CycloideiCy*cloi"de*i\ (s?-kloi"d?-?), n. pl. [NL., fr. Gr. ky`klos circle + -oid.] (Zo["o]l.) 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.