The Collaborative International Dictionary of English v.0.48:

Equus \E"quus\, n. [L., horse.] (Zo["o]l.)
   A genus of mammals, including the horse, ass, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Equus
    n 1: type genus of the Equidae: only surviving genus of the
         family Equidae [syn: Equus, genus Equus]