MONOGRAPH OF THE PETRELS. 



The dimensions of four specimens were as follows : — Axis, 2.45-2.53 inches ; diameter, 

 1.58-1.74. 



Adult. General colour above brown, with indistinct ashy-brown margins to the 

 feathers of the mantle, the dorsal feathers and scapulars edged with paler brown or 

 ashy-white, the scapulars being blackish-brown, and contrasting somewhat with the 

 mantle and lower back ; rump and upper tail-coverts uniform dark brown, with 

 concealed ashy bases ; wing-coverts brown, the greater series with concealed 

 grey bases, turning to white at the extreme base ; outer median-coverts slightly greyer 

 externally and fringed with white at the ends, like the greater series ; bastard-wing, 

 primary-coverts, and quills, blackish, the inner secondaries browner and more like 

 the back ; tail-feathers blackish-brown ; head and hind-neck blackish brown, darker 

 than the mantle ; lores and sides of face dark ashy-grey, the ear-coverts browner ; 

 throat white, like the rest of the under-surf ace of the body, with ashy bars and frecklings 

 on the sides of the cheeks and sides of the neck ; the fore-neck and chest ashy-grey, a 

 little darker grey on the sides of the body ; breast white, faintly shaded with ashy- 

 grey, the abdomen more ashy-brown ; under tail-coverts dark ashy-brown, the 

 longer ones blackish-brown ; axillaries ashy-brown, with slight whitish mottlings 

 at the ends ; under wing-coverts white, slightly mottled with ashy-grey near the edge 

 of the wing ; marginal coverts ashy-grey ; quills dark brown below, with a slight sheen 

 of ashy-grey ; " bill light grey, except the upper part from the groove and the hook 

 at tip, which are black, as also the edges of the lower mandible and its hook ; tarsi 

 and feet whitish-pink, somewhat dusky on the joints of the under-side ; iris pale 

 brown " (Hoist MSS.). Total length about 17.5 inches ; culmen, 1.65 ; wing, 11.85 ; 

 tail, 5.4 ; tarsus, 1.9 ; middle toe and claw, 2.35. 



Another specimen, or co-type, is in the British Museum, having been presented 

 by the late Henry Seebohm, and, like that described above, was procured on 

 Krusenstern Island by Mr. Snow in the spring of 1883. It differs from the type in 

 being almost entirely white below, with a few ashy frecklings on the hinder cheeks 

 and sides of neck, and with a certain amount of ashy dusting on the sides of the body. 

 Total length about 17.5 inches ; culmen, 1.55 ; wing, 11.5 ; tail, 5.2 ; tarsus, 1.95 ; 

 middle toe and claw, 2.2. 



A third specimen obtained by Mr. P. A. Hoist on Sulphur Island is of the white- 

 breasted phase, and agrees with the co-type. 



Salvin observed that, even in the small series which was at his disposal in 1896, 

 there was some variation in the colour of the under-surface of the body, one of the 

 typical specimens being pure white, while the other was greyer, " especially over the 

 breast, flanks, and lower abdomen." 



The Hon. Walter Rothschild has drawn attention to these differences in his 

 " Avifauna of Laysan." He was at first inclined to consider the brown-breasted 

 birds as immature, but he is now convinced that the darker individuals represent a 



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