446 Illinois State Lahorutory of Natural Histonj. 



The square, strong head of this species is related to its 

 mode o£ life, but the cylindrical body, the large rounded pectoral 

 fin, and relatively high coloration, give the fish the aspect of a 

 darter among the suckers; and its habit of searching for its food 

 among the stones in swift and shallow waters is another point 

 of affinity with that interesting group. Curiously different as 

 are the food and feeding habits of this species when compared 

 with its nearest ally, Catostomus teres, the alimentary structures 

 are not remarkably unlike. The pharyngeals are somewhat 

 lighter, the pharyngeal teeth more slender and more promi- 

 nently cuspidate, and the gill-rakers somewhat stouter, possibly 

 affording a better apparatus for the separation of the relatively 

 large insect larvae upon which this species chiefly feeds. Its 

 alimentary structures are extremely different, however, from 

 those of the Etheostoraatidae, whose food, haunts, and habits 

 it copies so closely. It is, in short, a molluscan feeder, which 

 has become especially adapted to the search for insect larvae 

 occuring in rapid water under stones. 



The pharyngeals bear about forty teeth on each side, 

 which are unusually high, thin, and acute, all the upper ones 

 with an uncommonly prominent hook or cusp at the internal 

 angle. The six lower teeth are cultrate, without hook or dis- 

 tinct grinding surface, but only two or three are noticeably 

 thickened. 



The anterior gill-rakers are short and stout, twenty-five in 

 number, six of them on the horizontal part of the arch. Those 

 of the upper series are thin plates with the base about half the 

 length, and are one third to one half as long as the cor- 

 responding filaments. The lower rakers of the series, more 

 prominent than those of C. teres, are much like the upper, 

 but shorter, the height scarcely equal to the base. There are 

 five or six tubercles on the upper edge of each. The remain- 

 ing gill-rakers, similar to those just mentioned, interlock by 

 their tips, which are much more prominent and more tuber- 

 culate than those of Moxostoma. The stouter filaments of 

 the strainer are probably related to the larger and more active 

 insect larvas on which this species feeds. 



The intestine is small, considerably convoluted, and about 

 twice the length of the head and body. 



