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 charac- 

 ters 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 over- 

 hung 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 undemonstra- 

 tive 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 



