298 



H^MATOPUS. 



Emigration 

 along Atlan- 

 tic coast of 

 America. 



Emigration 

 along Pacific 

 coast of 

 America. 



now generally regarded as specifically distinct, under the name of Japanese Oystercatcher 

 {H. osculans), but the difference, though constant, is very slight. 



Probably the same catastrophe which drove the Japanese Oystercatcher to the east, an 

 unusually late cold spring, induced a second party to start from the winter-quarters in 

 Ceylon, in order to emigrate in a different direction in search of more advantageous 

 breeding-grounds, which they appear to have found in Australia, where they were in process 

 of time differentiated into the Australian Pied Oystercatcher [H. longirostris) . 



These three species represent the group of Oystercatchers which emigrated along the 

 Atlantic coast of the Old World, and may be characterized as having red legs and a white 

 rump, as well as white bellies. 



Their nearest allies are two or three species inhabiting the New World, which pre- 

 smnably emigrated along its Atlantic coast, a theory confirmed by the fact that their 

 descendants range at present much further north on the east coast of America than they 

 do on the west coast \ 



Leaving Greenland to the left, the ancestors of the North- American Pied Oyster- 

 catcher {H. palliatus) probably retreated from the Polar ice down Baffin's Bay, and 

 gradually extending their range southwards along the Atlantic coast of North and South 

 America, rounded Cape Horn, and turning northwards again along the Pacific coast of 

 South America their descendants have extended their range northwards as far as Lower 

 California, M'hich appears to be the present limit of the emigration of this party. This 

 route precisely corresponds (so far as is known) with the present range of the species, 

 except that it is not now found north of Labrador. 



The Falkland-Island Pied Oystercatcher {H. leucopus) 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. 



On the Galapagos Archipelago a species of Oystercatcher has recently been discovered 

 which appears to be exactly intermediate been H. palliatus and li. leucopios, having the 

 smaller dimensions of bill of the former, but the darker mantle of the latter. As the 

 dimensions of the bill are a very variable character in this genus, and the colour of the 

 mantle a very stable one, I have treated H. galapagensis as a subspecies of the latter form. 



These two (or three) species represent the Atlantic New-World group of Oystercatchers, 

 which may be characterized as having flesh-coloured legs, white bellies, and dark rumps. 



Turning now to the Pacific Ocean, it is obvious that the North-American Black 

 Oystercatcher {H. niger) and its southern allied race, which range from Alaska to California, 

 and from Chili through the Strails of Magellan to the Falkland Islands, emigrated along 



^ This difference cannot be explained by an equivalent diiference in the range of the isothermal lines. 

 On the Atlantic coast H. palliatus breeds as far north as the July isothermal of 52°, but on the Pacific coast 

 it only ranges up to the July isothermal of 72°. 



