426 
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 glaciation 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- 
ocephalus and Etheostoma ceruleum), five minnows (Campostoma 
anomalum, Notropts heterodon, Ericymba buccata, Hybopsis kentuck- 
zensis, and Notropis blennius), two stonecats, and the little brook sil- 
verside (Labidesthes). i 
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. 
