Size large, the plumage of the sexes differing very little, but the male much larger than the female. Bill of moderate length, considerably raised at the base and of nearly the same width throughout, furnished above in the male with a fleshy knob that becomes greatly developed in the breeding-season (fig. 101). Wing with a prominent tubercle in front of the bend. Tail of 12 feathers, rounded. Lower end of trachea expanded on the left side only. Hind toe with a narrow lobe.
This genus contains two species, one found in India and Africa,, the other in South America