''m'i^] ALLEN — MAMMALS 59 



ceptible except on close inspection. The pelage of winter is remarkably 

 thick and long, that of the back some 23 mm., slightly shorter on the head, 

 but the ears are quite hidden. Feet thinly haired, 'drab' with a silvery 

 tinge. Tail, above, like the body; below, whitish. At the wrist, ventrally, 

 is a cluster of stiff whitish hairs, which, however, do not cover the palm; 

 tarsus well haired with pale brownish. 



Skull and teeth. — The skull appears to be slightly larger than in cither 

 of the two other forms at present known. There is no tendency to the loss 

 of the small outer triangle of the last lower molar, such as Miller records in 

 case of the European M. schisticolor, for in both specimens it is well marked 

 off on each side. 



Measurements. — The type was measured by the collector, as follows: 

 total length, 114 mm.; tail, 15; hind foot, 18. In a second specimen these 

 dimensions were, respectively, 103, 20, and 18. Skull: condylobasal 

 length, 25.8; zj'gomatic breadth, 16; mastoid breadth, 13; interorbital 

 constriction, 3.7; depth of brain-case at the middle, 7.8; nasal, 7; dia- 

 stema, 8; maxillary tooth-row, 7.5; mandibular tooth-row, 7. 



Remarks. — This is the third species described of this rare genus. 

 It is represented by two good specimens, both of which were found 

 dead on the snow by Mr. Koren. One was at the foot of a small 

 declivity, the other out in the open, where he saw it a long distance 

 away. Mr. Koren is inclined to think that these two individuals 

 had come out onto the snow and, having been unable to find their 

 burrows again, were soon frozen to death in the intense cold. The 

 extraordinarily long, thick pelage would seem suited to protect 

 them against any degree of frost, however. 



This peculiar lemming differs markedly from M. schisticolor of 

 northern Europe and M. morulus of the Altai Mountains, in the 

 almost complete suppression of the rufous area of the back, so that 

 at a short distance it appears a uniform dark slaty, or ' neutral gray.' 



I have named it in honor of Mr. John E. Thayer, to whose 

 active interest in zoological exploration this important discovery 

 is due. 



Dr. J. A. Allen (1903, p. 153), in describing Lemmus obensis 

 chrysogaster from the west coast of the Okhotsk Sea, refers to it, 

 as a synonym, Middendorff 's Myodes schisticolor. This record was 

 based on a skin and skull from the same region, and was supposed 

 by Middendorff to represent the European species. In view of the 



