=The True Perches: Percidæ.=—The great family of _Percidæ_ includes fresh-water fishes of the northern hemisphere, elongate in body, with the vertebræ in increased number and with only two spines in the anal fin. About ninety species are recorded, the vast majority being American. The dwarf perches, called darters (_Etheostominæ_), are especially characteristic of the clear streams to the eastward of the plains of the Missouri. These constitute one of the greatest attractions of our American river fauna. They differ from the perch and its European allies in their small size, bright colors, and large fins, and more technically in the rudimentary condition of the pseudobranchiæ and the air-bladder, both of which organs are almost inappreciable. The preopercle is unarmed, and the number of the branchiostegals is six. The anal papilla is likewise developed, as in the _Gobiidæ_, to which group the darters bear a considerable superficial resemblance, which, however, indicates no real affinity. [Illustration: FIG. 239.—Large-mouthed Black Bass, _Micropterus salmoides_ (Lac.). (From life by Dr. R. W. Shufeldt.) ] =Relations of Darters to Perches.=—The colors of the _Etheostominæ_, or darters, are usually very brilliant, species of _Etheostoma_ especially being among the most brilliantly colored fishes known; the sexual differences are often great, the females being, as a rule, dull in color and more speckled or barred than the males. Most of them prefer clear running water, where they lie on the bottom concealed under stones, darting, when frightened or hungry, with great velocity for a short distance, by a powerful movement of the fan-shaped pectorals, then stopping as suddenly. They rarely use the caudal fin in swimming, and they are seldom seen floating or moving freely in the water like most fishes. When at rest they support themselves on their expanded ventrals and anal fin. All of them can turn the head from side to side, and they frequently lie with the head in a curved position or partly on one side of the body. The species of _Ammocrypta_, and perhaps some of the others, prefer a sandy bottom, where, by a sudden plunge, the fish buries itself in the sand, and remains quiescent for hours at a time with only its eyes and snout visible. The others lurk in stony places, under rocks and weeds. Although more than usually tenacious of vitality, the darters, from their bottom life, are the first to be disturbed by impurities in the water. All the darters are carnivorous, feeding chiefly on the larvæ of _Diptera_, and in their way voracious. All are of small size; the largest (_Percina rex_) reaches a length of ten inches, while the smallest (_Microperca punctulata_) is, one of the smallest spiny-rayed fishes known, barely attaining the length of an inch and a half. In Europe no _Etheostominæ_ are found, their place being filled by the genera _Zingel_ and _Aspro_, which bear a strong