184 MICROTIN^ 



developed, extending over the ujjj^ci" surface from the forehead 

 to the base of the tail and to the flanks ; the precise hue of the 

 mantle varies from a shade between " sayal-brown " and " russet " 

 to one between " vernon-brown " and " mars-brown." Fore- 

 head (and sometimes the whole upper surface of the head), 

 cheeks, shoulders, flanks, thighs and lower rump grey, inter- 

 mediate between " neutral grey " and " drab." Ventral surface 

 between " pale smoke grey " and " pale neutral grey." Hind- 

 feet a little narrower and with less developed nails than in M. 

 thayeri ; more robust and with more prominent plantar tubercles 

 than in M. schisticolor; " cinnamon drab " or else " light neutral 

 grey " to " drab-grey ' above. Tail less hairy than in either 

 M. schisticolor or M. thayeri; above coloured like the feet but 

 darker, below very light grey. 



Skull slightly larger than that of M. schisticolor and M. morulus ; 

 most closely resembling that of M. saianicus. It agrees with 

 the latter in the large size and convexity of the auditory bullae; 

 but differs in having the squamosals more widely separated 

 anteriorly (by 2-3 mm., instead of 1-1; bistephanic breadth 

 4*3-5 instead of 3-9) ; and in the palate being furnished with 

 a jjosterior median spinous process. 



Upper incisors robust as in M. thayeri and M. saianicus ; cheek- 

 teeth not peculiar. 



For cranial a)id external ■measureme^ds, see tables at end of 

 volume. 



Remarks. — This form, as was to be expected, has now been 

 shown by Vinogradov to be more nearly related to the neigh- 

 bouring species M. saianicus and M. thayeri than to the more 

 western members of the genus {M. morulus and M. schisticolor). 

 Vinogradov calls attention to the well-developed interorbital 

 crest and to the divergent lachrymal crests which extend from 

 the anterior end of the interorbital crest to the anterior angles 

 of the orbits in M. middendorffi; those crests are, of course, 

 developed in fully mature specimens of all the species, and they 

 merely indicate that Vinogradov has been fortunate enough to 

 work with really mature material. 



5. Myopus thayeri G. M. Allen. 

 1914. Myojms thayeri G. M. Allen, Proc. New Engl. Zool. Club, 5, 

 p. 58. 



Type. — Mus. Comp. Zool. Harvard Univ., No. 15, 264; adult 

 male, skin and skull, collected March 28, 1912, by J. Koren. 



Type locality. — Nijni Kolymsk, near the mouth of the Kolyma 

 River, N.E. Siberia. 



Range. — Known only from the type locality. 



Characters.- — Size as in M. schisticolor or slightly larger, hind- 

 foot 18 mm., condylo-basal. length 25-8, dorsal rufous mantle 

 practically absent. Fur (in winter pelage) remarkably thick 



