DUCKS, GEESE, AND SWANS 45 



10. Upper and lower outlines of upper 

 mandible beyond nostril convex. 



Querquedula, p. 52. 

 10'. Upper and lower outlines of upper 

 mandible beyond nostrils straight. 

 Nettion, p. 51. 



5'. Hind toe with a flattened membraneous lobe. 

 6. Graduation of tail less than length of bill from 



nostril Aythya, p. 56. 



G'. Graduation of tail much more than length of 



bill from nostril. 

 7. Anterior edge of nostril in front of middle of 



culmen Clangula, p. 59. 



7'. Anterior edge of nostril back of middle of 



culmen. 



8. Upper mandible widest back of nostril, 

 and not conspicuously elevated nor swol- 

 len at base. 



9. Feathers ending in straight line across 

 forehead .... Harelda, p. 01. 

 9'. Feathers ending in point of acute tri- 

 angle on forehead. 



10. Upper mandible constricted to small 

 nail-like tip. 



Charitonetta, p. 60. 

 10'. Upper mandible rounded at tip. 



Histrionicus, p. 61. 



8'. Upper mandible widest at anterior edge 

 of nostril, and elevated or swollen at 

 base (except in female and immature 

 O. americana) . . Oidemia, p. 62. 



1 . Tarsus as long as or longer than middle toe without claw. 

 2. Neck as long as or longer than body . . Olor, p. 70. 

 2 . Neck shorter than body. 



3. Bill and feet always black .... Branta, p. 67. 

 3'. Bill and feet never entirely black, usually reddish or 



yellowish. 



4. Bill as wide as deep at base . . Philacte, p. 69. 

 4'. Bill much deeper than wide at base. 



5. Depth of bill at base more than half the length 



of culmen ; adults mainly white . Chen, p. 65. 



5'. Depth of bill at base less than half the length of 



culmen ; adults never white . Anser, p. 66. 



GENUS MERGANSER. 



General Characters. -- Bill slender and approximately cylindrical in front 

 of nostrils, armed along edges of mandibles with sharp, strongly recurved 

 teeth ; head crested in both sexes. 



KEY TO SPECIES. 



1. Nostril near middle of bill, about .50 from feathers. 



americanus, p. 46. 

 1'. Nostril near base of bill, about .25 from feathers . serrator, p. 46. 



