_Range._--Intermontane region of the United States from south-central Washington south to Catavina, Baja California, and from southeastern California eastward to southeastern Utah. Marginal occurrences (unless otherwise indicated, after Hatfield, Jour. Mamm., 17:258, 1936) are: _Washington_ (Dalquest, Univ. Kansas Publ., Mus. Nat. Hist., 2:165, 1948): Maryhill; Vantage; Almota. _Oregon_: Watson. _Idaho_: 8 mi. W Rogerson (Davis, Mamms. Idaho, p. 120, 1939). _Nevada_: Middle Stormy Spring (Hall, Mamms. Nevada, p. 151, 1946). _Utah_: Goodridge. _Arizona_: 11 mi. NW Kayenta; Tinajas Altas. _Baja California_: Catavina; San Jose; Laguna Hanson. _California_: Dos Palmos Spring; Banning; Victorville; 12 mi. below (down river) Bodfish; Little Lake; 2 mi. S Benton Station. _Nevada_: 2 mi. NW Morgans Ranch; Deephole. _Oregon_: Princeton. _Diagnosis._--Size medium for the species; total length, 71.8(66-74); tibia, 12.0(10.7-13.5); forearm, 29.4(27.8-31.8); greatest length of skull, 11.9(11.5-12.3); breadth of braincase, 6.3(6.1-6.4). Color between Drab Gray and Smoke Gray, dorsally; between Smoke Gray and Pale Smoke Gray, ventrally (after Hatfield, Jour. Mamm., 17:257, 1936). +Pipistrellus hesperus merriami+ (Dobson) _Vesperugo merriami_ Dobson, Ann. and Mag. Nat. Hist., 18(ser. 5): 124, August, 1896. _Pipistrellus hesperus merriami_ Grinnell, Proc. California Acad. Sci., 3(ser. 4):279, August 28, 1913. _Type locality._--Red Bluff, Tehama County, California. _Range._--California west of the Sierra Nevada; the Sacramento Valley, the San Joaquin Valley, and the Coast Range from San Francisco Bay south to San Diego County. Marginal occurrences (after Hatfield, Jour. Mamm., 17:260, 1936, unless otherwise noted) are: _California_: Dales on Paines Creek; Fyffe; Yosemite Valley; Shaver Ranger Station; Springville; Fort Tejon; Painted Gorge (P. H. Krutzsch, MS); Carrizo Creek; thence northward up the coast probably to San Francisco Bay; in the Sacramento Valley west to Rumsey. _Diagnosis._--Size medium for the species; total length, 71.3(66-78); tibia, 11.2(10.6-11.7); forearm, 28.9(27.5-30.8); greatest length of skull, 11.8(11.3-12.2); breadth of braincase, 6.4(6.0-6.6). Color Buffy Brown to Army Brown, dorsally; Wood Brown to Buffy Brown, ventrally (after Hatfield, _op. cit._: 258, 260). +Pipistrellus hesperus australis+ Miller _Pipistrellus hesperus australis_ Miller, N. Amer. Fauna, 13:90, October 16, 1897. _Pipistrellus hesperus apus_ Elliot, Field Columb. Mus., pub. 90, zool. ser., 3:269, March 8, 1904. Type from Providencia Mines, Sonora, Mexico. _Type locality._--Barranca Ibarra, Jalisco, Mexico.