The Food of Fresh-Wafer Fishes. 453 



Among the vegetable elements, distillery slops (eaten by 

 three of the specimens) were the most important (twenty-one 

 per cent.). The rather insignificant amount of aquatic vegeta- 

 tion (six per cent.) was distributed as usual among a number 

 of the lower plants, chiefly duckweeds and the unicellular Alga?. 



IcTioBus CYPRiJfUS, LeS. River Carp; Carp Sucker. 



Under this specitic head I include, for the purposes of this 

 paper, all the so-called species of river carp sometimes separated 

 under the genus Carpiodes, and hitherto described under some 

 eight specific names. This form is abundant in the great rivers 

 of the State and in their larger tributaries, and also in Lake 

 Michigan and the smaller lakes of northern Illinois. It is 

 extremely common in the lakes and ponds of the river bottoms, 

 but occurs in running water in smaller numbers than the 

 other species of its genus. 



In its structures of food prehension it exhibits an extreme 

 development and a correlative degradation of branchial appa- 

 ratus and pharyngeal structures respectively. The gills are re- 

 markably compacted, the upper and lower ends nearly meeting 

 when the mouth is closed. The pharyngeal protuberances are 

 enormous, almost filling the branchial cavity. Anterior gill- 

 rakers in two series, as usual, the upper about sixty-seven in 

 number on three fourths of the arch, the longest a little longer 

 than the corresponding filaments. The lower part of the gill 

 with about ten thick, papillar, coherent ridges extending down- 

 ward a distance equal to the length of the filaments of the 

 same vicinity. The longer rakers have each two closely alter- 

 nating rows of tubercles on the inner edge, roughened with 

 extremely minute denticles. Inner surface of the arch with 

 transverse tuberculate ridges springing from the bases of the 

 rakers of the gill, and terminating inwardly in slight projec- 

 tions representing the posterior row of rakers. The other 

 arches are similarly tuberculate and ridged, and the whole ap- 

 paratus closely embraces the pharyngeal thickenings. Pharyn- 

 geal bones very thin and brittle, less than a millimeter thick in 

 a fish ten inches long, the thickness one seventh the height to 

 the base of the teeth. The latter about two hundred, minute 

 above, gradually increasing downwards, but not much thick- 



