482 PROCEEDINGS OF THE NATIONAL MUSEUM. 



extended with a series of short jerks as the male called tick-tick- 

 quo-ack. At the last note the hill opened widely and the head was 

 thrown forward, and then immediately withdrawn to the first posi- 

 tion, when the display continued as before. 



There is little question that similar air-sacs will be found upon 

 examination in other species of the genus Erismatura as recognized 

 at present. KeiT* in describing the courtship of E. vittata (wit- 

 nessed near Buenos Aires, Argentina) says that at one stage the male 

 ''stretches out his neck on the surface of the water right in front of 

 him, and then ruffles up the feathers of his neck and inflates Ms crop 

 [italics mme] until his neck seems to disappear altogether." And 

 Bennett 2 writmg on E. australis says that this species has habits 

 identical with those of E. vittata as described by Kerr ^ "even to the 

 peculiar manner of courtship adopted by the male bird." From 

 examination of study skins of males of other species of ducks in the 

 collections of the United States National Museum, that are placed 

 now in the anatme subfamily Erismaturinae, it is expected that 

 tracheal air-sacs similar to that described in the male ruddy duck 

 may be found. The additional species seen are: 



Thalassornis leuconotus (Smith). 



Thalassornis insularis Kichmond (female only seen) . 



Nomonyx dominicus (Linnaeus) . 



Erismatura leucocepMla (ScopoU). 



Erismatura ferruginea Eyton. 



All these species have the skin of the neck full and loose so that in 

 no case was there a slit made aroimd the head by the collectors who 

 prepared the birds. In addition the skin on the necks of these birds 

 beneath the feathers is thick and leathery to the touch as though 

 underlaid by heavy dermal muscle. 



It is worthy of note that m the species of ducks at present 

 known to have no dilation of the syrinx in the males some other 

 peculiarity of the trachea or mouth is present. According to Forbes^ 

 in Biziura lohata there is a small distensible sac contained in a loose 

 gular fold of skin with its opening in the mouth anterior to the fraenum 

 linguae. In Oidemia nigra the trachea and the bronchi of the male 

 are both somewhat dilated. Oidemia fusca has a remarkable swelling 

 below the larynx contaming a separate chamber communicating by 

 two slits with the trachea. The peculiarities of Erismatura jamai- 

 censis are described in this paper. 



1 Kerr, J. G., Extracts from letters of, Ibis, 1890, p. 360. 



2 Beiinett, K. H., Letter from. Ibis, ISOl, p. 143. 



8 Forbes, W. A., Collected Scientific Papers, 1885, pp. 355-356. 



