AVE S. 



75 



with oil, garnished next the skin with a thick down, and in- 

 tended to protect them from the water in which they live ; 

 length of neck often much exceeding that of the feet, which 

 permits certain species to seize their food at the bottom of 

 shallow waters ; sternum very long, affording complete pro- 

 tection to the greater portion of their viscera, and having on 

 each side but one emargination or oval hole furnished with 

 membrane; gizzard generally muscular; inferior larynx 

 simple, but in one family inflated into cartilaginous capsules. 

 Four families. 



FAMILY I. BRACHYPTERiE. 



Legs placed farther back than in any other birds, which 

 renders walking painful to them, and obliges them to stand 

 when on land in a vertical position ; flight feeble, or none at 

 all ; plumage very dense, smooth and glossy like silver ; 

 they swim under water by the aid of their wings. Three 

 genera. 



Genus Colymbus, Lin. Diver. 



Beak smooth, straight, compressed and pointed ; nostrils 

 linear ; they consume a great many fish. Three remarkable 

 subgenera, distinguished by the form of their feet. 



Subgenus Podicfps, Lath. Grebe. 



Toes widened by membranes, the anterior only united at 

 the base ; middle nail flattened. 



Subgenus Mergus, Briss. Diver proper. 



Feet palmated ; nails pointed ; northern birds seldom 

 breeding among us, but migrate south during winter. 



Subgenus Uria, Briss. Guillemot-. 



No thumb ; feathers as far as the nostrils ; wings still 

 shorter than those of the Divers. 



Genus Alca, Lin. Auks. 



Beak very much compressed, elevated vertically, trenchant 

 towards the rear, and generally ridged across ; feet entirely 

 palmated, and wanting the thumb. [Northern Seas.] 



Genus Aptenodytes, Forst. Penguin. 



No flight ; small wings, furnished with traces of plumage, 



