Barriers to Dispersion of River Fishes 12% 
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; ft 
while the rivers of Texas, with the.same general fauna as those 
farther north, have also a few distinctly tropical types,t 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,4 
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 tristechus. 
{ Jordanella, Rivulus, Heterandria, etc. 
t Heros, Tetragonopterus. 
§ Lucifuga and Stygicola, fishes allied to the cusk, and belonging to the 
family of Brotulide. 
|| Amblyopsis, Typhlichthys. 
 Lepisosteus tristechus. 
