13IRDS — IIIRUNDINIDAE — HIRUNDO. 



307 



Family lU RU Js D T N ID A E . 

 Siib-raniily IIIUUNDININAE. 



Bill trijngu'ar, very short and broad, much depressed ; tlic ridgo much less than luilf the head ; Iho gonys two-thirds thi^ 

 jCngth; the ga|io extending to below the eyo. Primaries nine; the first longest, and, with the second, considerably longer 

 than the olhora ; the secondaries and tcrtials not reaching the middle of tlio primaries; the secondaries deeply cniargiiiato 

 Wings very long, reaching beyond the commencement of the Cork of tho tail, which i.s gtnerally more or less deeo. Tarsi 

 Bculullale, very short, less than the lateral toes, the inner of which is more deeply cleft than the outer. 



The feet of the true swallows follow the general insessorial type in having three anterior toes 

 and one posterior, none capable of being moved much from their normal position. This, with the 

 much larger and differently shaped bill, as well us the nine primaries, instead of ten, readily 

 distinguisli them from the Cypselidae. 



Comparative measurements of species. 



IimUNDO, Liiiiiaeus. 



i/irundo, Linn. Syst. Nat. 1735. — Gray, Genera, I, 184.5. 



Ch. — Nostrils basal, small, oblong, and covered partly by a membrane. Tail more or less forked ; the outer lateral feather 

 Bomctiines greatly lengthened. Tarsi shorler than the middle to?, and scutellated. Tarsi naked. Toes long, slender, the 

 lateral ones unrqual. Claws moderate, curved, acute. 



Of this genus there are two well marked sections among the United States species — one with the 

 tail excessively forked, owing to the great elongation of the lateral tail feathers; the other with 

 the tail nearly square, or but slightly forked. The species will range as follows : 

 IIiRUXDO. — Tail excessively forked. 



Steel blue above ; forehead and throat chestnut brown ; belly reddish white... iZ". Iwrreorum. 

 Pctrochelidon. — Tail nearly even, or moderately forked. 



Tail emarginate. Forehead, throat, and rump reddish brown ; throat with a large black 



spot P. hot ifrons. 



Tail moderately forked. Beneath entirely white ; above opaque green ; upper tail coverts 

 purple r. thalassina. 



