ALLEN: AMERICAN COLLARED LEMMINGS. 521 



nasals, medially, 8.5; zygomatic breadth 20.7; interocbital breadth 4; ' 

 mastoid breadth 14.8; upper molar row (alveoli) 8.2; lower molar 

 row (alveoli) 7.7. 



Molt. — As in D. hudsonius, there is much individual variation in 

 the time of molt, due to age, vigor, or other causes. Specimens in 

 various transitional stages of molt from the pure white of winter to 

 the brilliant coat of summer often present a xery peculiar appearance. 

 A large series from Point Barrow, Alaska, illustrates very well the 

 course of the spring change. Midwinter specimens are pure white, 

 the bases of the hairs slaty. There is sometimes a slight yellowish 

 wash along the hips. In March, the first indication of the change is 

 seen in a pale yellowish tinge along the top of the head and fore-part 

 of the back, where by parting the fur, the tips of the new hairs are 

 seen nearly reaching the level of the winter coat, their buffy rings and 

 minute black tips giving the soiled appearance. A March 11th speci- 

 men from Point Barrow is in this condition. By early April this 

 yellowish wash overspreads the top of the back, except the rump. 

 By middle or late April a narrow brownish dorsal stripe is discernible 

 and an oval area over the back is decidedly yellowish or pale brown 

 medially. During May the new hair grows in and the white hair 

 disappears from the central part of the back progressively toward 

 the sides, until by the first week of June, the full summer coat is 

 complete. The gradual course of the replacement of the white by 

 the colored hairs produces a constant change in general tint of the 

 coat according to the greater or less amount of dilution by the white 

 hairs, though in old animals the change is less gradual, and irregular 

 patches of white hair are retained much later, while the new hair 

 on account of its slower growth is in marked contrast by its shortness. 



The progress of the fall molt cannot be traced from the specimens 

 available. A single immature male from Point Humphreys, Sep- 

 tember 28, 1913, is in an intermediate stage. The white winter hair 

 has come in on the head and lower surfaces, and on a broad strip the 

 length of the back, where, however, enough of the old coat still re- 

 mains to produce an indistinct black median stripe and a buffy wash 

 on the shoulders. Along the sides, the white hair is less developed, 

 so that these parts are still brownish. 



Several immature specimens from Griffin Point, collected by Mr. 

 Dixon in June 1914, seem to be losing the first dull yellowish coat 

 and acquiring the adult pelage. This apparently grows in from the 

 sides and rump tozvard the median line, the converse of the seasonal 

 changes. A complete series shows the gradual acquisition of the 



