_Diagnosis._--Size large for the species; total length, 82.0(80-86); tibia, 12.4(11.9-13.0); forearm, 32.8(31.7-34.1); greatest length of skull, 12.7(12.3-13.1); breadth of braincase, 6.6(6.3-6.8). Color between Buffy Brown and Wood Brown (after Hatfield, _op. cit._:261, 262). +Pipistrellus subflavus+ (Synonomy under subspecies) _Range._--Canadian to Tropical life-zones of eastern North America from Quebec southward to Honduras. _Characters._--Sayal Brown to darker than Mummy Brown, dorsally; total length, 73-89; foot more than half as long as tibia; tragus tapering and straight; dorsal profile of skull convex in interorbital region; inner upper incisor bicuspidate; outer upper incisor unicuspidate (lacking accessory cusp on anterointernal face); P1 viewed from occlusal face more than a seventh of area of canine and visible from labial aspect; lower, third premolar as high as anterior cusp of canine; lower premolars less crowded than in _P. hesperus_ and distance between canine and first molar less than length of second lower molar. _Remarks._--In winter this species hibernates in caves in clusters of fewer than fifty individuals, but in summer fewer of the bats live there and at this season some have been captured as far as thirty miles from any such retreat suggesting that the bats inhabit other types of shelter. The wide range of this species in respect to life-zones is noteworthy; it occurs in the Canadian Life-zone (Joliet, Quebec), the Tropical Life-zone (30 km. SSE Jesus Carranza, Veracruz) and in the intervening life-zones. The longer thumb of this species, in comparison with that of _Pipistrellus hesperus_, was verified by measuring the thumb including its claw and the pad at the base of the thumb in 12 _P. s. veracrucis_ and 10 _P. h. maximus_. In _veracrucis_ the mean was 5.9 millimeters and the extremes were 5.5 and 6.4. In _maximus_ the corresponding figures were 3.9, 3.6 and 4.3. +Pipistrellus subflavus subflavus+ (F. Cuvier) _V[espertilio]. subflavus_ F. Cuvier, Nouv. Ann. Mus. Hist. Nat. Paris, 1: 17, 1832. _Vespertilio erythrodactylus_ Temminck, Monogr. de Mamm., II, 13me monogr., p. 238, 1835-1841 (not seen--after Miller, N. Amer. Fauna, 13:90, October 16, 1897). _Scotophilus georgianus_ H. Allen, Smithsonian Miscl. Coll., No. 165, Vol. 7 (art. 1), p. 35, June, 1864. _Vesperugo carolinensis_ H. Allen, U. S. Nat. Mus. Bull. 43:121, March 14, 1894. _Pipistrellus subflavus_ Miller, N. Amer. Fauna, 13:90, figs. 22,23, October 16, 1897. _Type locality._--Eastern United States, probably Georgia.