\Xan*thid"i*um\, n.; pl. {Xanthidia}. [NL., fr. Gr.
xanqo`s yellow.] (Bot.)
A genus of minute unicellular alg[ae] of the desmids. These
alg[ae] have a rounded shape and are armed with glochidiate
or branched aculei. Several species occur in ditches, and
others are found fossil in flint or hornstone.