°^ J Allen, Origin and Distribution of N. A. Birds. I7 h ] 



bia, and thence northward into southern British Columbia. It thus 

 includes the so-called 'Central' and 'Pacific' Provinces of Baird 

 and most subsequent writers, excepting of course the more 

 elevated parts of the Rocky Mountain plateau. It is thus coex- 

 tensive with Dr. Merriam's 'Arid Sonoran.' While it is true 

 that a narrow belt along the Pacific coast, from southern Califor- 

 nia northward to the Alaskan Peninsula, possesses a few peculiar 

 types, and lacks a few of those occurring in the region immediately 

 to the eastward, the differentiation is on the whole too slight to 

 give the Pacific coast district the rank of a region coordinate in 

 grade with the formerly so-called Middle and Eastern Provinces. 

 These differences serve at best merely to mark oft' from the interior 

 region at large a tier of narrow coast faunae of the same grade as 

 those bordering the Atlantic coast, although the latter, owing to 

 the widely different physiography of the eastern and western 

 borders of the continent, have a much greater east and west 

 extent. 



The Arid Province, like the Humid, is divisible into two sub- 

 provinces, namely, ( 1 ) a northern or Campestrian S?tbprovince, 

 and (2) a southern or Sonoran Subprovince (see PI. IV). These 

 two regions correspond respectively with Dr. Merriam's 'Arid 

 Upper Sonoran' and his k Arid Lower Sonoran' ; just as the two sub- 

 provinces of the Eastern Province correspond with his 'Humid 

 Upper Sonoran' and 'Humid Lower Sonoran,' as laid down on his 

 'Second Provisional Bio-geographic Map of North America,' 

 except that the 'humid' and 'arid' portions of his 'Transition Zone' 1 

 are also included respectively in the Alleghanian and Campestrian 

 Subprovincec. The Sonoran Subprovince is equal to Dr. Mer- 

 riam's restricted 'Arid or Sonoran subregion proper' plus his 

 'Lower Californian subregion,' while the Campestrian Sub-prov- 

 ince includes his 'Great Basin subregion' and his 'Great Plains 

 subregion.' 2 The name 'Campestrian' has reference to the fact 

 that this subprovince is largely made up of plains, including as it 

 does the greater part of the Great Plains, the Plains of the Saskat- 

 chewan, and the Plains of the Columbia and Snake Rivers. 



Many species are limited in their southward distribution by the 

 southern border of the Campestrian Subprovince, but few genera 



1 Cf. Proc. Biol. Soc. Washington, VII, 1892, pp. 26-33, and accompanying map. 



2 Cf. N. Am. Fauna, No. 3, 1890, p. 25. 



18 



