

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 



