The Collaborative International Dictionary of English v.0.48:

Anas \A"nas\, n. [L., duck.] (Zool.)
   A genus of water fowls, of the order Anseres, including
   certain species of fresh-water ducks.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Anas
    n 1: type genus of the Anatidae: freshwater ducks [syn: Anas,
         genus Anas]