THE GENUS CHORDEILES SWAINSON — OBERHOLSER. 23 



purpose is, of course, to aid in comparison of specimens. So diffi- 

 cult, in fact, are the birds of tliis genus, that, owing to the wide range 

 of individual and other variation in them all, it is quite out of the 

 question to prepare a satisfactory key for use without recourse to 

 properly determined material. The present attempt at a key is based 

 entirely on adults, since the juveniles are not represented completely 

 enough in our series to be included. This key is, of course, dicho- 

 tomous, and first sets oS. the forms of each species, then the sexes of 

 each. 



KEY TO THE SPECIES AND SUBSPECIES OF CHORDEILES, BASED ON ADULTS. 



o\ Abdomen and crissum pure wliite; jugulum pale grayish; basal portion of 



tail, secondaries, and of inner primaries largely wliite; 3 outer primaries 



without white or buffy spots ; axillars and part of under wing-coverts pure 



white. iChordeiles rupestris.) 



b\ Larger; fourth primary (counting from outermost) without a white spot; 



tail with much less brown at base and elsewhere; dark brown tips of 



rectrices not mottled with paler. (Males,) 



&. Upper parts darker Chordeiles rupestris zaleucus. 



c^ Upper parts lighter. 

 d\ Somewhat smaller ; upper surface much darker, the deep brown mark- 

 ings dacidedly larger; breast much less heavily spotted, sometimes 



even nearly immaculate Chordeiles rupestris rupestris, 



d\ Somewhat larger ; upper surface much lighter, the deep brown mark- 

 ings decidedly smaller; breast much more heavily spotted. 



Chordeiles rupestris xyostictus. 



b\ Smaller; fourth primary with usually a spot of white; tail with more 



brown at base and elsewhere ; dark brown tips of rectrices mottled with 



paler. (Females.) 



&. More grayish above; white spot on inner vane of fourth primaiy very 



large and reaching shaft; inner webs of rectrices with large dark 



brown spots or broad bars Chordeiles rupestris zaleucus. 



<?. More ochraceous or buffy above; white spot on inner vane of fourth 

 primary absent or very small and not reaching shaft. 

 d!\ Larger; upi)er surface lighter, less heavily marked with dark brown; 



breast more heavily spotted Chordeiles rupestris xyostictus. 



d^. Smaller; upper surface darker, more heavily marked with dark 



brown ; breast less heavily spotted Chordeiles rupestris rupestris. 



a' Abdomen and crissum barred with blackisli or brown ; jugulum dark brown 

 or blackish ; basal portion of tail, secondaries, and of inner primaries not 

 nearly all white, but mostly brown ; 3 outer primaries with a large white 

 or buffy spot; axillars and all of under wing-coverts heavily barred with 

 dark brown or blackish. 

 6^ White or buffy patch on usually 4 outer primaries situated between the 

 tips of the fifth and eighth primaries (counting from the outermost) ; 

 primary coverts and outer webs of primaries and secondaries with con- 

 spicuous spots or bars of buff or ochraceous; first (outermost) primary 

 usually shorter than second. (Chordeiles acutipennis.) 

 c\ Larger; wing speculum larger and white; a white subterminal bar on 

 tail; throat-patch white. (Males.) 



