Vo1 ' llfo^ 11 ] Brooks, Notes on American Ducks. 363 



Those relating only to adult males are disregarded as these 

 can be separated by any one without difficulty. 



1. Nail. A mericana— Nail flattened or depressed, not conspicuously 

 raised above the contour of the bill when viewed from the side, and not 

 arched in its transverse section towards base. 



Length of nail, c? , less than .46 in., longest .44, shortest .38, average 

 .406; 9 , less than .40, average .37. 



Islandica — Nail arched in both longitudinal and transverse sections, 

 showing as a conspicuous hump above the contour of the bill. 



Length of nail, d\ over .46, longest .53, shortest .48, average .508; 

 9 , over .40, longest .46, shortest .41, average .43. 



2. Shape of bill. Americana— Bill not conspicuously tapered when 

 viewed from above. 



Width at a point through anterior angle of nostril, c? , over .69, widest 

 .82, narrowest .70, average .74; 9 , over .60, average .69. 



Islandica — Bill conspicuously tapered, width taken as above, c? , less 

 than .69, widest .68, narrowest .63, average .65; 9 , less than .60, widest 

 .59, narrowest .55, average .57. 



3. Color of head in 9 • A mericana— "Hair brown or grayish amber." 

 Islandica — "Deep sepia or purplish snuff brown." (Ridgway.) 



4. Shape of Skull. Americana — Frontals continuing the slope of cul- 

 men, without trace of a bulge. 



Islandica — Frontals conspicuously bulging in adult males, hardly less 

 so in immature males of second year, bulge distinctly noticeable to the 

 touch in adult females, and faintly so in juvenals. 



Something might be made out of the amount of black at base 

 of greater coverts. This is decidedly more in islandica, usually 

 showing beyond the overlap of the lesser coverts, and sometimes 

 covering the entire feather. In young males commencing to show 

 the white cheek patch a crescentic formation is sometimes ap- 

 parent in americana, this is due to the fact that the white feathers 

 commence to come in along the edge of the bill, following the 

 curve of its base, but it may be noted that this crescent is con- 

 fined to the lower portion of the bill, in islandica it continues up 

 to the mental angle, even in its first stages. 



The diagrams of bills appended are drawn from dried speci- 

 mens, as this will be the condition of most of the birds to be com- 

 pared with them. 



The tomia is apt to roll up and enclose the under mandible 

 in drying, sometimes more on one side than the other, giving the 

 bill a lop-sided appearance. 



