Bill short, higher than broad at the base, not much flattened at the tip, tapering slightly throughout, more rapidly and rounded at the end; culmen nearly straight; nostrils rather nearer to the tip of the bill than to the base; lamella? short, stout, not close together. Wings pointed ; tail rather long, much rounded, of 16 stiff feathers; legs short, placed far aft; tarsus scutellate in front, hind-toe broadly lobed. The posterior end of the sternum is prolonged as in Merganser.
This genus of Diving Ducks contains three species, all of northern range, and all, as a rule, keeping to the sea, except in the breeding-season. One species has occasionally been obtained in Northern India.