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 this 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 off the forms of each species, then the sexes of 

 each. 



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



a 



. Abdomen and crissum pure white; jugulum pale grayish; basal portion of 



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



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



white. (Chordeiles riipestris.) 



&\ 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 darlier Chordeiles rupestris zaleucus. 



cl Upper parts lighter. 

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

 ings clacidedly 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 prlmaiy very 



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



brown spots or broad bars Chordeiles rupestris zaleucus. 



c\ More ochraceous or buffy above; white spot on inner vane of fourth 

 primary absent or very small and not reaching shaft. 

 d\ Larger; upper 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 ru/pestris. 



i^ Abdomen and crissum barred with blackish 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. 

 h\ 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 subtermiual bar on 

 tail; throat-patch white. (Males.) 



