272 EEVIEW OF AMEHICAN BIEDS. [pART I. 



lower mandible falling within its chord. Nostrils superior, broadly open, and 

 nearly circular, without any adjacent membrane, the edges rounded. Legs 

 stout. Tarsus equal to middle toe without claw ; the joint feathered ; lateral 

 toes about equal ; the basal joint of the middle toe half free internally, rather 

 less so externally. Claws strong, much curved 



The preceding diagnosis is intended to characterize two groups 

 of Swallows, differing especially from all others in their thickened 

 form, robustness of bill and feet, and especially in .the elongated, 

 comparatively powerful bill, the upper jaw de(;urved, its commissural 

 edge much sinuated from the base, instead of as in all the others — 

 being nearly straight to near the tip — so that a line from angle of 

 mouth to tip will include the whole lower jaw. With these characters 

 in common, there are two well-marked subgenera, recognizable as 

 follows : — 



Pkogne. Plumage glossy black above. Tail deeply forked, the lateral feathers 

 much and gradually pointed. Bill most robust ; upper outline convex 

 from base. Tarsus with a few feathers only at base, on inner face. 



Ph^opeoone. Plumage dull mouse brown above. Tail emarginate, or but 

 slightly forked ; the lateral feathers very abruptly pointed, and rounded. 

 Bill weaker and more depressed ; upper outline straight to near the tip. 

 Tarsus with a line of feathers along inner edge for two-thirds the length 

 from base. 



a. Progne, Bole. 



Bill notched, robust, and deep ; the commissure much sinuated, convex, and 

 ascending to the nostrils, then concave to the tip. Maxilla convex above from 

 base ; lower mandible slightly convex below, mnch more so above. Frontal 

 feathers with a few bristles at base ; none appreciable in chin. The upper 

 joint of tarsus covered with feathers slightly adherent along inner face above, 

 but not extending along the groove. Scutellae distinct. Lateral toes about 

 equal, reaching to base of middle claw ; all the claws very strong, and much 

 curved. Tail much forked ; the feathers much pointed ; the wings pointed, 

 reaching beyond tip of tail. Plumage compact ; glossy black above, with 

 purple, violet, or blue reflection. Below either similarly colored, or with 

 white belly and crissum. 



I have found it very difficult to come to any definite conclusion in 

 reference to the species of Progne inhabiting the continent of Ame- 

 rica, or to determine with accuracy their geographical distribution, 

 notwithstanding the large number of specimens examined, including 

 those in the Phila. Acad, of Nat. Sciences. This is due, in great 

 measure, to the variation of plumage with age and sex — the young 

 birds of one species representing the adult plumage of another and 



