The Ganoids 257 
used to stir up the mud in which are found the minute organisms 
on which the fish feeds. Under the paddle are four very minute 
Fie. 192.—Paddle-fish, Polyodon spathula (Walbaum). Ohio River. 
barbels corresponding to those of the sturgeons. The vernacular 
names of spoonbill, duckbill cat, and shovel-fish are also derived 
from the form of the snout. The skin is nearly smooth, the tail 
is heterocercal, the teeth are very small, and a long fleshy flap 
covers the gill-opening. The very long and slender gill-rakers 
Fic. 198.—Paddle-fish, Polyodon spathula (Walbaum). Ohio River. 
serve to strain the food (worms, leeches, water-beetles, crusta- 
ceans, and alge) from the muddy waters from which they are 
_ taken. The most important part of this diet consists of En- 
tomostracans. The single American species, Polyodon spathula, 
abounds through the Mississippi Valley in all the larger 
streams. It reaches a length of three or four feet. It is often 
taken in the nets, but the coarse tough flesh, like that of our 
inferior catfish, is not much esteemed. In the great rivers of 
China, the Yangtse and the Hoang Ho, is a second species, 
Fie. 194.—Psephurus gladius Giinther. Yangtse River. (After Giinther.) 
Psephurus gladius, with narrower snout, fewer gill-rakers, and 
much coarser fulcra on the tail. The habits, so far as known, 
are much the same. 
Crossopholis magnicaudatus of the Green River Eocene 
shales is a primitive member of the Polyodontide. Its rostral blade 
