RARER BRITISH BIRDS. 73 



propose the subgeneric name of Polysticta, (many-marked,) 

 alluding to the variety of its colours. 



We shall then proceed through the true Marine or Diving 

 Ducks, with the ribs coming far backwards over the abdo- 

 men, the sternum large and broad, the pelvis narrow, the feet 

 large, and the hind toe largely lobated, (under which divi- 

 sion we place the genera Somateria, Leach ; Oidemia, Fleming ; 

 Clangula, Fleming; Harelda, Leach,) to those which often 

 frequent fresh water, and occasionally feed on land ; charac- 

 terised by having the sternum narrower; the pelvis broader, 

 but ribs shorter, not going so far backwards ; and feet smaller 

 than in the last division; hind toe not lobated, or only slight- 

 ly so : under which come the genus Anas, Linnaeus ; with its 

 sub genera, Querquedula, Willoughby ; Chauliodus, Swainson ; 

 Rhynchaspis, Leach ; Dafila, Leach ; Boschas, Swainson ; and 

 the genus Tadorna, Leach. 



The Geese, (genus Anser,) and the Swans, (genus Cygnus,) 

 are now the only genera among our British Ducks that remain. 

 The former we shall place next to the Ducks, but divided from 

 them by having the keel of the sternum deeper ; the margins of 

 the bill less laminated ; the hind toe small in proportion to the 

 size of the birds ; trachea, simple. The species of the genus 

 Anser, found in our islands, are divided into two sub genera, 

 viz. Anser, Ray ; and Bernicla, Stephens ; in the latter of which 

 the hind toe is smallest, and the bill shorter in proportion to the 

 head than in the former. 



The genus Cygnus may be at once distinguished from Anser 

 by the greater length of the neck ; the still smaller size of the 

 hind toe in proportion to that of the bird, the tarsi being 

 shorter; and by the trachea, which is simple in some of the 

 species, entering the keel of the sternum. A list of the genera 

 L 



