ifi-i] Grinnell : Mammals and Birds of tht Colorado Valley 261 



seven or eight black tail bars are narrower, thus making the light 

 intervals broader; the whole tail is thus very much lighter colored. 



(3) The "black" color of the hairs is in many places not so intense. 

 being, particularly on the tail and head, of a deep vandyke brown. 

 Fading evidently brings a browning of the dark hairs to some extent. 



(4) The under fur is very much paler in color. Dorsally it is Vandyke 

 brown instead of bistre; on the sides and belly it grades through cin- 

 namon to pale clay color. In the facial region the typical coon pattern 

 is present, but the white markings are not so conspicuously contrasted. 

 This is due to the less intense black, and to the fact that the pilenm 

 is scarcely darker than the rest of the back. The post-mental area 

 and the median nasal stripe are rather pale vandyke brown. Only the 

 transocular black patch is retained in nearly its usual distinctness. 

 The whiteness of the backs of the ears is a notable feature; and there 

 is altogether lacking the black patch behind the ears usually so well 

 marked in psora. 



In a general way pallidus thus differs from psora in very much 

 paler coloration. The two specimens from the vicinity of Imperial are 

 topotypes of pallidus, and accord closely with the brief description of 

 the form as given by Merriam. These two topotypes are the palest 

 of our pallidus, but it will be observed from the list that they were 

 secured in Hay. As might be expected from this circumstance, they 

 had evidently been subjected to much more wear than especially our 

 Needles and Melleu specimens, which are somewhat darker. It is easy 

 to see that the cutting off of the black tips of the long hairs in the 

 latter, particularly on the mid-dorsal region, would result in a decided 

 paling in the general color. 



Eliminating this factor of wear, and the slight amount of fading 

 which very probably occurs (even though these nocturnal animals 

 may not be exposed to intense sunshine to any large extent as they 

 probably spend the day in drift piles or thickets rather than in trees), 

 I cannot see that those specimens from farthest up the river are any 

 paler than those from farther down the river, or than the topotypes. 



It would not be reasonable, therefore, to hold that the apparently 

 darker animals farthest up the river from the assumed center of differ- 

 entiation (Colorado delta) indicate intergradation with darker coons 

 to the northward, even though this might lie expected. It is even pos- 

 sible that the cliff-confined river above forms an effectual barrier to 

 the north, so that there has been little chance of mingling of coon 

 strains from eLsewhere. Pallidus may be hemmed in by ordinarily 

 uncrossable barriers, and hence has attained a clear-cut specific identity. 



