“Tree-Ducks” of the genus Dendroceygna. 47 
pneumatic. Without doubt this character varies throughout the 
Anseres, not only within the genera, but, as in the case of 
Dendrocygna, even the same species may have it quite different in. 
all respects. 
Prof. Burne’s sketches of the arrangement and character of 
the xiphoidal processes in Dendrocygna are both aceurate and 
interesting. They show that there is always a single pair of 
“notches” present, and the posterior lateral processes thus 
formed are always longer than the middle broad one, the postero- 
lateral angles of which latter may be somewhat produced outward, 
as in Dendrocygna arborea (No. 1434) and Dendrocygna autumnalis 
(454) and 1431 of the Collection of the Royal College of Surgeons 
of England. 
Prof. Burxe’s sketch of the xiphoidal extremity of D. javanica 
(1432) shows that, in that species, the postero-lateral xiphoidal 
processes are both longer and broader than in other species, with 
their distal ends somewhat expanded. 
This character in D. eytoni (1430) my correspondent shows agr ees 
very well with what we find in D. bicolor. 
There is very considerable variation in this matter throughout 
the Anseres; but the variations consist in the relative lengths 
of the lateral processes; the form of the mid-xiphoidal process; 
whether there is a pair of large, elliptical foramina present, or 
a pair of notches, and the form of the distal ends of the processes, 
— that is, whether they are expanded or otherwise. Now very 
decided differences may be found to exist in the same genus; for 
instance, in Aix galericulata there are a pair of elongate elliptical 
foramina present, with a nearly straight transverse xiphoidal border; 
while in Aix sponsa there is a pair of notches present, the mid- 
xiphoidal process is broad, and its postero-lateral angles produced 
as long, sharp projections. The posterior lateral processes are long 
and slender, with their extremities somewhat expanded. This is the 
condition in Aymenolaemus malacorhynchus and other forms. 
Already I have shown, in my Osteology of Birds, that Mergus 
serrator (figs. 3 and 4) has large, elliptical foramina instead of 
notches, which is also true of Olangula islandica (fig. 26), and I can 
now add that it is likewise true of Charitonetta albeola, where the 
foramina are very large and oval, and posteriorly come close to the 
edge of the long, transverse posterior border of the body of the bone 
(No. 16627, Coll. U. S. Nation. Mus.). 
