70 THE STORY OF THE BIRDS 



The sub-order Anseres (the Swans, Geese, Ducks, 

 and Mergansers) contains birds that cannot 

 readily be confused with the members of any 

 other order or group. Their most characteristic 

 external features are their generally broad flat 

 bills, furnished with a nail at the tip of the 

 upper mandible, which are either serrated or 

 furnished with lamellae, and their webbed feet, 

 all the anterior toes being united by a mem- 

 brane. The bill varies a good deal in shape, 

 from the short sub-conical one characteristic 

 of the Geese to the broad spatulate one of the 

 Shovellers and the narrow elongated one of 

 the Mergansers, or furnished with a small hook 

 in the latter, and some others. The chin-lobe 

 in the genus Biziura is remarkable. The wings 

 in some species are armed with spurs. The 

 tail varies a good deal in shape, but is generally 

 short, rounded in some, cuneate in others, and 

 less frequently singularly spine-like and rigid. 

 The peculiar formation of the trachea in some 

 species in this order has already been alluded 

 to {conf. p. 49). A marked similarity of habit 

 runs through the birds of this sub-order — all, 

 or nearly all, the species are eminently aquatic, 

 marine or inland. Most are gregarious at some 

 time of the year or another. The peculiarities 



