The Collaborative International Dictionary of English v.0.48:

Isospondyli \I`so*spon"dy*li\, n. pl. [NL., fr. Gr. 'i`sos equal
   + ?, ?, a vertebra.] (Zool.)
   An extensive order of fishes, including the salmons,
   herrings, and many allied forms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Isospondyli
    n 1: most primitive teleost fishes; all are soft-finned: salmon;
         trout; herring; shad; sardines; anchovies; whitefish;
         smelts; tarpon [syn: Isospondyli, order Isospondyli]