The Food of FroHh-Water Fishes. 463 



had eaten praetieallj nothing but Crustacea, nearly all Am- 

 phipoda ( A.llorchestes) and Isopoda (Asellus), the former 

 eaten by nine, and the latter by two — both together mak- 

 ing forty-seven per cent, of the entire food. As might be 

 supposed from the small size of these specimens, Entomostraca 

 were apparent in the food, although in moderate numbers 

 (five per cent). The forms recognized were Simocephalus, 

 Chydorus, Pleuroxus, Alona, Cypris, Candona, Cyclops, and Can- 

 thocamptus. A planarian worm was noted in one, and speci- 

 mens of Difflugia in another. A single example had eaten a 

 small fish. Most of the insects were Chironomus larvae (twen- 

 ty-five per cent.), case-worms, and larvae of day flies (twelve per 

 cent.). 



Comparing the principal genera of this family, as repre- 

 sented by the one hundred and twenty specimens examined, 

 we find that the larger deep-water species from the great rivers 

 of the State are apparently ichthyophagous ; that the relatively 

 minute stone cats feed on the smaller insect larvee and the 

 medium sized Crustacea ; that the spotted cat is essentially in- 

 sectivorous ; that among the ball-heads the yellow cat eats the 

 largest percentage of fishes and the marbled cat the smallest ; 

 that the latter feeds more generally upon Unio than any of the 

 other species; and that moUusks at large make about one sixth 

 of the food of the group of species which feeds upon them. 



FAMILY AMIID^. 



Amia calva, Linn. Dog Fish; Mud Fish; Grindle. 



This species is very abundant throughout the State in the 

 lakes and larger streams, and also common in ponds of south- 

 ern Illinois. Not commonly eaten, but often caught for sport. 



The food of twenty-one specimens taken from northern, 

 central, and southern Illinois, in April, May, June, August, Sep- 

 tember, and October, was wholly animal, about one third of it 

 fishes, among which were recognized some undetermined cypri- 

 noids and a small buffalo fish (Ictiobus). The other important 

 elements were mollusks — about one fourth — and crustaceans 

 (forty per cent.), insects being represented by an insignificant 

 ratio (two per cent.). Even the usually abundant Chironomus 



