482 Illinois State Lahoratorij of Natural History. 



one fourth of their food from this genus. Besides the above 

 families, smaller quantities of the bivalve moUusks occurred in 

 the food of one of the suufishes (Lepomis pallidus) and — 

 doubtless by accident only — in the gizzard shad. 



The gasteropod moUusks (snails of various descriptions) 

 were more abundant than bivalve forms in the sheepshead and 

 the sunfishes and all the smaller fishes which feed upon Mol- 

 lusca, but less abundant in the suckers and the catfishes. In the 

 sheepshead they made one fifth of the food of the twenty-five 

 specimens examined, but the greater part of these had not yet 

 passed the insectivorous stage, this being much longer con- 

 tinued in the sheepshead than in many other fishes. A few of 

 these univalve Mollusca occurred in the food of the common 

 perch and in certain species of sunfishes, especially in the super- 

 abundant bream or pumpkin-seed. They made fifteen per cent, 

 of the food of the minute top minnows, and occurred in smaller 

 quantities among the darters, the grass pickerel, the mud min- 

 nows, and the cyprinoids. The heavier river snails, Vivipara 

 and Melantho, were eaten especially by the cylindrical suckers, 

 and the catfishes. The delicate pond snails (Succinea, Limnsea, 

 and Physa) were taken chiefly by the smaller mollusk-eating 

 fishes, — a few of them also by the catfishes and the suckers. 



Further particulars concerning the molluscan food may be 

 obtained by the interested reader from the list of food elements 

 at the end of this article. 



INSECTIVOROUS SPECIES. 



It is from the class of insects that adult fishes derive the 

 most important portion of their food, this class furnishing, for 

 example, forty per cent, of the food of all the adults which I 

 examined. 



The principal insectivorous fishes are the smaller species, 

 whose size and food structures, when adult, unfit them for the 

 capture of Entomostraca, and yet do not bring them within 

 reach of fishes or Mollusca. Some of these fishes have peculiar 

 habits which render them especially dependent upon insect 

 life, — the little minnow Phenacobius, for example, which, ac- 

 cording to my studies, makes nearly all its food from insects 

 (ninety-eight per cent.) found under stones in running 



