Source : Webster's Revised Unabridged Dictionary (1913)

Mytilus \Myt"i*lus\, n. [L., a sea mussel, Gr. ?.] (Zo["o]l.)
   A genus of marine bivalve shells, including the common
   mussel. See Illust. under {Byssus}.

Byssus \Bys"sus\, n.; pl. E. {Byssuses}; L. {Byssi}.[L. byssus
   fine flax, fine linen or cotton, Gr. by`ssos .]
   1. A cloth of exceedingly fine texture, used by the ancients.
      It is disputed whether it was of cotton, linen, or silk.
      [Written also {byss} and {byssin}.]

   2. (Zo["o]l.) A tuft of long, tough filaments which are
      formed in a groove of the foot, and issue from between the
      valves of certain bivalve mollusks, as the {Pinna} and
      {Mytilus}, by which they attach themselves to rocks, etc.

   3. (Bot.) An obsolete name for certain fungi composed of
      slender threads.

   4. Asbestus.

Source : WordNet®

Mytilus
     n : type genus of the family Mytilidae: smooth-shelled marine
         mussels [syn: {genus Mytilus}]