500 Illinois State Laboratory of Natural Itistory. 



species allied in classification but differing with respect to the 

 structures concerned in the appropriation of food are given by 

 the following examples. 



Two species of minnows, Chrosomus erythrogaster and 

 Semotilus atromaculatus — the first represented by fourteen speci- 

 mens, and the second by six, all collected from a small tributary 

 of the Fox, near Piano, Sept. 8, 1882 — were brought into com- 

 parison with reference to their food, with the result that the 

 characteristic differences of the species, as shown in the general 

 discussion of the group published in our Bulletin 6, Vol. L, 

 were clearly manifested by this small number. In the former 

 lot seventy-five per cent, of the food was mud, the remainder 

 being indiscriminate vegetable debris; while in the latter the 

 entire mass consisted of insects (chiefly terrestrial) except a 

 single insect parasite (Grordius). 



From one of the permanent ponds or so-called lakes of 

 southern Illinois, covered in September with a film of Wolffia 

 and other vegetation, three specimens of Gambusia patruelis and 

 five of Umbra ^imi were examined. The former had eaten little 

 but Wolffia, which amounted to more than ninety per cent, of 

 the food, the remainder consisting of Entomostraca, mollusks, 

 and aquatic insect larvae, while the Wolffia made less than 

 sixty per cent, of the food of the Umbra, — about one fourth 

 consisting of Entomostraca, and the remainder of unrecognized 

 insects. 



Two minnows of similar range {Phenacobius mirabilis 

 and Notropis whipplei) agree essentially in gill structure 

 and pharyngeal teeth, and differ but little in the relative 

 length of intestine; and they have consequently been placed by 

 me in the same alimentary group.* They are unlike, however, 

 in the form of the mouth and in their haunts and feeding habits. 

 This difference is reflected in the food of a small collection 

 made in the Galena River, in April, 1880, three specimens of 

 Phenacobius having eaten only aquatic larvae and pupae (nearly 

 all chironomid), while the food of the Notropis, represented 

 by six specimens, was of a varied character, containing 

 few aquatic larvae (only one per cent, of Chironomus), but con- 

 sisting chiefly of miscellaneous collections of terrestrial insects, 



* Bull. 111. St. Lab. Nat. Hist., Yol. I., No. 6, p. 76. 



