The Collaborative International Dictionary of English v.0.48:

Pecopteris \Pe*cop"te*ris\ (p[-e]*k[o^]p"t[-e]*r[i^]s), prop. n.
   [NL., fr. Gr. pe`kein to comb + petri`s a kind of fern.]
   (Paleon.)
   An extensive genus of fossil ferns; -- so named from the
   regular comblike arrangement of the leaflets.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pecopteris
    n 1: Carboniferous fossil fern characterized by a regular
         arrangement of the leaflets resembling a comb