82 The Fond 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 Alga3, 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 Cyprinid* 

 related to the habit of feeding upon mollusks. 



Summary foe 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 diff"erence 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, 



