PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 217 



twenty. Independent of the inconvenience of tliis character, when the 

 birds moult their rectrices, I may confess that I only in a few cases 

 have been able to count twenty-four tail feathers; and the inconstancy 

 of the number of these feathers I have found pervading the whole group, 

 this character changing individually, so that it is not at all to be de- 

 pended upon. 



As a rule, the frontal apex of the ptilosis forms a sharp angle in 

 huccinator, whilst it always is rounded in columhianiis ; but I have also 

 seen specimens of the former which had the limit of the feathering 

 rounded as in the latter. In huccinator I also usually fouua the dis- 

 tance from the eye to the point of the mentioned frontal apex to be 

 larger than from the same point to the hind border of the nasal fossa?, 

 whilst the relation is quite the reverse in columhianus ; but I have also 

 met specimens of both species in which this character was only very 

 slightly expressed, the young columhianus especially having the culmen 

 feathered longer forward than the older birds. 



The position of the nostrils, those being situated more backwards in 

 the Trumpeter than in the Whistling Swan, is thus the only mark 

 which it is possible to express in a short diagnosis, and which I have 

 found constant and easily perceptible. 



