THE BIRDS OF THE JUAN FERNANDEZ ISLANDS 15 
which extends as a more pronounced eye-brow stripe above the eye. All these 
differences makes it impossible to confound these two Petrels with each other 
although both may be counted to the cookz-group. 
On the other hand the Petrel of Masafuera seems to resemble /%. c. 
leucoptera in its general appearance to such a degree that the present author 
at first believed these specimens to represent this species, in spite of the zoo- 
geographical difficulties for such a theory. To make sure about it I took the 
liberty of sending a specimen to Mr. GREGORY M. MATHEWS, wo kindly com- 
pared it with typical /ewcoptera and gave his decision, that it did not belong 
to the species mentioned. The bird from Masafuera was said to have a thicker 
bill and also differ in some other respects. From a zoogeographical point of 
view this was rather to be expected as not less than three different Petrels of 
the cook?-group according to Mathews are to be found between the habitat of 
leucoptera and Masafuera. 
The description of the new race may be as follows: Crown, sides of head 
and hind-neck, blackish decidedly in contrast with the grey of the back. On 
the forehead white edges to the feathers more or less conceal the black bases 
of the feathers so that a mottled appearance is produced, white edges in de- 
creasing development to be seen to the level of the eyes. Lores white in 
front, then somewhat mottled, but the blackish of the crown surrounds the 
eyes as well in front as below. Back rather deep grey, somewhat slaty, new 
feathers with blackish edges, worn feathers with narrow light edges. A blackish 
patch on the rump. Upper tail-coverts a little paler grey than the back. Tail- 
feathers black at the ends, the covered parts more or less slaty, and finally 
white towards the base, especially on the inner web. The outermost quill may 
be almost white on the inner web, partly mottled grey and white towards the 
end as the outer web. (In other specimens the inner web is mottled and the 
outer pale grey). Anterior scapulars like the back. Long scapulars black like 
the lesser wing-coverts, bastard-wing and the greater part of the primaries, the 
latter, however, broadly white on the proximal parts of the inner web. Median 
and greater wing-coverts dark ashy grey, the inner, however, black on the outer 
web. Secondaries grey on the outer web and at the end of the inner which 
for its greater part is white. Axillaries white, inside of wing white with black 
margin. Lower side from the throat and including the under tail-coverts en- 
tirely white. Mr. BACKSTROM says that the feet of this Petrel are wholly greyish 
black. In a dry state, however, the web does not look so very dark. 
According to Mr. BACKSTROM, this species is much rarer than Pt. externa. 
»It breeds, as far as I know», he writes, »only in the highest parts of the 
southern half of the island round Los Inocentes. Their nests are constructed 
like those of Pt. externa, but the tunnels are much shorter. They were found 
only in the dense fern-groves among the roots and decumbent stems of Dick- 
sonia.» 
As according to MATHEWS the true /P?. c. /eucoptera is surface-breeding, 
while this one is burrowing, this constitutes an important biological distinguishing 
characteristic. 
