The Collaborative International Dictionary of English v.0.48:

Onappo \O*nap"po\, n. (Zool.)
   A nocturnal South American monkey (Callithrix discolor),
   noted for its agility; -- called also ventriloquist monkey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ventriloquist \Ven*tril"o*quist\, n.
   One who practices, or is skilled in, ventriloquism.
   [1913 Webster]

   Ventriloquist monkey (Zool.), the onappo; -- so called from
      the character of its cry.
      [1913 Webster]