Dicrostozyx 23 July Meade River Coal Mine, Alaska This lichen-barren increases as one goes north and the ability of Dicrostozyx to assume the summer pelage may give it the advantage by concealing coloration over Lemmus. The latter would certainly stand out on the gray (generally) background. Another factor, of course, would be the presence of marshes, to which Lemmus seems to be particularly food- or adapted. Until data is accumulated we must assume an equal ability to survive in the snow and cold. However, the lack of furred feet in Lemmus may be significant. Cover is significant and it is my impression that Lemmus prefers more cover than Dicrostozyx. Both utilize what is available, but there is less where the latter is normally taken. In any case the original observation of the concealing coloration of the summer pelage of Dicrostozyx on the lichen-barren barrens is, I think, solid.