CONCLUSIONS. \)3 



pared with the raDge of Luxilus cornutus. lu tbe genus Ceratichiliya^ G. 

 higuttatus probabl^^ occurs in every stream from the Susquelianna to the 

 Great Salt Lake, while four other species of the same genus, C. micro- 

 pogon^ C. monachuSj C. zanemiis, and G. labrosus, are each, so far as is 

 known, confined to a single river-basin. 



XII. In any river-basin, the most abundant species (of small fishes) 

 are usually (a) those peculiar to it, or {b) those of the widest distribution. 

 In illustration of this, we may notice the abundance of Godoma pyrrlio- 

 melas and Notropis pJiotogenis in the Santee; of Godoma stigmatura and 

 JjUxUus cornutus in the Alabama; of Godoma eurystoma and Geratichthys 

 higuttatus in the Chattahoochee; of Godoma xwnura and Notemigomis 

 americanus in the Ocmulgee. To this rale, howe%'er, there are many 

 exceptions and modifications. 



XIII. In general, the further south any river-basin lies, the more 

 species are peculiar to it, and the greater the differences between its 

 fauna and that of the neighboring streams. In illustration of this, the 

 differences existing between the fauute of the Alabama and Chatta- 

 hoochee may be compared with those between the fauujB of the Susque- 

 hanna and Delaware. Twelve genera are known to be common to the 

 Chattahoochee and Alabama, and twenty-three to the Suj>quehannaand 

 Delaware. In the Southern streams, the process of evolution of specific 

 forms seems to have gone on more rapidly. This matter, however, 

 requires further investigation. 



XIV. Species of the widest distribution often have breaks in their 

 range which cannot be accounted for by any facts now in onr posses- 

 sion. Luxilus cornutus, so abundant in all the waters of the North and 

 West, does not occur, so far as is known, in any of the rivers between 

 the ISTeuse and the Alabama, in both of which streams it is abundant. 

 Various species range over several river basins and then cease abruptly. 

 Amiurus brunneus is abundant from the Santee to the Chattahoochee, in 

 the latter river the most abundant food-fish, while in the very next river- 

 basin, the Alabama, it is unknown. 



XV. Many species of wide distribution which are absent in certain 

 streams are there represented by certain other related species, which 

 may be regarded as modified descendants. Thus, in the South Atlan- 

 tic streams, Ghccnobryttus gulosus is represented by Ghccnobryttus viridis, 

 Kotemigonus chrysoleucus by JS'otemigonus americanus. In the South- 

 west, Eupomotis aureus is represented by Eupomotis palUdus ; in the 

 West, Noturus gyrinus by Koturus sialis, Noturus insigjiis by Noturiis 



