_Distribution._--Forested areas of the entire state. This species is migratory and first appears about the middle of May. September 15th is the latest recorded occurrence, when one was seen at Seattle, King County. Marginal records are: Sportsmans Lake (W. W. D.), in the northwest; Carson (Taylor and Shaw, 1929: 9) in the southwest; Pass Creek Pass (W. W. D.) in the northeast; and Bly (Taylor and Shaw, 1929: 9) in the southeast. _Remarks._--The chocolate-brown color phase of the silver-haired bat is most common east of the Cascade Mountains, while almost all specimens from western Washington represent the black phase. This medium-sized bat is the darkest-colored species living in the state, ranging from chocolate-brown to nearly black. Numerous white-tipped hairs give the upper parts a frosted appearance. The upper surface of the interfemoral membrane is well furred, a character shared only with _Lasiurus_. The dental formula (i. 2-2/3-3, c. 1-1/1-1, p. 2-2/3-3, m. 3-3/3-3 = 36) is the same as that of _Corynorhinus_. The small ears and short tragus immediately distinguish the silver-haired bat from the long-eared bat. The genus _Lasionycteris_ contains but a single species, of which no geographic races have been described. It ranges across North America from coast to coast and from central Canada southward, in forested areas, nearly to Mexico. This species is known to be migratory, and southern records probably do not represent breeding individuals. In Washington these bats have been taken in the Transition, Canadian, and Hudsonian life-zones. They were found near clearings in forests of open pine woods in the arid section of eastern Washington, near mountain hemlock thickets in the high mountains, and in the dense rain-forests of the Pacific Coastal area. [Illustration: FIG. 40. Distribution of the silver-haired bat. _Lasionycteris noctivagans_, in Washington.] The size and flight of the silver-haired bats are distinctive, and after some experience it is possible to identify them in the air. It is an early flier, usually appearing just after the swallows roost. They fly at a considerable height, rarely coming within forty feet of the ground. The wings are moved with a "fluttery" motion, and their flight is interrupted by frequent short glides. They fly more rapidly than the big brown-bats, and twist and dart sideways more frequently. Compared with big brown-bats, silver-haired bats are relatively gregarious, and six to a dozen individuals were seen in the same area. They generally hunt in sweeping circles, from fifty to one hundred yards in diameter. In the daytime the silver-haired bats hide beneath slabs of loose bark on dead trees. Near Cottage Lake, King County, two individuals were found beneath the bark on an old, lightning-blasted stub. The dark color of the bats blended with the charred surface of the stub.