64 FISHES OF ILLINOIS 



comparatively short and large. As the body deepens, the pharyn- 

 geal bones become longer, the pharyngeal teeth smaller and more 

 numerous, with diminished grinding surface; the gill-rakers are 

 longer and more numerous, making a more effective straining 

 apparatus, and the intestines become longer and smaller. Cor- 

 responding to these differences of structure, mollusks form a 

 larger percentage of the food of the cylindrical suckers, and 

 Entomostraca and vegetable food a very much greater part of 

 that of the deep-bodied species. All the species commonly 

 swallow much mud, since they collect most of their food from 

 the bottom by suction, to which their protractile mouths and 

 fleshy lips are peculiarly adapted. 



As food fishes they do not hold a high place, the flesh being 

 rather coarse, dry, and either flavorless or strong, and always pro- 

 vokingly full of small bones. The buffalo and sucker fishery is 

 nevertheless an important one in the Mississippi Valley and the 

 Great Lake region. (See under Ictiobus.) Of the 15 species 

 found in the waters of the Illinois alone, about one third have 

 a greater or less commercial value. 



Key to the Genera of CATOSTOMID^^ found in Illinois 



a. Dorsal fin elongate, with 25 to 40 developed rays. 



b. Posterior fontanelle almost obliterated by the union of the parietals; head 



small and slender, its length 6 to 7 times in body; lips with several series 



of tubercle-like papillae Cycleptus. 



bb. Posterior fontanelle well developed, extending forward between frontals a 

 distance equal to more than % of their length; head 3% to 5 times in body; 

 lips plicate, striate, or smooth 



c. No anterior fontanelle, the frontals being closely joined with the ethmoid; 



cheek somewhat shallow and foreshortened, distance from eye to lower 

 posterior angle of preopercle about % of that to upper corner of gill-cleft; 

 subopercle broadest at its middle, subsemicircular Ictiobus. 



cc. Anterior fontanelle well developed, separating anterior edges of frontals and 

 notching ethmoid; cheek relatively deep and long, eye about equidistant 

 between upper corner of gill-cleft and infra-posterior angle of preopercle; 

 subopercle broadest below its middle, subtriangular Carpiodes. 



aa. Dorsal fin short, with 10 to 18 developed rays. 



d. Lateral line more or less incomplete or wholly wanting; scales large and uni- 



formly- distributed, 30 to 50 in lateral line. 



e. Lateral line entirely wanting at all ages Erimyzon. 



ee. Lateral line more or less developed in adults Minytrema. 



dd. Lateral line complete and continuous. 



f. Scales small and crowded anteriorly, the number in the lateral line 55 to 110 



(except in C. nigricans, for which see below ff) Catostomus. 



ff. Scales large and nearly equal all over the body, 40 to 55 in the lateral line. 



g. Air-bladder in two parts; scales 48 to 55 in lateral line 



Catostomus (Hypentelium) nigricans. 



gg. Air-bladder in three parts; scales larger, 40 to 50 in lateral line. 

 h. Upper lip protractile, lower entire or incised only part way to anterior margin. 



i. Pharyngeal teeth compressed; mouth wholly inferior Moxostoma. 



ii. Lower pharyngeal teeth much enlarged, subcylindrical and truncate; mouth 



somewhat oblique, lips very thick Placopharynx. 



hh. Upper lip not protractile; lower lip in two separate lobes Lagochila. 



