3 1 4 Barriers to Dispersion of River Fishes 



gars* and marine sharks compete for the garbage thrown over 

 from the Pensacola wharves. In Lake Pontchartrain the fauna 

 is a remarkable mixture of fresh-water fishes from the Missis- 

 sippi and marine fishes from the Gulf. Channel-cats, sharks, 

 sea-crabs, sunfishes, and mullets can all be found there to- 

 gether. It is therefore to be expected that the lowland fauna 

 of all the rivers of the Gulf States would closely resemble that 

 of the lower Mississippi; and this, in fact, is the case. 



The streams of southern Florida and those of southwestern 

 Texas offer some peculiarities connected with their warmer 

 climate. The Florida streams contain a few peculiar fishes ;f 

 while the rivers of Texas, with the same general fauna as those 

 farther north, have also a few distinctly tropical types, J immi- 

 grants from the lowlands of Mexico. 



Cuban Fishes. The fresh waters of Cuba are inhabited by 

 fishes unlike those found in the United States. Some of these 

 are evidently indigenous, derived in the waters they now in- 

 habit directly from marine forms. Two of these are eyeless 

 species, inhabiting streams in the caverns. They have no 

 relatives in the fresh waters of any other region, the blind 

 fishes || of our caves being of a wholly different type. Some of 

 the Cuban fishes are common to the fresh waters of the other 

 West Indies. Of Northern types, only one, the alligator gar,^[ 

 is found in Cuba, and this is evidently a filibuster immigrant from 

 the coasts of Florida. 



Swampy Watersheds. - - The low and irregular watershed 

 which separates the tributaries of Lake Michigan and Lake 

 Erie from those of the Ohio is of little importance in determining 

 the range of species. Many of the distinctively Northern fishes 

 are found in the headwaters of the Wabash and the Scioto. 

 The considerable difference in the general fauna of the Ohio 

 Valley as compared with that of the streams of Michigan is due 

 to the higher temperature of the former region, rather than 



* Lepisosteus tristaechus. 

 t Jordanella, Rivulus, Heterandria, etc. 

 J Her os, Tetragonopterus. 



Lucifuga and Stygicola, fishes allied to the cusk, and belonging to the 

 family of Brotulida. 



|| Amblyopsis, Typhlichthys. 

 If Lepisosteus tristcechus. 



