“Tree-Ducks” of the genus Dendrocygna. 49 
far removed from such a species as Aiöx sponsa, still, apart from 
the presence of a small manubrium in the Goose, it bears a closer 
resemblance to the sternum of a specimen of Chen hyperboreus nivalis, 
than to the sternum of any other one of the Anseres before me 
at the present time (No. 18611, Coll. U. S. Nation. Mus... This 
resemblance is not only apparent but actual, to the extent of matching, 
character for character, almost throughout; but this in no way applies 
to the remainder of the skeleton in these two birds. 
The appendicular skeleton. 
The Pectoral Limb. As the two North American represent- 
atives of the genus Dendrocygna are pretty good fliers, — though 
not as powerful ones, perhaps, as some others of the Anatinae — 
teals and garrots, for instance they have the skeleton of a wing 
very well developed indeed. The long bones composing it are strong 
and of large caliber and proportions, while the two carpals are 
correspondingly so. 
The humerus possesses all the usual ornithie characters as 
found among the Anatinae generally; although upon comparing 
the bone in the two sexes of Dendrocygna autumnalis and D. bicolor 
and different specimens, some differences are to be observed, both 
in regard to lengths and other particulars. For example, in a female 
D. autumnalis (454) of the ArMSTRonNG series, this bone has a length 
of 10,4 cms, and is completely pneumatice with a large, subeircular 
pneumatie foramen occupying its usual site Another specimen of 
the same species (455 $&) has a length of 10,1 cm, with a similar 
pneumatic foramen; while a female, also of this species (453), has 
a like pneumatic humerus, which possesses a length of but 9,8 cm. 
'The female, No. 457 of this series, of D. bicolor unfortunately has 
both humeri so shattered by shot as to be rendered useless for the 
purposes of accurate measurement. However, the bone is pneumatic 
like the rest. In a male of this species (D. bicolor, 456) the shaft 
‘of the bone is somewhat slenderer than it is in D. autumnalis, and 
it has an extreme length of 10 cm. The same large, pneumatic 
‘opening exists at the base of the pneumatic fossa, and air — as 
in all the previously described ones — is admitted to the entire 
‚cavity of the bone. 
The D. autumnalis (No. 1491) of the osteological collection of 
Zool. Jahrb. NXXVIII. Abt. f. Syst. 4 
