This genus may be recognized by its elongate form, long neck, and lengthened and pointed middle tail-feathers. There are 16 rectrices as a rule (I have found one skin with 18). The bill is rather narrower than in Anas and a little broader towards the point than at the base ; the wings- are long and pointed. It is a well-marked type.
Three species are referred to this genus: of these two are confined to the Southern hemisphere; the third is Indian.