314 CALIFORNIA ACADEMY OF SCIENCES. 



green, more yellowish below, but, unlike Piranga, with a 

 blue patch on the head. What this blue was derived 

 from is not apparent, unless it is separate pigment which 

 is wanting in Piranga. 



FAMILY HIRUNDINID.E. THE SWALLOWS. 



All the members of this family are specialized beyond 

 the streaked plumage, and the tendency is for the back 

 to be darker than the breast, both being marked with 

 solid colors instead of mottlings or streaks. All this is 

 the result of specialization in accordance with the gen- 

 eral laws of pigment deposition. The colors and mark- 

 ings which cannot be explained by these general laws 

 appear to be the result of sexual selection. 



GENUS PROGNE. THE MARTINS. 



(7) Adult male more conspicuously colored than 

 female; young like adult female. 



Prevailing colors, black (metallic bluish), gray, white. 



The male represents the culmination of specialization 

 in a black plumage, enhanced, by sexual selection, by 

 burnished blue lustre. The female has the underparts 

 gray, becoming white posteriorly, showing the manner 

 in which the black plumage was assumed, the abdomen 

 probably having been affected last. 



GENUS PETROCHELIDON. THE CLIFF SWALLOWS. 

 GENUS CHELIDON. THE BARN SWALLOWS. 



(1) Adult male like female; young like adult but 

 duller. 



Prevailing colors, black, blue-black, white, chestnut, 

 cinnamon, gray, brown. 



The general tendency in these two genera, is, as in 

 Progne, to have the back dark metallic black with 

 greenish or bluish reflections, and the under parts more 



