The Collaborative International Dictionary of English v.0.48:

Dinichthys \Di*nich"thys\, n. [NL., fr. Gr. ? terrible + ?
   fish.] (Paleon.)
   A genus of large extinct Devonian ganoid fishes. In some
   parts of Ohio remains of the Dinichthys are abundant,
   indicating animals twenty feet in length.
   [1913 Webster]