Vol. XXIII 



1906 J Clark, Pterylosis of Swifts and Hummingbirds. 77 



the 10 rectrices the middle pair is shortest, the outer ones longest; 

 in streubeli, however, there is a sexual difference, for the tail is only 

 a very little forked in the female, while in the male the fork is deep 

 and the feathers narrowed. Of the 10 primaries, either the ninth 

 or tenth may be longest. The quincubital wing has 8 or 9 sec- 

 ondaries and the alula is made up of 2 or 3 feathers. 



Specimens examined. 



Cypselus. 



Nitzsch describes and figures the pterylosis of Cypselus apus, 

 but the arrangement of the feathers and tracts on the head and 

 neck are certainly not as he shows it, unless we are to believe that 

 this genus differs radically from all other known swifts. He says 

 there are "achtzehn Schwingen," which is probably correct. 



Trochili. 



The hummingbirds are another group in which the pterylosis 

 is remarkably uniform and quite distinctive, so that the figures 

 given of Troehilus alexandri will answer with slight changes for 

 any other species. The tracts are well defined and the apteria are 

 perfectly bare. The head is not thickly or uniformly clothed but 

 on the contrary the feathers tend to form longitudinal rows or 

 narrow tracts with more or less definite apteria between. Thomp- 

 son (:01) figures and describes admirably no less than 10 apteria 

 on the head of Patagona, and other hummingbirds show the same 

 general arrangement. Of these apteria, the most important are 

 those to which he gives the names frontal and supraocular, both 



