 

 as distinct as are any two conterminous regions. 



I feel confident, therefore, that any naturalist who will study the 

 materials I have here brought together in a form to admit of easy 

 comparison, will arrive at the conclusion that the system of Zoological 

 Regions established by Dr. Sclater cannot be improved by the union 

 of two such fundamentally distinct areas as are those which he has 

 termed the Palaearctic and Nearctic Regions. 



Alfred R. Wallace. 



