68 The Food of the Smaller Fresh - Water Fishes. 



POTAMOCOTTUS MERIDIONALIS, Gill. GOBLIN, Bl.OB. 



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 tliat 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 furnislied with ctenoid scales. Undeter- 

 mined aquatic larva^ (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 GASTEROSTEID^. 



Of the interesting little stickle-backs, two species were studied, 

 only one of whicli is common in the State. 



EUCALIA INCONSTANS, Kirt. BlAOK 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. 



