“Tree-Ducks” of the genus Dendrocygna. 39 
preacetabular portions and spreading behind (Fig. 69, P1.10, and 
Fig. 84, Pl.11). We have seen that this is distinetly not the case 
in the pelvis of the Tree-Ducks, wherein this composite bone is 
narrow and elongate, as in the case of Mergus. As a matter of 
fact, the pelvis of Dendrocygna bicolor or D. autumnalis agrees much 
better, indeed, very much better with the pelvis of Mergus serrator 
than it does with any duck, goose or swan with which I am at 
present acquainted. 
To appreciate this, one will have but to turn to p. 265 of 
my “Osteology of Birds” (in: State Mus. N. Y.) and note there 
figs. 7 and 8, — the first being of Mergus serrator, and the second 
Somateria dresseri. They are my own drawings and upon dorsal 
view. Now Somateria possesses an unusually elongate pelvis for a 
duck, the more ordinary form being seen in Spatula clypeata (fig. 21 
of the same volume), or in Fig. 84 of Pl. il of the present paper, 
which is the pelvis of Acx galericulata. Moreover, in the pelvis of 
Mergus serrator, the posterior ilio-ischiac margin or border is entire; 
it possesses three pairs of pelvic ribs, as in a Tree-Duck, and 
in general form and character the bone, in these two species, is 
almost identical. 
Apart from the pelvis, however, all the rest of the skeleton of 
Mergus serrator is very unlike that of Dendrocygna, — a fact the osteo- 
logist, who knows anything of the skull, trunk skeleton and limb- 
bones of the mergansers, will recall. 
The Shoulder Girdle. Fundamentally, as well as actually, 
the several bones composing the pectoral arch, in either species 
of the two American Tree-Ducks, are different from the correspond- 
ing ones as they occur in any true swan (Olor, Oygnus etc.) 
In Olor columbianus the os furcula is highly pneumatic, with 
groups of pneumatic foramina upon the outer aspect of either clavic- 
ular limb, and the lower part of the arch is modified in form in 
order to admit of the passage of the trachea to the thoracie cavity. 
In Dendrocygna no such modification is present in the os furcula, 
and, moreover, the bone is non-pneumatic; the clavicular limbs 
flattened from side to side, the whole having a broad, U-shaped form, 
as in allthe Anatinae. Dranta has the furcula of a narrower 
U-arch, with the free ends of the clavicular limbs drawn out into 
pointed extremities, as in all Anserinae and Anatinae. Either 
clavicular limb, on the upper border of its arch, at some little 
distance anterior to its free end, there is a distinct tubercle present 
