440 Illinois State Lahoratonj of Natural History. 



FAMILY HYODONTID^. 



Hyodon" tergisus, LeS. Moon Eye; Toothed Hereiistg. 



This species, not common in our collections, is represented 

 in these studies by only five specimens, obtained from the Illinois 

 River at Peoria and Havana, on four dates in August and 

 October of two different years (1878 and 1887). Their food 

 consisted wholly of insects (two thirds of them terrestrial) with 

 the exception of a trace of univalve MoUusca. A single one, 

 two and seven eighths inches long, had derived its food about 

 equally from terrestrial and aquatic insects, including Orthop- 

 tera, Chironomus larvae, and Corixa tumida. 



FAMILY OATOSTOMATID^. 



One of the most striking characteristics of the fish fauna of 

 Illinois, and indeed of the Mississippi Valley, is the prominence 

 of the sucker family, which includes within our limits six 

 genera and fifteen recognized species. Several of these are 

 among the most abundant of our larger fishes, and most are 

 very generally distributed. 



With reference to the essential characteristics of their food, 

 I find them dividing into three tolerably distinct groups. The 

 first includes the cylindrical suckers (Moxostoma, Catostomus, 

 and the like), in which the pharyngeal bones are heavy, the 

 lower teeth thick and strong, usually with a well-developed 

 grinding surface, and the gill-rakers short, thick, and few. 

 In the second are the deep-bodied suckers, in which the 

 pharyngeal jaws and teeth are well developed, although not as 

 strung as in the cylindrical group, while the gill-rakers are of 

 moderate length and number. The third contains the still 

 deeper-bodied and thinner species, with light pharyngeal jaws 

 and teeth, and long, slender, and more numerous gill-rakers. 

 To this group belong the species commonly placed in the 

 genus Carpiodes. Or, if we arrange the genera in a series, with 

 reference to their food structures, we shall find Placopharynx 

 at one extreme and Carpiodes at the other, the change consist- 

 ing in a gradual increase in number, length, and effectiveness 



