“Tree-Ducks’” of the genus Dendrocygna. 23 
In the Mallard, it is sometimes partially divided in the longi- 
tudinal direction, mesially, by the development of a nasal septum 
{No. 4975, Coll. U. S. Nat. Mus.). In Chloephaga poliocephala this 
foraminal aperture is extensive, and situated at the middle of the 
short superior mandible of that göose; while in Harelda hyemalis, 
it is completely closed over by a thin, osseous layer, composed, 
apparently, of an independant ossification formed in the roof of the 
mouth in this duck. 
In Branta c. hutchensi, the maxillo-palatines are spongy and 
produced far forwards. They form the sides of this foramen, which 
latter, in this species, is narrow and elongated. Skulls of Branta 
canadensis at hand possess a conformation similar to this. 
Thus it will be observed, as already stated above, that all the 
osseous structures occurring at the base of the cranium in Dendro- 
cygna are essentially as we find them in the several representatives 
of the genus Anas, especially in A. platyrhynchos and A. rubripes. 
Next to these, in the matter of such agreement, come such species 
as Marila valisineria; the teals (Nettion ete.), and Mareca. 
In Chen hyperboreus there is, on the under surface of the superior 
mandible, on either side, just within the tomial margin, a chain of 
elevated, roughened tubercles, which are biggest posteriorly, and 
shade off to disappear entirely at some distance from the apex. In 
these geese, the general concavity, on the nether side of this man- 
dible, is notably shallow. The osseous tubercles just described are 
not to be found in the skulls of any other species of geese examined 
by me. 
Many variations occur in the morphology of the anterior ex- 
tremities of the palatines. The simplest form of one of these bones 
is seen in Dendrocygna, either bicolor or autumnalis (Pl. 8, Figs. 53 
and 54). Here the mesial margin of the bone is nearly straight 
and entirely devoid of any projections. 
Passing to the Mallard (A. platyrhynchos), we are to note that 
a palatine, just before arriving at the maxillo-palatine mass, throws 
off a short, blunt, little process, which is directed forwards to abut 
against the aforesaid mass, thus creating a distinct foramen to its 
outer side. This foramen, in some skulls of the Mallard, may be 
formed by the process itself, the latter only reaching the maxillo- 
palatine in part, and the remainder closing in the foramen (No. 4995, 
Coll. U. S. Nation. Mus.). In the Canvas-back, a palatine is straight, 
with both borders smooth, and very slightly enlarged at its anterior 
