62 BIRDS AND MAMMALS OF EAST SIBERIA [^Vof 



P.N.E.Z.C. 



V 



To judge from descriptions alone, it is similar in many of its charac- 

 ters to L. minusculus, described by Osgood from the base of the 

 Alaska peninsula, but seems less brightly colored, though of about 

 the same size. It probably is the Siberian representative of this 

 animal. 



Dicrostonyx chionopaes sp. nov. Kolyma White Lemming. 



Type, skin and skull, no. 15,263, M. C. Z., adult male, from Nijni 

 Kolymsk, near the mouth of the Kolyma River, eastern Siberia, collected 

 October 15, 1911, by Johan Koren. 



General characters. — A dwarf species, smaller than M. torquatus, but with 

 a relatively large skuU. 



Description. — The type and only specimen has nearly completed the 

 change to winter coloration. It is entirely white, except for a small patch of 

 hazel on the top of the head and nape, and one on the center of the chest, 

 remains of the summer coat. Elsewhere the fur is slaty at the base and 

 white terminally, with — in the mid-dorsal region — a substratum of russet- 

 tipped hairs intermixed with a few black hairs, which, however, do not 

 show sufficiently to darken the pure white, and appear to be part of the 

 summer pelage. The two middle claws of the fore feet are already much 

 enlarged, as typical of the winter condition in this genus, but have not yet 

 become much swollen in their lower half. 



Skull. — Compared with Dicrostonyx from Alaska, Greenland and 

 Labrador, the skuU shows no great pecuharities, except that the inter- 

 parietal is nearly rectangular in outline without an anterior projecting 

 point. It is slightly smaller in all its proportions than Middendorff's 

 figure, natural size, of the skull of D. torquatus from the Taimyr peninsula, 

 of western Siberia. It is quite adult, with the basi-occipital suture soHdly 

 fused and ridged. 



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

 total length, 4.56 inches (116 mm.); tail, 0.57 inch (14.6 mm.); hind 

 foot, 0.78 inch (20 mm.). Skull: condylobasal length, 27.5 mm.; pala- 

 tal length, 16; diastema, 9; nasals, 8.8; zygomatic breadth, 18; interorbital 

 constriction, 3; breadth between tips of postorbital processes, 12; mastoid 

 breadth, 13.8; interparietal, 4.7X2.3; length of incisive foramina, 5.5; 

 greatest breadth outside last upper molars, 7; audital bulla, 7.5X5.2; 

 maxillary tooth-row, 7; mandibular tooth-row, 6.8. 



Remarks. — Hitherto but a single species of Dicrostonyx has been 

 recognized as occurring in the Old World. This is the Mus tor- 



