278 MICROTIN^ 



Characters. — Size very large and colour very variable. Adults 

 usually yellowish or greyish above, with a darker (often sooty) 

 dorsal stripe. Eed-backed individuals are in a small minority, 

 and even these have the face grey. In the type (representing the 

 colour phase that seems to be most usual), the sides, flanks, cheeks, 

 and face are smoke grey, somewhat shaded with yellowish and 

 drab, darkening on back into a broad dorsal stripe of sepia, and 

 paling off on under parts to light smoke grey. Hands and feet 

 dull grey. Tail indistinctly bicoloured, dusky above, dull grey 

 below ; both it and the feet hairier than in E. gapperi. 



Skull larger than that of E. gapperi (including E. g. ochraceus), 

 the braincase more angular, the interorbital constriction deeper, 

 and the post-orbital squamosal processes much more strongly 

 marked. Dentition normal. 



No skull measurements recorded. 



For external measurements, see table at end of volume. 



Remarks. — Mr. Bangs (Proc. Biol. Soc. Washington, 11, p. 

 239) describes this as the commonest small mammal about 

 Hamilton Inlet, and says : " Several times while walking through 

 the forest Mr. Goldthwaite discovered one sitting upon a spruce 

 branch ' like a squirrel.' I have never known of this arboreal 

 habit in other species. The range of individual colour variation 

 ... is simply astounding, and it seems incredible that extremes 

 from the series can belong to the same species, yet any specimen 

 picked out can be graded by the most delicate stejjs into any of 

 the other extremes." The plate, illustrating Mr. Bangs' paper, 

 is said to show " admirably a few of the most pronounced colour 

 phases." 



Genus : 6. ASCHIZOMYS Miller. 



1898. Aschizomys Miller, Proc. Acad. Nat. Sci. Philadelphia, 1898, 



p. 368; Hinton, Ann. Mag. N.H., [9], 11, 192, p. l47 (genus). 



Genotype. — Aschizomys lemmhius Miller. 



Range. — Known only from Plover Bay, Behring Strait, Siberia. 



Characters. — General outward form lemming-like. Tail very 

 short, the caudal vertebrae shorter than the hind-foot and but 

 slightly longer than the terminal hair-pencil. Plantar tubercles 6. 

 Mammary formula unknown. 



Skull essentially as in Evotomys, broad, depressed, lightly 

 built, smooth and rounded, with the palatal structure of typical 

 Evotomys; alveolar capsule of m^ forming a conspicuous hump 

 at the mouth of the sphenorbital fissure. 



Mandible with the m^ displaced lingually by the shaft of the 

 incisor and encapsuled as in E. rufocanus and Microtus. 



Cheek-teeth persistently growing, but with the general pattern 

 and rounded salient angles of typical Evotomys; m^ small and 

 weak with well-developed fourth outer angle. 



