270 FISHES OF ILLINOIS 



teeth; lower pharyngeals separate, with sharp teeth; pyloric caeca few; 

 anal papilla usually more or less developed; air-bladder small and ad- 

 herent, 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 Etheostomina;, 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 spe- 

 cies — 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 fre- 

 quently eaten by other predaceous fishes, as well as by numbers of 

 their own family — burbot, black bass, bullheads, yellow perch, sun- 

 fish, and crappies being among the species in whose food we have 

 found one or another species of the Percidcs. 



Key to Illinois Genera of the Family PERCIDiE 



a. Pseudobranchiae 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 serras 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 4 

 of its greatest depth Perca. 



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

 present; small species, not exceeding 8 or 9 inches, usually inuch 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. 



