﻿Contribution from the Zoological Laboratory of Indiana University , 



No. 176. 



South America West of the Maracaibo, Orinoco, 

 Amazon, and Titicaca Basins, and the 

 Horizontal Distribution of Its 

 Fresh-Water Fishes 



By Carl H. Eigenmann, Dean of the Graduate School, and Head 

 of the Department of Zoology in Indiana University 



Physical features. The Pacific slope of South America, 

 4,000 miles long, rarely over 100 miles wide, resembles a veritable 

 shoe-string in shape. Conditions in this area vary from extreme 

 wet to extreme dry, from wet tropical to dry temperate and wet 

 temperate and cold as one goes south from Panama to Cape 

 Horn. 



The rainfall in the Canal Zone exceeds 200 inches per annum; 

 in Buenaventura it is said to be between 250 and 400 inches per 

 year. This condition prevails to the Rio Esmeraldas in Ecuador 

 (Veatch, Quito to Bogota, p. 163), South of the Esmeraldas the 

 country becomes more and more arid. On the coasts of Peru 

 and of Chili south to Copiapo the rainfall is negligble; it does 

 not average one inch per annum. In Peru all of the water for ag- 

 riculture is derived from the rivers descending from the moun- 

 tains, and in a portion of Chili, between the Loa and Copiapo, 

 even this source fails. In Serena, central Chili, the annual 

 amount has ranged from about 2 to 8.5 inches per annum be- 

 tween 1869 and 1910; in Santiago between 4 and 31 inches; the 

 latter a great extreme in one of the years between 1873 and 1910. 

 In Concepcion the rainfall has been between 26.6 and 40 inches 

 during the period 1876 to 1910, in Valdivia between 73 and 143 

 inches in 1872 to 1910, and at Puerto Montt between 71 and 128 

 inches. 



The amount of rainfall also varies very greatly with the alti- 

 tude at any cross-section. Behind the coast range there are lo- 

 cal dry areas even in the wet regions of Colombia. The upper 

 Dagua river runs thru such a rain shadow between Caldas and 

 Cisnero, and the upper Cauca runs in the shadow of the western 

 Cordillera, and is comparatively arid. 



