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Indiana University Studies 



As a result of this article and much propaganda, the Smith- 

 sonian Institution and the Field Museum undertook a joint 

 survey of the fish fauna of Panama. The survey was not begun 

 until the work on the canal had made many changes in the natural 

 habitat of the fishes, but Meek and Hildebrand's "The fishes of 

 the fresh-waters of Panama" published in Field Museum Natural 

 History Zoological Series, X, 1916, pp. 217-374, must remain the 

 last word on the distribution of the fresh-water fishes of the canal 

 region before the canal united the waters of the two slopes. They 

 spent two seasons, January to May, inclusive, 1911, and from 

 January to March, inclusive, 1912, in the field and covered the 

 territory from the eightieth meridian to Colombia. I covered 

 rivers from the boundary of Panama south. I have made free 

 use of Meek and Hildebrand's results in the series of articles of 

 which the present paper forms one. 



The problem of the origin of the fauna of Panana resolves 

 itself into the questions of the origin of the Pacific slope fauna, 

 particularly that of the Tuyra, and the question of the origin 

 of the fauna of the Chagres. 



We may consider first the origin of the Tuyra fauna and then 

 that of the Chagres. 



The Atrato-Tuyra Problem. The Atrato plain east of the 

 Tuj'ra river is very low and extends close to the divide between 

 the Atrato and Tuyra which, at its lowest point, is but about 400 

 feet high. On the Pacific side the slope is longer, but also for the 

 most part low. About half the distance between the mouth of 

 the Atrato and the Crest is influenced by the tide. 



On the easterly side of the Gulf of Panama [but on the Pacific coast] lies 

 the Gulf of San Miguel, which is an excellent harbor, carrying tide water 

 halfway across the isthmus. The Savana River enters this gulf from the 

 north, and the Tuyra River from the southeast, while the Chucunaque, 

 heading near the Chepo and flowing southeasterly, is a tributary of the Tuyra. 

 Report of the Isthmian Canal Commission, 1899-1901 p. 50. 



The lowest point in the divide between the Tuyra and the 

 Atrato given in the Canal Commission's map of this region is 

 800 feet. The International Railroad Survey gives the pass of 

 Cajon as 400 feet and this is the height given by Self ridge. While 

 this pass or divide is less than 100 feet higher than the Istmina 

 pass between Atrato and San Juan, the nature of the territory 

 is evidently quite different. The gradient from the Atrato to 

 the San Juan is very gradual. 



