The Collaborative International Dictionary of English v.0.48:

Cycloidei \Cy*cloi"de*i\ (s?-kloi"d?-?), n. pl. [NL., fr. Gr.
   ky`klos circle + -oid.] (Zool.)
   An order of fishes, formerly proposed by Agassiz, for those
   with thin, smooth scales, destitute of marginal spines, as
   the herring and salmon. The group is now regarded as
   artificial.
   [1913 Webster]