The Ganoids 



21 



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 



FIG. 9. 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 



FIG. 10. Paddle-fish, Polyodon spathula (Walbaum). Ohio River. 



serve to strain the food (worms, leeches, water-beetles, crusta- 

 ceans, and algae) 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, 



FIG. 11. 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 Polyodontida. Its rostral blade 



