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mens, one procured in the fall and the other in the spring, are in 

 different plumages from the type, which is a midsummer bird, thereby 

 attesting the entire distinctness and perfect dissimilarity of this 

 species from any other yet known. But important and creditable as 

 these two discoveries are, the new facts in regard to the geographical 

 distribution of certain species, brought to light by Mr. Aikeu's inves- 

 tigations, are of even greater value. 



These facts are, first, the much greater northeastward range of forms 

 heretofore supposed to be confined to the Colorado Province, in Ari- 

 zona ; second, the occurrence in the mountains of Colorado of many 

 species found upon the Sierra Nevada, which seem to be entirely want- 

 ing in the intermediate widely spread area of the Great Basin; and, 

 third, the occurrence in the mountains of Colorado of many strictly 

 eastern species, not previously traced beyond the eastern border of 

 the Plains. The latter result of Mr. Aiken's collecting in Colorado, 

 joined to that of Mr. Allen in the same Territory and that of the 

 writer, and subsequently Mr. Allen and other ornithologists in Utah, 

 establishes the Rocky Mountain Eange as the dividing line, or, more 

 properly, the meeting ground, of the avi-faunse of the Eastern and 

 Western Regions, this system being, throughout its whole extent, 

 almost as nearly related to the one as to the other, though, as would 

 be expected from the physical conditions of the country, the western 

 element preponderates. Besides these discoveries in the geographical 

 distribution of the species, new facts in relation to the range, habits 

 or other peculiarities, of certain species are among other of the very 

 satisfactory results of Mr. Aiken's ornithological explorations in Col- 

 orado. As a particular example, I may mention the discovery of the 

 fact that Corvus cryptoleucus, formerly supposed to be confined to the 

 Llano Estacado of Texas, is a very common bird along the eastern 

 base of the Rocky Mountains, as far north as Cheyenne ! 



Upon examining a map of Colorado, it will be seen that the topog- 

 raphy of this Territory is peculiarly favorable to an extremely varied 

 fauna. The water-shed of the Continent runs across it almost in the 

 middle, the streams on the eastern slope flowing into the Gulf of 

 Mexico through the western tributaries of the Mississippi River, and 

 those of the western slope emptying into the gulf of California, 

 through the northeastern tributaries of the Rio Colorado. The direct 

 result of its central position between several drainage systems is 

 that the general eastern and western fauna? meet, or overlap ; the 

 birds characteristic of the Rio Grande district also enter its limits by 

 following the head waters of that stream northward into San Louis 

 Park and the adjacent country, while those of the Arizona district 

 follow the northeastern tributaries of the Colorado River, and diffuse 

 themselves over the western portion. In the northwestern corner 



