194 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



is expressly stated "that at no stage of growth is this a character to be 

 depended upon." 



In their size they seem not to differ. Mr. Dresser gives the total 

 length of the adult male of gihhus at about four and a half to five feet, 

 the gape 3.55 inches, and the tarsus 4.5 inches ; and of the adult immu- 

 lahiUs, respectively at about five feet, 3.6, and 4.25 inches. The differ- 

 ences in the length of the wing, 27 inches as against 23.5, and yet more 

 in the length of the tail, 10 to 6.8, are certainly quite considerable, but 

 not more shan sometimes occurs in the same species, especially as it is 

 probable that the feathers of the specimen from North-Repps are not fully 

 developed. 



Finally, there are the osteological differences described by Mr. Pel- 

 ERIN (Mag. Nat. Hist., 1839, p. 178), which I have had no occasion to 

 verify, and which I cannot remember to have seen confirmed or denied 

 by any other thar Mr. Yarrell himself. 



The English ornithologists may after this be right when they urge the 

 independence of C. immiitabilis, and it should be a great offense against 

 the science if one would unite these two forms and hereby cut off", or at 

 least trouble, the study of this particular phenomenon. 



As far as my investigations go, they also agree with the results of the 

 English authors. In Schlegel's Catal. Mus. P.-B., YI, Anseres, p. 79, 

 a male "de I'ann^e" is enumerated under Cygnus olor (Gmel.) as 

 killed on the Lake of Haarlem in the month of December, 1840. The 

 description of this interesting specimen, which certainly belongs to C. 

 immutahilis Yarr., is as follows : 



Mus. Leiden, C olor No. 3 (<?, Lalce of Haarlem, Holland, December, 

 1840). 



Length of the bill along the gape, 102""' ; from the tip to the fore 

 border of the nostrils 60, and to the eye 131'"'". Length of toes with 

 claws: Outer toe 139, middle toe 145, inner toe 112, and hind toe 30'""\ 

 Tarsus 95, tail 158, and wing 565'""'- The distance from the tip of the 

 bill to the fore border of the knob 82""", the knob itself being 6'"'" high. 



The whole plumage pure white, with a faint rose-colored shade on the 

 •wing-coverts, and a rust-colored tinge on the crown and chin. The tar- 

 sus and toes yellowish-gray, the webs grayish-yellow. The original color 

 of the bill cannot be recognized in the dried specimen. 



If one compare the above dimensions with those given on Table IV, it 

 will be seen that they agree quite well with the smallest specimen. The 

 small size of the frontal knob, and the remarkably light feet, are very 

 characteristic features, combined with the white plumage. I therefore 

 regard the identification of this specimen with G. immutahilis to be un- 

 questionable. 



As to the colors of the young, I refer to the descriptions given above. 



