“Neuer, | Colors of West Coast Mammals. 213 
be of more use in this species than in Sccurus fossor, for instance, is 
not easy to understand. There is another and more serious difficulty 
in the way of thus explaining it. Mr. J. A. Allen has shown in his 
article ‘‘ Seasonal Variations in Color in Sciurus hudsonius,’’* that 
the black stripe in this species becomes indistinct or obliterated in 
winter pelage, and the same is in all probability the case with the 
variety in question. Whether the black streak were of use as a 
recognition marking or as a sexual mark it would be of greatest im- 
portance during the breeding season at which time it is wanting. 
There are many markings in this group which are difficult to ex- 
plain. Thus, Sczwrus fossor, of the Sierra Nevada Mountains, and 
S. fossor nigripes, of the Coast Range, are not strikingly different, 
except that in the latter the hind feet are darker than the back (ap- 
parently at all seasons either black or dark brownish), while in the 
former the feet are lighter than the back (silvery or whitish gray). 
What influence could have produced this modification is not easily 
seen, for it could hardly have any utility as a recognition mark, nor 
could it have been produced by the direct action of the environment. 
- Inthe genus Zamzas we have, as Mr. Allen has observed,} a strik- 
ing example of a plastic group which has spread from a common 
center in comparatively recent times, and rapidly differentiated. 
There can be little doubt that the streaks so characteristic of the 
_ group are of some utility, for otherwise natural selection would have 
a tendency to obliterate them. Ina few forms this has been done, 
_ possibly for protection in open districts. The most obvious use of 
these markings, it would seem, would be for recognition in the 
darkness of the burrow, in which situation they would greatly facili- 
_ tate in locating the position of the body of one individual to its mate. 
In forms in which the streaking has attained the maximum of inten- 
sity a broad white line on each side is bordered by black, which 
relieves it so well that in the dark all that is visible of the animal is 
the white stripe down each side of theback. The white patch on the 
_ back of the ear might also facilitate recognition in the dark, and 
be classed with the socialistic markings. In accounting for the 
great number of variations in the group, Dr. Allen says:{ “ From 
; ae s *Bull. Am. Mus. Nat. Hist., iii, No.1, pp. 41-44. 
--——s ¢Bull. Am. Mus. Nat. Hist., iii, No. 1, pp. 45-116. 
seer te | : : il ane ‘p. 53. 
