412 Birds of Colorado 
from which it seems to have been recorded is between Albuquerque 
and Mesilla on the Rio Grande in New Mexico (Brewster, ‘‘ Bull. Orn. 
Club,” VII., p. 147). 
Family HIRUNDINIDA. 
Bill short, flat, very broad at the base, triangular 
in shape when viewed from above ; edges of the mandibles 
smooth, upper slightly notched. Gape very wide, rictal 
bristles weak. Wings long and sharp-pointed, of nine 
primaries only, the two outer (8th and 9th) the longest 
and subequal to one another; tail of twelve feathers, 
usually more or less forked ; feet short, small and weak, 
ill adapted for progression on the ground. Only one 
moult in the year, in spring. Sexes usually alike and the 
young closely resembling the adults. 
The Swallows form a well-marked and sharply isolated 
family with no very close allies. Over a hundred species 
are recognised, and they are distributed all over the 
globe, except in the Arctic and Antarctic regions. 
Key or THE GENERA. 
A. Nostrils rounded, opening superiorly, without operculum or 
overhanging scale. 
a. Larger—wing over 5; tail distinctly forked. Progne, p. 413. 
b. Smaller—wing under 5; tail square  Petrochelidon, p. 415. 
c. Smallest—wing under 4:5 ; tail square ; outer primary roughed 
with hooks Stelgidopteryx, p. 422. 
B. Nostrils elongate or oval, opening laterally below an operculum 
or overhanging scale. 
a. Lower part of the tarsus with a tuft of feathers. 
Riparia, p. 421. 
b. No tuft of feathers on the lower part of the tarsus. 
a? Tail very strongly forked for at least } of its length; 
the outer feather attenuated; a white spot on the 
inner web of each tail-feather. Hirundo, p. 416. 
b?. Tail less strongly forked ; the outer feathers not attenu- 
ated ; no white spots on the tail. 
a’ Taillonger, about 4 wing, forked for about } its length. 
Iridoprocne, p. 418. 
b? Tail shorter, about 3 wing, forked for about } its length. 
Tachycineta, p. 420. 
