Source : Webster's Revised Unabridged Dictionary (1913)

Stigmaria \Stig*ma"ri*a\, n. [NL. See {Stigma}.] (Paleon.)
   The fossil root stem of a coal plant of the genus
   {Sigillaria}.

Underclay \Un"der*clay`\, n. (Geol.)
   A stratum of clay lying beneath a coal bed, often containing
   the roots of coal plants, especially the {Stigmaria}.