554 Bulletin American Museum of Natural History. [Vol. XIX, 



form of the hind foot broad and short in Phenacomys and 

 long and slender in M. drummondi and certain differences 

 in the size and position of the plantar tubercles, however, will 

 usually suffice for their discrimination. In the reddish brown 

 fall dress, with the underparts more or less tinged with buff 

 (September, October, and November specimens), of M. drum- 

 mondi there is a well-marked contrast in color with July and 

 August specimens of Phenacomys constablei; but the adult fall 

 pelage of the latter is not as yet known. 



24. Synaptomys (Mictomys) andersoni, sp. nov. ANDERSON 

 LEMMING VOLE. 



Type, No. 20467, $ ad., Level Mountain, northern British Cokimbia, 

 September u, 1902; M. P. Anderson. 



Above dark brown, faintly suffused with clay color and strongly 

 varied with blackish, the head, including the sides of the nose and 

 cheeks, concolorous with the back; under surface ashy gray, rather 

 sharply denned against the yellowish brown flanks; tail bicolor, the 

 dorsal third blackish, the sides and lower surface dull grayish; upper 

 surface of fore and hind feet blackish brown, the hind feet rather 

 darker than the fore feet; ears small, wholly concealed in the fur. 



Total length, 120; tail vertebras, 25; hind foot, 18; ear, 11.5. 

 Skull: Naso-occipital length, 24.6; basal length, 23; zygomatic 

 breadth, 1-4.5; mastoid breadth, 11.5; interorbital constriction, 3; 

 length of braincase, 14; length of rostrum (front. edge of nasals to 

 braincase), n; length of nasals, 6; length of incisive foramina, 4.2; 

 length of upper toothrow, 6.6. General form of the skull much as in 

 S. wrangeli, but bullse much more inflated, especially anteriorly, and 

 the posterior loop on the last upper molar much larger, about two- 

 thirds as large as the middle loop; reentrant angle on outer side of 

 last molar deeper, nearly as deep as in S. truei. 



Synaptomys andersoni is based on a single adult specimen 

 collected on Level Mountain, northern British Columbia, Sep- 

 tember n, and is in heavy fall pelage. Its nearest known 

 geographical representative is 5. wrangeli, from Wrangel, 

 Alaska, from which it is apparently quite distinct, it in some 

 features more resembling S. dalli from Nulato, Alaska. The 

 species is named for Mr. M. P. Anderson, whose very careful 

 field work has so greatly contributed to the success of the 

 Stone Expeditions of 1902 and 1903. 



