MUSEUM OF COMPARATIVE ZOOLOGY. 121 



The observations made the past summer (given below in detail) 

 establish the occurrence of a number of eastern species at points several 

 hundred miles to the westward of the westernmost point from which 

 they have been previously recorded ; and in like manner other western 

 species were found occurring at points considerably to the eastward of 

 points from which they were before known. Northern species were also 

 found at localities considerably south of their previously known range, 

 both Anthus ludovicianus and Leucosticte tephrocotis being found breed- 

 ing above timber-line in the mountains of Middle Colorado. A more 

 extensive overlapping of the habitats of eastern and western species is 

 thus established than there was previous evidence of, which may tend 

 to modify the currently received boundary between the Eastern and 

 Middle Provinces of the North American Region. This boundary has 

 generally been considered as running in the United States near the 

 100th meridian, or " at the edge of the sterile plains." But the dis- 

 tinctively " Plains species " are nearly all found now to range eastward 

 over the prairies, the others first appearing somewhat to the westward. 

 Tims of about twenty species that are distinctively characteristic of the 

 Plains, fully one third occur on the prairies of Illinois and Wisconsin, 

 another third are met with as far east as Missouri, and the others range 

 more or less regularly into Eastern Kansas. In other words, all the 

 species of the Plains occur in Kansas at points from two hundred to 

 three hundred miles to the eastward of the 100th meridian, and 

 most of the others extend to the woodland districts eastward of the 

 Mississippi. On the other hand, many eastern species follow up the 

 rivers to the most western limit of trees, sometimes to a distance of 

 three hundred miles west of their formerly supposed western limit, 

 where they mix with western species not commonly supposed to occur 

 much to the eastward of the eastern base of the Rocky Mountains. 



The fauna? of the middle and western portions of the continent pre- 

 sent peculiarly broken and irregular areas, in consequence of the great 

 irregularity of the surface of the country. The more southern fauna), 

 while occupying the lower table lands, extend also up into the lower 

 mountain valleys, to a limit varying with latitude and the peculiar local 

 conditions of the valleys themselves. Above this basal zone occur sev- 

 eral other zones, which an; continuous for considerable distances along 

 the main chains, but also embrace distant insular patches in the more 

 isolated groups of mountains. The higher zones arc still less regular 



