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Indiana University Studies 



parts of the Tuyra and Mamoni basins would be submerged. 

 This condition may have obtained during the lifetime of some of 

 the present species and it may be argued that the migration from 

 the Magdalena to the Atrato and Chagres has been very recent. 

 Its beginning may, however, have antedated the last submergence, 

 the species having been preserved in the higher tributaries of the 

 rivers. Leaving this speculation aside and assuming that the 

 present distribution has developed during the present configura- 

 tion of the country, did the Chagres fauna arrive by land or by 

 sea or by both routes? The answer to this question ought to give 

 us an index to the general question of the migration of fiesh- water 

 faunas over land and sea. 



The Atrato pours a large amount of fresh water into the Gulf 

 of Darien, which ought to facilitate the migration of fresh-water 

 fishes between this gulf and the Chagres. But a comparison of 

 the faunas of the Atrato, Tuyra, Chepo, and Chagres shows that 

 only Hyphessobrycon panamensis got into the Chagres that, as 

 far as we know now, did not also get into the Tuyra and Chepo. 



Many species crossed the divide between the Atrato and the 

 Tu3Ta. As stated above, of the 50 species in the Tuyra, 19 are 

 still found in the Atrato, and the genera of 20 more are represented 

 in Colombia. Some species coming from the Atrato got no farther 

 than the Tuyra, but 11 of the 19 species that presumably went 

 from the Atrato to the Tuj^ra got into the Rio Chepo. Sixteen 

 more of the Chepo' s 37 species probably came from the Tuyra. 



Of the 10 species in the Chepo not found in the Tuyra, Hoplias 

 microlepis reappears m Guaj^aquil, 6 find their farthest south in 

 the Chepo, the other 3 belong to the Pacific slope Gobiidse, some 

 of which are found far south of the Tuyra and will probably be 

 found in it. 



Five of the 19 species that presumably went from the Atrato 

 to the Tm r ra and Chepo arrived unchanged m the Chagres; 

 Rhamdia wagneri, Pimelodella chagresi, Chcetosto?nus fischeri, Piabu- 

 cina panamensis, and Hypopomos brevirostris. Several more of 

 the Tuyra species not directly from Atrato are unchanged in the 

 Chagres. 



A number of species of the Tuyra, Chepo, or the Pacific slope 

 opposite the Chagres have closely related species in the Chagres. 

 Such pairs are Ancistrus spinosus and chagresi; Rceboides occi- 

 dentalis and guatemalensis ; Brycon striatulus and chagrensis; 

 Brycon argenteus and petrosus; Creagrutus a finis and notropoides; 

 Dormitator latifrons and maculatus; Eleotris picta and pisonis; 



