MONOGRAPH OF THE PETRELS. 



rather browner, with a distinct shade of slaty-grey on the throat, sides of face, and 

 sides of neck ; lesser wing-coverts black ; the median and greater coverts drab-brown ; 

 the latter, as well as the inner secondaries, narrowly fringed with white ; primary- 

 coverts and quills black, the inner secondaries browner, like the scapulars ; lower 

 rump sooty-brown, like the back, with some more or less white feathers on each side ; 

 upper tail-coverts white, with dusky shaft-lines, the lateral ones fringed with white at 

 the tip, the central ones for the most part ashy-brown, more or less centred with white ; 

 tail-feathers black ; head and neck dusky-brown, with an evident plumbeous shade ; the 

 under tail-coverts sooty-brown ; some of the lateral coverts more or less white at their 

 base ; under wing-coverts and axillaries brown like the breast, the lower primary- 

 coverts and quill-lining somewhat more ashy-brown. Total length about 8 inches ; 

 culmen, 0.7; wing, 6.1; tail, 3.1; fork of tail, 0.85; tarsus, 1; middle toe and 

 claw, 1.05. 



Adult female, Similar in colour to the male. Total length 8 inches ; wing, 6.3. 



A nestling from Casco Bay, Maine, is covered with long down of a sooty-brown 

 colour, and very woolly in texture. 



A good deal of variation takes place in the amount of white edging to the drab 

 greater wing-coverts, and also in the dusky markings on the white upper tail-coverts. 

 Sometimes the lateral coverts are narrowly fringed with dusky markings at the tip, and 

 at others the black tips are as broad as in 0. castro, which species, however, is easily 

 distinguished by its white lateral under tail-coverts. I imagine that the white 

 edgings to the wing-coverts are broader and more distinct in the younger birds, 

 though there is really very little difference in plumage between the mature and 

 immature birds in all the species of Fork-tailed Petrels. 



The specimens described are a pair of nesting birds obtained on St. Kilda by 

 Mr. Charles Dixon in June, 1884, and now in the Seebohm Collection in the British 

 Museum. 



The bird figured in the Plate is an adult male from Grand Menan, New Brunswick, 

 in our own collection. It should be observed that the lighter brown wing-patch is not 

 sufficiently indicated in the picture. 



10 



