The Collaborative International Dictionary of English v.0.48:

Ganoidei \Ga*noi"de*i\, n. pl. [NL. See Ganoid.] (Zool.)
   One of the subclasses of fishes. They have an arterial cone
   and bulb, spiral intestinal valve, and the optic nerves
   united by a chiasma. Many of the species are covered with
   bony plates, or with ganoid scales; others have cycloid
   scales.
   [1913 Webster]

   Note: They were numerous, and some of them of large size, in
         early geological periods; but they are represented by
         comparatively few living species, most of which inhabit
         fresh waters, as the bowfin, gar pike, bichir,
         Ceratodus, paddle fish, and sturgeon.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Ganoidei
    n 1: a group of mostly extinct primitive bony fishes
         characterized by armor-like bony scales [syn: Ganoidei,
         order Ganoidei]