pattern seems clear: _nuchalis_ and _ruber_ (as well as _varius_) were separated into montane, coastal, and eastern segments respectively, probably by glaciation (it seems to me in the Pleistocene), and have since re-established contact with one another. The grouse genus _Dendrogapus_ is divided into a Great Basin species, _D. obscurus_, which extends northward into British Columbia, and a Rocky Mountain species, _D. fuliginosus_, that is found in the Sierra Nevada and northward along the coast and Cascades into British Columbia. Although the two kinds have at times been considered conspecific, they differ in voice, hooting mechanism, and characters of the downy young, and so far no actual intergradation between the two has been shown (Grinnell and Miller, 1944:113). These grouse thus seem to offer additional evidence for a Pleistocene, possibly Wisconsinan, separation of the boreal fauna into a Rocky Mountain and a Pacific coastal segment. A notable sidelight on these data is the frequency with which species in the Sierra Nevada have their closest relatives in the Rocky Mountains, rather than in the geographically nearer Cascades or coastal areas. This similarity in fauna of the Sierra Nevada and the Rockies was noted long ago by Merriam (1899:86). RELATIONSHIPS WITH OTHER SPECIES During the Sangamonian interval, isolated segments of the once widespread ancestral _Sorex vagrans_ quite possibly persisted in such places as the Sierra Nevada, coastal southern California, the mountains of Arizona, New Mexico, and southern Mexico, and in the Black Hills (see fig. 6). One might expect that by Wisconsinan time these populations would have become reproductively isolated from their parent stock. They would therefore have remained specifically distinct when Wisconsinan _Sorex vagrans_, reoccupied these outlying areas, and may still be found isolated in places peripheral to the range of the ancestral species. [Illustration: FIG. 10. Probable distribution of _S. veraepacis_, _S. longirostris_, and the _S. ornatus_ group (stipple) and of their Wisconsinan ancestors (lines). Heavy line indicates limits of Wisconsinan glaciation.]