LIMOSA. 



383 



All the Old- World species possess cha- 

 racter ffl and not h. 



All the New- World species possess 

 character h and not a. 



The only species recorded from Green- 

 land, Iceland, and the Faroes, and 

 breeding in Western Europe, pos- 

 sesses character c and not d. 



All the Old- World species possess cha- 

 racter a and not b. 



All the New-World species possess 

 character h and not a. 



The only species recorded from Green- 

 land, Iceland, and the Faroes, and 

 breeding in Western Europe, pos- 

 sesses character c and not d. 



Although both of the American species 

 occur on the Atlantic coast of North 

 America, the commonest of the two 

 possess character c and not d. 



On the Pacific coast of North America 

 the commoner of the two species 

 possesses character d and not a. 



On the Pacific coast of the Old World 

 both species {a and d) occur. 



The only species breeding on the At- 

 lantic coast of North America pos- 

 sesses character c and not d. 



On the Pacific coast of North America 

 the only species found north of the 

 tropics possesses character d and 

 not a. 



On the Pacific coast of the Old World 

 both species {a and d) occur. 



It is difficult to avoid the conclusion that the same causes have produced similar efi"ects Ancient 



in the two genera. If this hypothesis be true, the Bar-tailed Godwits emigrated through 

 Behring Straits, the ancestors of L. fedoa following the American coast, and those of 

 L. uropi/ffialis the Asiatic coast. The descendants of the latter gradually extended their 

 range westwards, until in post-glacial times the European examples were more or less 

 isolated and differentiated from their Asiatic confreres and became L. rufa. The Black- 

 tailed Godwits represent the party which chose the Atlantic route, the ancestors of 

 L. hudsonica having followed the Atlantic coast of America, and those of L. melanura the 

 Atlantic coast of Europe. The latter gradually extended their range into Asia, and in 

 post-glacial times the eastern examples were more or less isolated and diff'erentiated from 

 their fellows, and have now become L. melanuroides. 



The present distribution of the species comprising the genera Totanus and Limosa is 

 so satisfactorily accounted for, on the assumption that the ancestors of each genus were 

 differentiated from each other before the Post-Pliocene Glacial Epoch, and appears to be 

 so inexplicable, if the differentiation of the combined group be regarded as post-glacial, that 

 I am convinced that I was wrong in uniting the two genera in my ' History of British 

 Birds.' The difierence already alluded to in the profile of the keel of the sternum of the 

 species belonging to the two genera is an additional reason for regarding them as distinct, 

 as is also the difference in the extent of the frontal feathers beyond the gape, though the 

 latter character is probably an unimportant one. 



routes of 

 emigration. 



