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Indiana University Studies 



The genera of 20 more Tuyra fishes are represented in Colom- 

 bia. Concerning the origin of most of the 19 species there cannot 

 be any doubt; they are abundant in the Atrato-Magdalena, and 

 find their farthest north in the Tuyra or at least in the southern 

 half of Panama. They moved from the Atrato to the Tuyra. 



Such undoubtedly are Phanagoniates macrolepis, Ageneiosus 

 caucanus, Loricaria variegata, Curimatus magdalencs, Astyanax 

 fasciatus, Ctenolucinus beani, Hoplias malabaricus and Hypo- 

 pomus brevirostris. 



It is possible that some species have more recently gone from 

 the Tuyra to the Atrato , but originally all of them went in the 

 other direction. There is no direct evidence that any specifically 

 Pacific slope forms have come over to the Atrato. The tide of 

 migration has all flowed westward. The strictly west-slope 

 things like Awaous transmontanus and Philypnus maculatus have 

 not come across into the Atrato. A number of species whose 

 ancestors came from the Atrato have become more or less modi- 

 fied in the Tuyra. Trachycorystes a?nblops is a modified fisheri, 

 Pimelodus punctatus a modified clarias. 



The species common to the Atrato-Tuyra (18 per cent) as 

 compared with the number of species common to the Atrato and 

 San Juan (30 per cent) may be taken as an inverse measure of 

 the difficulties in crossing from the Atrato to the Tuyra and from 

 the Atrato to the San Juan. 



The 11 species of the Tuyra not found in the Atrato or not 

 represented by a species of the same genus are: 



1. Lasiancistrus planiceps, 2. Leptancistrus canensis, 3. Astro- 

 blepus longifilis, 4. Apareiodon dariensis, 5. Compsura gorgonce, 

 6. Pseudocheirodon affinis, 7. Hemibrycon dariensis, 8. Sternarchus 

 rostratus, 9. Mollienisia caucana, 10. Philypnus maculatus, 11. 

 Awaous transmontanus. 



Of these the genera of numbers 1, 3, 4, 7, 8, 9, 10, and 11 are 

 found in the Magdalena or the San Juan and will most proba- 

 bly be found in the Atrato between the two. Leptancistrus is 

 derived from Lasiancistrus, Compsura and Pseudocheirodon from 

 Cheirodon, both found in Colombia. The genera of numbers 1 to 

 8 find their farthest north in Panama. 



Every consideration shows the close affinity of the Tuyra 

 fauna to that of the Atrato, from which it has in large part been 

 derived. 



The Chagres Problems. The completion of the Panama 

 Canal has greatly modified the Chagres basin and merged it with 



