148 Bulletin American Museum of Natural History. [Vol. XXXVI, 



The East Andean Fauna, however, is but the more northern portion of a 

 belt of forest which extends southward to central Bolivia. Expressed in 

 miles, the West Andean Fauna measures from north to south about 850 

 miles, the East Andean, with its subdivisions, nearly 2500 miles. 



Something more than isolation is required to explain the presence in the 

 Western Andes of so large a number of species in proportion to its area. 

 The Subtropical Zone of the Central Andes, with its narrow basal connection 

 with the East Andean Fauna and long peninsula-like projection, is almost 

 insular in its isolation; but it has few indigenous species. If this fact is 

 attributable to its inaccessibility, one may reply that the subtropics of the 

 Western Andes are even less accessible. It therefore seems reasonable for 

 us to believe that the Subtropical Zone of the Western Andes, as well as the 

 Tropical Zone at its western base, received its life in part from what is now 

 upper Amazonia, before the Andes were sufficiently elevated to act as an 

 effective barrier between the Subtropical Zones lying on their eastern and 

 western slopes. Since, however, this was obviously at a later date than 

 that at which the Tropical Zones of the eastern and western slopes were 

 separated, there is a closer relation between the life of the upper than 

 between that of the lower zones. 



List of Species and Subspecies which Characterize the West Andean Subtropical Fauna. 



Nothocercus intercedens Veniliornis oleaginus aureus '■ 



Penelope perspicax ' Formicarius nifipectus carrikeri '■ 



Geotrygon bouroieri ^ Grallaricula costaricensis 



Leptotila verreauxi occidentalis ^ Synallaxis azara? media '' 

 Phoethomis syrmatophorus syrmato- Siptornis erythrops griseigularis 



phorus Automolus ignobilis 



Agyrtria viridiceps Xenioopsis subalaris subalaris ' 



Thalurania fannyi verticeps Margarornis stellata 



Phaiolaima rubinoides aequatoriaUs Picolaptes warscewiczi 



HeHanthea coeUgena ferruginea Campylorhynohus puoherani 



Vestipedes aurelise eaucensis Poecilotriocus ruficeps rufigene ^ 



Adelomyia melanogenys oervina Pseudotriccus annectens 



Cyanolesbia emmae Elaenia pudica brachyptera ' 



" ccelestes Myiarchus eephalotes 



Schistes albogularis Masius corunulatus 



Eubucco boureieri occidentalis ' Attila brasiliensis paramba; 



Semnornis rhamphastinus Rupicola peruviana sanguinolenta 



Andigena nigrirostris occidentalis Euohlornis riefferi occidentalis 

 Aulacorhynchus albivittatus phseolaemus Pyroderus scutatus occidentalis 



Ghloronerpes rubiginosus gularis * Thryophilus nigricapiUus connectens 



1 Found also on the western slope of the Central Andes. 



2 Found also on both slopes of the Central Andes. 



