MUSEUM OF COMPARATIVE ZOOLOGY. 385 



ing up the direction of the former river to the approaches of the Great 

 Desert, nearly on the meridian mentioned [the 100th], proceeds north- 

 ward, forced sometimes more or less westward, especially along the 

 Platte, sometimes eastward. It crosses the Platte between Forts 

 Kearney and Laramie and intersects the Missouri between Fort Ran- 

 dall and Fort Pierre, perhaps near Fort Lookout, as it is between the 

 first mentioned two points that in ascending the river we find the 

 change to take place in the ornithology of the country. Soon after 

 crossing the northern boundary of the United States the line rapidly 

 inclines westward and extends to the Rocky Mountains." To the 

 southeastward this region embraces the whole of the United States, 

 except perhaps the southern portion of Florida, which is decidedly 

 "West Indian and tropical in its affinities. To the northward it em- 

 braces the whole northern and eastern portions of the continent up to 

 the Arctic Realm. 



The "Western Region commences at the western border of the East- 

 ern, and extends thence to the Pacific coast. In the United States its 

 area is about two thirds that of the Eastern Province, but a little farther 

 to the northward it narrows rapidly, and is finally bounded in this direc- 

 tion by the Alaskan mountains.* To the southward it of course merges 

 in Mexico into the Tropical Realm, but its southern limit is not as yet 

 well known. While its varied character renders it subdivisible into 

 several more or less distinct longitudinal areas, each of which may be 

 again divided transversely into numerous fauna? and florae, many species 

 range throughout its whole extent and give to it a certain degree of 

 homogeneousness. This portion of North America is, however, as yet 

 too indefinitely known, geographically and meteorologically, as well as 

 ontologically, to admit of the exact definition of its primary and 

 ultimate life regions. 



The Eastern Province, notwithstanding its larger area, has not only 

 a less number of ornithological faunae than the Western, but has also 

 a smaller number of species represented in it, as well as a smaller 

 number exclusively restricted to it. The following list of one hundred 

 and eight species embraces most of the birds that are exclusively 

 restricted to the Eastern Province, and hence those that distinctively 

 characterize this Province. 



* According to Mr. W. H. Dall. See Proc. Bost. Soc. Nat. Hist., Vol. XII, p. 144, 

 Dec, 1868*. 



vol. ii. 25 



