208 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



of tlie nail. It will further be easily seen in the same figure that a 

 straight line laid along the upper border of the nostrils in the Hooper 

 will go almost parallel with the culmen, whilst this in Bewick's Swan 

 will form a much more obtuse angle with the same.* 



It will not be diflBcult in general in these birds to notice through the 

 skin of the bill the outlines of the bones which lie underneath. Espec- 

 ially easy will one be able to discern the outlines of the processus 

 maxiUaris of the nasal bone with the open angle lying back and below the 

 same, between the named processus and the arcus zygomaticus {x on figs. 

 15, 16), together with the angle lying above and to the front (yon the same 

 figures), formed by the 2)roc£ss us maxiUaris and intermaxillaris of the os 

 nasale. 



In all the specimens which I have examined it has shown itself that 

 the processus maxiUaris in 0. cygmis is much more inclined than in 0. 

 hewiclii, in which it is more perpendicular, so that perpendicular lines 

 through the upper points of the angles x and y in the figures, descending 

 to a line parallel with the commissure, have a not inconsiderable dis- 

 tance from each other in hewicJcii, whilst they come together, or almost 

 so, in the Hooper; or, in other words, in the latter the point of the angle 

 X extends so far forward that it comes almost under the point of the 

 angle y, which is far from being the case in Bewick's Swan. The re- 

 lation can be very clearly seeu in the sketches. 



I have thus always found the formation of the bill, in old as well as in 

 young specimens; and I have but little doubt that this relation, which 

 agrees with the greater height of the bill in hewicMi, will show itself to 

 be au excellent, easily perceived, and constant mark, and that by this 

 the difficulty of distinguishing the young birds of both species by the 

 assistance of outward marks is satisfactorily settled. 



Besides, if one compare the two above-mentioned young birds, sepa- 

 rately described (see pp. 206 and 207), which would have taken, the ensu- 

 ing spring, the white i^lumage of the old birds, the color does not show 

 any particular difference. Exactly the contrary to what Mr. Dresser 

 (Birds of Eur., April, 1880) describes,! the young heicickii now before me 

 is considerably lighter than my specimen of the Hooper. Besides, the 

 former has on the back numerous blackish hairlike stripes, formed by 

 the dark-colored shafts, whilst they in the other are not darker than 

 the radii. Another young specimen of the Hooper, belonging to the 

 Bergen Museum, and which I have described in Nyt Mag. for Naturv., 

 XXV, p. 145, is similar to the one in my collection. 



*Naumann has already drawn attention to this feature. 



t Said to resemble the young of C. musicus, but is, of course, mi;ch smaller, and the 

 coloration of the plumage is rather darker. 



