eurypterus

from The Collaborative International Dictionary of English v.0.48

Eurypterus \Eu*ryp"te*rus\, n. [NL., fr. Gr. ? broad + ? a
   wing.] (Paleon.)
   A genus of extinct Merostomata, found in Silurian rocks. Some
   of the species are more than three feet long.
   [1913 Webster]