As suggested by Dalquest in 1953 (p. 62) and by Handley in 1959 (p. 119) and 1960 (p. 473), the yellow bats, _Lasiurus ega_ (Gervais) and _Lasiurus intermedius_ H. Allen, so closely resemble the hoary bat, _Lasiurus cinereus_ (Palisot de Beauvois), and the red bats, _Lasiurus borealis_ (Mueller) and the seven related species listed below, that all are properly included in a single genus. Many of the common characteristics are enumerated above in the diagnosis of the genus (see also Handley, 1960:473). [Illustration: FIG. 3. Diagram of bones of right arm and third finger (middle digit) including cartilage on distal end of terminal (3rd) phalanx. Percentages are in terms of the over-all length of the arm and third finger.] A listing of the differences between the species is less impressive than a listing of the resemblances. The yellow bats differ less from the red bats than does the hoary bat, _L. cinereus_, which differs from all of the others as follows: talonid on m3 larger; p4 single-rooted instead of double-rooted; hypocone on M1 and M2 smaller; coronoid process lower; ossified part of tympanic ring, which shields the petrosal, larger; humerus relatively shorter; forearm relatively longer; first phalanx of middle finger relatively shorter; presternum including keel longer than wide instead of _vice versa_. The differences in the sternum and proportions of the forelimb reflect the more rapid flight of the hoary bat. The yellow bats differ from the red bats and hoary bat in long rostrum, pronounced sagittal crest, high coronoid process, absence of the first upper premolar, long first phalanx of the third digit and short terminal (3rd) phalanx of the same digit. Features in which the red bats are extreme in the genus are short rostrum, short forearm, and relatively longer second phalanx of the third finger. The red bats differ only slightly one from another. Next to nothing is known of extinct Tertiary ancestors of species of the genus _Lasiurus_. Also relatively little is known about _Lasiurus_ in the Pleistocene. Consequently, evolution of the living species has to be inferred almost entirely from what is known about their structure, habits, and geographic distribution. Figure 4 presents some ideas concerning relationships. [Illustration: FIG. 4. Postulated relationships of species of the genus _Lasiurus_.] LIST OF NAMED KINDS OF THE GENUS LASIURUS The words "type from" indicate that a specimen or specimens served as basis for the name. The words "type locality" signify lack of knowledge as to whether a specimen was preserved. Red Bats _Lasiurus borealis borealis_ (Mueller), 1776, type from New York. [_Vespertilio_] _noveboracensis_ Erxleben, 1777, based, in part, on "Der Neujorker" of Mueller (_ante_). _Vespertilio lasiurus_ Schreber, 1781, type locality, North America. _Vespertilio rubellus_ Palisot de Beauvois, 1796, type locality unknown.