NORTH AMERICAN BIRDS. 
f}. Bill eylindrical or compressed at base, where not broader 
than deep. 
g'. Partition between nostrils very thin (very much nar- 
rower than width of a single nostril), entirely 
within the nasal tubes. 
i. Gonys very slightly or not at all concave, the tip 
not distinctly decurved ; nasal tubes decidedly 
longer than gonys... Fulmarus. (Page 57.) 
#2, Gonys very strongly concave, the tip distinctly de- 
curved ; nasal tubes not decidedly longer (usu- 
ally shorter) than gonys (except in Bulweria). 
@. Depth of bill at shallowest part more than 
one-fourth the length of the lower man- 
dible, measured along the side. 
j. Tail more or less graduated, and without 
white tip. 
. Tail less than half as long as wing, 
and graduated for less than one- 
third its length ; cutting-edge of 
lower mandible decidedly: con- 
cave; nail of lower mandible oc- 
cupying at least one-third the 
total length of the mandible, 
measured along its side; plu- 
mage and size very variable. 
4Estrelata. (Page 63.) 
k’, Tail more than half as long as wing, 
and graduated for more than 
one-third its length; cutting- 
edge of lower mandible straight, 
or very slightly concave; nail 
of lower mandible occupying de- 
cidedly less than one-third the 
total length of the mandible, 
measured along its side; color 
uniform dusky ; wing about 8.00. 
Bulweria. (Page 69.) 
f. Tail slightly rounded, and with a distinct 
white tip. 
Cutting-edge of lower mandible 
straight, and nail of lower man- 
dible occupying less than one- 
third its total length, as in Bul- 
weria; plumage bluish above, 
and on sides of chest, the lower 
