CHAEADKIUS. 



95 



Three toes. 



C. VIRGINICUS 

 C. MORINELLUS 

 C. FULVUS . . 

 C. PLUVIALIS . 



GEOGRAPHICAL DISTRIBUTION 



(during the breeding-season). 



Arctic Region. 



American. 



Eurasian. 

 East Asian. 

 West Eurasian. 



} 



Four toes. 



C. HELVETICUS. 



C. VEREDTJS 



C. AUSTRALIS 



C. TOTANIROSTRIS 



PaLjEarcttc Region. 

 Mongolia. 



Australian Region. 

 South. 



Neotropical Region. 



Falkland Islands. 



Tierra del Fuego. 



Patagonia. 



C. RUFIVENTRIS. 



C. MODESTUS. 

 C. SOCIABILIS. 



If we regard the true Plovers as congeneric with the rest of the group (and it is very 

 difficult to imagine that C. obscurus can belong to a different genus from that which 

 contains C. helveticus), it seems most probable that they emigrated along the Pacific coast 

 of America until they came to the Aleutian Islands, where the ancestors of C. fulvus and 

 C. pluvialis crossed over to Asia, the former becoming isolated in India, and the latter in 

 Africa, whilst the ancestors of C. helveticus followed the coast to South America. During 

 the warm post-glacial period all three returned to the polar basin, and one of them, although 

 very imperfectly isolated east and west of Behring Straits, has through the lapse of time 

 become imperfectly differentiated into two subspecies, which are distinguished as C. fulvus 

 and C. virginicus. 



There seems to be some plausibility about this theory of the distribution of the true 

 Plovers ; but if we regard them as post-glacial species, a still more probable theory of 

 distribution presents itself. 



If we assume that their ancestors were a circumpolar species during the post-glacial 

 period, and that the first interruption in the continuity of the area of their distribution was 

 caused by the glaciers of Greenland, it is reasonable to suppose that the consequence of 

 this semi-isolation was the differentiation of the Hudson's Bay Plovers into Grey Plovers 

 with black axillaries from the Lapland Plovers which became Golden Plovers with white 

 axillaries, the two being connected together by a series of intermediate forms producing 

 a Plover with grey axillaries at Behring Straits, which was partially split in two when 



Emigra- 

 tions. 



