^°i89i!'''] PROCEEDIxNGS OF THE NATIONAL MUSEUM. 11 



tomatiiue, aud Serrasalmoninm are certaiuly autochtlious of South 

 America and probably later differentiatious. The Tetragonopterime, 

 Hydrocyonime, and CrenuchirKe are, as has been shown under " Hela- 

 tions of the South American Fresh- water Fauna," found both in Africa 

 and South America. Xo doubt need be entertained about tlie origin of 

 the genera now found in South America, as they are all peculiar to it. 

 "On theother hand," says Dr. Giinther (Study of Fishes, p. 233), " the ex- 

 istence of so many similar forms on both sides of the Atlantic affords 

 much support to the supposition that at a former period the distance be- 

 tween the present Atlantic continents [Africa and South America] was 

 much less, and that the fishes which have diverged towards the east 

 and west are descendants of a common stock which had its home in a 

 region uowsubmerged under some intervening partof the ocean."* Cer- 

 tain it is that the great preponderance of Tetragonoi)terin(e and Hydro- 

 cyonbue are found in South America, and that there these subfamilies 

 probabl}" had their origin. 



Such anomalies as the presence of one species ot Greniichince in South 

 America and another in Africa is at present uuexplainable. 



The two families of the Oymnonoti need few words. They are not, 

 and probably ne%^er have been, found outside South America. 



The OsfeogIossld(e are probably a family in its last stages. 



In the Galaxiidce and Aplochitonida', which belong to the south 

 temperate fauna, is seen the wide distribution of genera, and even of 

 species, common in the north temperate regiou. There seems to be 

 nothing anomalous in their i)resent wide distribution. 



The Folycentridie, like the Steniopygidce aud Electroj)horid(e have not 

 been found beyond South America, and they are undoubtedly autoch- 

 thons. 



GEOGRAPHICAL DISTRIBUTION. 



The distribution of the neotropical fishes presents well nigh all pos- 

 sible conditions. There are species and genera of marine families 



* Wallace says in this connection : " Tiie great continent of South America, as far 

 as we can judge from the remarkable characteristics of its fauna and the vast depth 

 of the oceans east and west of it, has not during Tertiary, and probably not even 

 during Secondary times, been united with any other continent, except through the 

 intervention of North America. » » * What its earlier condition was we can not 

 conjecture, but there are clear indications that it has been broken up into at least 

 three large masses, aud probably a number of smaller ones, and these have no doubt 

 undergone successive elevations aud subsidences, so as at one time to reduce their 

 area and separate them still more widely from each other, and at another period to 

 unite them into continental masses. The richness and varied development of the 

 old fauna of South America, as still existing, proves, however, that the country has 

 always maintained an extensive area; and there is reason to believe that the last 

 great change has been a long continued and steady increase of its surface, resulting 

 in the formation of the vast alluvial plains of the Amazou, Orinoco, and La Plata, 

 and thus greatly favoring the production of that wealth of specific forms which distin- 

 guishes South America above all other parts of our globe." 



