128 



the specimens. One third of this consisted of Algse, chiefly of th- 

 filamentous forms, the remainder being miscellaneous fragments o 

 exogenous plants, chiefly evidently aquatic. 



Local and Individual pecidiaritins. — The general summaries of the 

 food of so many individuals from so great a variety of situations 

 often disgaise interesting and important facts relating to the food 

 resources of the species, since an element taken in large quantity 

 by one or two specimens may figure in the general average in such 

 an insignificant ratio as to lead to the inference that its occurrence 

 is merely accidental. In other words, general averages for a variety 

 of situations will not necessarily indicate all the food resources open 

 to the species. These can only be demonstrated by exhibiting the 

 pecidiarities of the record as well as its general average characters. 

 For example, the fact that only eleven per cent, of the food of this 

 species consisted of Algae has a somewhat different aspect when we 

 learn that one of the specimens had eaten nothing else, and that 

 they made three fourths of the food of another. Three specimens 

 had eaten only insects, and these made ninety per cent, or more 

 of the food of three others. Two had eaten nothing but Entomos- 

 traca, all the Cypris vidua previously mentioned. Vegetable struc- 

 tures made the entire food of four, and ninety per cent or more of 

 the food of three other specimens. Three out of four individuals 

 taken at Nippersink Lake in May had derived from ninety to one 

 hundred per cent, of their food from terrestrial beetles of a single 

 family (Rhynchophora), while ephemerid larvae occurred in the food 

 of three others in ratios exceeding seventy-five per cent. 



Hybopsis stramineus, Cope. Straw-colored Minnow. 



This insignificant species has been found by us in rivers and 

 small streams throughout the State. 



The gill-rakers were few and short. 



Only five specimens were studied, all from rivers in Central Illi- 

 nois. About three fourths of their food consisted of animal matter, 

 nearly all neuropterous larvae (fifty-eight per cent.), Ephemeridae 

 standing at forty-eight per cent., and case worms at ten. Crustacea 

 were ten per cent., all Cyclops except a trace of Canthoeamptus. 

 About one fourth of the food was vegetation, chiefly seeds of grasses, 

 occurring, of course, only accidentally in the water. Two had de- 

 rived from ninety to one hundred per cent, of their food from 

 ephemerid larvae, and four of the five had eaten vegetation amount- 

 ing to as much as eighty per cent. 



LuxiLus coRNUius, Raf. Shiner. 



This large and fine minnow is probably the commonest fish in 

 Illinois, occurring in lakes and streams of all sizes everywhere 

 throughout our limits. 



The gill-rakers are short and few, and of insignificant develop- 

 ment, and the intestine is shorter than the head and body. 



Twenty-one specimens were studied, from all parts of the State 

 and at various seasons of the year. Animal food amounted to two- 

 thirds of the whole, fourteen per cent, being fishes, eaten, however. 



