Misled by the variations of colour, due to age, sex, or season, in this species, Linnæus described different examples of it under the names of _Anas clangula_ and _A. glaucion_; whilst even in our own day the females and immature birds are known as “Morillons,” and regarded as distinct from the much-rarer adult males or “Golden-Eyes,” which are locally termed “Rattle wings” or “Whistlers” from the noise produced by the wings during flight. The Golden-Eye forms the type of the well-marked genus _Clangula_ of Fleming and of Boie, and is known to most modern ornithologists as _C. glaucion_. The male is a singularly striking and beautiful bird, with the general colour of the upper parts black, shot with metallic-green tints on the head, which is adorned with a small, yet distinct, drooping crest; with a large white patch at the base of the bill under each eye, and with the drooping, elongated scapulars, and the underparts, white. The female is much less conspicuous, the black being replaced by dark brown, the elongated scapulars are wanting, and the spot under the eyes only faintly indicated. The white double alar speculum is, however, very strongly marked in both sexes. The Golden-Eye is certainly more addicted to fresh-water than the sea, and in most cases only quits these inland lakes and ponds, when continued frost compels it to do so. It then prefers such coasts as are low-lying, especially delighting in estuaries. It usually arrives in the British Islands in October, and remains in them until the following April or May. It is not so gregarious as some of the other Ducks, and generally assembles in parties rather than in flocks, the larger gatherings being caused by exceptional circumstances. Its habits very closely resemble those of allied birds. It is seldom seen on the land, and there walks with the waddling gait peculiar to most Ducks; on the water, however, it is active and graceful enough, swimming well, and diving with great celerity, usually seeking by this means to escape from danger. The note of this Duck is a low croaking _kurr_, uttered both when the bird is flying and when at rest. Its food consists of crustaceans, molluscs, small fishes, and various water plants and weeds. Most of this is obtained by diving; and whilst a flock of birds is feeding, several individuals keep watch, all never diving together.