Source : Webster's Revised Unabridged Dictionary (1913)

Physa \Phy"sa\, n. [NL., fr. Gr. ? a bellows.] (Zo["o]l.)
   A genus of fresh-water Pulmonifera, having reversed spiral
   shells. See {Pond snail}, under {Pond}.

Source : WordNet®

physa
     n : any member of the genus Physa