1797. _Nycteris_ B[orkhause]n, Der Zoologe (Compendiose Bibliothek gemeinnuetzigsten Kenntnisse fuer alle Staende, pt. 21), Heft 4-7, p. 66. Type, _Vespertilio borealis_ Mueller [= _Lasiurus borealis_]. _Nycteris_ Borkhausen is a homonym of _Nycteris_ G. Cuvier and E. Geoffroy St.-Hilaire, 1795, type _Vespertilio hispidus_ Schreber, 1774 [= _Nycteris hispida_], from Senegal. Although _Nycteris_ Cuvier and Geoffroy St.-Hilaire is a _nomen nudum_, Opinion 111 of the International Commission of Zoological Nomenclature establishes the name as available for a genus of Old World bats. On this basis, _Nycteris_ Borkhausen is not available for the New World genus. _Nycteris_ E. Geoffroy St.-Hilaire, 1803, is a synonym of _Nycteris_ Cuvier and Geoffroy St.-Hilaire, 1795, as given status by the Commission. 1831. _Lasiurus_ Gray, Zool. Misc., No. 1, p. 38. Type, _Vespertilio borealis_ Mueller. 1871. _Atalapha_ Peters, Monatsber. K. Preuss. Akad. Wiss., Berlin, p. 907, and other authors [_nec Atalapha_ Rafinesque, 1814]. _Type species._--_Vespertilio borealis_ Mueller. _Diagnosis._--Interfemoral membrane large and most of its upper surface furred; mammae 4; third, fourth and fifth fingers progressively shortened; ear short and rounded; skull short and broad; nares and palatal emargination wide and shallow (width transversely exceeding length anteroposteriorly); sternum prominently keeled; i. 1/3, c. 1/1, p. 1/2 or 2/2, m. 3/3; when two upper premolars present, anterior one minute, peglike, and displaced lingually; M3 much reduced, area of its crown less than a third that of M1. Members of this genus are notable for having three and even four young (more than other bats). In North America at least _L. borealis_ and _L. cinereus_, are migratory. Provisional Key to the Recent Species of _Lasiurus_ 1. Color reddish or grayish (not yellowish); normally two premolars on each side of upper jaw. 2. Occurring on Antillean islands (color reddish). 3. Length of upper tooth-row less than 4.5 mm. (occurring on Hispaniola and Bahamas) _L. minor_. 3'. Length of upper tooth-row more than 4.5 mm. (not occurring on Hispaniola and Bahamas). 4. Greatest length of skull less than 13.9 mm. (occurring on Cuba) _L. pfeifferi._ 4'. Greatest length of skull more than 13.9 mm. (occurring on Jamaica) _L. degelidus._ 2'. Occurring on mainland and coastal islands of North and South America; also on Galapagos and Hawaiian islands (color reddish or grayish). 5. Total length more than 120 mm.; color grayish _L. cinereus._ 5'. Total length less than 120 mm.; color reddish. 6. Upper parts brick red to rusty red, frequently washed with white; lacrimal ridge present.