BIRDS OF NORTH AND MIDDLE AMERICA. 715 
Rhaphidura Oates, Birds» Burmah, ii, 1883, 6. (Type, Acanthylis. leucopygialis 
Blyth.) 
Acanthura 4 Gumpine, Zool. Journ., iii, 1827, 407. (Type, Hirundo acuta 
“Stephens” i. e. Gmelin.) 
Small Cheturine Swifts (wing about 100-130 mm.) resembling 
Cypseloides but with the hallux relatively much smaller (less than 
half as long as inner toe) and with shafts of the rectrices more rigid, 
usually conspicuously extruded terminally. 
Nostrils elliptical, nearly parallel, for the most part anterior to the 
latero-frontal anti; distance from tip of longest secondary to that 
of longest primary about two-thirds the total length of wing; tenth 
and ninth primaries longest, usually nearly or quite equal in length, 
but sometimes one or the other a little shorter, the tenth (outer- 
most) more or less narrowed (sometimes subacuminate) terminally; 
tail (to base of spines) less than two-ninths to more than one-third 
as long as wing, truncate or slightly rounded, very firm, the shafts 
very rigid and, usually, conspicuously extruded terminally, forming 
spine-like tips; tarsus equal to or longer than middle toe with claw, 
entirely naked, nonscutellate; outer toe slightly shorter, the inner 
toe slightly to decidedly shorter, than middle toe; hallux very 
small and weak, less than half as long as inner toe.? 
Coloration.—Plain sooty or blackish, sometimes with a gray or 
whitish rump-patch or band, one species with the rump, tail-coverts, 
and tail light gray in contrast with rest of plumage. 
Nidification.—Nest in form of a half saucer or shallow cup, com- 
posed of dried twigs glued together by salivary excretion and at- 
tached by same substance to the inner wall of a hollow tree, chimney, 
or similar place. 
KEY TO THE SPECIES AND SUBSPECIES OF CHETURA. 
a. Under-parts of body and under tail-coverts gray or sooty, concolor with or paler 
than tail. 
b. Rump brownish gray or grayish brown, concolor with tail and not conspicu- 
ously lighter than back; tail relatively shorter (only two-sevenths as long 
as wing). 
c. Under parts and rump darker brownish gray or grayish brown. 
d. Larger (wing 122-133 mm.); pileum and back not blackish. (Eastern 
North America, south to eastern Mexico in winter.) 
Cheetura pelagica (p. 717). 
a?’ AxayOa, thorn, spine; odpd, tail. (Richmond.) 
b According to Lucas (Auk, xiii, 1896, 82) Chetura (C. pelagica at least) is peculiar 
among the North American genera of Swifts in lacking the deltoid muscle. This 
muscle is present not only in other North American genera but also in Tachornis, 
Streptoprocne, Collocalia, and Macropteryz (double in the last, single in the rest). It 
is not known, however, whether it is-present or absent in Panyptila, Claudia, Mi- 
cropus, or Cypseloides, or other species of Chxtura than C. pelagica. (See Auk, xvi, 
1899, 77, as to deltoid muscle in Streptoprocne.) 
