saddleback \sad"dleback`\, n.
   1. anything saddle-backed; esp., a hill or ridge having a
      concave outline at the top.
      1913 webster

   2. zool.
      a the harp seal.
      b the great blackbacked gull larus marinus.
      c the larva of a bombycid moth empretia stimulea
          which has a large, bright green, saddle-shaped patch
          of color on the back.
          1913 webster
see also:
larus marinus empretia stimulea