The Collaborative International Dictionary of English v.0.48:

Leatherback \Leath"er*back`\, n. (Zool.)
   A large sea turtle (Sphargis coriacea), having no bony
   shell on its back. It is common in the warm and temperate
   parts of the Atlantic, and sometimes weighs over a thousand
   pounds; -- called also leather turtle, leathery turtle,
   leather-backed tortoise, etc.
   [1913 Webster] Leatheret