Xiphosura
         n 1: horseshoe crabs and extinct forms [syn: {Xiphosura}, {order
               Xiphosura}]

English Dictionary: Xiphosura	by the DICT Development Group
From WordNet (r) 3.0 (2006) [wn]:
Xiphosurus polyphemus n large marine arthropod of the Atlantic coast of North America having a domed carapace that is shaped like a horseshoe and a stiff pointed tail; a living fossil related to the wood louse Synonym(s): horseshoe crab, king crab, Limulus polyphemus, Xiphosurus polyphemus
From Webster's Revised Unabridged Dictionary (1913) [web1913]:
d8Xiphura \[d8]Xi*phu"ra\, n. pl. [NL., from Gr. xi`fos sword +       [?] tail.] (Zo[94]l.)       Same as {Limuloidea}. Called also {Xiphosura}.          {X ray}. See under {Ray}.