300 



1LEMATOPUS. 



gradual extension of the breeding- areas of many species of birds has been remarked over 

 and over again. As regards the Oystercatchers, it seems to me that we can almost trace 

 their history from the origin of the genus in the small area of the Polar Basin, its dispersal 

 along the four great coast-lines or highways leading southwards, and its subsequent 

 distribution, sometimes by sudden emigration, sometimes by a gradual extension of its 

 range, until it has become nearly cosmopolitan. 



KEY TO THE SPECIES. 



There appear to be seven distinct species of Oystercatchers, but three of them may be 

 again subdivided into local races, which vary slightly in the length and thickness of the 

 bill, as is hereafter explained. The seven species may be diagnosed as follows : — 



Legs pale flesh-colour 



Entire plumage nearly 

 black. 



palliatus • 



leucopus • 



niger • . 

 - unicolor 



Rump white 



longirostris 



osculans. 



ostralegus 



Mantle and rump greyish 

 brown. 



y No white on primaries. 



White shaft-streak extending 

 a little on outer web of 

 4th primary, much ou 5th. 



This key to the species applies to young in first plumage, as well as to adults. The 

 young of H. ostralegus bears a superficial resemblance to H. palliatus, as does also that of 

 H. osculans, in both species the black parts of the adult plumage being frequently brown 

 in the young ; but H. palliatus may always be recognized by its brown instead of white 

 rump, or by the absence of white on its primaries. The differences between thesub specific 

 allies of H. leucopus, H. niger, and II unicolor, and their respective parent forms are pointed 

 out in the pages devoted to each of the latter. 



