Placoganoidei \Plac`o*ga*noi"de*i\, n. pl. [NL., fr. Gr. pla`x, plako`s, a tablet + NL. ganoidei. See {Ganoidei}.] (Zool.) A division of ganoid fishes including those that have large external bony plates and a cartilaginous skeleton. [1913 Webster]