124 SCIENCE SKETCHES. 
faune of the different river basins appear to be 
more distinct from one another. Certain ripple- 
loving types! are represented by closely related 
but unquestionably different species in each river 
basin, and it would appear that a thorough ming- 
ling of the upland species in these rivers has never 
taken place. 
With the lowland species of the Southern rivers 
it is different. Few of these are confined within 
narrow limits. The streams of the whole South 
Atlantic and Gulf Coast flow into shallow bays, 
mostly bounded by sand-spits or sand-bars which 
the rivers themselves have brought down. In 
these bays the waters are often neither fresh nor 
salt; or rather, they are alternately fresh and 
salt, the former condition being that of the winter 
and spring. Many species descend into these 
1 The best examples of this are the following: in the Santee 
basin are found Motropis pyrrhomelas, Notropis niveus, and Notropis 
chloristius ; in the Altamaha, otropis xenurus and Notropis calli- 
semus ; in the Chattahoochee, Motropis hypselopterus and Notropis 
eurystomus ; in the Alabama, /Votropis cwruleus, Notropis trichrois- 
tius, and Notropis callistius. In the Alabama, Escambia, Pearl, 
and numerous other rivers, is found /Votropis cercostigma. This 
species descends to the sea in the cool streams of the pine-woods. 
Its range is wider than that of the others, and in the rivers of 
Texas it reappears in the form of a scarcely distinct variety, 
Notropis venustus. In the Tennessee and Cumberland, and in the 
rivers of the Ozark range, is Votropis galacturus ; and in the upper 
Arkansas Wotropis camurus,—all distinct species of the same 
general type. Northward, in all the streams from the Potomac to 
the Oswego, and westward to the Des Moines and the Arkansas, 
occurs a single species of this type, Motropis whipplei. But this 
species is not known from any of the streams inhabited by any of 
the other species mentioned, although very likely it is the parent 
stock of them all. 
