eigenmann: fresh water fishes. 333 



L Sternarclms byasiliensis Reinhardt. 

 AL Eigcinnaiuiia virescens (Valenciennes). 

 AL Sternopygus niacriirus Miiller & Troschel. 

 AL Gynuwtiis carapiis Linnaeus. 



? Synbranclms. 



? Arapaima. 

 A Packyunts sqnamiphmis Agassiz. 



* Pachy?tn{s fyancisci Cuvier & Valenciennes. 

 L CitharicJitJiys spilopterus Gunther. Marine. 



While this list shows many species and several peculiar genera 

 as a whole, except for the absentees of many Amazonian genera and 

 species, the fauna of this river does not differ more from that of the 

 Amazon at Para than that of Para differs from the fauna of the Amazon at 

 Tabatinga. Its fauna is much more like that of the Amazon than the fauna 

 of the Colorado is like that of either the Rio Grande or the Lerma. A cer- 

 • tain number of genera and species may always be expected to be peculiar. 



Has this area a primitive fauna and did it serve as a center of distribu- 

 tion ? If the theory of the population of the lowland streams from these 

 ancient highlands is correct, we may reasonably infer that the genera 

 now occupying this region are part of the ancient fauna. The San Fran- 

 cisco, occupying an isolated position in the very center of the old land 

 mass, may serve as the basis of the discussion. Only the fresh-water 

 families are of consequence in this discussion. The BimocepJialidce, 

 Arapaimidce, LepidosireiiidcB, Osteog/ossidce, and Argiidce are absent. 

 Some of these, as the Argiidce, might have developed from other forms 

 that may have emigrated from this place, but not so the others. For 

 these others the Brazilian plateau cannot have been the center of 

 divergence. This is also the case with the Seryasalmonince, Mylince 

 and GymnotidcE. These are found in the San Francisco, but -not in the 

 coastwise streams east of the San Francisco basin. Have they in th? 

 past migrated from this place as a center ? Possibly, but probably not, 

 for while these are found to the west, north, and south of the San Fran- 

 cisco basin, they are not found to the east in the coastwise streams. It 

 is, therefore, very probable that the San Francisco obtained these forms 

 from the west, where they swarm and from where the south certainly ob- 

 tained them, and that they have not yet succeeded in crossing the eastern 

 boundary of the San Francisco. It is less probable that they migrated 



