SCIURIDiE— GEOGRAPHICAL DISTRIBUTION AND VARIATION. G51 



well known in all the species of Arctomys. In numerous instances, these 

 melanistic individuals and melanistic forms have been described as distinct 

 species, while in reality they are generally so sporadic in their occurrence as 

 to render them hardly worthy of recognition, even as varieties. 



" The gradual increase of our knowledge in respect to the character of 

 these melanistic forms, and especially in regard to the extent and character 

 of geographical variation, necessarily leads to the modification of our views 

 in respect to the status of many forms that have formerly passed current 

 as more or less well-established species, and also to consequent changes 

 in nomenclature. The representatives of few groups are more variable in 

 respect to color, even among individuals of the same species inhabiting the 

 same locality, than the arboreal Squirrels. Add to this the considerable 

 amount of geographical variation that obtains among them, and the very con- 

 siderable changes attendant upon season in respect to the character of the 

 pelage, and we shall no longer feel surprised at the profusion of synonyms 

 that attach to many of the species." * 



In several species of North American Sciuri, a tendency to fulvous- or 

 rufous-bellied forms is noticeable. This is commonly developed at the south- 

 ward, but in one instance occurs in the moist region of the Pacific coast, 

 north of the fortieth parallel, namely, in Sciurus hudsonius var. dbuglassi. 

 It also prevails to a marked degree in all three of the varieties of Sciurus 

 niger (including the S. "cinereus'', S. "vuljrinUs", and S. "ludovicianus"), but 

 especially in that (var. ludovicianus) inhabiting the Mississippi Valley, where, 

 as already noted, there is a marked increase in the intensity of the rufous of 

 the ventral surface in passing southward from the Great Lakes to the Gulf. 

 S. collicei, which ranges northward to Arizona, also runs into a rufous-bellied 

 phase in Mexico, while all of the other species found south of the United 

 States are either always orange or dark rufous below, or present this colora- 

 tion as the prevalent or normal one; white- or grayish-bellied specimens 

 of any species from the warmer parts of the two Americas being exceptional. 

 Not only, also, is there a greater tendency to redness on the ventral surface, 

 but this color often involves the outer (as well as the inner) surface of the 

 limbs, and frequently extends high up on the sides of the body, especially 

 anteriorly. The dorsal surface is also quite generally suffused with either 

 bright fulvous or rufous, while the middle of the lower surface of the tail is, 



* Proc. Bost. Soc. Nat. Hist. vol. xvi, 1874, pp. 27~-->&>, 284, 285. 



