CATOSTOMUS FINE-SCALED SUCKERS 87 



south to Arkansas. It is especially abundant in swift and rapid 

 streams, and is rarely found in muddy water. Its avoidance of 

 muddy situations is illustrated especially by its distribution in Illi- 

 nois, not a single collection of this species having been made by us 

 from the persistently turbid waters of the lower Illinoisan gla- 

 ciation. It is rare in the southern third of the state, and was taken 

 by us but once from any locality of extreme southern Illinois. It 

 has occurred in our collections most abundantly in the headwaters 

 and smaller tributaries of the Illinois, the Kaskaskia, the Embarras, 

 and the Big Vermilion, in the northern and eastern parts of the 

 state. 



The most striking peculiarities of this fish are related to its 

 haunts and feeding habits. The large bony head and the unusually 

 developed pectoral fins, together w4th the full lips and the papillose 

 mouth, are all related to the fact that it seeks its food in the more 

 rapid parts of streams, pushing about the stones upon the bottom 

 and sucking up the ooze and slime thus exposed, together with the 

 insect larvae upon which it mainly depends for food. The slender 

 body, the large pectoral fins, and the comparatively high coloration 

 of this species give it the aspect of a darter among the suckers, and 

 its active habit and the peculiar character of its food resources is 

 another point of affinity with that interesting group. It has also, 

 like the darters, the habit of resting quietly on the bottom, sup- 

 ported by its paired fins, w^here its coarsely mottled colors serve well 

 to conceal it among the surrounding stones. 



Proportionately to the number of collections made by us, this 

 species was about three times as abundant in central Illinois as in 

 southern, and three and a half times so in northern Illinois as in cen- 

 tral. It was much commonest in the smaller rivers and about half 

 as abundant in creeks, although not wholly wanting in either the 

 larger rivers or in the glaciated lakes of northeastern Illinois. It 

 was not taken by us at all off really muddy bottoms. 



Widely different as are the food and feeding habits of this species 

 and those of the common sucker, its nearest ally in our waters, 

 their alimentary structures are not remarkably unlike. The 

 pharyngeals of the present species are somewhat lighter, the 

 pharyngeal teeth more slender and more prominently hooked, and 

 the gill-rakers somewhat stouter, thus affording a better apparatus 

 for the retention of the relatively large insect larvae upon which this 

 species chiefly feeds. It is, in short, a molluscan feeder which has 

 become especially adapted to the search for insect larvae occurring 



