Source : Webster's Revised Unabridged Dictionary (1913)

Ceratodus \Ce*rat"o*dus\, n. [NL., fr. Gr. ke`ras, ke`ratos horn
   + ? tooth.] (Zo["o]l.)
   A genus of ganoid fishes, of the order Dipnoi, first known as
   Mesozoic fossil fishes; but recently two living species have
   been discovered in Australian rivers. They have lungs so well
   developed that they can leave the water and breathe in air.
   In Australia they are called {salmon} and {baramunda}. See
   {Dipnoi}, and {Archipterygium}.

Source : WordNet®

ceratodus
     n : extinct lungfish