22 CALIFORNIA ACADEMY OF SCIENCES [Peoc. 4th Ser. 



lars and interscapulars are dark gray with conspicuous white 

 tips. New inner primaries, new upper wing-coverts, new tail- 

 coverts, and new feathers on the under parts and about the 

 head are also appearing. Some alternation is manifested in the 

 replacement of the upper wing-coverts. An examination of 

 the tail shows the two inner and the two outer rectrices to be 

 new. The outer ones are not those of the full adult, but are 

 dusky save for a terminal whitish spot on the outer web. 



No. 1350 C. A. S., male, from forty miles south of Cocos 

 Island, September 2, 1905, is very much like the bird just 

 described, and has in addition some whitish streaking on the 

 fore part of the crown. This specimen seems to exemplify 

 more fully the plumage developed during the first prenuptial 

 moult. The three outer primaries of one wing and the two 

 outer of the other have not been replaced, nor have the two 

 rectrices nearest to each of the outermost rectrices. Nos. 1348 

 and 1349, taken near Clipperton Island on August 5 and 8 

 respectively, are adult in every particular, save for a few dark 

 feathers in the lower parts. 



The fourteen downy nestlings collected on Clipperton Island 

 on August 10, show some variation in age and size, which can 

 perhaps be best indicated by the measurements of the culmen 

 and tarsus of the largest and the smallest. Largest : Culmen 

 15.6 mm.; tarsus 17.1 mm. Smallest: Culmen 11.8 mm.; 

 tarsus 13.9 mm. All exhibit the egg-tooth. Mr. Saunders' 

 description of a chick^ about three days old does not quite 

 describe the conditions which exist in the Academy's series of 

 chicks. The specimens are "streaked with grayish brown and 

 dull white on the upper surface," but the white down is tipped 

 with rufous. All the down of the upper surface appears as 

 though the ends of the filaments of each tuft were twisted 

 together, giving the surface a bristled appearance. There is 

 more or less variation in the relative amounts of dark and light 

 coloring, producing accordingly either a darker or a lighter 

 dorsal aspect. 



Two adults from the Revilla Gigedo Islands are in plumage 

 quite worn, and show new feathers appearing in the back, 

 among the upper wing-coverts, and in the breast. In one 

 specimen the moult of the body-plumage is more advanced 



^Cat. Birds Brit. Mus., v. 25, p. 109. 



