31 <•> 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



it is usual to see individuals in perfect summer garb as to the anterior 

 half of their bodies, though without a particle of overhair on the pos- 

 terior half, excepting the tail, which retains the winter coating until 

 this time, new hair beginning to appear just as the summer coat has pro- 

 ceeded backward from the nose to a point behind the shoulders. Twenty 

 adults, taken from September 3 to December 21, fail to show clearly 

 the progress of the change from summer to winter coat, though a con- 

 siderable change does take place, as is instantly appreciated when speci- 

 mens in fresh summer coat are compared with those taken in December, 

 when the winter coat is prime. In the summer pelage underfur is absent 

 on the belly, the skin appears between the sparse overhair, and the hair 

 is short throughout. In winter the belly is well covered with underfur, 

 and the entire coating longer. There are no positive color differences. 

 In July and August the posterior half of the body usually becomes sun- 

 burnt, and changes to a dull, brownish color. When the overhair falls 

 out in masses the plumbeous underfur soon changes to the same brown 

 color until replaced by the incoming summer pelage. Lactation seems 

 to exert but little influence upon the season of molting. Males acquire 

 the summer coat, as a rule, no earlier than females. Quite young speci- 

 mens were collected from July to November, showing that the season of 

 reproduction is quite irregular or that more than one litter of young is 

 raised in a season. The young are similar to their parents, but with 

 the colors brighter and often more strongly washed with brownish 

 posteriorly. 



Cranial measurements <;/' J '/ adults of Otospermophilus grammurus from the Verde Basin, 



Arizona. 



a American Museum of Natural History. 



