The lemming mouse is similar in appearance and habits to the meadow mice; the head and body are four and one-half inches to five inches long; the tail from one to one and one-half inches. The back is a grizzled gray-brown, showing a yellowish tinge; the belly is gray-white; the fur is sprinkled with black hairs. The dull color and short tail distinguish this mouse from all others except the Oregon meadow mouse. The latter is slightly smaller, the hair is less woolly, but field distinction is difficult or impossible. _Specimens in park collection:_ None. The genus _Phenacomys_ is found in the western United States and most of Canada, inhabiting the mountain summits and colder zones. The Olympic phenacomys of Mount Rainier occurs only at the higher elevations, 4,500 to 8,500 feet in the park, and its range extends into the Olympic Mountains, as well as southward along the Cascade crest into central Oregon. The alpine parks and windswept slopes well above forest line are the home of the hardy little lemming mice. One of the common names for the animal, heather vole, is suggestive of the locality where they may be found, finding shelter in the protection afforded by the low-growing masses of the heather. Their range is not entirely confined to the alpine country, however, since records have been established in the upper forested areas, down to a low elevation of 4,000 feet. The only conspicuous evidences of the presence of the heather vole are the tidy, compact winter nests of dried grass, lichen, and other plant fibers. These nests, constructed on the ground under the snow, are apparently abandoned when the snow melts, and it is difficult to discover other signs of the animal’s activities. Like the meadow mice, the mountain lemming mouse is a staple item in the diet of the predators. CASCADE RED-BACKED MOUSE _Clethrionomys gapperi cascadensis_ Booth The red-backed mouse is slightly larger than a house mouse; in a typical specimen the head and body are about four inches long, the tail slightly less than two inches. The distinguishing characters which separate this animal from the other mice are the broad, reddish-brown stripe over the back from the forehead to the base of the tail (this stripe distinguishes it from the held mice), and the inconspicuous ears and short tail which are so different from the large ears and long tail of the white-footed mouse. _Specimens in park collection:_ RNP-17, RNP-62, RNP-63, RNP-65, RNP-66, RNP-67, RNP-68, RNP-69; Longmire Museum, Park Headquarters. The many species of red-backed mice occur generally over the wooded sections of North America. The Cascade red-backed mouse is found in the Cascade Mountains from British Columbia southward into Washington, east into northern Idaho and northeastern Oregon. In Mount Rainier National Park it occurs generally from park boundaries to forest line.