THE FRESH-WATER FISHES OF 



PATAGONIA. 



INTRODUCTION. 



The interest in the Patagonian fresh-water fish fauna is entirely out of 

 proportion to its diversity and centers largely in its origin. Only about 

 twenty-nine species of fishes are known to live or enter the fresh waters 

 south of the line joining Valparaiso and Bahia Blanca. These few species 

 fall, according to their origin, into four distinct groups. 



1. Immigrants from the sea are: [a) in the process of acclimatization, 

 species of Menidia and Atherinopsis, or [b] may be looked upon as long 

 established, species of Perciclithys and Percilia. Members of a are 

 found in all the rivers ; members of b are found in the north chiefly, but 

 reach the Santa Cruz river. 



2. Immigrants from the fresh waters on the north : a very small overflow 

 from the extremely rich fauna to the north and still retaining their generic 

 affinity with northern forms. Here belong the species of the genera 

 CJieirodon and Astyanax, which are very widely distributed in tropical 

 South America and are not known to extend much south of the Rio 

 Negro. Here also belongs Hatcheria, a southern modification of the 

 widely distributed Pygidinm. 



3. Autochthons, or of doubtful origin. Here belongs the highly inter- 

 esting Dipiouiyste, which is found on the northern border of Patagonia, 

 but is not a derivative of the tropical American fauna. It is a relict of 

 the original catfishes, in which the maxillary is still functional as a tooth 

 bearer. Here belongs also Nematogenys, a catfish related to Pygidium. 

 Like the members of group 2, these species are confined to the northern 

 fringe of the Patagonian area. 



4. There remain unaccounted for the members of i\\& Aploc/iifomdce, Ga- 

 laxiidce and Petyomyzouidcc, chiefly of southern Patagonia. The two 

 former Boulenger puts in his Haplomi, an order of odds and ends of 

 fishes, containing such relicts as the Percopsidcc, Amblyopsidce of North 



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