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Indiana JJn'vvcrsU // Studies 



That the similarity on the two sides is not of very recent date 

 is shown by an examination of the fauna at the eastern base of the 

 Andes. Very little is known of the fauna of eastern Colombia 

 and western Venezuela. What we do know of it indicates that 

 the Maracaibo fauna is probably identical with the Magdalena 

 fauna, i.e. differs no more from it than the latter differs from the 

 Atrato fauna. Almost all we know of Lake Maracaibo was 

 recorded by Cuvier and Valenciennes. I have had recent oppor- 

 tunities to examine the fishes from and about Barrigon, Villa- 

 vicencio, and the Llanos to the northeast of them. I find that 

 a number of genera of wide eastern distribution which have not 

 been found in the Magdalena basin come up to the base of the 

 Cordilleras east of Bogota. They are Chasmocranes, Imparfinis 

 and Sciades, three catfishes; Erythrinus, Copeina, Hemigrammus, 

 Moenkhausia, Knodus, Creatochanes, Stevardia, Acestrorhyn- 

 chus, all Characins; Apistogrammus, and Crenicichla of the Cich- 

 lidse. All of them are widely distributed in the east. Did they 

 develop in the east since the formation of the Cordilleras of Bogota 

 or have the}^ migrated to the base of these Cordilleras after they 

 had become an effective barrier? Other conspicuous absentees 

 in the Magdalena are genera of wide distribution in the east which 

 have not been found near the base of the Andes of Colombia. 

 They are the genera of the Hemiodinse, Nannostomus, Tetra- 

 gonopterus, the Agoniatinse, the Stethapri'oninse, Serrasalmoninse, 

 Mylinse, Acestrorhamphus, all of which belong to the Characidse, 

 Paehyurus of the Scisenidse, Chsetobranchopsis and Cichla of the 

 Cichlidse, Electrophorus the electric eel, the gigantic Arapaima, 

 and the ancient Osteoglossum. 



It would be desirable in pursuit of a possible further study of 

 the origin of the Magdalena fauna to make collections in the 

 Maracaibo basin and thence east by way of the Pass of Hato, 

 800 feet into the Orinoco basin. 



A comparison of the genera in the upper Cauca above the 

 rapids of Antioquia and in the Potaro river of Guiana above the 

 Kaieteur fall shows that the two- regions have but three genera 

 in common. They are Pj^gidium, Astyanax, and Rivulus, all 

 genera of the very widest distribution in the whole of South 

 America. The species of the three genera are different in the 

 Cauca and the Potaro. In other respects the faunae of the Cauca 

 and the Potaro are very different. 



