The Lemmings of the Genus Synaptomys. 



61 



palate breaks down to the interpterygoid notch. This ridge 

 separates the post-palatal pits and projects backward into the 

 post-palatal notch. In Mictomys the supraorbital ridges unite 

 in a single median ridge; in Synaptomys they are normally sep 

 arated by a sulcus. 



The differences in enamel pattern of the molar teeth in the 

 four species of Midomys now known are sho.wn in the accom 

 panying illustration (Fig. 4). The teeth are large and broad in 

 M. innuitus and dalli ; smaller and much narrower in wrangeli 

 and truei. The reentrant angles on the outer side of the lower 

 molars are deepest in truei (d'} ; shallowest in wrangeli (&'). 



FIG. 4. Knamel pattern of molar teeth in type specimens of 



Mictomys. X 5- 



a, b, c, d, upper series ; a', b', c' , d', lower series. 



a. Mictomys innuitus, Ft. Chimo, Ungava. 



b. Mictomys wrangeli, Wrangel, Alaska. 



c. Mictomys dalli, Nulato, Alaska. 



d. Mictomys truei, Skagit Valley, Washington. 



Synaptomys (Mictomys) innuitus True. 

 Mictomys innuitus True, Proc. U. S. Nat. Mus., XVII, 243, April 26, 1894. 



Type locality. Fort Chimo, Ungava, Labrador. 



General characters. Size and general appearance similar to Synaptomys 

 cooperi; ear slightly longer than in Synaptomys; tail shortest of the four 

 known species of Mictomys. 



Color (of alcoholic). " Upper surfaces grayish brown, as in Synaptomys; 

 under surfaces gray ; face pale brown ; lips, end of nose, and chin white ; 

 feet pale brown ; tail bicolored, pale brown above, white below." From 

 continued immersion in alcohol the color of the upper parts has now 

 changed to reddish brown. 



Cranial and dental characters. Skull as a whole very broad and flat; 

 brain case strongly depressed ; zygomata broadly spreading and standing 

 out squarely from rostrum ; audital bullse strongly inflated anteriorly, the 

 anterior border strongly convex forward. Contrasted with M. wrangeli, 



