80 The Food of the Smaller Fresh - Water Fishes. 



all respects similar to those given for tlie other members of this 

 group. Filamentous Algae, diatoms, and a few accidental fungus 

 spores, were the only objects found imbedded in the quantities of 

 mud which filled each intestine. 



Summary of the Group. 



If we average the results of the four species studied, belonging 

 to this first group, we shall find that about tliree-fourths of the 

 contents of the stomach and intestine consist of soft, black mud, 

 the remaining fourth being derived from both animal and vegetable 

 substances, about three times as much from the latter as from the 

 former. The animal food is chiefly insects, both terrestrial and 

 aquatic, and the vegetation is divided about equally between Al- 

 gae and miscellaneous fragments of higher plants. This group, 

 with long intestine and grinding pharyngeals, is consequently to 

 be considered as essentially limophagous. We find this peculiar 

 form of pharyngeal teeth associated only with intestines of this 

 type. 



Group II. 



Intestines moderately long; pharyngeal teeth hooked, with grinding 

 surface. 



Chrosomus erythrogaster, Raf. Red-bellied Dace. 



This species is locally abundant, although not generally com- 

 mon. It occurs in clear streams in the northern part of the State, 

 but has not been taken by us in Central or Southern Illinois. 



The length of the fish is contained one and two-thirds times in 

 the length of the intestine; the gill-rakers are few and rather short, 

 triangular, acute, and about one-fifth the length of the corre- 

 sponding filaments. 



I examined carefully but three specimens of this species, de- 

 rived from two localities. These were alike in the presence of 

 great quantities of mud, which amounted to about eighty-seven 

 per cent, of the contents of the intestine. The animal food was 

 confined to a trace of Cladocera. The vegetation amounted to 

 thirteen per cent., partly tissues of aquatic plants, with traces of 

 fungi, but chiefly Algai of various forms, including a little Oscil- 

 latoria. 



