RARER BRITISH BIRDS. 
87 
new to the British Isles, but to the world, certainly belongs to 
Mr. Yarrell, whose interesting paper on it was read before the 
Linnean Society, January 19, 1830. 
Bewick’s Swan differs considerably in size from the common 
wild one, or Hooper, being about one-third less, and measuring 
from the point of the bill to the end of the tail three feet nine 
inches ; the Hooper measuring from the same points five feet. 
From the point of the bill to the edge of the forehead it measures 
three and a half inches ; length of the tarsi is three inches and 
three-quarters ; the number of tail feathers eighteen in the new 
species. The following are the measurements of the Hooper 
from the same points: — Point of bill to forehead, four inches 
and three-eighths ; length of tarsi, four inches ; number of tail 
feathers, twenty. 
In colouring, except in that of the bills, the birds perfectly 
resemble each other, at least in our specimens ; and it appears 
to undergo the same changes in its progress to maturity that the 
Hooper does, being at first grey, and afterwards white. The 
bill in both species is black, with yellow markings at the base ; 
which, in the new species, end abruptly a little behind the 
nostrils, but in the Hooper are pointed. 
Besides these external differences, which leave no doubt of 
the validity of the species, the following internal ones distinguish 
them ; which, had any doubts existed before, must at once remove 
them. The distinctions of which I speak are in the organs of 
voice, or tracheae. The tracheal tube in both species enters the 
keel of the sternum. In the new species, at the point from 
which it recurves towards the bronchia?, being the point at which 
it penetrates deepest into the sternum, it takes a horizontal 
position ; the part of the tube going from the point of recurva- 
ture towards the mouth, or upper extremity of the tube, being 
