96 



CHAEADEIUS. 



the birds were forced to leave the Polar Basin, but were able to keep up some communication 

 by way of the Aleutian Islands. 



The Dotterels probably came down from the Polar regions by way of the European 

 coast and emigrated eastwards. C. morinellus was probably isolated in the basin of the 

 Mediterranean ; C. veredus in the islands of the Malay Archipelago ; C. rufiventris in North 

 Austraha ; C. australis in South Australia ; C. sociabilis in Patagonia ; and C, modestus in 

 the Falkland Islands ; whilst C. totanirostris emigrating westwards probably reached South 

 America across the Atlantic. 



A hind toe , 



KEY TO THE SPECIES. 



rufiventris • • 



sociabilis • • • 

 modestus. 



Underparts more or less 

 black in summer, white -{ 

 in winter. 



helveticus. 

 pluvialis . 

 fulvus • • 



morinellus 



Middle toe without the claw c veredus 

 less than half length of ^ 

 tarsus. 



Innermost primaries and secon- 

 daries broadly tipped with 

 white. 



Middle toe and claw longer 

 than tarsus. 



y Barred tail. 



y Grey axillaries. 



totanirostris. 



australis 



Buff-chestnut axillaries. 



The species belonging to the subgeneric group of Pluviales are very easy to diagnose. 

 There is no difficulty in finding well-marked characters, which are unaffected by age, 

 sex, or season. The colour of the underparts, which varies with the seasons, is only intro- 

 duced to link the species more closely together : the key is complete without this character. 

 Other more important characters, such as the black axillaries of C. helveticus, are omitted 

 because the key is complete without them. 



