86 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



tomium nearlj^ straight, with subtermiual notch distinct. Nostril lon- 

 gitudinal, narrowly ovate, opening laterally, overtiiing by a rather 

 broad membraneous operculum, the feathering of frontal antise reach- 

 ing only to its posterior end or but slightly beyond. Rictal bristles 

 obsolete. Tail not more than half (nor less than two-fifths) as long as 

 wing, more or less emarginated, but depth of the emargination never 

 more than one-fifth its length, usually less (sometimes much less), the 

 lateral rectrices broad to near tips where rather suddenly but not con- 

 spicuously contracted, the tip rounded. Tarsus longer than middle 

 toe (without claw), the extreme upper portion feathered; basal phalanx 

 of middle toe united to that of outer toe by at least half, usually nearly 

 the whole, of its length, adherent to the inner by half to much less 

 than half its length; claws of lateral toes reaching nearly or quite to 

 base of middle claw. 



Coloration. — Upper parts (of adults) glossy steel blue or green, the 

 rump white in four out of five species; under parts white, including 

 under tail-coverts. 



Nidification. — Nest in holes of trees or buildings, composed of fine 

 grasses, feathers, etc. ; eggs immaculate white. 



Range. —Continental portions of temperate and tropical America. 

 (Five species.) 



This very natural group of swallows presents considerable variation 

 in details of structure, especially in the relative size antl width of the 

 bill, as noted above. The bill is proportionately smaller and narrower 

 in /. hicolor (the type species) than in any other, this being the only 

 species which has the rump concolor with the back. In I. meyeni the 

 bill is equally small but is relatively much broader, this species having 

 the rump white, as in the others except I. hicolor. The bill is rela- 

 tively largest in I. alblUnea, in which the post-nasal portion of the 

 maxillary tomia is conspicuously dilated, the length of the exposed 

 culmen being about equal to the distance from the nostril to the eye, 

 the other species having it much shorter. The basal adhesion of the 

 anterior toes is greatest in /. hicolor, I. albilmea., and /. lexicoptera., in 

 which the first phalanx of the middle toe is united to that of the outer 

 toe for practically its entire length. It is least in I. meyenl, in which 

 the adhesion extends for onl)' about half the distance. 



KEY TO THE SPECIES OF IRIDOPROCNE. 



a. Rump glossy steel blue or green, or dark brownish gray, concolor with back. 

 (North America; south in winter to Cuba, British Honduras, and Guatemala.) 



Iridoprocne bicolor (p. 87) 

 aa. Rump wh^e. 



h. Greater wmg-co verts broadly edged with white; upper tail-coverts partly white. 

 (Colombia, Ecuador, and Guiana to southern Brazil. ) 



Iridoprocne albiventris (extralimital)« 



aHirundo albiventer Boddaert, Tabl. PI. Enl., 1783, 32 (based on Hironddle cL ventre 

 blanc de Cayenne Daubenton, PL Enl., vii, pi. 546, %. 1); Baird, Review Am. Birds, 



