DUTCH BORNEO-EXPEDITION. 175 
eyebrow; a young, not yet fullgrown female with white 
bill and casque, which latter is but faintly developed, and 
ashy gray eyebrow, and moreover what I should call 
a nearly adult female (the sex is thoroughly stated) with 
black bill and casque, and hardly any trace of a gray 
superciliary stripe, and the naked skin round the eye and 
at the base of the lower mandible dark flesh-color (N° 1392 
from Poelau), and an adult female (N° 78) from the Upper 
Mahakkam, with black bill, well-developed black casque 
and very distinct gray superciliary stripe. — Iris in adult 
and young birds of both sexes reddish brown, bill in adult 
males yellowish white with black basal edge, in the adult 
female black, in young birds of both sexes white; feet 
dark greenish gray. 
Salvadori, in his Uccelli di Borneo, followed Blyth and 
others in separating the black-billed birds as a distinct 
species, a supposition which is followed by Vorderman in 
his above quoted contribution to the Ornithology of Sumatra. 
I cannot agree with this supposition, but yield to the 
opinion of Schlegel’s who, in his Catalogue of the Bucerotes, 
p. 7, considers the black-billed birds the adult females of 
Buceros malayanus, and the white billed adult birds as the 
males, while young birds of both sexes should have the 
bill white. This latter supposition is not in contradiction 
with the four young birds in the Leyden Museum, which 
all have the bill white. Mr. Grant, in his Catalogue of the 
Bucerotes in the British Museum (Vol. XVII, p. 369) seems 
not to agree with the opinion of Schlegel’s, as he says 
that the only difference between male and female is to be 
found in the color of the superciliary stripe, which should 
be white in the male and gray in the female. The black 
bill is considered by him to indicate a transitional stage 
of immaturity to be found in both sexes, while young birds 
of both sexes should have white bills. As to the supposi- 
' tion of the black bill being representing a stage of imma- 
turity, I cannot agree with Mr. Grant, nor can I consider 
the color of the superciliary stripe as a characteristical of 
Notes from the Leyden Museum, Vol. XXI. 
