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POPULAR SCIENCE MONTHLY 



arisen in South America from 

 the Characinidge and Siluridas 

 since the separation of the two 

 continents. 



Similarly, other families found 

 in Africa and not in South Amer- 

 ica have either arisen in Africa 

 since that time or have immi- 

 grated from the east. 



A land connection, whether a 

 land bridge, intermediate conti- 

 nent or land wave, between the 

 two continents is imperative. 

 This land connection must have 

 existed before the origin of exist- '<• 

 ing genera and before many of 

 the existing families. 



B. Conclusions and Bird's-eye 



View of the Problems. 



' f 



America, south of the Tropic 

 of Cancer, contains four (or five) 

 distinct faunas. These faunas 

 are the Transition, the Mexican, 

 the South American and the 

 Patagonian. 



The northernmost, or Transi- 

 tion fauna, is characterized large- 

 ly by instrusive elements from both the north and the south. It is 

 found on the Atlantic slope from the tropic to the Isthmus of Tehuan- 

 tepec and on the Pacific slope of this Isthmus. 



The Mexican fauna is unique, and occupies a narrow strip inclu- 



12 Members of the Gymnotid-e. a, o7er- 

 narchorhy achus curviroxtris (Boulenger); 

 6, Sleatogenys elegans (Steindachner) ; c, 

 Utemarchus brasiliensis (Reinhardt); d, 

 Eigenmannia virescens ( Valenciennes) ; 

 e, Giton fasciatus ( Pallas) ; /, Rham- 

 phichthys marinoratus (Castelnau). 



