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



known as yet only from Ecuador, doubtless occur in it; for it must always 

 be remembered that not only are there portions of this fauna which have 

 never been visited by an ornithologist, but also that in no other part of 

 tropical America is the collector confronted by more unfavorable conditions 

 than those which prevail in the humid coastal district of Colombia. 



Of the 150 species and subspecies which are known to characterize this 



Fig. 4. Range of Zarhynchus wagleri. A Tropical Zone species of the Pacific Coast which ranges 

 northward to Mexico. 



fauna in Colombia, less than fifty can be classed as representative races of 

 widely distributed species, leaving therefore approximately one hundred, 

 or two-thirds the known characteristic forms, as autocthonous. 



This remarkably large proportion for a continental area of such com- 

 paratively limited size indicates that the environment is unusual, the isola- 

 tion effective, and possibly also that the region was formerly more extensive. 



