DUCKS, GEESE, AND SWANS 45 
10. Wing more than 8 . . Anas, p. 47. 
10'. Wing less than 8. 
11. Upper and lower outlines of upper 
mandible beyond nostril convex. 
Querquedula, p. 52. 
11'. Upper and lower outlines of upper 
mandible beyond nostrils straight. 
Nettion, p. 51. 
6'. Hind toe with a flattened membraneous lobe. 
7. Graduation of tail less than length of bill 
from nostril .... Aythya, p. 56. 
7'. Graduation of tail much more than length 
of bill from nostril. 
8. Anterior edge of nostril in front of middle 
of culmen .... Clangula, p. 59. 
8'. Anterior edge of nostril back of middle of 
culmen. 
9. Upper mandible widest back of nostril, 
and not conspicuously elevated nor 
swollen at base. 
10. Feathers ending in straight line across 
forehead . . . Harelda, p. 61. 
10'. Feathers ending in point of acute tri¬ 
angle on forehead. 
11. Upper mandible constricted to small 
nail-like tip. 
Charitonetta, p. 60. 
11'. Upper mandible rounded at tip. 
Histrionicus, p. 61. 
9'. 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. Bill and feet always black .... Branta, p. 67. 
2'. Bill and feet never entirely black, usually reddish or 
yellowish. 
3. Bill as wide as deep at base . . Philacte, p. 69. 
3'. Bill much deeper than wide at base. 
4. Depth of bill at base more than half the length 
of culmen; adults mainly white . Chen, p. 65. 
4'. 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. 
