330 



GEOGRAPHICAL DISTRIBUTION 



peculiarity is numerically of less importance than some of the 

 Subregions of the Neotropical Kegion, as the following table will shew 

 more plainly : — 



* These numbers, calculated according to the formerly received boundaries of 

 the Nearctic "Region," are certainly overstated, but means of arriving at a more 

 accurate computation are not now forthcoming. 



A considerable majority of the Nearctic Families and genera 

 seem to be generally distributed throughout the whole area, which 

 we may fairly call a Subregion, and consequently its division into 

 Provinces is not easily effected, their delimitations resting rather on 

 differences of species than of higher groups. Of the many attempts 

 to subdivide the Subregion, that of Baird ^ seems to be the most 

 successful.^ He long ago pointed out the existence of three Pro- 

 vinces in its southern portion, the most easterly of which may be 

 termed the " Alleghanian," since it extends from the Atlantic 

 across the mountains whence it is named, and over the valley of 

 the Mississippi and its prairies to about long. 100° W. where the 

 sterile plains begin. Then its boundary turns northward, crossing 

 the Platte and intersecting the Missouri about Fort Lookout. 



^ "The Distribution and Migrations of North American Birds," Am. Journ. 

 Sc. aiidArts, ser. 2, xli. pp. 78-90, 1S4-192, 337-347 (January, March, and May, 

 1866). Reprinted This, 1867, pp. 257-293. German translation, Journ. f. Orn. 

 1866, pp. 244-269, 338-352. 



" I make this assertion though aware of the views to the contrary expressed 

 by Dr. Merriam in his "Results of a Biological Survey of the San Francisco 

 Mountain Region and Desert of the Little Colorado, Arizona " {North American 

 Fauna, No. 3. Washington: 1890). He arrives (p. 24) at the conclusions "that 

 the whole of extratropical North America consists of but two primary life regions, 

 a Boreal region, which is circumpolar ; and a Sonoran or Mcxicantable-land region, 

 which is unique." The first of these, it will be seen, supports my contention of 

 the essential unity of the Nearctic and Palsearctic areas. The second is one the 

 probability of which I will not dispiite ; but I think that at present the facts 

 adduced in its support are hardly suflicient to warrant its adoption by naturalists, 

 who, not being Americans, must necessarily be acquainted with them only at 

 second hand, especially as I am disposed to consider that Dr. Merriam's enumera- 

 tion (pp. 26-28) of the "causes which determine distribution," however well they 

 may fit the area of which he treats, ma}' not be of universal application. 



