Vor. II, Pr. 11] LOOMIS—A REVIEW OF THE TUBINARES 37 
thermore, the Wedge-tailed Shearwater appears to be repre- 
sented only by the dark phase on the Kermadec Islands. 
According to Dr. Edward A. Wilson, the percentage of Giant 
Fulmars of the light phase increases with the latitude, the 
greatest number being observed where the ice conditions are 
persistent. It is evident that the geographic distribution of 
the light and dark phases of the Tubinares is independent of 
climatic conditions. 
In part VI I have described an instance of complete mela- 
nism in the Black-vented Shearwater. This specimen and 
extreme white specimens of the same species have an appear- 
ance similar to that of the light and dark phases of the Wedge- 
tailed Shearwater (plates 15, 17). Ii such sporadic melanism, 
through the virility of an individual, persisted on an island, at 
the outset there might be a melanism restricted to relatively 
few individuals, as in the dichromatism of the Wedge-tailed 
Shearwater in the Hawaiian Archipelago. Later, if the mela- 
nistic phase largely swamped the light phase, the result might 
be as in the Wedge-tailed Shearwater on San Benedicto 
Island. Ultimately, if the melanistic phase supplanted the 
light phase, the situation might be like that in the Wedge- 
tailed Shearwater on the Kermadec Islands. In brief, if 
sporadic melanism became an inherited character, there would 
result a persistent melanism, or dichromatism. 
GEOGRAPHIC VARIATION 
The isolation of the Tubinares at the breeding stations favors 
colony peculiarities; for example, in the dark phase of the 
Wedge-tailed Shearwater breeding on the Kermadec Islands 
the bill is generally grosser than in the dark phase of this 
species breeding on San Benedicto Island, Revilla Gigedo 
Group. According to the tables of measurements in part VI, 
the “Socorro Petrels’ of the Los Coronados Islands, Lower 
California, average greater in their dimensions than the 
“Socorro Petrels” of the San Benito Islands, about 250 nauti- 
cal miles to the southward. In the shearwater, and perhaps in 
the storm petrel, the geographic variation is overshadowed by 
dichromatic variation. The Dark-rumped Petrel in the Gala- 
1 Nat. Antarct. Exp., N. H., v. 2, Aves, p. 96. 
