Lasiurus ega Southern Yellow Bat _Diagnosis._--Upper parts yellowish-brown (much as in _Lasiurus intermedius floridanus_ from Louisiana) having overlay of grayish or blackish anterior to shoulders; hair on basal half of interfemoral membrane more yellowish than elsewhere; size medium (forearm 42.7-52.2; condylocanine length 14.6-16.3). This species occurs from the southwestern United States (Palm Springs, California, and Tucson, Arizona) southward into Uruguay and northeastern Argentina. Of the six currently (see Handley, 1960) recognized subspecies of _L. ega_, four occur only in South America, and two occur only in North America. Cabrera (1958:115) regarded _Dasypterus ega fuscatus_ Thomas (1901:246), based on three specimens from Rio Cauquete, Rio Cauca, Colombia, as a synonym of _Dasypterus ega panamensis_ Thomas (_loc. cit._) that was based on a specimen from Bogava, 250 meters elevation, Chiriqui, Panama. The latter name has line priority over _fuscatus_. Cabrera (1958:116) remarked that: "Las diferencias que Thomas senalo entre el _Dasypterus_ de Panama y el de Colombia (_fuscatus_) nos parecen estar dentro de los limites de la variacion individual, siendo ademas muy raro que una especie de quiroptero este representada en Colombia y en Panama por razas diferentes." On July 16, 1958, at the British Museum of Natural History, one of us (Hall) examined the holotypes of _panamensis_ and _fuscatus_, as well as other materials used by Thomas, and readily perceived the differences that he pointed out. Thomas' description, although terse, is accurate. _L. e. fuscatus_ is much more blackish than _panamensis_. We are inclined to retain the two names as applicable to two subspecies. Whether or not _fuscatus_ is synonymized under _panamensis_, the holotype of _panamensis_ is an intergrade between the almost black Colombian animal (_fuscatus_) and the paler individuals in Central America and territory north thereof. Even so, the holotype of _panamensis_ more closely resembles the blackish Colombian population than the paler populations to the north and the name _panamensis_, therefore, is correctly applicable to the bat from Panama, but not to bats of the species _Lasiurus ega_ from farther north as most authors (see, for example, Hall and Kelson, 1959:194, map 143; and Handley, 1960:474) suggested was the case. For the populations north of Panama the name _Lasiurus ega xanthinus_ (Thomas) (1897:544) needs to be used. Lasiurus ega xanthinus (Thomas) 1897. _Dasypterus ega xanthinus_ Thomas, Ann. Mag. Nat. Hist., ser. 6, 20:544, December, type from Sierra Laguna, Baja California. 1953. _Lasiurus ega xanthinus_, Dalquest, Louisiana State Univ. Studies, Biol. Ser., 1:61, December 28. _Geographic distribution._--Southern California, southern Arizona, and northern Coahuila southward through Mexico to southern Costa Rica.