90 BULLETIN" 86, UNITED STATES NATIONAL MUSEUM. 



Chordeiles acutipennis exilis is much more like the widely separated 

 Yucatan form, Chordeiles acutipewnis microme^ns^ than like the 

 intervening and undoubtedly close ally, Chordeiles acutipennis acuti- 

 pennis. Other than this, the geographical variations of this species 

 present no peculiarities. 



The five forms here treated under Chordeiles aciitipennis are un- 

 doubtedly all subspecies, and the three heretofore recognized currently 

 pass as such. The Peruvian Chordeiles acutipennis exilis doubtless 

 intergrades geographically with Chordeiles acutipennis acutipennis^ 

 though we have seen no actual intermediates. Although Chordeiles 

 acutipennis micromeins ^ has in the breeding season no geographical 

 connection with Chordeiles a. acutipennis^ its individual variation in 

 both size and color bridges the gap between the characters of these 

 two forms ; while the same is practically true of Chordeiles acutipen- 

 nis micromeris^ and the much more widely separated Chordeiles 

 acutipe7inis exilis. The northern Chordeiles acutipennis texensis 

 passes into Chordeiles acutipennis micromeris '^ in southern Mexico, 

 intergrading both geographically and individually; and similarly 

 into Chordeiles acutipennis inferior^ in southern California and ex- 

 treme northern Lower California. Actual geographical intermedi- 

 ates are, however, few in the material examined, doubtless from 

 lack of specimens from the particular localities where intergradation 

 takes place ; but intermediates due to individual variation are of 

 frequent occurrence. 



The characters which serve to separate the several subspecies con- 

 sist largely in differences of size, principally of wing and tail, some- 

 times also of exposed culmen, tarsus, and middle toe ; the colors and 

 general tone of upper surface and lower parts, light or dark; the 

 width of both the dark bars and the light interspaces on the posterior 

 lower surface ; and the width of the light bars on the tail. 



Geographical distribution. — The breeding range of Chordeiles 

 acutipennis as a species extends, in South America, from southern 

 Brazil to Venezuela and Colombia, including, as well, the islands of 

 Tobago and Margarita ; also to British Honduras, Guatemala, Mexico, 

 and the southwestern portion of the United States. It winters also 

 in the remaining countries of Central America. The typical race, 

 Chordeiles acutipennis acutipennis^ occupies an area in South America 

 approximately twice as great as the combined range of the four other 

 subspecies. Of the latter, Chordeiles acutipennis texensis has a range 

 of considerable extent ; but Chordeiles acutipennis exilis and Chor- 



1 See p. 100. 



2 See p. 109. 



