may ascribe the difficulty in finding good generic characters within the group. Sharply defined genera occur where the intervening types are lost. The darter is one of the very latest products in the evolution of fishes. [Illustration: FIG. 243.—The Zingel, _Zingel zingel_ (Linnæus). Danube River. (After Seelye.) ] =The Darters: Etheostominæ.=—Of the darters, or etheostomine perches, over fifty species are known, all confined to the streams of the region bounded by Quebec, Assiniboia, Colorado, and Nuevo Leon. All are small fishes and some of them minute, and some are the most brilliantly colored of all fresh-water fishes of any region, the most ornate belonging to the large genus called _Etheostoma_. The largest species, the most primitive because most like the perch, belong to the genus _Percina_. First among the darters because largest in size, most perch-like in structure, and least degenerate, we place the king darter, _Percina rex_ of the Roanoke River in Virginia. This species reaches a length of six inches, is handsomely colored, and looks like a young wall-eye. [Illustration: FIG. 244.—Log-perch, _Percina caprodes_ (Rafinesque). Licking Co., Ohio. ] The log-perch, _Percina caprodes_, is near to this, but a little smaller, with the body surrounded by black rings alternately large and small. In this widely distributed species, large enough to take the hook, the air-bladder is present although small. In the smaller species it vanishes by degrees, and in proportion as in their habits they cling to the bottom of the stream. The air-bladder is least developed in those species which cling closest to the bottom of the stream. [Illustration: FIG. 245.—Black-sided Darter, _Hadropterus aspro_ (Cope & Jordan). Chickamauga River. ] The genus _Hadropterus_ includes many handsome species, most of them with a black lateral band widened at intervals. The black-sided darter, _Hadropterus aspro_, is the best-known species and one of the most elegant of all fishes, abounding in the clear gravelly streams of the Ohio basin and northwestward. _Hadropterus evides_ of the Ohio region is still more brilliant, with alternate bands of dark blue-green and orange-red, most exquisite in their arrangement. In the South, _Hadropterus nigrofasciatus_, the crawl-a-bottom of the Georgia rivers, is a heavily built darter, which Vaillant has considered the ancestral species of the group. Still more swift in movement and bright in color are the species of _Hypohomus_, which flash their showy hues in the sparkling brooks of the Ozark and the Great Smoky Mountains. _Hypohomus aurantiacus_ is the best-known species. [Illustration: FIG. 246.—Green-sided Darter, _Diplesion blennioides_ Rafinesque. Clinch River. Family _Percidæ_. ] _Diplesion blennioides_, the green-sided darter, is the type of numerous species with short heads, large fins, and coloration of speckled green and golden. It abounds in the streams of the Ohio Valley.