HIRUNDINIDA. 269 
all others the bill weaker, more depressed, the commissure nearly straight 
to near the tip. 
The middle toe is lengthened ; the tarsus equal to the toe without the claw, 
its joint with tibia having overhanging feathers attached, which extend 
on the inner face of the tarsus a short distance, in /7Zirundo, Tachycineta, 
Pterochelidon, Progne. ‘Tarsus similarly feathered, but proportionally 
longer—being equal to middle toe and half the claw, in Neochelidon, 
Atticora, Pygochelidon, and Stelgidopteryx. It is of the same proportion, 
but entirely bare of feathers in Callichelidon and Notiochelidon. 
In Cotyle alone are there short feathers attached to the posterior face of tarsus 
near the lower end. Here also alone the lateral claws are very long, 
reaching considerably beyond the base of the middle claw. 
In Progne and Pheoprogne the basal joint of middle toe is adherent but little 
more than half way externally, about half way internally; almost the 
same on both sides. In almost all the rest it is adherent externally 
nearly to the end, and about half way internally, except in Tachycineta 
thalassina, where the adhesion is complete on both sides, except at the 
end of the inner; in Neochelidon and Notiochelidon, where the basal and 
half the middle joint: and in Atticora, where the basal and the whole 
middle joint are adherent externally. : 
In Stelgidopteryx the edge of the wing (outer edge of outer primary) is pro- 
vided with a series of stiff recurved hooks; in all other American genera 
these are entirely wanting, though said to exist in the African genus 
Psalidoprocne, Cab. 
The following synopsis may aid in determining the genera and 
subgenera of American Hirundinide, although the succession is not 
strictly natural :— 
Nostrils broadly oval, or circular; opening upwards and for- 
ward, and exposed; without overhanging membrane. 
Edge of wing smooth. Tarsus short, stout; equal to 
middle toe without claw; feathered on the inner 
side above. Nostrils almost or entirely without 
membrane. 
Bill stout; culmen and commissure much 
curved. Frontal feathers without bristles. 
Tail deeply forked. Color lustrous black; 
belly and crissum sometimes white . . Progne. 
Similar to last, only culmen straight to near tip; 
tarsus with feathers along inner edge for 
basal half or two-thirds. Fork of tail shal- 
low. Color mouse brown above; white be- 
neath . - : 2 ms : - Phaoprogne. 
Bill rather weaker; commissure and culmen 
nearly straight to near tip. Frontal feathers 
bristly. Tail nearly even. Throat, rump 
