The Collaborative International Dictionary of English v.0.48:

Macaca \Macaca\ prop. n.
   A genus of macaques including the rhesus monkey (Macaca
   mulatta), much used in laboratory biomedical research.
   Formerly called Macacus.

   Syn: genus Macaca.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Macacus \Ma*ca"cus\, n. [NL., a word of African origin. Cf.
   Macaco, Macaque.] (Zool.)
   A genus of monkeys, found in Asia and the East Indies, now
   usually called Macaca. They have short tails and prominent
   eyebrows. See also Macaca.
   [1913 Webster]