506 



brighter and smaller southern form in the eastern Atlantic States. 

 On the arid plains of the Platte and Upper Missouri rivers it pre- 

 sents a markedly paler or more fulvous phase, well illustrated by 

 specimens from the Black Hills. This form becomes even still 

 paler and more fulvous at the eastern base of the main chain of 

 the Rocky Mountains, between latitude t.V and 47°, where it be- 

 gins to pass by insensible stages of gradation into the so-called 

 $ci,,r,i« Rirhardsoni of the Iiockv Mountains north of 45°, and 

 the so-called Sciurus Fremonti of the Rocky Mountains south of 

 about the same parallel. In the collections made in Western Wy- 

 oming, near the Yellowstone Lake, occur many specimens which 

 are soexaetlv intermediate between the three forms (S. Un<l.-« ■»<'»■•<. 

 S. Hh'hunUnni and ,V. Fremont!) whose habitats here meet, that it 

 is impossible to say which of the three forms they most resemble. 

 At the same time specimens can be selected which will form a se- 

 ries of minute gradations from the pale form of Hudsonius from 

 the Plains, on the one hand, to the Richardsoni and Fn>„\n, t ti 

 forms on the other. To the southward of this district we soon 

 pass into the region of the typical Fremont;, and to the westward 

 and northward into the habitat of the Richardsoni type. Kven 

 the country about the sources of the Gros Ventres Fork of the 

 Snake River, is alreadv within the range of the true Richards;,,!. 

 The habitat of S. Richards,,,,! extends from the main chain of the 

 Rocky Mountains, north of latitude 11", to the Cascade Range. 

 Here it becomes mixed with S. I)o„,,h,ss,\ which scai cely dilfers 

 from S. Richardsoni, except in being a little darker above, and m 

 bavin-- the ventral surface more or less strongly tinged with buff. 



ward to Northern California, and northward probably to Sitka. 

 In Northern California the S. Douglassi meets the range of the 

 true S. Fremont), between which two forms there is here the most 

 gradual and intimate intergradation. In this group we have uence 

 four forms which, in their extreme phases of mutual divergence, 

 appear as diverse as four good, congeneric species need to, but 

 which, at points where their respective habitats join, pass into 

 each other as gradually as do the physical conditions of the locah- 



The Tamias quadrivittatus group 1 presents an equally or even 

 more striking range of variation in color, and also varies to an 

 unusual degree in size. Beginning at the northward, we find that 

 specimens from as far south as lYmliiua. and thence northward, 

 are quite undistinguishable from specimens from Northeastern 

 Asia, or the so-called Tumiax " P,dl,t*i" (T. Pallas! lhdrd-- /. 

 striata* of most European authors). This form is found to only 

 a limited extent south of the northern boundary of the United 



