In their Checklist of Palacarctic and Indian Mammals, 1758 to 1946, issued in 1951, J. R. Ellerman and T. C. S. Morrison-Scott regard the true sheep of the Old World as all belonging to the genus Ovis and, except for the Bighorn Sheep of Siberia and Canada, all to the sub-genus Ovis also. They allow four species: Ovis ammon, the Argali; Ovis orientalis, the Asiatic Mouflon; Ovis laristanica, the Laristan Sheep, and Ovis musimon, the Mouflon.