SCIURID/E— SPERMOPHILUS OBSOLETUS. 



807 



and in the younger specimens ; beneath, strongly yellowish-white. The spots 

 on the back are bordered posteriorly with black. The tail is terete toward 

 the base, broader and tufted at the end ; above, basally colored like the back, 

 toward the end varied with black, and with a subterminal black border edged 

 with yellowish-white. Ears nearly obsolete; soles either naked or hairy, 

 according to the season ; nails long, slender, and moderately curved. 



This form is closely related to S. spilosoma, to which I formerly referred 

 it as a variety, and I am still far from sure that such is not its true relation- 

 ship. The two forms, in their extreme phases of differentiation, are quite widely 

 different in coloration, but in the younger stages they are almost inseparable. 

 The skull of S. obsoletus is rather narrower in proportion to its length than 

 that of jS. spilosoma, and the nasals are longer. In size, proportions, form of 

 the tail, and markings, the two are identical, but the tone of the coloration is 

 quite different. In S. spilosoma, the general color above is light reddish- 

 brown or cinnamon ; in S. obsoletus, pale yellowish-brown. Some of the 

 younger specimens of obsoletus, as No. 3223, from the Laramie Plains, show 

 a decided cast of reddish, and are scarcely distinguishable from examples of 

 spilosoma from Texas. Its recognition as specifically distinct from S. spilo- 

 soma is merely provisional and made with much doubt. 



S. obsoletus was first described by Mr. Kennicott, in 1863, from speci- 

 mens collected in Southern Wyoming, Dakota, and Utah, in 1857 and 1858. 

 The subjoined list of specimens shows it to range from the Black Hills and 

 Fort Kearney westward to Utah. Nothing further is known respecting its 

 distribution, and none of the recent expeditions to this region have apparently 

 met with it. It is to be hoped that future explorers will be able to add 

 to our knowledge of its history. 



Table CXII. — Measurements of three skulls of Spermophilus obsoletus. 



