_Distribution._--The northwestern Cascades, from Mt. Baker northward. _Remarks._--The relationship of this race to _artemisiae_ remains to be worked out. [Illustration: FIG. 109. Distribution of the northern lemming mouse in Washington. A. _Synaptomys borealis wrangeli._ B. Possible range of _Synaptomys borealis artemisiae_.] _Description._--Lemming mice may be recognized by their short, thick bodies, slightly larger than the bodies of the common house mouse (_Mus_); short tails, which are less than 20 per cent of their total length; small, inconspicuous ears; and grooved upper incisors. Mice of the genus _Synaptomys_ range over much of boreal North America. Two species and eleven races are recognized by Howell (1927B: 9). _Synaptomys borealis_ ranges westward across Canada from Labrador to the Pacific Coast and from Alaska south to Washington. The lemming mice are terrestrial and inhabit runways similar to those of meadow mice (_Microtus_). They are alpine in distribution. Shaw (1930: 7-10) found them among typical annual herbs in a cold, boggy mountain valley. Other than this, nothing is known of the species in Washington. Indeed little is known of the life history of any member of the genus. The lemming mouse possesses four pairs of mammae, two pectoral and two inguinal. It is the most primitive of the microtines. It seems to be of boreal origin but is not known from the Old World. It was evidently forced southward by the Pleistocene glaciers into Washington and is now retreating northward in the wake of the ice. The only specimens recorded from Washington are from the northern border of the state. =Phenacomys intermedius= Merriam Heather vole _Description._--Heather voles are heavy-bodied, short-legged mice, closely similar in general appearance to other microtines that occur in Washington. Their dull, brownish upper parts, lacking a distinct reddish dorsal stripe, separate them from the red-backed mice (_Clethrionomys_) and the lack of grooves on their upper incisors separates them from _Synaptomys_. Their relatively short tail (30 per cent or less of their total length) separates them from most meadow mice (_Microtus_). There are no external characters which serve to separate them from all species of _Microtus_ and the teeth must be examined certainly to identify _Phenacomys_. In _Microtus_ the angles between the cusps of the inner and outer sides of the lower molars are of approximately equal depth, but in _Phenacomys_ the angles on the inner side of the lower molars are at least twice as deep as those of the outer side of the jaw. In addition the molars of _Phenacomys_ are rooted while those of _Microtus_ are not.