EIGENMANN : FRESH WATER FISHES. 363 



migrated to the Pacific slope subsequent to the formation of the Andes and 

 after the obliteration of the interoceanic sea, if such existed in the place sup- 

 posed, and long after the colonization of the coast streams of Minas, etc. 



If the supposition be established, that few, if any, ancient Atlantic slope 

 forms reached the Andes in time to cross the divide by going from stream 

 to stream along oceanic channels, it indicates very strongly that the 

 fresh-water species were unable to bridge the gap between the ancient land 

 masses, Archiplata and Archiguiana and the Andes. Such inability to 

 cross even moderate seas would be strong evidence that they could not 

 have crossed the Atlantic, and that there must have been continuous land, 

 or land at frequent intervals or better still, a land wave carrying the fami- 

 lies common to Africa and South America from a center to both these 

 continents. 



The fact that the Pacific slope fauna is generically all but identical with 

 the Atlantic slope fauna, and that the latter is generically different from the 

 African fauna, makes it certain that the Pacific slope fauna was derived 

 from the Atlantic slope fauna long after Guiana was separated from Africa. 



VIII. The Necessity and Evidence of a Former Land 

 Connection Between Africa and South America. 



Not a single species of South American fresh-water fishes is found in 

 North America, nor do any North American species reach South America. 

 Two prominent South American families, the Characidce and CiclilidcE 

 have representatives as far north as the Rio Grande basin, and one of these 

 has succeeded in crossing over into Cuba, evidently from Yucatan ; on the 

 other hand, several members of the North American fauna have repre- 

 sentatives as far south as the Isthmus of Tehuantepec. The North 

 American fauna is entirely distinct from the tropical American fauna. 



But four genera of fresh-water fishes of South America north of Pata- 

 gonia are found in any other continent than North America. These are 

 Synbranchus, Agonostonius, Cotylopits and Fiindiilus. The first is found 

 also in brackish water, the second belongs to the marine family MitgilidcE 

 and the other to the PonciliidcE. Synbranchus (map, p. 354) is found 

 in India, Ago7Wsto7nus in Middle America, West Indies, northern South 

 America and New Zealand, Australia, Celebes, Mauritius and Comoro 

 Islands. There is no reason why Agonosfonins may not have been inde- 

 pendently evolved in the South Sea and in America from marine mugilids. 



