150 Mr. 0. Salvin on the Genus Geothlypis. 



I have already shown that though G. velata and G. chiriquen- 

 sis are more nearly related to one another than they are to G. 

 cequinoctialis, the latter intercepts their range. The following 

 hypothetical explanation of this fact in geographical distribution 

 seems admissible. 



Anterior to the union of Guiana with the mainland of South 

 America the ancestral race of the present Geothlypis velata and 

 G, chiriquensis held territorial sway from Brazil to Veragua, or, 

 perhaps, if Central America was then cut by channels, to the ex- 

 treme northern limit of the spurs of the Andes. At that time 

 the ancestors of G. aequinoctialis were restricted to the island of 

 Guiana. When the union of this latter tract of covintry with the 

 continent took place, G. cequinoctialis began to spread over the 

 valley of the Amazon, and westward through Venezuela and Co- 

 lumbia, driving the contemporary form of G. velata southwards 

 into Brazil, and forcing a small detached remnant northwards 

 into the recesses of the remote volcano of Chiriqui. Isolated 

 from its parent stock and incapable of stemming the tide of in- 

 vasion by an antagonistic race, this small remnant was prevented 

 from spreading over Central America by the contemporary form 

 of G. poliocephala, which then occupied Costa Rica and held its 

 own against pressure from the south. Thus hemmed in, it found 

 at last a resting-place in Chiriqui, where alone it has survived, 

 and where it gradually assumed the features which now distin- 

 guish it. 



G. aquinoctialis and its allies appear to be residents in the 

 countries in which they are found. G. semiflava, G. speciosa, and 

 G. melanops are also residents, the first in western Ecuador and 

 the last two in Mexico. 



There remain three migratory species, whose lines of migration 

 as well as the southern limit of their wandering I now proceed 

 to show. 



Geothlypis trichas, of which the summer range spreads over the 



stronger; tlie upper plumage is not so briglit, being more tinged with 

 ochre ; the under plumage is more uniform in colour, the throat being of 

 not so bright a yellow, and the colour of the abdomen more ochraceous 

 in tint. 



