DUCKS, GEESE, AND SWANS 45 



10. Upper and lower outlines of upper 

 mandible beyond nostril convex. 



Querquedula, p. 5J. 



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. 



6'. 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. (U. 



9'. Feathers ending in point of acute tri- 

 angle on forehead. 

 10. Upper mandible constricted to small 

 nail-like tip. 



Charitonetta, p. w. 

 10'. Upper mandibh> 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 v^thout claw. 



2. Neck as long as or longer tlian body . • Olor. p. <U. 



2 . Neck shorter than body. 



.3. Bill and feet always black . . . • Brantap(.<. 



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



yellowish. «i.-t *.« po 



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



4'. Bill much deeper than wide at bjise. 



5 Depth of l)ill at base nu)re than half the length 



of culmen ; adults mainly white . Chen. p. 60. 



5' Depth of bill at base hss than halt th.- h-ngth of 



culmen ; adults n.-ver white . Aliser, p. bb. 



GENUS MERGANSER. 



General Characters. - Bill slender and appn.xiu.ately ^Nly''^;^-^^^" ^;:^ 

 of n..strils. armed along edges of maud.Ues with sharp, strongh Iecm^ed 

 teeth ; head crested in both sexes. 



KKY TO KrKriK„S. 



1. Nostril »e..- n,i,ldk. of l,in, about .»> fron, '--"-- ^^,j^„„„, ^ 4,,. 

 1'. Nostril ne,u- l.use of l.ill, about .-T, from feathers . aerrator. ,, 4(1. 



