508 



With the fulvous type of Tamias quadrivUtatus occurs a rufous 

 of Spermophilus grammurus ; but the form of Sciurus HinUonins 

 occurring over the same area, presents the exceptional condition 

 of a minimum amount of rufous." 



Respecting the mammals and birds of the continent as a whole, 

 Mr. Allen recognizes at least five more or less well marked areaB 

 characterized by certain peculiarities of color variation, and finds 

 a striking correlation between these areas and the prevalent ten- 

 dencies of color-increase and the amount of aqueous precipita- 



"The first region we propose now to define is that of the Atlantic 

 Slope, which will include not only the country east of the Allegha- 

 nies, but a large part of the British Possessions, extending west- 

 ward at least as far as Fort Simpson, and thence northward and 

 westward to Alaska, including, apparently, all of that territory 

 north of the Alaska Mountains, with an annual rainfall through- 

 out the whole of this extended region of about thirty-five to forty- 

 five indies. Over this region (to which we may give the general 

 term of Atlantic Region)- the colors may be regarded as of the 

 average or normal type, those of other regions being either of a 

 diminished or increased intensity. 



The second region will embrace the Mississippi Valley, or more 

 properly the Mis-4>sippi Uasin, and may hence be termed the Mis- 

 sissippi Region. Here the annual rainfall reaches forty-live in 

 fifty-live inches, and over a small area east of the Lower Missis- 

 sippi even exceeds sixty inches. The tendency here is so often 

 to an increase of fulvous and rufous tints, that we may regard this 

 as the distinctive chromatic peculiarity of the region, these tints 

 heir maximum in the limited area of greatest humidity, 

 but a general increase in intensity of color is also more or less 

 characteristic of the region. A third region embraces the central 

 portion of the Rocky Mountains, and being developed most 

 strongly within the present territory of Colorado, and being also 

 mainly included within that territory, may he termed the C»l«fudn 

 Region. The tendency here again," as compared with the imme- 

 diately adjoining districts is to a general increase of intendiy of 

 color, with a No a marked inclination to the development of rufous 

 and fulvous tints, this region being also within the influence of a 



mi- lily is here less than in either of the other regions alreadx de- 

 fined, the annual aqueous precipitation amounting to only ahoiit 

 twenty-four to thirty indies ; hut it is yet greatly in excess of that 

 of ihe districts immediately surrounding it. 



The fourth region may be regarded as made up of the and 

 plains and deserts of the great central plateau of the Continent, 

 including not only the "Great Plains," usually so called, but the 



