The Collaborative International Dictionary of English v.0.48:

Myxophyceae \Myxophyceae\ prop. n. (Biol.)
   A former term for the natural family Cyanophyceae.

   Syn: family Myxophyceae, Schizophyceae, family
        Schizophyceae.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Cyanophyceae
    n 1: photosynthetic bacteria found in fresh and salt water,
         having chlorophyll a and phycobilins; once thought to be
         algae: blue-green algae [syn: class Cyanobacteria,
         Cyanophyceae, class Cyanophyceae]