406 ON THE SKELETON OE THE MUSK-DTJCK. 



In the Mergansers it is also slender, and almost quadrangular ia 

 section. 



The outer and middle toes are of equal length, as in Tachi/eres 

 and Somateria^ for example. 



In the form of its patella Biziura is unique among the Anseres. 

 This sesamoid is of great size, pyramidal in shape, triangular at 

 its base, and rising into a great crest whose anterior border 

 looks inwards : further, as in the Cormorants, it is traversed 

 by a tunnel for the ambiens. In no other duck is the patella 

 completely'^ssified ; and only in Tacliyeres is there any approach 

 thereto in size, but in this genus it remains fibrous throughout 

 life. 



SUMMAEY. 



Unfortunately the Erismaturinae are represented in the 

 National Collection, in so far as skeletons are concerned, only 

 by a single specimen each of Erismatura jamaicensis and" 

 E. vittata and a sternum of Nomonyx. This fact, and the still 

 immature condition of the skull in the skeleton of Biziura now 

 under consideration, makes any generalization as to the affinities 

 of Biziura^ as indicated by osteological characters, a matter of 

 difiiculty. The genera Erismatura, Thalassiornis, Nomonyx, and 

 Biziura have been placed together by Count Salvadori (Cat. 

 Birds Brit. Mus. vol. xxvii.) in a separate subfamily — the Eris- 

 maturinse. This he places between the Euligulinse on the one 

 hand, and the Merganettinse and Merginse on the other. 



The osteological characters of these groups certainly do not 

 seem to bear out this classification. 



The Erismaturinge should be merged in the Euligulinse, 

 since they are undoubtedly closely allied to the genera Aytliya 

 and Fuligula, and more distantly to Clangula. On the other 

 hand, the genera Tacliyeres, Sarelda, Sistrionicus, (Edemia, 

 Seniconetta, Somateria, and Eriojietta might well be placed 

 together in a separate subfamily — the Somateriinse. They have 

 much in common, and are quite distinct from the Euligulinse. It is 

 open to question whether the Merganettinse should be separated 

 from the Merginse. 



Biziura is primitive in some respects, in the skull foi" example, 

 and highly specialized in others, as in the form of the pelvis 

 and of the hypapophyses of the vertebrse. 



The remarkable gular pouch of this bird was figured and 

 described by Eorbes (P. Z. S. 1882). 



