30 



INDIANA UNIVERSITY 



D. The Stethaprionin^e 



The Stethaprioninae are like some of the Tetragonopterin^e, 

 but have a procumbent predorsal spine. They are deep, com- 

 pressed fishes, easily distinguished by the peculiar predorsal spine 

 which, however, very probably does not indicate community of 

 descent. Fowlerina, for instance, with three species, one in the 

 Amazons and northward, another in the Paraguay, and another 

 in the San Francisco, has been derived from Moenkhausia and 

 very probably at least twice from different species, once in the 

 San Francisco and once in Guiana. Stethaprion may have been 

 derived from Ctenobrycon. 



General Conclusions. 



1. The Tetragonopterinae are the dominant subfamily of South 

 American Freshwater Fishes. They are found from tide level to 

 the highest altitude attained by fishes in South America exclusive 

 of Cyclopium and from Patagonia to New Mexico. 



2. The same character may and does appear independently 

 in various members of a homogeneous group of animals. 



3. As a result of the independent origin of the same charac- 

 ters in different species, some of the genera of the Tetragonopte- 

 ringe are polyphyletic. 



4. Species of different genera living together in some isolated 

 area may be derived the one from the other and be more nearly 

 related pliylogenetically than they are to other members of the 

 same genera in other areas. 



5. Evolution is actively in progress, i. e., a number of species 

 of Characins are in an unstable condition. 



6. Material for evolution may appear in a widely distributed 

 iish over its entire range, or 



7. Material for evolution may appear in a distinct locality or 

 restricted area of the range of a fish with very wide distribution 

 while no such material appears in the general range. 



8. The same new form may arise from a widely distributed 

 species at isolated points or throughout its entire range wherever 

 the suitable stimulus is present or wherever the proper selection 

 is taking place. 



