10 
If we turn now from these examples of habit groups to a classi- 
fication by habitats—from physiological to spatial ecology—from a dis- 
cussion of the food of fishes to the subject of their local distribution and 
their assemblage in what are called animal associations, we shall find a 
similar state of affairs to that just noticed. Some of our fresh-water fishes 
are so widely and thoroughly distributed over a large variety of situa- 
tions that they may be likened to the omnivorous class in the classifica- 
tion by habits, while others are as narrowly limited in habitat as is the 
carnivorous pike in respect to its food. For my detailed data of local 
distribution I shall have to draw almost wholly on our Illinois observa- 
tions, for the reason that we have made in Illinois much larger and more 
intensive collections of our native fishes than have been made in any 
other state—larger, indeed, as I believe, than in any other area of like 
size anywhere in the world. 
The blunt-nosed minnow (Fig. 18) is an example of what we may 
call omnilocal distribution, the map of its local occurrences in Illinois 
(Map XXVII), being a fair abstract of the map of localities for all our 
Illinois fish collections. It is relatively rare only in our larger rivers, 
the frequency of its occurrence there being, by our data, as 5 to 34 for 
the smaller rivers, and to 43 for creeks. That is to say, if we were to 
take equal numbers of fish collections from each of these classes of 
waters throughout the state until we found this species five times in 
larger rivers, we might expect to find it about thirty-four times in small 
rivers, and about forty-three times in creeks. It is not limited in its range 
or habitat by its choice of food, for it feeds mainly on mud, and that it 
could easily find almost anywhere in Illinois. It prefers streams with 
a rocky bottom, it is true, its occurrence in such waters having a fre- 
quency of 46 as compared with 27 in other places ; and the kinds of vegeta- 
tion mixed with the mud of its intestinal contents give us reason to think 
that it nibbles and sucks the slime from stones and other submerged 
objects. 
Contrast with this, now, the distribution map of the spot-tailed min- 
now (Map XXXVIII), and another minnow species, Notropis heterodon 
(Map XXXIV), not well enough known to have received an English 
name. The spot-tailed minnow, very common in lakes and ponds and 
especially in the Great Lakes, occurs elsewhere mainly in the larger 
rivers, its average frequency in our collections in these two situations 
being as 33 to 3.5 in the smaller streams. That is, we have found it nearly 
ten times as common in the larger waters as in the smaller ones; and its 
