cviii FISHES OF ILLINOIS 



ratios of frequency of occurrence in such situations range from 43 

 to 88 per cent., and which may consequently be called limophagous 

 fishes. These are the warmouth sunfish, the black and the yellow- 

 bullheads, the pirate-perch, a single darter (Boleosoma camurum), 

 and two minnows, the golden shiner and the common shiner (No- 

 tropis cornutus. ) 



It is interesting to find, by an examination of our maps, that all 

 these 7 species are freely distributed over the lower Illinoisan glacia- 

 tion of the southern part of the state, where, as we have already 

 shown, only fishes indifferent to a peculiarly persistent turbidity of 

 the water are likely to occur. 



By selecting from this same list of 62 species those with the lowest 

 ratios of frequency over a muddy bottom, we get 13 species (with 

 ratios of 4 to 10 per cent.) which evidently avoid such situations; 

 and these, again, are without exception so distributed that the area 

 of the lower Illinoisan giaciation is almost never entered by them. 

 These are one of the native carp (velifer), a species of red-horse (aure- 

 olum) , the small-mouthed black bass, two darters (Hadropterus phox- 

 ocephahis and Etheostoma coeruleum), five minnows (Campostoma 

 anomalum, Notropis heterodon, Ericymba buccata, Hybopsis kentuck- 

 iensis, and Notropis blennius), two stonecats, and the little brook sil- 

 verside (Labidesthes). 



A more precise statement and a fuller discussion of the ecological 

 relations of our fishes, including statistics of companionship for the 

 various species, as shown by the frequency of their joint occurrence 

 in collections, must be left for later contributions. 



Attention may be profitably called, in conclusion, to the econo- 

 mic significance of the details of distribution of the various species, 

 as influenced both by geographical and ecological conditions, since a 

 proper understanding and application of these facts will prevent 

 wasteful efforts to introduce species where they do not belong and 

 can not thrive. Indeed, the more detailed our knowledge of favor- 

 able, and even optimum, conditions for the different species, and 

 the more exact, also, our acquaintance with the relations of each 

 species of fish to its companion species in any associate assemblage, 

 the more intelligent, and hence the more successful, in the long run, 

 will be our efforts to extend the range and multiply the numbers 

 of the more useful species and to lessen the numbers of those espe- 

 cially injurious. 



