Chaulelasmus Bonaparte, Comp. Geog. List B. of Eur. and N. Am., p. 56 (1838).
Type, Anas strepera Linn.
In this genus the bill is smaller than in Anas and the lamellae more developed; the tail is of sixteen feathers ; the speculum is quite different, being of black and white only, glossy but with no green, blue or purple reflections. As in Ducks, colour-pattern is probably a character of considerable importance it suffices, together with the other small differences, to maintain the separation of this genus.