Fig. 186.—Chub of the Great Basin, Leuciscus lineatus (Girard). Heart Lake, Yellowstone Park. Family Cyprinidæ.
"Facts of distribution in the eastern district of North America are these. Several species of fresh-water fishes occur at the same time in many Atlantic basins from the Merrimac or from the Hudson to the James, and throughout the Mississippi Valley, and in the tributaries of the Great Lakes. On the other hand, the species of each river may be regarded as pertaining to four classes, whose distribution has direct reference to the character of the water and the food it offers: first, those of the tide-waters, of the river channels, bayous, and sluggish waters near them, or in the flat lands near the coast; second, those of the river channels of its upper course, where the currents are more distinct; third, those of the creeks of the hill country; fourth, those of the elevated mountain streams which are subject to falls and rapids."
In the same paper Prof. Cope reaches two important general conclusions, thus stated by him:
"I. That species not generally distributed exist in waters on different sides of the great watershed.
"II. That the distribution of the species is not governed by the outlet of the rivers, streams having similar discharges (Holston and Kanawha, Roanoke and Susquehanna) having less in common than others having different outlets (Kanawha, or Susquehanna and James).
Fig. 187.—Butterfly-sculpin, Melletes papilio Bean, a fish of the rock-pools. St. Paul, Pribilof Islands.
"In view of the first proposition, and the question of the origin of species, the possibility of an original or subsequent mingling of the fresh waters suggests itself as more probable than that of distinct origin in the different basins."
Questions Raised by Cope.—Two questions in this connection are raised by Prof. Cope. The first question is this: "Has any destruction of the river faunæ taken place since the first elevation of the Alleghanies, when the same species were thrown into waters flowing in opposite directions?" Of such destruction by submergence or otherwise, Prof. Cope finds no evidence. The second question is, "Has any means of communication existed, at any time, but especially since the last submergence, by which the transfer of species might occur?" Some evidence of such transfer exists in the wide distribution of certain species, especially those which seek the highest streamlets in the mountains; but except to call attention to the cavernous character of the Subcarboniferous and Devonian limestones, Prof. Cope has made little attempt to account for it.
Prof. Cope finally concludes with this important generalization: