on the Genus Coereba. 493 



by tlie species inhabiting Peru, Ecuador, Columbia, and 

 Venezuela) is definitely restricted to a long mountain 

 system (the Andes), together with its easterly extension as 

 the Sierras of Merida and the Cordilleras of Venezuela; and 

 this system of mountains has only become elevated to any 

 considerable heights since late Miocene or early Pliocene 

 times. On the other hand, we find the race ivithout any 

 wing-spots is definitely restricted to all that vast area of 

 land which lies to the eastward of the continent and which 

 is now known as Brazil and the Guianas. 



Two well-differentiated species now inhabit these last two 

 areas — viz., C. chloropyga and C. guianensis ; and their 

 original centres of distribution correspond with two well- 

 defined land-areas, which in middle Tertiary days were 

 insular and separated from each other and from the low 

 Andean chain by long inland extensions of the sea, as 

 shown in the inset map. 



Thus, on the one hand, we have a very ancient land-mass, 

 represented to-day by the denuded Archsean and Palaeozoic 

 rocks forming the central uplands and mountainous coast- 

 regions of Brazil (the home of C chloropyga); while, on 

 the other hand^ we have another insular mass of Archsean 

 mountains, comprising to-day the more elevated parts of 

 Guiana and the Sierras of Pacaraima, Boraima, and others, 

 which are now the topotypical home of C. guianensis. 



Both these insular land-masses and the long Andean 

 chain have (geologically speaking) only recently been linked 

 up by the filling of the intervening seas with alluvial deposits, 

 plus the effects of the general elevation of the continent. 

 Thus they have remained sufficiently isolated and distinct in 

 physical characteristics, even up to recent geological times, 

 to give origin to the two races under consideration. 



Turning now to Central America and the Antilles, we 

 find the ivhite-iving -spotted race still restricted to the long 

 mountainous system which is continued through the Central 

 American States as a more or less direct (if only physical 

 and not geological) prolongation of the Andes. We can, 

 moreover, trace this mountain system eastwards by way 



