64 BIRDS AND MAMMALS OF EAST SIBERIA [^VoL' V*^ 



better defined. In some skins the tail is nearly uniform ochraceous 

 above, while in others it is mainly black with ochraceous hairs at 

 the sides or tip. Between these extremes all degrees of variation 

 occur. Mr. Koren obtained most of his specimens in buildings, 

 or under loose sticks, boards, and the like. One, even, was found 

 aboard his schooner. 



Microtus koreni sp. nov. Koren's Meadow Mouse. 



Tyye, skin and skull, no. 15,213, M. C. Z., adult female from Nijni 

 Kolymsk, near the mouth of the Kolyma River, northeastern Siberia, 

 collected November 1, 1911, by Johan Koren. 



General characters. — A large dark species, rather coarsely haired; tail 

 twice as long as the hind foot; skull large and angular, palate deeply pitted, 

 its lateral bridges strongly developed; its median termination tending to 

 develop a point; audital bullae large ; teeth of the M. araaKs type. 



Description. — The type is in freshly assumed winter pelage, of the usual 

 Microtus style, the hairs slaty at the base, with a broad subterminal band 

 of pale ochraceous, and tipped with black. The back is strongly lined with 

 black hairs, giving a very dark effect; toward the sides the black hairs are 

 fewer, and the subterminal rings are buffy. Feet, above, a silvered brown, 

 near 'dusky drab.' Ears nearly hidden in the fur. 



Ventral surfaces of body and limbs, white, the basal third of the hairs 

 slaty. In the type the belly is faintly washed with buffy, but this is not 

 the case in other specimens. Tail sharply bicolor, blackish brown above, 

 white beneath, rather coarsely haired. 



Skull and teeth. — The skull of the type is somewhat narrowed in the 

 interorbital region, and strongly ridged. Midway on the sides of the 

 brain-case a strong angular ridge marks the attachment of the cheek 

 muscles. The nasals expand abruptly near the middle of their length, 

 and taper posteriorly to the level of the inner edge of the zygoma, where 

 they are slightly exceeded by the ascending branch of the premaxillary. 

 The interparietal is fairly broad, its anterior boundary strongly brace- 

 shaped, with a decided median projection. The posterior border is slightly 

 convex. The incisors do not noticeably project. The incisive foramina 

 are narrow, and contract posteriorly. The palate is marked by two deep 

 grooves, with minute pits, and ends in a decided median point. The 

 lateral bridges in the type, and even in the youngest examples, are strongly 

 developed. The meso-pterygoid fossa is narrowly horseshoe-shaped in 

 outline. The audital bullae are very large and high, well rounded ante- 

 riorly. 



