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):

Myxophyceae
    n 1: former terms for Cyanophyceae [syn: Myxophyceae, family
         Myxophyceae, Schizophyceae, family Schizophyceae]