68 
The Food of the Smaller Fresh ■ Water Fishes. 
POTAMOCOTTUS MEKIDIONALIS, Gill. GOBLIN, BlOB. 
Although this fish has not hitherto been recorded from the 
State, we have found it abundant in small streams in Southern 
Illinois, and a single specimen has been sent us from McHenry 
County, near our northern limits. The first of these situations is 
in a limestone region, where small caves are not infrequent; but 
the second is in an area deeply covered by drift, with rock no- 
where exposed. 
The general appearance of this fish is not unlike that of a cat- 
fish, the head being broad and flat, the mouth very large, and the 
skin smooth. The gill-rakers are few, short and thick, and of in- 
significant character; the pharyngeals are similar to those of Aphre- 
doderus, but form thicker and larger plates; the intestine is short 
and simple, its entire length being less than that of the head and 
body. 
Six specimens of this species, taken in Southern Illinois, had 
eaten only animal food, about one-fourth of which consisted of 
fishes, one of which was furnished with ctenoid scales. Undeter- 
mined aquatic larvae (thirty-six per cent.) and other insects, 'were 
estimated at forty-four per cent, of the food. Crustacea, all belong- 
ing to the genus Asellus, eaten by two of the fishes, composed the 
remaining twenty-nine per cent. The general resemblance of the 
food of this species to that of Aphredoderus seemingly corre- 
sponds to the similar character of their alimentary structures. 
FAMILY GASTEROSTEIDHD. 
Of the interesting little stickle-backs, two species were studied, 
only one of which is common in the State. 
Eucalia inoonstans, Kirt. Black Stickleback. 
This fish is abundant in streams and lakes in the northern part 
of Illinois, but has not been taken by us south of Rock River. 
Its mouth is small; the gill-rakers are long and slender (about 
half as long as the corresponding filaments), but are not unusually 
numerous; the pharyngeal apparatus is insignificant or wanting; 
and the intestine is short and simple, not longer than the head and 
body together. 
