KEY TO THE FAMILIES OF FRESHWATER FISHES 

 OF MAINE 



1. Mouth a sucker-like disc without jaws; gill openings seven; paired 

 fins absent 



Sea Lamprey 

 Petromyzonidae 



p. 16 



Mouth with true jaws; gill slits four, protected by a gill cover; 

 paired fins present 2 



2. Caudal fin not symmetrical (heterocercal), caudal vertebrae ex- 

 tending into the upper lobe of the caudal fin 



Atlantic Sturgeon 

 A cipenseridae 



p. 18 



Caudal fin more or less symmetrical (homocercal) 3 



10 



