S0IURID2E— SPEKMOPHILUS RICHARDSONI. 851 



siderable number of localities, through which its complete intergradation 

 with the larger, paler, and more fulvous form of the north is clearly shown. 

 In its extreme phase, var. townsendi is widely different in color from var. 

 richardsoni, yet the extreme phases of differentiation are intimately and insep- 

 arably connected. There is, likewise, a wide range of individual variation, as 

 shown by the Camp Carling and Fort Bridger series, not only in respect to 

 coloration, but in the size of the ears and the length of the tail, as is also the 

 case in var. richardsoni. 



In No. 3378, from Fort Bridger, the general color above is decidedly 

 blackish, varied with pale yellowish-brown. No. 3374 is less black, and is 

 strongly washed with pale reddish-brown. No. 3370 is more grayish, but 

 still largely varied with black and more faintly washed with pale reddish- 

 brown. The darkest phase represents the S. armatus of Kennicott, while 

 the lighter is his S. elegans, as shown by his types. Others, from the same 

 localities as the above, showing a tendency to small indistinct quadrate spots, 

 are his S. townsendi. Between these is every possible shade of intergradation. 

 With the greater duskiness of the general color of the dorsal surface, the 

 prevailing color of the tail is black, both above and below. There is gener- 

 ally a distinct basal bar of black in addition to the broad outer one, which, in 

 the northern form, is but faintly indicated. The darkest specimen is one from 

 Soda Springs, Oreg., which is nearly black above, profusely and finely mottled 

 with yellowish-gray. The tail is dark ochrey-brovvn and black, edged with 

 whitish-gcay. The skull is not different in size or other characters from 

 average adult examples from other localities further eastward. 



In both this variety and var. richardsoni, the tail-vertebrae alone vary fully 

 an inch in length. In the table of measurements, the northern form appears 

 to have much the longer tail ; but the series of over sixty specimens of var. 

 richardsoni shows that in the average there is no material difference in respect 

 to this character in the two forms. Many of the northern specimens have 

 tails as short as any of the southern examples, while some of the southern 

 specimens have tails as long as the longest northern-tailed examples. A part 

 of the apparent difference in respect to the length of the tail as given in the 

 tables is perhaps due to different methods of measurement. 



GENERAL REMARKS RESPECTING SPERMOPH1LUS RICHARDSONI AKD ITS VARIETIES. 



Differential characters and affinities. — Spermophilus richardsoni 

 approaches quite nearly in size to S. franklini, but, in color, proportions, and 



