96 FISHES OF ILLINOIS 



on animal food. In Campostoma, a typical mud-eater, it is five to 

 nine and a half times the length of the head and body, and is wound 

 spirally about the air-bladder, while in the more strictly insectivo- 

 rous genera it is only two thirds to five sixths as long as the head and 

 body taken together. The mud-eating forms also differ from the 

 Others in the fact that the pharyngeal teeth have a large grinding 

 ■surface at the free end, and are without the terminal hook-like proc- 

 esses with which those species are provided which feed mainly on 

 insects. 



Although the cyprinoids are mostly of small size, the European 

 carp and a few native species, some of which are abundant on the 

 Pacific slope in America, attain a considerable weight. 



There are some two hundred genera in the world and about a 

 thousand species. In Illinois there are fourteen genera and thirty- 

 six species known, seventeen of the latter belonging to the single 

 genus Notropis. All our native species are small and commercially 

 insignificant except as they are used for bait and serve as a valuable 

 food resource for other fishes. The top of the head in spring males, 

 and often also the fins and sides — particularly the sides of the caudal 

 peduncle — are covered with small tubercles called pearl organs, and 

 the fins and lower parts of the body are, in the breeding season, 

 Often highly colored with bright pigments, either red, satiny-white, 

 yellow to orange, or black. The young of the deeper-bodied species 

 are much more slender than the adults and have much larger eyes. 

 -They may also show color markings not found in adults of the same 

 species, such as a caudal spot or a black lateral stripe. 



Taken as a group the minnows are, on the whole, fishes especially 

 of the creeks and smaller rivers, and they show, in these situations, 

 a decided preference for a more or less rapid current and for a clean 

 bottom rather than one of mud. There are notable exceptions, as 

 already said, but the general fact is well shown by our data of fre- 

 quency of occurrence in the various ecological situations, drawn 

 from the 24 Illinois species of which we have collections numerous 

 enough to make them available for this study. Of these 24 species, 

 6 are more than usually abundant in the larger rivers, 20 are extraor- 

 dinarily so in rivers of the second class and 19 in creeks, 5 are more 

 numerous than the average in lowland lakes, and only 1 is un- 

 usually so in upland lakes of glacial origin. 



Only two of these 24 species were most "abundant in the larger 

 rivers, and 6 in the smaller rivers. Fourteen species were found 

 most frequently in creeks, 1 was most abundant in lakes, another in 

 the bottom-lands, and another in clear upland lakes. If we mav 



