270 FISHES OF ILLINOIS 



teeth; lower pharyngeals separate, with sharp teeth; pyloric cseca few; anal 

 papilla usually more or less developed; air-bladder small and adherent, often 

 wanting. 



Fresh waters of cool regions of the northern hemisphere, 

 mostly confined to eastern North America and Europe; genera 

 about 25; species about 125, the majority of them small and 

 belonging to the American subfamily of Etheostomince, or darters. 

 Besides these little-known but unusually interesting and really 

 beautiful small fishes, of which we have 23 species in Illinois, 

 the family contains three of our best known and most highly 

 valued food and game species — the yellow perch, the wall-eyed 

 pike, and the sauger. Taken together, they form a group of 

 highly organized, shapely, powerful, and active fishes, thoroughly 

 equipped for the predatory life, and filling an important place 

 in the ecological system of our inland waters. All are strictly 

 carnivorous, and ranging as they do from a length of an inch or 

 an inch and a half for the least darter to one of three feet for 

 the wall-eyed pike, they are able to inhabit all waters, to search 

 all situations, and to draw their food supplies from every class 

 of aquatic animals, the turtles and the larger and heavier mol- 

 lusks only excepted. On the other hand, although they are 

 swift swimmers, and well armed for self-defense, we have found 

 them frequently eaten by other predaceous fishes, as well as by 

 numbers of their own family — burbot, black bass, bullheads, 

 yellow perch, sunfish, and crappies being among the species in 

 whose food we have found one or another species of the Percidce. 



Key to Illinois Genera of the Family PERCID^ 



a. Pseudobranchise well developed; branchiostegals 7; no anal papilla; fishes 



growing to a weight of one pound or more; preopercle distinctly serrate 

 below and behind, the lower serrse antrorse. 



b. Canine teeth on jaws and palatines; body subcylindrical, elongate, greatest 



width about % greatest depth Stizostedion. 



bb. No canine teeth; body moderately compressed, the greatest width about $ 



of its greatest depth Perca. 



aa. Pseudobranchise small or wanting; branchiostegals 6; anal papilla usually 



present; small species, not exceeding S or 9 inches, usually much smaller; 



preopercle entire or nearly so. 



c. Premaxillaries not protractile, free only at the sides, connected in front with 



the skin of the forehead, from which they are not separated by a cross 

 groove. 



d. Cranium not compressed or much elevated back of eyes, its elevation* not 



more than % of its breadth;* body as a rule more or less slender and little 



* Measurement of breadth and elevation is made from a point just behind the eye, situated 

 on the boundary between the top of the cheek (marked by a slight bulge outward from the 

 cranium, by being scaled, or, usually, by a postorbital pore) and the thinly and smooth-skinned 

 parietals. 



