148 BuUetin 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 

 elective barrier between the Subtropical Zones lying on their eastern and 

 wiestern 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. 



I4st of Species and Subspecies which Characterize the West Andean Subtropical Fauna. 



Nothocercus intercedens Veniliornis oleaginus aureus ' 



Penelope perspicax '■' Formicarius rufipectus carrikeri ' 



Geotrygon bourcieri ' Grallaricula oostaricensis 



Leptotila verreauxi occidentalis ' Synallaxis azara? media '' 

 PhcEthornis syrmatophorus syrmato- Siptornis erythrops griseigularis 



phorus Automolus ignobilis 



Agyrtria viridioeps Xenioopsis subalaris subalaris ^ 



Thalurania f annyi verticeps Margarornis stellata 



Phaiolaima rubinoides sequatorialis Picolaptes warscewiczi 



Helianthea coeligena f erruginea Campylorhynchus pucherani 



Vestipedes aureliae caucensis Pcecilotriccus ruficeps rufigene ^ 



Adelomyia melanogenys oervina Pseudotriocus anneotens 



Cyanolesbia eimnse Elsenia pudioa brachyptera ' 



" coelestes Myiarchus oephalotes 



Schistes albogularis Masius corunulatus 



Eubucoo bourcieri occidentalis ' Attila brasiliensis parambaj 



Semnornis rhamphastinus Rupicola peruviana sanguinolenta 



Andigena nigrirostris occidentalis. Euchlornis riefferi occidentalis 

 Aulacorhynchus albivittatus phaeolEemus Pyroderus scutatus occidentalis 



Chloronerpes mbiginosus gularis ' Thryophilus nigricapillus connectens 



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



2 Found also on both slopes of the Central Andes. 



