121 



specimens from Southern Illinois lakes. A considerable quantity ol' 

 unicellular Algse was also taken by one. Mollusks, eaten by two, 

 were reckoned at five per cent., all Physa. Insects drop to fourteen 

 per cent., cliieliy undetermined larva). No terrestrial forms were 

 recognized. Corresponding to the greater development of the gill- 

 rakers, we lind the Entomostraca assuming greater importance in 

 the food. These were reckoned at ten per cent. ; three per cent, 

 additional consisting of Crangonyx gracilis . 



Family CYPEINID.E. 



This family includes all the fishes properly known as "minnows,"" 

 embracing, in fact, by far the larger part of the smaller fishes of 

 the State. Both in number and in variety of species it is much the 

 most important family of fresh-water fishes. It includes, in Illinois, 

 about forty species, nearly or quite one fourth the whole number 

 known to occur in our territory. They occur in all waters from the 

 Mississippi Kiver and Lake Michigan to the smallest streams and 

 ponds ; but are much the most abundant in creeks and rivulets. 

 The species differ greatly with respect to their favorite haunts, some 

 affecting the principal lakes and larger rivers, others occurring most 

 commonly in clear and rapid brooks, while still others are most 

 frequent in the sluggish and muddy streams of prairie regions. The 

 principal economic interest of the fishes of this family is due to the 

 well-known fact that they furnish an important part of the food 

 supply of larger species. 



But little has hitherto been done upon their food in the United 

 States. In fact, I have seen nothing more accurate or comprehen- 

 sive than the following general statement made by Prof. Cope, in 

 his paper on the Cyprinidae of Pennsylvania:* 



"These difi'erences of habit are associated with peculiarities of 

 food and of the structure of the digestive system. Few families of 

 vertebrates embrace as great a variety in these respects as the pres- 

 ent one. There are carnivorous, insectivorous, and graminivorous 

 genera, which are distinguished as among mammalia ; the former by 

 the abbreviation, the last by the elongation of the alimentary canal. 

 In the former the teeth are usually sharp-edged or hooked, in the 

 latter truncate, hammer, or spoon-shaped. 



"In the American genera, as far as included in the scope of this 

 essay, the peculiarities of the intestines correspond with the food. 

 In the AUmrneUua rnhyijrons^ they are but four fifths the length of 

 head and body (excluding caudal fin). In Hgpsilepis kentiichioisis,' 

 Photogcnis leueops, Arggreus atroiinsits'-^ and uasiUus, Ericgmha Imccata, 

 and Exoglossiun mariUiugua, about seven ninths; ^he food of the last 

 five species is insects and crustaceans, the last depending largely 

 on MoUusca. In the species of Ceratichthys, Semotilus, and Hybop- 

 sis, with Ilgpsilrpsis cornutua.^ fifteen sixteenths to equal the length; 

 the habits insectivorous. The genera with longer intestines are, 



* Trans. Amor. Philosopliieal Society. Vol. i:f. \:-\v Sories, pjige 'M>A. 



'Miniiilus or Xotropis. -Pliotogcni.s analoist-aniis. -'Rliiniehthys. ^Liivilns o )rnutii5. 



