228 FISHES OF ILLINOIS 



glaciation. It is more abundant north than south, the fre- 

 quency ratios of our 121 collections of it being approximately 

 as 1, 2, and 3, for southern, central, and northern Illinois respec- 

 tively. 



It occurs in a great variety of waters from Lake Michigan 

 and the northeastern glacial lakes of Illinois to the borders of 

 the main stream of the Illinois River and the muddy lakes of 

 the Illinois bottoms, commonest, however, in the quieter and 

 clearer parts of the waters which it inhabits. We have found 

 it somewhat most abundant in the smaller rivers (coefficient 

 1.67), and next in the glacial lakes (1.13) and in lowland lakes 

 and sloughs (1.01). It is not infrequent, however, in our collec- 

 tions from creeks and the larger rivers (.76 and .77). 



Outside the state, it is present in all the Great Lakes, and 

 ranges thence southward to Florida and southwestward to 

 Missouri, Arkansas, and Texas. 



It seems to live wholly on the animal plankton, apparently 

 catching its minute prey one by one, as a pike captures fish. 

 Its mouth, though small, is well equipped with teeth, and its 

 gill-rakers are unusually well developed, being numerous, 

 slender, armed with minute denticles, and longer than the gill- 

 filaments. Corresponding to its predaceous habit, its intestine 

 is uncommonly short, the whole alimentary canal being consider- 

 ably shorter than the body without the head. The food of 

 twenty-five specimens, obtained from widely scattered localities, 

 was wholl}^ animal, and consisted mostly of minute larvae of 

 gnats (Chironomus) and many species of Entomostraca, both 

 copepods and Cladocera. Land insects and spiders, washed or 

 fallen into the water, were also frequent in its food, including 

 forms as small as plant-lice, chalcids, springtails, and thrips. 

 One specimen had taken a very small unrecognizable minnow. 



Family APHREDODERIDjE 



the pirate-perches 



Body oblong, elevated at base of dorsal, compressed behind; caudal 

 peduncle thick; scales strongly ctenoid; sides of head scaly; lateral line im- 

 perfect; skeleton osseous; anterior vertebra 1 simple; ventrals thoracic, with a 

 small spine and more than 5 soft rays; dorsal fin single, with 3 or 4 small 

 spines; anal with two slender spines; caudal rounded; no mesocoracoid: gill- 

 membranes slightly joined to isthmus anteriorly; branchiostegals 6; pseudo- 

 branchiae obsolete; gill-rakers tubercle-like, dentate; preopercle and pre- 

 orbital with free edges sharply serrate; opercle with a spine; mouth some- 



