4 BULLETIN 86, UNITED STATES NATIONAL MUSEUM. 



Geographical distribution. — Nearly all of South America, the West 

 Indies, Central America, and North America excepting the far 

 northern part. 



Faunal distribution. — All or parts of the Patagonian, Brazilian, 

 Subandean, Amazonian, Antillean, and Central American subregions 

 of the Neotropical Eegion; the Sonoran and Boreal subregions of 

 the Nearctic Region; but avoiding the barren grounds and alpine 

 summits of the circumpolar Arctic Region. 



Variance in generic characters. — No two of the three species at pres- 

 ent composing this genus, Chordeiles virginianus, Chordeiles acuti- 

 pennis, and Chordeiles rupestris, are exactly alike in structural char- 

 acters, although they all agree with the generic diagnosis above 

 given. In Chordeiles virginianus^ type of the genus, the first (out- 

 ermost) primary is usually longer than the second, occasionally 

 about equal, but rarely shorter; the secondaries relatively short, 

 the shortest usually not reaching the tips of the primary coverts 

 by at least 5 millimeters, often much more; and the distance from 

 the bend of the folded wing to end of shortest secondary generally 

 less than from the latter point to the tip of fourth primary (count- 

 ing from the outermost) ; outer pair of rectrices relatively narrow 

 and their tips much rounded; maxillo-palatines relatively rather 

 broad and somewhat triangular; anterior processes of the palatines 

 relatively rather broad and strong; vomer very narrow; pterygoids 

 with an antero-exterior angle which approaches the palatine; inter- 

 orbital region very broad; and the ridges on median portion of 

 frontals not strongly developed. 



In Chordeiles aeutipennis, however, the outermost (first) primary 

 is usually shorter than the second, occasionally about equal or longer; 

 secondaries longer than in Chordeiles virginianus, the shortest usually 

 not falling short of the tips of the primary coverts by more than 3 

 millimeters, commonly longer or at least not shorter than the pri- 

 mary coverts ; the distance from the bend of the folded wing to the 

 end of the shortest secondary greater, usually decidedly so, than the 

 distance from the latter point to the end of the fourth primary; 

 outer pair of rectrices relatively broader than in Chordeiles vir- 

 ginianus, and their tips more truncate; maxillo-palatines relatively 

 rather narrower and more elongated ; anterior processes of the pala- 

 tines more slender; vomer rather broader; pterygoids without a dis- 

 tinct antero-exterior angle; interorbital region somewhat narrower; 

 and the ridges on median portion of frontal bones more conspicuous. 



In Chordeiles rupestris the first (outermost) primary is longer than 

 the second ; the tertials are relatively longer than in Chordeiles virgi- 

 nianus and Chordeiles acutipennis, usually reaching or overreaching 



