In the study of the geographical distribution of our fresh water fishes, we are able to make a few generalizations as follows: Two rivers in the same latitude, and belonging to the same great drainage basin, and draining similar areas, will have similar fish faunas. Thus we find a great similarity in the fishes of the Washita and the Tennessee rivers, a much greater similarity than we do in the fishes of the Washita and the Cedar rivers. If the stream is a large one, the fishes near its source will be much unlike those near its mouth. The fishes of Minnesota differ greatly from those of Louisiana, though the drainage of these two States is in the Mississippi river basin. Limestone streams have in them more species of fishes than do sandstone. All things being equal, the larger of two or more streams will contain the most species of fishes. There are few, if any, rivers as rich in species as the Mississippi river and its tributaries. It drains one slope of each of our two great mountain systems, besides an immense area of wood-land and prairie, and numerous swamps and marshes. Its upper course and many of its upper tributaries lie in the region once covered by glaciers, though now traversed by great moraines. Its fishes are as diversified as the area it drains. In its mountain streams we find such fishes as the trout, darters, minnows and suckers. In the upland streams are darters, shiners, suckers, sunfishes and small-mouthed black bass. In the channels of the larger tributaries are found the large suckers, buffalo fishes, gar pike, channel catfish, drum, pike and pickerel. The lowland streams contain the dogfish, pirate perch, some sunfishes, the large-mouthed black bass, some suckers, catfishes and other species. Minnows, darters, suckers and sunfishes are found in lowland, upland and mountain streams, though not the same species in each. These fishes belong to families which are made up of many species, some being strictly upland, others strictly lowland, each having a limited range. In the same way we have fresh water fishes and salt water fishes; some fishes, as the trout and salmon and eel, live in both salt and fresh water. Many other fishes, as the killifishes, thrive best in brackish water. Each species of fishes is best fitted for a particular region into which it has been forced to live, either to escape its enemies or to be able to get a living easiest. In its migrations it has moved along lines of least resistance, and has colonized those streams where Mother Nature has been able to do the most for it. The darters are small, perch-like fishes, which seldom exceed a length of six inches, the average being about three. All are active and swift swimmers and well suited for a life among the rocks and swift water of our smaller streams. All countries have small, swift, rocky streams, but few have darters. In their stead we find loaches, gobies, characins, sculpins, and the like.