42 EXTINCT AND VANISHING MAMMALS 



(6) Dinomyidae, giant hystricoid rats, two species of two 

 genera. 



(7) Dasyproctidae, agoutis, three insular species of the 

 typical genus. 



The last four families belong to the New World Hystrico- 

 morpha and have their relatives in South America, where they 

 probably originated. J. E. H. 



Family SCIURIDAE: Squirrels 



KAIBAB, OR WHITE-TAILED, SQUIRREL 



SCITJRUS KAIBABENSIS Merriam 



Sciurus kaibabensis Merriam, Proc. Biol. Soc. Washington, vol. 17, p. 129, 1904 ("Head 

 of Bright Angel Creek, top of Kaibab Plateau, north side of Grand Canyon of 

 Colorado, Arizona"). 



FIGS.: Nelson, 1918, p. 448, lower fig. (col.); Goldman, 1928, p. 127, pi. 16 (photo- 

 graph). 



This is perhaps the handsomest of the North American 

 squirrels, a close relative of Abert's squirrel, with long-tufted 

 ears, which ranges from Colorado into Mexico. The white- 

 tailed squirrel has become isolated on the north side of the 

 Grand Canyon in the high Kaibab Plateau and has developed 

 striking color characters, such especially as its large white tail. 

 Because of its restricted habitat and conspicuousness it may be 

 included here. 



In its general appearance it resembles Abert's squirrel, but 

 the under parts are mainly black instead of white, and the tail 

 is practically all white instead of on the under side only. The 

 back is dark grizzled gray, with a wash of ferruginous from 

 shoulders to rump. The ears are blackish in summer but 

 rimmed anteriorly with gray in winter; the ear tufts are black, 

 the face, fore feet, and toes mixed gray and black; hind feet in 

 summer mainly gray but in winter mainly black. The tail is 

 ample and bushy, white, with an indistinct buffy-gray stripe 

 down the middle of the upper side. Size about that of a gray 

 squirrel. 



The Kaibab squirrel is found in a restricted area about 40 

 miles in length and 20 miles in greatest width, at the broadest 

 (southern) part of the Kaibab Plateau. Isolated here from its 

 nearest allies of the south side of the Grand Canyon, it is con- 

 fined to the portions of the plateau where the yellow pine 



