NATATORES. 471 



no difference in the weight of the sexes, neither is there any 

 visible variation in their colouring, nor do they appear to be 

 subject to any seasonal change." 



Head, chin, back and sides of neck, upper part of the back, 

 lesser wing-coverts, edge of the under surface of the wing, 

 and the primaries sooty brown ; wing-coverts, back, and 

 upper tail-coverts white, each feather tipped with sooty brown ; 

 basal half of the tail white, apical half sooty brown ; under 

 surface white ; the under tail-coverts tipped with sooty brown ; 

 beneath the eye a small streak of white ; bill blackish brown ; 

 irides and feet very dark brown. 



Genus PRION, Lacipede. 



At least four species of this form frequent the seas washing 

 the southern parts of Australia. These fairy-like birds are 

 individually very numerous, for I have seen them in flocks of 

 thousands. They are truly oceanic birds, seldom if ever near- 

 ing land except for the purpose of breeding, when they take up 

 their abode on the most isolated spots, such as St. Paul, Am- 

 sterdam, Tristan d'Acunha, Prince Edward Islands, Kergue- 

 len's Land, &c. Their broad laminated bills are evidently 

 formed for procuring some peculiar kind of food, of which 

 doubtless the lower sea-creatures known as Medusa form a 

 part. Besides the singular form of their bills, their delicate 

 grey colouring at once distinguishes them from the rest of the 

 Petrels. Generally speaking, this is a southern form, but one 

 species has occurred north of the line, and in our own seas. 

 The species alluded to is the P. brevirostris, so named by me 

 at the meeting of the Zoological Society of London held on 

 the 12th of June 1855, and for a knowledge of which I was 

 indebted to my late friend William Yarrell, who informed me 

 it had been captured on the Island of Madeira or on the 

 neighbouring rocky islets called the Desertas. The sexes 

 present no external difference either in coloiu* or size. 



