July 7, 1905.] 



SCIENCE. 



19 



of tropical America has been derived from the 

 Athmtic slope fauna. Only three of the genera 

 of fresh-water fishes of the Pacific slope are 

 peculiar to it; all the rest are identical with 

 Atlantic slope genera. Even many species 

 are identical on the two sides. The indica- 

 tions are that in the main the Pacific slope 

 fauna was derived from the Atlantic slope 

 fauna in times much more recent than the 



be ample to keep apart two marine faunas is 

 not necessarily a barrier to the intermingling 

 of two fresh-water faunas. It is quite within 

 the range of possibilities that the Atlantic 

 slope fauna ascended the Chagres and suc- 

 ceeded in crossing the low divide and descend- 

 ed the Pacific rivers. The Chagres route has 

 a rival farther south. In Colombia the Cor- 

 dilleras form four separate chains. The east- 



Pacific Slope. 



Rhamdia cinerascens Gilntlier Western Ecuador. 



Rhamdia wagneri Giinther Bayano. 



Pimelodus clarias (Blocli) Bayano. 



Pimelodella modestus (Giinther) Esmeraldas. 



Pitnelodella chagresi (Steind. ) 



Pimelodella gracilis ( Val. ) 



Ancistrus chagresi (Eigenmann & Eigenmann) 



Hemiancistrus aspidolejns Giinther Bayano. 



Chwtostomus fischeri Steind Bayano. 



Loricaria variegata Steind Bayano. 



Loricaria uracantha Kner & Steindachner Bayano. 



Loricaria lima Kner Bayano. 



Sturisoma panamensis Eigenm. & Eigenm Bayano. 



Hoplias malaiaricus Bloch Bayano. 



Hoplias microlepis Giinther Western Ecuador. 



Curimatus magdalenos Steind Mamoni. 



Brycon striatulus (Kner) Pacific slope of Panama. 



Astyanax panamensis Giinther Bayano. 



Astyanax rutilus Jenyns Western Ecuador. 



Astyanax ceneus Giinther 



Raehoides guatemalensis Giinther Huamuchol. 



Gasteropelecus maculatus Steind Bayano. 



Luciocharax insculptus Steind Bayano. 



Eigenmannia humholdti (Steind) Mamoni. 



Pcecilia gillii Kner & Steind 



PoEcilea punctatus Kner & Steind 



Symbranchits marmoratus Bloch 



Geophagus jurupari Heckel 



Cichlasoma parma ( Giinther ) 



Cichlasoma godmanni (Giinther) Baj^ano. 



Atlantic Slope. 

 Chagres. 

 Chagres. 

 Chagres. 

 Chagres. 

 Chagres. 

 Chagres. 

 Chagres. 



Chagres. 



Chagres. 



Magdalena. 



Chagres. 



Chagres. 



Magdalena. 



Chagres. 



Motagua. 



Chagres. 



Chagres. 



Chagres. 



Magdalena. 



Entire east slope. 



Chagres. 



Chagres. 



Entire east slope. 



Chagres. 



Chagres. 



obliteration of the interoceanic connection be- 

 tween the Pacific and Atlantic. An exam- 

 ination of the distribution of the genera with 

 representatives on the Pacific slope on the 

 Atlantic side of the continent shows that 

 nearly all have a very wide range and are 

 found either in the Rio Magdalena or the 

 Chagres. This indicates that the present 

 fresh-water fauna of the Pacific slope crossed 

 the divide somewhere near Panama. It is to 

 be borne in mind that a barrier which may 



ern, east of the Rio Magdalena, the central, 

 between the Magdalena and its tributary, the 

 Cauca, the western, west of the Cauca, and 

 finally, a coast range. Between the western 

 Cordillera and the coast Cordillera is a trough 

 whose highest point is but 300 feet above sea 

 level. 



In the west Cordilleras to the east of this 

 trough arise two rivers, both of which flow 

 into the longitudinal valley, where one, the 

 Atrato, flows to the north into the Caribbean, 



