Grinnell (1918: 241-242) points out that, although bats are not subject to isolation by topographic barriers, as most wingless mammals are, they may be restricted by ecologic barriers in the same way as are other small mammals. This is particularly true of _Myotis_ in Washington. Of the eight species in the state, five are represented by one subspecies west of the Cascade Mountains and another, paler subspecies in the more arid country east of the Cascades. The mobility of bats makes it difficult to determine their origin and migrational history. Five of the _Myotis_ found in Washington seem to belong to the Pacific Coastal Fauna, and to have been isolated south of the last continental glacier. Complete isolation is unlikely as these species occur in the Cascade Mountains as well as in the Pacific Coastal Faunal Area, and three occur also in the Blue Mountains of southeastern Washington. The differentiation of the Coastal type of _Myotis_ may have come about through habitat selection, of the type discussed by Miller (1942: 25). One western Washington _Myotis_ (_M. keenii_) seems to belong to a northern fauna, and to have extended its range south to Washington. All seven species of the desert-living _Myotis_ found in eastern Washington have subspecies which seem to have been derived from the Great Basin Faunal Area. =Myotis lucifugus= (Le Conte) Big myotis _Myotis lucifugus_ is represented by two geographic races in Washington. The species ranges across Canada and the United States, from the Atlantic to the Pacific and from the northern limit of tree growth to southern Mexico. [Illustration: FIG. 33. Distribution of the big myotis in Washington. A. _Myotis lucifugus alascensis._ B. _Myotis lucifugus carissima._] It usually proves rather difficult to separate _Myotis lucifugus_, on the basis of external features, from other species with which it may occur. Its large foot (9-10 mm.), short ear (when laid forward not extending past nose) and the absence of a keel on the calcar separate it from all species except _Myotis yumanensis_. From the latter species, _lucifugus_ may be distinguished by the gradually rather than abruptly rising forehead, as seen in cleaned skulls, and by more shiny, metallic color of fur. Little is known of the habits of this bat in Washington. It usually appears after dusk, and most specimens are shot over ponds or lakes, where the reflection of light from the sky on the water allows the hunter enough light to sight a gun. A few specimens were collected in deep forests. Its flight and feeding habits are not known to differ from those of other species with which it was associated, except at the south end of Lake Chelan, Chelan County, where two individuals were shot as they hovered near the tops of pine trees and seemed to be picking insects from the branches. I have never found this bat in its daytime retreat. A specimen taken at Sportman's Lake, San Juan County, held one embryo on June 26, 1938.