EIGENMANN : FRESH WATER FISHES. 369 



two continents. The South American and African elements of these two 

 families must have been derived from some intermediate land-mass or 

 must have gone from one continent to the other over a land bridge. 

 That this connection, whatever it was, must have been obliterated before 

 the Tertiary, is evidenced by the facts that the Tertiary deposits of 

 Taubate and Parana show existing genera and that there are many South 

 American types, as the Gyniuotidce, Electrophoridcs, BwiocepJialidcE, 

 LoricariidcE, Argiidce, Pygidiidcs, Gallic JitJiyidce, Hypophthalmidcs , et al., 

 not found in Africa, that have all arisen in South America from the 

 CharacidcB and Siliiridce since the separation of the two continents. 



Similarly, other families found in Africa and not in South America 

 have either arisen in Africa since that time or have immigrated from the 

 East. 



A land connection, whether a land bridge, intermediate continent or 

 land wave between the two continents, is imperative. This land connec- 

 tion rriust have existed before the origin of existing genera and before 

 many of the existing families. 



On the other hand, Boulenger (Les Poissons au Bassin du Congo, 

 VIII) explains the similarity of the South American and African faunas 

 as " without doubt the result of the persistence in these two parts of the 

 world of types more generally distributed at a very remote epoch which 

 have disappeared in other regions, as palaeontology shows us, among others, 

 to be the case with the Dipneustes, which belong to this category. 



" Nothing is gained by explaining these similarities by interpolating a 

 hypothetical continental continuity which could not have existed except 

 at a time previous to the development of the groups of teleostean fishes 

 which Africa and South America possess in common." 



IX. The Points of Origin and Lines of Dispersion of Tropical 



American Fresh-water Fishes. 



The study of the distribution of fresh-water fishes has led to these 

 general conclusions.^ 



The origin and distribution of the fresh-water fishes of tropical South 

 America has come about as follows : 



' It has been sufficiently emphasized in the first section of this report that the fauna of "Archi- 

 plata" or Patagonia is not related to or contains but a few intrusives from the Tropical American 

 Fauna. 



