llf) 



A careful comparison was made of the food of specimens of vari- 

 ous ages — those, consequently, in which the situation of the vent 

 was widely different — but nj differences of food whatever were dis- 

 tinguishaljle. It is highly probable, consequently, that the explan- 

 ation of this peculiar character must be sought elsewhere than in 

 the food With respect to the pther relations of food to structure, 

 we have at present only to note the coincidence of fishes and aquatic 

 insects as the principal elements of the food with the large mouth 

 and inferior development of the gill and pharyngeal apparatuF, and 

 short and simple intestine. 



Family COTTID^E. 



This curious family, chiefly marine, is represented in the State 

 T3y several species from Lake Michigan, mostly from its deeper 

 waters, and by a single one recently discovered in our streams. 



POTAMOCOTIUS MERIDIONALIS, 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 lime- 

 stone region, where small caves are not infrequent ; but the second 

 is in an area deeply covered by drift, with rock nowhere 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- 

 dodei'us, 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. Undetermined 

 aquatic larvae (thirty-six per cent.) and other insects, were esti- 

 mated at forty-four per cent, of the food. Crustacea, all belonging 

 to the genus Asellus, eaten by two of the fishes, composed the re- 

 maining twenty-nine per cent. The general resemblance of the food 

 of this species to that of Aphredoderus seemingly corresponds to the 

 similar character of their alimentary structures. 



Family GASTEEOSTEID.E. 



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

 only one of which is common in the State. 



EUCALIA INCONSTANS, Kirt. BL4CK STICKLEBACK. 



This fish is abundant in streams and lakes in the northern part 

 of Illinois, but has not been taken by us south of Hock River. 



