FRESHWATER FISH FAUNA 



197 



Fig. 5. Distribution of the North American freshwater catfishes, 

 family Ictaluridae. Fossil occurrences of Ictalurus are shown for western 

 North America only. (Modified from Rostlund, 1952, maps 18-20; 

 Mexican portion original.) 



blackfish (Dallia), which lives in Alaska and Siberia. Although the 

 present distribution suggests a North American origin, all known 

 fossils, including the primitive genus Palaeoesox (Berg, 1936), are 

 from the Eocene to Miocene of Europe. 



The North American catfishes, comprising about 6 genera and 35 

 species, barely enter the western fauna with a single species in the 

 Yaqui River. That these fishes formerly occurred much farther 

 north in the West has already been pointed out. All known fossils 

 are North American, as is the present distribution (Fig. 5). 



Trout-perches constitute a singular group represented by two 

 monotypic genera, Columbia (Fig. 6) restricted to the basin of that 

 name in the West, and Percopsis, of much wider distribution in the 

 East. With the closely related monotypic pirate perches (Aphredo- 



