124 SCIENCE SKETCHES. 



faunae of the different river basins appear to be 

 more distinct from one another. Certain ripple- 

 loving types 1 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 Notropis pyrrhomelaSy Notropis niveus, and Notropis 

 chloristius ; in the Altamaha, Notropis xtznurus and Notropis calli- 

 setmts ; in the Chattahoochee, Notropis hypseloptertis and Notropis 

 eurystomus ; in the Alabama, Notropis cceruleus, No'ropis trichrois- 

 tius, and Notropis callistius. In the Alabama, Escambia, Pearl, 

 and numerous other rivers, is found Notropis 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 vcnusttis. In the Tennessee and Cumberland, and in the 

 rivers of the Ozark range, is Notropis galactunis ; and in the upper 

 Arkansas Notropis catmirus, 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, Notropis 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. 



