104 BIRDS OF ILLINOIS. 



SUBFAMILY CYGNIN-aS. THE SWANS. 



1. Olor. iThejlargest of the American Anatidce (total length more than three feet); color 

 of the plumage entirely pure white in adults, grayish in young. (Page 105.) 



SUBFAMILY ANSERINE. THE GEESE. 



A. Serrations on cutting-edge of upper mandible visible from the outside through a con- 



spicuous "grinning space;" bill and feet light colored. 



2. Chen. Bill very stout, its depth through the base eaual to much more than half 



the length of the culmen; color of adults white, with blackish primaries, or else 

 with head and part of neck white, the wing-coverts bluish gray. (Page 110.) 



3. Anser. Bill weaker and more depressed, its depth through the base less than 



half the length of the culmen; color never white, nor with white head, nor 

 with bluish gray wing-coverts. (Page 115.) 



B. Serrations on edge of upper mandible visible only near the angle of the mouth, the 



sides of the bill without "grinning space ;" bill and feet blackish. 



4. Branta. Head partly or wholly black; upper and under tail-coverts white. 



(Page 118.) 



SUBFAMILY ANATIN-ffi. THE DUCKS. 



A. Lores densely feathered. 

 a. Tail normal. 



b. Hind toe without a distinct membranous lobe or "flap." 

 c. Bill not spatulate. 



d. Tail-feathers narrow and pointed at tip. 



e. Tail graduated for less than one third its total length (or else consist- 

 ing of only 14 feathers) and culmen shorter than middle toe without 

 claw. 



5. Anas. (Page 126.) 



f '. Tail graduated for more than one third its total length, consisting of 

 16 feathers, and culmen longer thau middle toe, without claw. 



6. Dafila. (Page 146.) 



d 1 . Tail-feathers broad and rounded at tips. 



7. Aix. (Page 152.) 



c 1 . Bill spatulate (much widened toward the end). 



8. Spatula. (Page 150.) 



h l . Hind toe with a broad membranous lobe or "flap." 



c. Feathering on lores or forehead not reaching beyond posterior border of 

 nostril. 

 d. Graduation of tail less than length of bill from nostril. 



9. Aythya. (Page 156.) 



d 1 . Graduation of tail much more than length of bill from nostril. 



e. Distance from tip of bill to loral feathering less than graduation of tail. 

 /. Distance from anterior end of nostril to loral feathers equal to or 

 greater than width of bill at base. 



Q. Distance from anterior end of nostril to tip of bill much less 

 than from same point to loral feathers; tail less than twice as 

 long as tarsus. 

 10. Glauoionetta. (Page 165.) 



