The Thinhorn sheep (Ovis dalli) is a species of sheep native to northwestern North America, ranging from white to slate brown in colour and having curved yellowish brown horns. There are two subspecies the nominate Dall sheep or Dall's sheep and the more southern subspecies, Stone sheep (also spelled Stone's sheep) (Ovis dalli stonei), which is a slaty brown with some white patches on the rump and inside the hind legs.