The Collaborative International Dictionary of English v.0.48:
Saddleback \Sad"dle*back`\, 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]