The members of this genus, though often regarded as congeneric with the Common Teal, differ considerably from that species in structure, plumage, and habits. The bill is broader, and instead of being the same width throughout, is wider towards the end, the nail is broader and larger. The labyrinth or bony enlarge¬ment of the lower portion of the trachea in the drake is differently shaped, being swollen on both sides and downward, whilst in the genera Anas, Nettium, and several others the inflation is on one side and upward. The flight is different, and all members of the present genus may be recognized by their blue or bluish-grey wing-coverts.
Of the five species referred to this generic group, four are American and mainly South American, the fifth is one of our migratory ducks.