34 



CALIFORNIA ACADEMY OF SCIENCES TProc. 4th Ser. 



ently bringing the moult to a dose. Nine Clipperton skins, 

 August 10, are passing through what I take to be the post- 

 nuptial moult. In some cases it seems to be almost completed, 

 and, with the exception of No. 1619, it has reached the remiges 

 in every case. Renewal of rectrices seems to proceed from 

 the center laterally, renewal of primaries from the proximal 

 to the distal, and renewal of secondaries apparently from the 

 distal to the proximal. There are exceptions to these rules, 

 certain feathers coming in out of turn. Ten Cocos specimens, 

 taken during the first half of September, are in a similar state, 

 but, if anything, are not quite so far advanced as the Clipper- 

 ton specimens. 



The bill of the adult bird in life is black at the tip, shading 

 through purple to indigo blue at the base. 



MEASUREMENTS (in millimeters) 



The 

 Males — Win 



following 



is a summary of the above measurements: 

 .g, 223-260 (244); tail 110-122 (117); culmen 

 37.4-43 (40.2); tarsus 11.9-13.2 (12.5); middle toe 20.4- 

 22.5 (21.7). Females— Wing 231-254 (241); tail 107-129 

 (119); culmen 36.7-41.6 (39.2); tarsus 11.1-12.8 (12); 

 middle toe 21-22.4 (21.7). 



