Vol. XXXVIl 



1919 



Loomis, The Galapagos Albatross. 371 



Independent of age and sex, the downy young have a light 

 phase and a dark phase connected by intermediates, constituting 

 a definite dichromatism. Plate XIV shows the upper surface of 

 the extremes in primary natal down (protoptyles). In the light 

 specimen (1180 C. A. S.) the general aspect was light drab-gray 

 and in the dark one (1185 C. A. S.) dark drab, medially lighter 

 below and varied with dull cream color above, especially anteriorly. 

 It may be, also, that there is a slight dichromatism in the adults, 

 for some nesting individuals are darker than others. It is signi- 

 ficant that the only transition nestling (1204 C. A. S.) before me 

 is passing from the dark phase of the natal down into the darker 

 style of the definitive plumage. 



To what extent dichromatism prevails among the albatrosses 

 is unknown. Certain of the plumages esteemed to be of specific 

 significance by some systematists I believe to be dichromatic. 

 The whole question of color variation in the albatrosses, and also 

 in the other Tubinares, needs a thorough investigation. 



In plates XV and XVI are illustrated the extremes in the general 

 shape of the bill in a series of thirty-three breeding birds obtained 

 on their rookery during eight days ending July 2, 1906. These 

 variations occur independently of sex and, so far as ascertained, 

 of age, the birds being sexually mature. Plate XV exhibits the 

 difference in the width of the bill in two males (1199 and 1221 

 C. A. S.). In the stouter bill the basal width of the upper man- 

 dible is 35.2 mm. and in the slenderer one 31 mm. Plate XVI shows 

 the variation in the concavity of the culmen in two females (1208 

 and 1225 C. A. S.). The greater concavity measures 6.5 mm. in 

 depth and the lesser 2.5 mm. The latericorn and ramicorn, it 

 will be noticed, also vary in form. Furthermore, the nasal tubes 

 in the entire series of specimens vary; even in the same individuals 

 the tubes may be unlike in shape. In their general dimensions, 

 the specimens differ as follows: 1 



Fourteen males: Wing, 550-593 mm. (572); tail, 142-158 (149); 

 culmen, 146-160 (153.2); basal depth of upper mandible, 30.3- 

 33.6 (31.7); basal width of upper mandible, 31-35.2 (33.4); tarsus, 

 91-103 (95.3); middle toe and claw, 125-138 (131.6). 



1 I am indebted to Mr. Edward Winslow Gifford for making the measurements here 

 summarized. 



