[56] Among these are perhaps _Teuthis_ (_Acanthurus_), _Ilisha_, _Salarias_, _Myripristis_, _Thalassoma_. Some such which have not crossed the Isthmus are _Cirrhitus_, _Sectator_, _Sebastopsis_, and _Lophiomus_. [57] "Fishes of Central America," 1869, 397. [58] _Proc. U. S. Nat. Mus._, 1885, 393. [59] Introduction to the "Study of Fishes," 1880, p. 280. [60] _Proc. U. S. Nat. Mus._, 1891, pp. 124-126. [61] _Citharichthys spilopterus_ and _C. gilberti_. [62] _Hæmulon steindachneri_ and _Gymnothorax castaneus_ of the west coast probably being identical with _H. schranki_ and _Gymnothorax funebris_ of the east coast. CHAPTER XVI DISPERSION OF FRESH-WATER FISHES[63] =Dispersion of Fishes.=--The methods of dispersion of fishes may be considered apart from the broader topic of distribution or the final results of such dispersion. In this discussion we are mainly concerned with the fresh-water fishes, as the methods of distribution of marine fishes through marine currents and by continuity of shore and water ways are all relatively simple. =The Problem of Oatka Creek.=--When I was a boy and went fishing in the brooks of western New York, I noticed that the different streams did not always have the same kinds of fishes in them. Two streams in particular in Wyoming County, not far from my father's farm, engaged in this respect my special attention. Their sources are not far apart, and they flow in opposite directions, on opposite sides of a low ridge--an old glacial moraine, something more than a mile across. The Oatka Creek flows northward from this ridge, while the East Coy runs toward the southeast on the other side of it, both flowing ultimately into the same river, the Genesee.