68 ANNALS NEW YORK ACADEMY OF SCIENCES 



•by the same three genera and more than 50 per cent of the Cichlidse of 

 "the Guapore are not found in the Paraguay. 



The diagram forming Plate XVI indicates the evolution and distribu- 

 tion of the cichlid fishes of the Amazon Valley and the rivers south of it. 

 Jit shows that river connections or interchanging of fauna and barriers 

 or isolation are not the important factors of geographical distribution, 

 but that the organic complex of the ancestral stock (three highland gen- 

 era — Oeophagus, Crenicichla and 2Equidens-Ciclilasoma) and the compo- 

 sition of the environmental complexes in which they came to live, pro- 

 duced by the rivers sinking into the Piano Alto, are the important factors. 

 The figure also shows that similar and identical evolution of the common 

 ancestral stock has taken place in similar environments and dissimilar 

 ■evolution in dissimilar environments regardless of whether the environ- 

 ments are or are not connected. (See Plate XV. 32 ) 



The phylogeny of the extra Amazonian species, i. e., more than thirty- 

 three (fifty-three existing in it), is not yet clear, but they will eventually 

 be deduced from the highland stock, because I have shown that the 

 Amazon Valley as we now know it has existed a comparatively short 

 time. 



The facts as shown on the diagram are almost exactly the opposite to 

 what one would expect, if land and water connections or isolation were 

 the important factors of living animal distribution. The numbers at 

 the end of the arrows show the number of new species which have un- 

 questionably descended from the old highland stock when it entered the 

 rivers which were gradually eroded in the Piano Alto. The diagram 

 also shows the basins connected or not and the identity of fanna in dis- 

 connected regions, such as Alto Parana and coastal streams. I have no 

 first hand knowledge of the Rio Orinoco ; hence I do not discuss it. 



Additional proof of similar evolution in similar environmental com- 

 plexes, even if they are not connected, is offered by the larger species of 

 South American fishes. For the sake of clearness, I have divided a 

 typical abbreviated list of large species of fishes into the following 

 ■classes : 



i 1. Large species of fishes found in the upper Guapore and Amazon, 

 ■and neither the genera nor the species found in the Paraguay-La Plata 

 basin. A few examples of such fishes are Cichla ocellaris, Phracto- 

 cephalus hemiliopterus, Brachyplaty stoma reticulatum and Electrophorus 

 electricus. To these and many other fishes may be added the large croco- 



32 Whether we should call these isolated species identical or by the same name may be 

 a debatable question. Not any two individuals are identical, but these species are not at 

 present distinguishable. 



