]-27 



at fifty per cent., more than half of it aeciflental vegetable rlrbris 

 partly from aquatic and partly from terrestrial plants. About one 

 fifth of the food consisted of Algse, half of which was filamentous 

 in character, and the remainder desmids, including Closterium and 

 various duitoms. 



The peculiar characters of the alimentary structures of this species 

 are very clearly refiected in this summary of its food, the elongate 

 intestine corresponding to the presence of mud, and the well-de- 

 veloped gill-rakers to the occurrence of Entomostraca. I have not 

 yet noticed any structural peculiarity of the Cyprinida; related to 

 the habit of feeding upon mollusks. 



Summary of 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 speci- 

 mens with those of the preceding group, to show the meaning of 

 the hooked form of the pharyngeal teeth. 



Group III. 



Intestines short, teeth hooked, with grinding surface. 



This group includes Hyhopsis. Luxilus, Lythrurus, Hemitremia and Platvgobio. My 

 studies were limited to three genera: Hybopsis, Luxilus. and Hemitremia. 



Hybopsis hudsonius, Clint. Spawn-eater. 



This fine mmnow is common everywhere to the northward, espe- 

 cially 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 at 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, Nipper- 

 sink Lake, and the Illinois River. Mud was found m noticeable 

 (quantities only in a single specimen, and there in small amount. 

 About seventy per cent, of the food consisted of animal substances, 

 three per cent, being fishes, taken by two of the minnows. One 

 had also eaten a small bivalve mollusk. Insects made half the 

 food, about one third of them of terrestrial species (Khyuchophora), 

 the remainder being chiefly larvae of ephemerids. A few Chirono- 

 mus larvae and an aquatic hemipter were the only other kinds de- 

 termined. Crustacea amounted to thirteen per cent., nearly all 

 Ostracoda {Ci/])ris vidua), taken by two of the specimens from Chi- 

 cago. Vegetable food stands at thirty-one per cent., eaten by ten of 



