264 FISHES OF ILLINOIS 



of the other sections. We have taken it most frequently from 

 the smaller rivers, about half as commonly from creeks, and 

 somewhat less commonly from the clear upland lakes of the 

 northeastern part of the state. It has occurred but rarely in 

 our collections from either the larger rivers or from lowland lakes 

 and sloughs. Its avoidance of such situations is especially 

 illustrated by the fact that it is recorded but five times in 546 

 collections examined by us from the Illinois River at Havana and 

 Meredosia; that is, only 5 per cent, of the collections of this 

 species have been made from these Illinois River localities, from 

 which 35 per cent, of all our collections came. Its very marked 

 preference for a swift current and a clean bottom is a matter of 

 common observation, and is shown also by the data of 'our 

 collections, according to which it has come from swift waters 

 more than three times as often as from a quiet current, and from 

 a bottom of rock and sand nearly twelve times as frequently 

 as from one of mud. 



These preferences bring about a wide separation between 

 this bass and the closely related species of the same genus the 

 large-mouthed black bass. These two species inhabit the same 

 general area, may often be found in the same streams, and feed 

 on the same food, differing only, so far as known, in respect to 

 the ratios of the principal elements. Nevertheless, they avoid 

 competition by a difference in the situations preferred. These 

 closely allied species have, according to our data, an associative 

 coefficient of 1.08, while the small-mouthed black bass and the 

 rock bass, differing in characters, habits, and food, have a 

 coefficient of 6.24. In other words, the latter two unlike species 

 are brought by a similarity of local preference into each other's 

 company about three and a half times as frequently as the like 

 species of black bass. The differences of local preference are not 

 so great, however, but that the two species are frequently found 

 together. According to Jordan and Evermann, "Some small 

 lakes that are rather shallow, whose bottoms are chiefly mud 

 and whose water is warm, are found to be well suited to the 

 straw bass [large-mouthed] and to be entirely without the small- 

 mouthed black bass. But small lakes of considerable depth, cool 

 water, and with bottom partly of mud and partly of sand and 

 gravel, such as Lake Maxinkuckee, seem equally well adapted 

 to both species." 



The small-mouthed bass is found wide-spread throughout 

 the country, from Lake Champlain and the River St. Lawrence 



