ALLEN: AMERICAN COLLARED LEMMINGS. 515 



General characters. — Above, in summer, a nearly uniform buffy 

 gray; a median blackish line from the nape, to tail, not sharply de- 

 fined; ear-tufts, sides of the body, and throat buff; belly gray. 

 Pattern of anterior two upper molariform teeth characteristic in 

 lacking the small postero-internal lobe found in other American 

 species; the last lower molar likewise lacks a supplementary antero- 

 internal fold. Posterior process of parietal usually not extending 

 back on the cranial surface to supraoccipital. 



Color. — Adult in summer: — general tone of upper parts, including 

 the head, a buffy gray, varying to nearly clear gray, a result of the 

 mixture of three sorts of hairs: some gray-tipped, others gray with a 

 buffy to ochraceous subterminal band and black points, and still 

 others longer and entirely black. The bases of the hairs are slaty, 

 and the intensity of the buffy tone depends on the greater or less 

 development of the subterminal buffy or ochraceous ring in the second 

 sort of hairs. A median black line extends from the forehead to the 

 tail, but is not sharply defined. The ears are marked by a tuft of 

 tawny hairs, surrounded by an indistinct grayish patch. A wash of 

 tawny extends from the axillae across the throat, sometimes con- 

 tinued medially to the chest. A paler tint of the same extends along 

 the sides and about the anal region. A buffy spot on each side of the 

 nose and around the eye. Tail like the back or with a tuft of long 

 gray hairs. 



Young in summer: — immature specimens are nearly similar to 

 adults, but of a darker, less clear gray; the black median line is more 

 sharply defined and extends to the point of the nose. The tawny 

 collar is very indistinct. 



Winter pelage: - — white throughout, the bases of the hairs slaty. 



Skull. — In the shape of the interparietal, with its two anterior 

 sides sloping distinctly forward to a median peak (Plate 1, fig. 4) this 

 species resembles the Greenland Lemming and the Alaskan species, 

 but the upper border of the squamosal frequently abuts against 

 the extreme lateral edge of the interparietal, whereas in the other 

 American species, a narrow tongue of the parietal usually separates 

 the two bones. The nasals are relativeh' long, and equal or slightly 

 exceed the ascending branch of the premaxillary in backward exten- 

 sion. With age, as in the other species, an angular ridge develops 

 along the outer edge of the parietal region, and thick, rounded supra- 

 orbital ridges border the upper margin of the orbit, increasing in size 

 in old animals till they nearly meet. 



The teeth differ remarkably from those of any known species in 



