eigenmann: fresh water fishes. 229 



antarctic continent. It is probable that the Galaxiidae were formerly 

 distributed as marine forms about the entire globe south of the tropic of 

 Capricorn and that certain species on adapting themselves entirely to a 

 life in freshwater have become localized in points as widely isolated from 

 each other as those in which we know them now." See also the quota- 

 tion under Galaxias, p. 271. 



However, the evidence from other sources of a former land connection 

 has become conclusive, and I am of the opinion that during the submerg- 

 ence of large parts of Patagonia during the late Pliocene the formerly 

 abundant freshwater fauna became exterminated with the exception of 

 those forms that were indifferently freshwater or marine. 



The Petromyzonidae offer still another difficulty. There is no place on 

 the American continents between the Mexican plateau and Central Chili 

 that harbors any species of the family. The northern and southern species 

 belong to distinct genera. At least two of the South American genera 

 are peculiar, while two others are found in Australia and New Zealand. 



A comparison of the Atlantic and the Pacific regions of Patagonia shows 

 the two slopes to be largely inhabited by the same forms, a fact easily 

 explained by the character of the species (anadromous or indifferently 

 marine or aquatic) together with the continuous way by ocean and series 

 of streams emptying at intervals between the Rio Negro and Santiago. 



A comparison of the species inhabiting the southern part of the region 

 from the Rio Santa Cruz south and the northern part from the Rio Santa 

 Cruz to the north shows us that the southern part of Patagonia is inhabited 

 by an extreme fauna limited to Galaxias, Aplochiton, Geotria and 

 Exomegas. 



To these are added on the north, on both sides, Pcrcic/if/iys, Diphniysfe 

 and Pygidinm, and on the west alone, Percilia, Nematogenys and Cheirodon. 

 On the east Astyanax and Gyrnnocharacinus appear before the La Plata 

 fauna proper is reached. They are outliers of the largest of the South 

 American families, the Characidce. 



BOUNDARY BETWEEN THE BRAZILIAN AND 

 PATAGONIAN REGIONS. 



The definitive boundary between these regions has not been determined, 

 since little is known of the fauna of the Rio Negro and nothing from the 

 region about 500 miles wide extending north from a line connecting the 



