THE BIRDS OF THE JUAN FERNANDEZ ISLANDS 1 5 



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 cooki-group. 



On the other hand the Petrel of Masafuera seems to resemble /V. 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 leucoptera 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 cooki-gxoyxp 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 Pt. c. leucoptera is surface-breeding, 

 while this one is burrowing, this constitutes an important biological distinguishing 

 characteristic. 



