246 FISHES OF ILLINOIS 



olive, with darker mottlings, the spots forming irregular rows. Head rather 

 large, 2.4 to 2.6; width of head 1.9 to 2.1 in its length; interorbital space 3.9 

 to 4.3; eye 4 to 5; nose longer than eye, 3.3 to 4.4; mouth very large, maxillary 

 nearly to back of orbit, 2.2 to 2.4 in head; operculum prolonged backward 

 and rounded behind as in Lepoinis and Eupoviotis, the membranous flap 

 narrow; gill-rakers 8 or 9 + rudiments, rather long and stiff. Dorsal X 

 (occasionally IX or XI), 9 or 10 (or 11); long and low, longest spine 3.5 to 

 4 in head; base of dorsal twice length base of anal; caudal lunate; anal III, 

 8-10; ventrals short of vent in females, to vent in males; pectorals short of 

 front of anal, 1.5 to 1.8 in head. Scales 6 or 7, 39-43, 11 or 12 (occasionally 

 13); lateral line usually complete; 6 to 8 rows of scales on cheeks. 



The warmouth is a heavy, wide-mouthed, red-eyed sunfish, 

 dark and mottled like the rock bass, but with less of bronze or 

 other showy color. This fish, the rock bass, and the green sun- 

 fish form a group of abundant Illinois species, all with large 

 mouths, and all feeding almost wholly on fishes and insects. 

 Notwithstanding this similarity of food, they seem to have 

 learned to inhabit the same area without serious mutual com- 

 petition by establishing different relations to their environment. 

 The rock bass, as already shown, lives by preference in clear 

 waters flowing over a rock bottom, while the present species is 

 the most of a mud lover of all of our sunfishes, as shown by its 

 preference for a muddy bottom, represented in our collections 

 b}^ the surprising coefficient of 7.33. Other factors of this 

 adjustment will be considered in the discussion of the green 

 sunfish. 



The warmouth is- essentially a species of lakes and ponds and 

 the smaller rivers, occurring also, but less generally, in creeks 

 and in rivers of the largest class. It is distributed throughout 

 the state— in the southern section mainlv in the smaller streams, 

 but in the northern half chiefly along the Illinois River. It is 

 abundant in the glacial lakes of northeastern Illinois, and has 

 come to us also from Lake Michigan. In the southern part of 

 the state it is common in the lower Illinoisan glaciation, to an 

 extent to indicate a deliberate preference for muddy water over 

 pure. It is seemingl}' a southern species by preference in this 

 state, the frequency ratios for the three sections being .44, .78, 

 and 1.78, from north to south. 



Lakes Michigan and Erie seem to mark its most northerly 

 distribution, and from these it is found to the Florida peninsula 

 on the southeast, and to Louisiana, Texas, and Kansas on the 

 south and west. It is said to be common in South Carolina, but 

 is most abundant west of the AUeghanies. It is everywhere a 



