82 
The Food of the Smaller Fresh - Water Fishes. 
terrestrial species. Crustaceans amounted to fifteen per cent., all 
Entomostraca. Vegetation stands at fifty per cent., more than 
half of it accidental vegetable debris, partly from aquatic and 
partly from terrestrial plants. About one-fifth of the food con- 
sisted of Algae, half of which was filamentous in character, and the 
remainder desmids, including Closterium, and various diatoms. 
The peculiar character of the alimentary structures of this 
species are very clearly reflected in this summary of its food, the 
elongate intestine corresponding to the presence of mud, and the 
well developed gill-rakers to the occurrence of Entomostraca. I 
have not yet noticed any structural peculiarity of the Cyprinidae 
related to the habit of feeding upon mollusks. 
Summary for the Group. 
The two species foregoing agree only in their mud-eating pro- 
pensity, — probably habitual in one and occasional in the other, — 
the first having the longer intestine, and the second the longer 
gill-rakers. To this last difference we doubtless must trace the 
different relations of these fishes to Entomostraca. 
I find nothing whatever, by comparison of the food of these 
specimens with those of the preceding group, to show the mean- 
ing of the hooked form of the pharyngeal teeth. 
Group III. 
Intestine short, teeth hooked, with grinding surface. 
This group includes Hybopsis, Luxilus, Lythrurus, Hemitre- 
mia, and Platygobio. My studies were limited to three genera: 
Hybopsis, Luxilus and Hemitremia. 
Hybopsis hudsonius. Clint. Spawn-eater. 
This fine minnow is common everywhere to the northward, 
especially in Lake Michigan and the other lakes of Northern 
Illinois, but not abundant south of the central part of the State, 
although it has been taken to its extreme southern limit. It has 
never occurred in our collections in the smaller streams, but is 
confined to the lakes, rivers, and creeks of some magnitude. 
The gill-rakers of this minnow are short and few. 
Seventeen specimens were studied, from Lake Michigan, 
