Mergellus Selby, Oat. Gen. Subgen. types Birds, p. 47 (1840).
Type by taut., Mergus albellus Linn.
The genus Mergellus possesses a small occipital crest, smaller in the females than in the males; the bill is about as long as the head, tapering throughout, with the culmen nearly straight; the nostril is large, oblong and placed about one-third the length of the bill from the forehead; the serrations are coarse; the tarsi are very short, placed far back on the body, with a large foot; the tail is rounded and consists of sixteen or, occasionally, eighteen feathers ; the wing is short and pointed; there is a single caecum.
There is but one species, of which the sexes differ considerably