OF THE GENUS MERGUS, i8S 
I have thought it right to call the attention of the Society 
to this difficulty in distinguishing the Dundiver, commonly 
bony labyrinth of the inferior larynx ; the Red-breasted Merganser possesses 
only one of these enlargements. It has happened that birds in the plumage 
of the Dundiver, proving on dissection to be males, and the windpipe being 
found to be furnished with only one enlargement, the conclusion has natu- 
rally enough been drawn, that these birds were the males of a separate and 
^distinct species (the supposed Mergus castor of Gmelin), and could not be 
assigned to any condition of the Goosander. Such specimens, however, 
had nothing to do with the true Dundiver ; they were immature males of 
the Red-breasted Merganser, and, therefore, prove nothing more than that 
the young of that species resemble in anatomical structure the adult birds, 
in like manner as the true m.ale Dundiver resembles the adult Goosander. 
This view of the subject explains the error in Montagu's reasoning on this 
point. The mistake seems to have originated in the Berlin Transactions ; 
in the third volume, tab. 7. fig. 5, there is a drawing of the trachea of the 
Dundiver; and in the fourth volume of the same v/ork, tab. 18. fig. 3, 
there is another of that of the Goosander ; the former with one enlarge- 
ment, the latter with two. Mr Simmonds, on the contrary, (Linn. Trans, 
vol. viii.), who dissected these birds, with a view to this disputed point, 
asserts that there is a perfect agreement in their internal structure; 
and the same opinion is maintained by M. Temminck in his " Manuel 
d'OrnithoIogie." These seeming contradictions are easily reconciled, by 
bearing in mind the close resemblance which exists between the plumage 
of the immature males of the Goosander and Red-breasted Merganser, 
and the consequent liability of their being confounded by the dissector." 
Those who still entertain any doubts on the subject, may easily satisfy 
themselves in this quarter of the island, where both kinds are sufficiently 
common. When a male bird, in the plumage of the Dundiver, is observed 
on dissection to have two enlargements in the course of the windpipe, it 
may then be considered as the young of the Goosander {Mergus merganser) ; 
when only one such enlargement is perceptible, it may safely be regarded 
as an iimiaature Red-breasted Merganser {Mergus serrator). The difference 
in the bill, as mentioned in the text, will form, it is hoped, a more import- 
ant external character of distinction than any previously pointed out. In 
regard to the title of Mergus castor (the bird indicated by it being an ima- 
ginary species), it should of course be erased from the list of specific 
names. 
