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84 BULLETIN 133^ UNITED STATES NATIONAL MUSEUM
The trachea, proceeding from above, was soft for the upper half,
below which it was hardened and firm for the space of 15 mm. ; ap-
parently the rings tended here to ossify. At this point the trachea
broadened gradually, and became again thin walled, until it reached
a diameter of 12 mm., when it contracted slowly until at the level
of the shoulders it was once more of normal breadth. There was no
bulla ossea.
On examining the freshly killed bird, I found that the skin of
the throat hung in a loose fold that began below the line of the
eye. In skinning this specimen it was noted tliat the neck was large,
so that the skin passed readily over the head.
The black-headed duck is a species of somewhat uncertain affini-
ties that requires more detailed anatomical study before its position
may be definitely laiown. The lack of a broad lobe on the hind toe,
the somewhat weakened form of the bill, and small feet are characters
that assign it to its present position in the subfamily Anatinae
near the freckled duck Stictoiietta naevosa. In the full, loose skin
of the neck, development of special, distensible sacs about the head
in the male, small wings, glossy, shining plumage, and lack of a
bulla ossea it suggests the Erismaturinae, a group from which
Ueteronetta differs, however, in lack of a lobed hind toe, small feet,
presence of an enlargement in the center of the trachea, and elon-
gated upper tail coverts. It is possible that the characters that ally
it with the latter group are due to convergent evolution, as the duck
in habits is similar to the ruddies. For the time it may be left in
its present position.
ERISMATURA VITTATA Philippi
Erismatura vittata Philippi, Wiegmann's Arch, fiir Naturg., 1860, pt. 1,
p. 26. (Chile.)
The small southern ruddy duck, though widely distributed, seems
to be rather rare in occurrence, as it was seen only in northern Pata-
gonia near General Koca, in the Territory of Hio Negro. The birds
were found in channels and long lagoons bordering the main stream
of the Rio Negro, where the water, though often deep, had slight
current, and was in places bordered by clumps of cattails or overhung
by low willows. A pair seen on November 27, 1920, were evi-
dently nesting, but the majority of the birds observed were males
that seemed to have completed breeding for this season. Frequently
three or four were found in compMiy swimming with heads drawn
in and spread tails held up at an angle. They were undemonstrative
save when occasionally one swam out to jerk the head up and
down two or three times, a custom common among males of many
ducks. A breeding male secured on November 27 was in full plum-
age, though the rectrices showed wear and in part were faded in