gyrodus

from The Collaborative International Dictionary of English v.0.48

Gyrodus \Gyr"o*dus\ (j[i^]r"[-o]*d[u^]s), n. [NL., fr. Gr.
   gyro`s round + 'odoy`s tooth.] (Paleon.)
   A genus of extinct o["o]litic fishes, having rounded teeth in
   several rows adapted for crushing.
   [1913 Webster]