O22 Mr. J. H. Gurney’s Notes on 
Mr. Ridgway, in a letter which he was so good as to write 
to me respecting it, says, “the bill is pale greenish yellow, 
not black or dusky, like R. uncinatus.”’ 
In Cassin’s original description of this species, in the 
‘Journal of the Academy of Natural Sciences of Phila- 
delphia,’ ser. 2, vol. i. pp. 21, 22, it is said that the bill is 
« yellowish white, inclining to bluish horn-colour at the base,” 
and the iris ‘‘ greenish yellow.” 
The following particulars relating to this subject are given 
by Gundlach in the ‘Journal ftir Orn., vol. 1. p. 77:— 
“ Bill light horn-colour; cere light green, with some few 
yellowish places; legs pale orange-yellow ; eyes bluish 
white.” 
Judging from Cassin’s article above referred to, and one 
by Ridgway at p. 159 of his ‘Studies of the American Fal- 
conid, it would seem that the transitions of plumage in 
R. wilsoni, so far as they are known, much resemble those of 
the other two species of the genus Regerhinus. 
I may now pass on to the genus Leptodon, which, as I have 
already mentioned, contains but a single species, L. cayen- 
nensis. 
The adult plumage of this species has long been well 
known ; it was figured by D’Aubenton in the ‘ Planches Enl.’ 
pl. 473, and by Spix in the ‘ Av. Bras.’ pl. 8; it is also suffi- 
ciently described in Mr. Sharpe’s volume. 
Younger specimens exhibit considerable variations of plu- 
mage, which require more detailed attention. The youngest 
I have examined is one from Demerara in the British Mu- 
seum—a newly flown nestling, in which the quill-feathers of 
the wings and tailare still encased, at the base, in the sheaths 
indicative of that age. In this specimen the following parts 
are pure white, viz., the entire head (excepting a very nar- 
row black mark immediately above the eye, which is pro- 
longed for a short distance behind it, and excepting also the 
feathers in the central part of the crown, which have shaft- 
marks and centres of a rather dark brown), the nape, the 
upper interscapulars, and the entire under surface, including 
the under wing-coverts; the mantle and the wings are dark 
