1877. ] On the Distribution of Fresh- Water Fishes. 609 
found in the head waters of both, although the faunæ of the 
lower courses may be different. In case the one stream flows 
northward and the other southward, the common fauna will be 
essentially that of the northernmost stream. 
In Northern Indiana, the same species occur in the head 
waters of the St. Joseph’s, Maumee, Wabash, and Illinois rivers, 
although these streams discharge their waters in widely different 
directions. This is accounted for in the fact that the swampy 
waters-shed is often overflowed, affording in the spring an easy 
water communication. | 
VI. Many species inhabiting small tributaries of any river are 
different from those abounding in the riverchannels. This fact is 
well known. 
Among the brook species may be enumerated Eucalia incon- 
stans, Chrosomus erythrogaster, Pecilichthys spectabilis, Xenotis 
lythrochloris, Semotilus corporalis, Xenisma stellifera, Salmo fon- 
tinalis, the species of Rhinichthys, etc., etc. Of the channel spe- 
cies, such as Hyodon, Haploidonotus, Dorysoma, Pomolobus, Roc- 
cus, all the buffalo-fishes and the larger cat-fishes, [chthelurus 
punctatus, Pelodichthys olivaris, Amiurus nigricans, and the like 
will serve as examples. 
VII. Many species inhabiting the upper course of a stream are 
different from those of the lower. This subject has been well 
discussed by Professor Cope,! but further investigations, especially 
of the rivers of the Southern States, are much to be desired. 
VIII. This difference in the upper and lower faunz is due 
chiefly to differences in physical conditions of either water, river- 
bed, food, or climate. 
IX. Hence, if in the same river basin there are two streams 
flowing into the larger stream, the one near the source, the other 
hear its mouth, and these two streams are similar in all known 
physical respects, their faunz will be similar, and if dissimilar 
they will have different faunæ. The general identity of the 
fishes of Elk River in Western Tennessee and those of Powell’s 
River may be noticed in this connection. 
X. Some species of fishes are confined strictly to a single river 
~ basin, while others, with apparently no better means of defense 
_ % of diffusion, are widely distributed, inhabiting many rivers. In 
illustration of this the narrow range of each of the colored species 
: tred to Photogenis may be compared with the range of Luvilus 
_ “rnutus, which extends from Maine to Arkansas and Montana.. 
1 Loco citato. 
39 
x. — 2. 10, 
