The Food of Fvesh-Watn- Fishes. 447 



The food of six specimens taken in the Fox River and 

 Mackinaw Creek contained no vegetation and but a small ratio 

 of mollusks (Spha^rium), but was nearly all aquatic insect 

 larvae (ninety-two per cent.). The great majority of these 

 were Ephemerida?, more than half the food consisting of a 

 single form, abundant under stones, belonging to the genus 

 Caenis. A few Chironomus larvae, taken by all the specimens, 

 some larvae of Coleoptera, and traces of terrestrial insects were 

 the only other elements. 



Erimyzox sucetta, Lac. Creek Fish; Chub Sucker. 



Everywhere abundant in streams and lakes, ascending 

 creeks in spring. Occurs in our collections from McHenry to 

 Union county. Rarely taken by us, however, and not repre- 

 sented in the material used for these studies. 



Pharyngeal jaws moderately heavy, short for the size of 

 the fish, bearing about sixty teeth, the lower ten filling the 

 lower third of the arch, these moderately enlarged, with incon- 

 spicuous grinding surface, the terminal edges being irreg- 

 ularly rounded. The remaining teeth are hooked, the upper 

 ones of the series crenate on the cutting edge. 



Anterior gill-rakers thirty-four in number, upper twenty- 

 one short and thick, about one third the length of the gill 

 filaments; tips of the lower members of the series laterally flat- 

 tened to a paddle shape. About eight of the lower gill-rakers 

 of the anterior series fuse to form a thick ridged pad. Rakers 

 of the remaining arches similar to those of Moxostoma, but 

 more prominent, the tips of the transverse plates projecting 

 further beyond the surface of the arch. 



This species presents an ovoid thickening of the palatal 

 region upon either side, which fills the greater part of the 

 branchial chamber, but is less conspicuous than in Ictiobus. 



Two young specimens, one and three fourths and three 

 inches respectively, differed but little, in food, from those men- 

 tioned on page seventy-two of Bulletin 3 (Vol. I.) of the Illi- 

 nois State Laboratory of Natural History. The larger one had 

 eaten chiefly the smallest of our Entomostraca (Canthocamptus), 

 with a trace of Chironomus larvae. The smaller had taken a 

 moderate ratio of Entomostraca (Cypris, Cyclops, and undeter- 



