ANATIDiE — THE SWANS, GP:ESE, AND DCCKS. 105 



0^ . Distance from anterior end of nostril to tip of bill much grreater 

 than from same point to loral feathers; tail more than twice aa 

 lone as tarftus. 



11. Charitonetta. (Page 170.) 



p. Distance from anterior end of nostril to loral fotithering much less 

 than width of bill at base. 



a. Distance from i)OSterior end of nostril to loral feathers equal to 

 or greater Ihan length of nostril; anterior outline of loral 

 feathering strongly convex. 



12. Hifltrionicus. (Page 171.) 



a'. Distance from ante' ior end of nostril to loral feathers less than 

 half the length of the nostril; anterior outline of loral feather- 

 ing forming a nearly straight line, running obliquely backward 

 and downward from near nostril to corner of mouth. 



13. Clangnla. (Page 173.) 



c'. Distance from tip of bill to loral feathers greater than graduation of 

 tail. 



14. Oidemia. (Page 179.) 



c^ Feathering of forehead or lores reaching anteriorly to or beyond posterior 

 end of nostril. 



15. Somateria. (Page 175.) 



Tail abnormal, its feathers narrow, with very stiff shafts, their base scarcely hidden 

 by the very short coverts. 



16. Erismatura. (Page 184.) 



Subfamily MERGIN-ffi.— The Mergansers. 



A. Serrations of mandible conspicuously tooth-like, and strongly inclined backward at 



tips. 

 17. Merganser. (Page 187.) 



B, Serrations of mandible short, blunt, and not distinctly inclined backward at tips. 

 18. Lophodytes. (Page IW.) 



Subfamily CYGNIN-aE.— The Swans. 

 Genus OL.OR Wagler. 



Olor Wagl. Isis, 1S32, 1234. Type, Anas cygnus LiNN. 



Gen. Chab. Neck very long (longer than the body); bill longer than the head (com- 

 missure longer than the tarsus), widening slightly to the end, the edges straight ; basal poi^ 

 tiou of the bill covered by a soft skin extending over the lores to the eye, the upper outline 

 running nearly straight back from the forehead to the upper eyelid, the lower runningfrom 

 the eye obliquely downward, in a nearly straight line, to the rictus. Nostrils situated a little 

 posterior to ihe middle of the maxilla, and quite near the culmen; no trace of a knob or 

 caruncle at base of the bill. Lower portion of the tibia bare ; tarsus much shorter than the 

 middle toe (but little longer than the inner), much compressed, covered with hexagonal 

 scales wliich become smaller on the sides and behind. Hind toe small, much elevated, the 

 lobe narrow. Tail very short, rounded or graduated, of 20 to 24 feathers. Wings rounded, 

 the second and third quills longest; primaries scarcely reaching beyond the ends of the 

 secondaries. Color entirely white, the sexes alike ; young pale grayish. 



The two North American species of Olor may be readily dis- 

 tinguished by the following chai'aoters: 

 —14 



