10 R. W. SkurkELDT, 
Regarded in its entirety, the skull (including the lower man- 
dible and hyoid arches) in either of these species of Tree-Ducks 
has, in its general aspect, a much closer resemblance to the same 
parts of the skeleton in an average duck, than to the corresponding 
parts in the skeleton of any true swan or goose in existence. The 
truth of this statement will be readily appreciated after comparing 
the skull of Dendrocygna autumnalis, shown in Fig. 12 of Pl. 3, with 
the skull of the swan, figured on Pl. 7 Fig. 40, or the geese on 
Pl. 5 Figs. 24 and 25. 
It is very evident that, in its general facies, the skull of 
the Dendrocygna more closely resembles the skull of such a true 
duck as is shown on Pl. 6 Fig. 32. This is even more apparent 
when we come to turn our attention to such comparisons with re- 
spect to the skulls viewed upon their superior aspects; for example, 
the Dendrocygna skull shown in Fig. 15 of Pl. 4 has a much closer 
general resemblance to the upper view of the skull of the mallard 
shown in Fig. 36 of Pl. 6, than it has to a similar view of the 
skull in any of the average swans or geese. In making such com- 
parisons as these, it would obviously be inadmissible to take into 
consideration the skulls of such ducks as the one shown in Fig. 26 
Pl. 5, or the skull of such a goose as we find in Fig. 17 on Pl. 4. 
The unusual cranial peculiarities of such species mask anything 
that we might hope to gain through such comparisons. 
Regarded upon its superior aspect (Fig. 15, Pl. 4), it is to be 
observed that the cranial vault of the skull in Dendrocygna autum- 
nalis is smooth and rounded, with a median, longitudinal furrow 
moderately indenting it, and carried forward to be lost in the de- 
pression of the fronto-nasal region. 
The superior margins of the orbital peripheries are rounded, 
with the edges thin, though not what migbt be termed sharpened. 
There is a minute backward-extending lacrymal process, and the 
frontal region is somewhat broader here than it is immediately over 
the center of the orbits. The fronto-nasal area is lozenge-shaped 
and considerably depressed. Posteriorly, it merges into the afore- 
said median longitudinal furrow; while anteriorly, it is carried 
forward to disappear on the upper surface of the superior mandible, 
over the anterior arcs of the narial apertures. Here the bridge is 
very narrow, and the superior nasal borders are thickened, especi- 
ally posteriorly. 
The superior mandible is uniformly convex, broadly rounded 
