ON THE OYSTERCATCHERS. 45 
to be the present limit of the emigration of this party. Their 
route precisely corresponds (so far as is known) with the present 
range of this species, except that it is not now found north of 
‘Labrador. 
2. Hematopus leucopus. — The Falkland Island Pied Oyster- 
catcher principally differs from its more wide-spread ally in 
having the brown parts replaced by black. Its range extends 
from the Falkland Islands and the islands in the Straits of 
Magellan to those on the south-west coast of Patagonia. This 
Species is unquestionably an offshoot of the preceding species, 
which has become differentiated in consequence of its having 
become isolated on the Falkland Islands, whence it probably 
spread later to the islands off the Patagonian coast. 
These two species represent the Atlantic New World group of 
Oystercatchers, which may be characterised as having flesh- 
coloured legs, white lower under parts, and dark rump. 
3. Hematopus niger.* — The North American Black Oyster- 
catcher, like all the Oystercatchers of the New World, has pale 
flesh-coloured legs, but, like all the Oystercatchers which passed 
through the Behring Sea, the whole of its plumage has become 
black. This species is a summer visitor to the Aleutian Islands 
and the southern shores of Alaska, breeding as far south as the 
coast of Upper California, where it is probably a resident, and 
wintering on the coast of Lower California. 
4. Hematopus niger ater. — The South American Black 
Oystercatcher only differs from its more northern ally in having 
generally a shorter and deeper bill. Examples in my collection 
of the northern form have bills 34 inches in length and 0°5 in. 
in depth, whilst others from Chili have bills 23 in. in length and 
0°6 in. in depth. It is said, however, that in a series of each the 
dimensions are found to overlap, so that the American ornitholo- 
gists very justly regard the two forms as only subspecifically 
distinct. This form is evidently the result of an emigration from 
the range of the preceding species, which has caused a colony to 
cross the Tropics and establish themselves as residents on the 
coasts of Chili, Patagonia, and the Falkland Islands; but the 
* Pallas described this species as inhabiting the Kurile Islands. It 
certainly does not do so now. The great Russian traveller may have been 
deceived, or it is possible that a stray bird had been driven across the 
Pacific from Alaska by a storm. 
