1882. ¥ROM PERU AND CHILI. 529 
two well-marked species, was probably, unless the direction of 
currents has materially altered, by Humboldt’s current northwards 
to the equator, thence across the comparatively feeble and conflicting 
equatorial currents, until the sforth equatorial drift led to the shores 
of Japan. 
On the coast of California occurs Larus heermanni, another mem- 
ber of this group, with an entirely black tail, and a hood in the im- 
mature state; the head gets lighter with age, but the underparts 
are washed with the dark grey so characteristic of Pacific forms. It 
has no very close ally in existence; for Larus modestus, a much 
slenderer Gull, restricted to the coasts of Peru and Chili, only re- 
sembles it in the hood of immaturity and in general coloration, and 
differs from it in having a tendency to lose the black markings on 
the rectrices with advance in age. And the isolated Larus fuligi- 
nosus, found only in the Galapagos group, differs from the other 
Pacific Gulls in having a hood at all ages and in losing the markings 
on the rectrices at maturity. It would seem asif this smoke-coloured 
species, stranded at the Galapagos, might be the nearest living 
representative of the ancestor of all these Pacific forms, and the one 
which at the same time links them to the type of the northern hemi- 
sphere. 
Between South America and the neighbourhood of New Zealand 
and Australia only Terns are found, no Gull of any kind being on 
record. Even LZ. dominicanus is absent from the South-Pacific 
islands, its line of connexion between South America and New 
Zealand being by the South Atlantic. But along the southern 
shores of Australia, from King George’s Sound to Tasmania, and 
(according to the labels on the specimens obtained by the Antarctic 
expedition) in New Zealand, is found a large dark-mantled Gull, 
Larus pacificus, Lath., which has an immense blunt bill of peculiar 
form, somewhat like that of Z. scoresbii, and further resembles the 
Pacific group in that the adult has a broad black band across the 
rectrices. It is an isolated form; but although it may be difficult 
to explain its existence at the junction of the waters of the South 
Pacific and South Atlantic, the fact seems worthy of attention. 
Apart from conjectures, there can be no doubt tbat the connexion 
between the pelagic birds of the northern and southern hemispheres 
is much closer in the Pacific than in the Atlantic. The closer 
resemblance between Stercorarius catarrhactes and 8. chilensis than 
between the latter and its present near neighbour, S. antarctéicus, is 
one proof of this; the intermediate position occupied by Sterna 
aleutiea of the Aleutian Islands, between the ordinary type of north- 
ern Tern and the intertropical group of sooty Terns, is still further 
evidence; but the strongest of all is perhaps in the case of Xema 
sabinii and X. furcatum. The former, a circumpolar species not 
known to breed south of the arctic circle, except on the shores of 
Behring’s Sea, extends its breeding-range in the North Pacific as far 
south as Alaska; and not only the young birds, which are always 
great wanderers, but also the adults of this species come down in 
winter as far as 12° S, lat., thus considerably overlapping the range 
