FISHES OF ILLINOIS 



Fig. 4 

 Heterocercal tail of Sturgeon (Acipenser). 



Heterocercal tail of Garpike {Lepisos- 



teus) . 



Fig. 6 

 Heterocercal tail of Dogfish {A7nia). 



Fig. 7 



Typical homocercal tail of Pike-perch 



(Stizostedion) . (After Jordan and 

 Evermann.) 



Fig. 8 



Ventral view of head of Large-mouthed 

 Black Bass, showing free gill-mem- 

 brane. 



Fig. 9 



Ventral view of head of Common Sucker 

 {Catostomus commerso7iH) , showing con- 

 nection of gill-membranes. 



