The Collaborative International Dictionary of English v.0.48:

Bellerophon \Bel*ler"o*phon\, n. (Paleon.)
   A genus of fossil univalve shells, believed to belong to the
   Heteropoda, peculiar to the Paleozoic age.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Bellerophon
    n 1: (Greek mythology) a mythical hero of Corinth who performed
         miracles on the winged horse Pegasus (especially killing
         the monster Chimera)