HIRUNDINID^ — THE SWALLOTVS. 203 



Family HIRXTNDINIDJE.— The Swallows- 



"Chab. Bill short, triangular, very broad at base (nearly as wide as long) and much 

 depressed, narrowing rapidly to a compressed, notched tip; mouth opening nearly to the 

 eyes. Primaries nine, graduating rapidly less from the exterior one; tail feathers twelve. 

 Feet weak; tarsi seutellate. shorter than middle toe and claw. Number of joints in toes 

 noi-mal; basal joints of middle toe partially or entirely adherent to lateral toes. Wings 

 long, falcate. Tail forked. Eyes small. Plumage compact, usually lustrous. All the 

 American species with a white patch on the sides under the wing, and with the irides 

 hazel or brown." (Kist. N. Am. Birds.) 



The Hirundinidce form a very well-marked group of birds, easily 

 distinguished from all others except the Cypselida (Swifts), to which 

 they exhibit a close resemblance in external appearance and habits, 

 but from which, apart from the internal structure, they differ rad- 

 ically in the possession of nine, instead of ten primaries ; twelve, 

 instead of ten tail-feathers ; seutellate tarsi, toes with normal num- 

 ber of joints (1, 2, 3, and 4, respectively, exclusive of ungual 

 phalanges), instead of a different proportion; differently shaped 

 nostrils, and other minor characters. 



The following synopsis, adapted from that in Hist. N. Am. B. 

 (Vol. I., pp. 326, 327), may serve to identify the North American genera. 



Genera oj I\ortli American Hirundinidce, 



A. Nostrils broadly oval, or circular; opening upwards and forward, and exposed; 

 without overhanging membrane. 



a. Edge of wing smooth. Tarsus short, stout; equal to middle toe without 

 elaw; feathered on the inner side above. Nostrils almost or entirely without 

 membrane. 



Bill stout; culmen and commissure much curved. Frontal feathers with- 

 out bristles. Tail deeply forked. Color lustrous black; belly and erissum 



sometimes white Progne. 



Bill rather weaker; commissure and eulmen nearly straight to near tip. 

 Frontal feathers bristly. Tail nearly even. Throat, rump, and erissum, 



and usually forehead, rufous; belly white Petroohelidon. 



6. Edge of wing in adult male armed with stiff recurved hooks. Bill larger 

 and more depressed. Tail emarginate only. Color uniform dull brown, the 

 erissum white Stelgidopteryx. 



B. Nostrils lateral; bordered behind and inside, or overhung by membrane, the 

 outer edge of which is straight, and directed either parallel with axis of bill or di- 

 verging from it. 



a. Tarsus short; about equal to middle toe without claw. Tibial joint feath- 

 ered; feathers extending along inside of upper end of tarsus. 



Tarsus bare at lower end. Lateral claws reaching only to base of middle. 

 Tail very deeply forked, much longer than closed wings; lateral feathers 

 linear and vey narrow at end, twice the length of central. Upper parts 



