52 



head, and this species derives, on the whole, a larger part of its 

 food from univalve than from bivalve moUusks, the former eaten 

 especially by half-grown specimens, and the latter being the 

 chief dependence of the adults. The ability of the catfishes to 

 tear the less powerful clams from their shells has been already 

 mentioned. Large clams were eaten freely by the full-grown 

 sheepshead — whose enormous and powerful pharyngeal jaws 

 with their solid pavement teeth are especially adapted to crush- 

 ing the shells of mollusks — and by the bull-heads (Amiurus), 

 especially the marbled cat. The small and thin-shelled Sphairi- 

 ums are much more frequent objects in the food of mollusk- 

 eating fishes than are the Unios. This genus alone made 

 twenty-nine per cent, of the food of our one hundred and seven 

 specimens of the sucker family, and nineteen per cent, of that 

 of a dozen dog-fishes. Among the suckers it was eaten greedily 

 by both the cylindrical and the deep-bodied species, although 

 somewhat more freely by the former. Even the river carp, with 

 its weak pharyngeal jaws and delicate teeth, finds these sufficient 

 to crush the shells of Sphaerium, and our nineteen specimens 

 had obtained about one fourth of their food from this genus. 

 Besides the above families, smaller quantities of the bivalve 

 mollusks occurred in the food of one of the sunfishes {Lepomis 

 palliihis), and — doubtless by accident only — in the gizzard 

 shad. The gasteropod mollusks (snails of various descriptions) 

 were more abundant than bivalve forms in the sheepshead, sun- 

 fish, and all the smaller fishes which feed upon Mollusca, but 

 less abundant in the suckers and the catfishes. In the sheeps- 

 head they made one fifth of the food of the twenty-five speci- 

 mens examined, but the greater part of these had not yet 

 passed the insectivorous stage, this being much longer continued 

 in the sheepshead than in many other fishes. A few of these 

 univalve Mollusca occurred in the food of the common perch 

 and in certain species of sunfishes — especially the superabundant 

 bream or pumpkin-seed. They made fifteen per cent, of the 

 food of the minute top minnows, and occurred in smaller quan- 

 tities among the darters, the little pickerel, the mud minnows 

 and the cyprinoids. The heavier river snails, Vivipara and 

 Melantho, were eaten especially by the cylindrical suckers and 



