1883.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 245 



In the first place, its body is relatively much shorter for Its width than 

 it is in those Ducks, while in front the manubrial process has entirely 

 disappeared. Again, the costal processes are loftier and more conspic- 

 uous The xiphoidal extremity of the bone is very broad and is pierced 

 well within its hinder margin, on either side, by an elliptical foramen, 

 as shown in Fig. 26, where it will also be observed that the carina does 

 not extend the entire length of the sternal body, but stops short at the 



Fig. 26. Pectoral aspect of sternum of Glaucionetta islandica; life size. From a specimen in the col- 



lection of the author. 



middle point of a raised line, that, being produced as it is, is tangent 

 to the posterior arcs of the xiphoidal fenestra?. 



The muscular lines take about the same course as they do in Spatula, 

 with the exception that their posterior ends are inclined inward rather 

 than outward, as in the form mentioned. 



This form of sternum agrees in many particulars with the bone as we 

 find it in Mergus, though in the Eider Ducks, as I have elsewhere 

 pointed out, the xiphoidal extremity is deeply two notched. 



Such differences certainly are significant, and must be awarded their 

 due share of weight in the search for affinities among the several forms 

 of this order, and it will be interesting to find with what similar char- 

 acters they are associated. , 



Another engaging subject in the anatomy of the Anatidce is the study 

 of the various" forms taken on by the osseous labyrinth at the biturea- 



