Vol. II, Pt. I] GIFFORD— BIRDS OF THE GALAPAGOS ISLANDS 99 



Adult Clipperton birds had the following colors of the 

 naked parts in life: Males — Bill glaucous blue; gular sac 

 indigo-blue; feet pea-green; iris silvery gray, distinct on the 

 outer edge, but nearly obscured by black on the inner edge. 

 Females — Bill olive-buff; gular sac indigo-blue, washed with 

 pea-green ; feet pea-green. 



Although the Academy's series of Revilla Gigedo birds is 

 very small, what few there are seem to be intermediate in 

 color between the Cocos and the Clipperton birds, leaning 

 distinctly toward the latter. 



None of the Academy's series are moulting the primaries. 

 Clipperton birds, however, have their primaries and tails 

 extremely abraded in many cases; in fact, among the females 

 it was impossible to obtain measurements of the length of tail, 

 as it was broken off in every case. Clipperton birds probably 

 renew their plumage by a postnuptial moult about September 

 and October. 



In the vicinity of San Benedicto and of Clipperton, we cap- 

 tured a number of birds which were passing from a brown 

 immature plumage into the adult plumage. Two small white 

 downy young from Cocos show the tip of the upper mandible 

 to be more abruptly decurved in birds of that age than in 

 adults. 



The measurements in Table XII, p. 117, show that Clipper- 

 ton birds average slightly larger than Cocos birds. 



A series of twenty-four eggs from Cocos Island are all 

 stained a dirty brown, evidently on account of the dampness 

 of the nests, which is incidental to the rains which deluge the 

 island daily. Sixteen of these eggs compose sets of two each, 

 while the remaining eight compose sets of one each. The 

 extreme and average measurements, in millimeters, for the 

 whole series are as follows: Length 50.3-63.1 (58.7); 

 breadth 37.5-42.5 (39.8). 



The measurements of the eight sets of two eggs each show 

 that there is some variation in size in the eggs of each set. 

 By sets these eggs measure as follows: 53.6X40, 54.5X40; 

 63X41.6, 58.9X39.5; 58.3X40, 55.5X38.2; 62.5X39, 59.7X 

 37.5; 62X39.9, 60X39.6; 60X40.2, 58.5X39.5; 63.1X42.5, 

 60.1X42; 62.2X40.7, 62.5X39. From the above it is plainly 

 seen that there is considerable variation in the ratio of length 



