80 
The Food of the Smaller Fresh - Water Fishes. 
all respects similar to those given for the 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 three-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 Algae of various forms, including a little Oscil- 
latoria. 
