III PROCELLARIIDAE Ol 
a distinct fork occurs in Oceanodroma. Sixteen rectrices are found 
in Ossifraga, fourteen in Fulmarus, Priocella, and Daption, twelve 
elsewhere. The small tongue is somewhat triangular, being rather 
larger in Ossifraga and Prion ; the syrinx is tracheo-bronchial ; 
and an after-shaft is present, though in some cases rudimentary. 
The soft, dense plumage shows various patterns of black, brown, 
grey, and white; the bill and feet may be black, brown, flesh- or 
horn-tinted, yellow, orange, or parti-coloured, but in Prion and 
Halobaena the latter are bluish. Light and dark phases are not 
uncommon, as in Mulmarus and Ossifraga ; the sexes are invari- 
ably similar; and the nestlings, which long remain helpless, are 
clad in thick down of a black, brown, grey, or white hue, through 
which the feathers appear gradually. Some white Albatroses 
have intermediate dusky stages of plumage, and do not gain the 
adult coloration at once, as most of the Family seem to do. 
DMomedea exulans is one of the largest birds that fly, exceeding 
a goose in size, While the smaller Petrels are hardly bigger than 
Finches. The range of the Order is world-wide, though a majority 
of species frequent the desolate tracts and islands of the southern 
oceans ; but even Albatroses breed in the North Pacific. 
Though the members of this Family can hardly be called 
gregarious, flocks of Shearwaters, Fulmars, and so forth are by 
no means an. uncommon sight from shipboard, and settlements are 
formed in the breeding season, which is almost the only occasion 
on which they voluntarily seek dry land.  Albatroses, Fulmars, 
the “Cape Pigeon” (Daption), and other allied forms are observed 
most commonly in the daytime, whereas those that nest under 
cover are to a great extent nocturnal during incubation, and 
are generally seen or heard after dusk. Whuile the whole group 
is oceanic, there is a wide difference between the powerful 
Albatros and its smaller and weaker relations in that respect, 
the latter journeying but little from the immediate neighbour- 
hood of their homes, and not accompanying ships for long dis- 
tances in the same way as the former. In the larger species the 
flight is strong and graceful,’ accompanied by circling, soaring, or 
sailing movements, the feet being extended below the tail; 
Shearwaters skim the waves in a curious twisting fashion, and 
the lesser Petrels flit with greater action of the wing close to the 
1 Here the late Professor Roy’s article on ‘‘ Flight” (A. Newton, Dict. Birds, 
1893, p. 260) may be consulted. 
