Cycloid scale

from The Collaborative International Dictionary of English v.0.48

Cycloid \Cy"cloid\, a. (Zool.)
   Of or pertaining to the Cycloidei.
   [1913 Webster]

   {Cycloid scale} (Zool.), a fish scale which is thin and shows
      concentric lines of growth, without serrations on the
      margin.
      [1913 Webster]