FISHES OF SOUTH AND MIDDLE AMERICA 519 



scisenoids and the herring tribe give to the South American fauna a 

 peculiarly marine flavor. But all these form but a small fraction of 

 the entire fauna, and their elimination would make little inroad on the 

 number of species. All are recent additions from the sea. 



There are also in South America a number of undoubted relicts of 

 former times, and if one should judge by the interest excited by the 

 genera Synb ran chits, Lepidosircn, Arapaima and Osteoglossum, it 

 would seem that these genera formed an important element in the 

 present fauna; but they are so few in number that they also might be 

 eliminated without any appreciable depreciation in the variety of the 

 South American fauna. 



After eliminating these, then, we come to the reigning element in 

 the present fauna, the element now in its prime and best suited to 

 contribute to the elucidation of the methods and paths of divergent 



5. Doras dorsalis C. A V., an Entrusted Catfjsh. 



and convergent evolution and the paths of dispersal. Chief of these 

 elements is the superorder Ostaryphysiae, composed of the Characinidas 

 with about 500 species; the Gymnotidae with about 30 species, and the 

 various families of catfishes with about 500 species. Pceciliidas, dom- 

 inant in middle America, contributed materially to the fauna — about 

 45 species. 



The largest contribution, aside from the characins and the cat- 

 fishes, is furnished by the Cichlida?, with about 145 species, in south 

 and middle America. 



The great variety of South American fishes is due to the divergence 

 in the types of characin, catfish, cichlid and pcecilid. 



3. 



Paucity of Middle American Fauna. 

 The fresh-water fauna of middle America is poor. No river except- 

 ing the Lerma harbors as many as 50 species. The genera south of the 

 isthmus of Tehuantepec are practically all South American with the 

 addition of pcecilids. 



