The Collaborative International Dictionary of English v.0.48:

Elasmosaurus \E*las`mo*sau"rus\, n. [NL., fr. Gr. ? a metal
   plate + ? a lizard.] (Paleon.)
   An extinct, long-necked, marine, cretaceous reptile from
   Kansas, allied to Plesiosaurus.
   [1913 Webster]