RARER BRITISH BIRDS. 
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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 
