merostomata

from WordNet (r) 3.0 (2006)

Merostomata
    n 1: used in some classifications; includes the orders Xiphosura
         and Eurypterida [syn: {Merostomata}, {class Merostomata}]

from The Collaborative International Dictionary of English v.0.48

Merostomata \Mer`o*stom"a*ta\, prop. n. pl. [NL., fr. Gr. me`ros
   thigh + ?, -?, mouth.] (Zool.)
   A class of Arthropoda, allied to the Crustacea. It includes
   the trilobites, {Eurypteroidea}, and {Limuloidea}. All are
   extinct except the horseshoe crabs ({Limulus}) of the last
   group. See {Limulus}.
   [1913 Webster]