The Collaborative International Dictionary of English v.0.48:

Water tiger \Wa"ter ti"ger\ (Zool.)
   A diving, or water, beetle, especially the larva of a water
   beetle. See Illust. b of Water beetle.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Diving \Div"ing\, a.
   That dives or is used or diving.
   [1913 Webster]

   Diving beetle (Zool.), any beetle of the family
      Dytiscid[ae], which habitually lives under water; --
      called also water tiger.

   Diving bell, a hollow inverted vessel, sometimes
      bell-shaped, in which men may descend and work under
      water, respiration being sustained by the compressed air
      at the top, by fresh air pumped in through a tube from
      above.

   Diving dress. See Submarine armor, under Submarine.

   Diving stone, a kind of jasper.
      [1913 Webster]