The Collaborative International Dictionary of English v.0.48:

Limnaea \Lim*n[ae]"a\ (l[i^]m*n[=e]"[.a]), prop. n. [NL., fr.
   Gr. limnai^os pertaining to a marsh, fr. li`mh a marsh.]
   (Zool.)
   A genus of fresh-water air-breathing mollusks, abundant in
   ponds and streams; -- called also pond snail. [Written also
   Lymn[ae]a.]
   [1913 Webster]