824 DR. J. E. GRAY ON NEW SPECIES OF CEBUS. [Dec. 12, 
of the wings is decidedly more conspicuous in that species than in 
C. wolfi. 
In the specimens before me the middle feather of the tail bears 
one transverse mark near its base in C. wolfi, whereas the corre- 
sponding feather bears four such marks in C. maillardi. In each 
species there is also a single mark near the end of the feather; 
but both this and the markings on the upper portion of it are 
much more distinct in C. maillardi than in C. wolfi. The shaft- 
markings on the throat in C. wol/fi are browner than in C. mail- 
lardi, and on the breast and abdomen they are not only browner 
but also broader, extending in C. wolfi to the under tail-coverts, 
which in C. maillardi are of a pure white. 
The inner side of the primaries in C. maillardi are a pure white 
near their base, the remainder being black. In C. wolfi the basal 
parts are yellowish white, and the remainder of the underside of 
the primaries are of a pale slate-colour, crossed with narrow bars of 
a darker slate-colour at intervals of about an inch, the tips of the 
feathers being also dark. 
The young male of C. wolfi resembles C. maillardi in a similar 
state, but is not so dark in its plumage, and is more rufous in the 
region of the abdomen, in which it resembles the young male of 
Circus assimilis. 
14, Notices oF soME APPARENTLY UNDESCRIBED SPECIES OF 
Sapasous (Cesus) 1N THE COLLECTION OF THE BRITISH 
Museum. By Dr. Joun Epwarp Gray, F.R.S., V.P.Z.S., 
F.L.S., Etc. 
(Plate XLV.) 
The distinction of the species of the American Monkeys is very 
difficult, and perhaps the genus Cebus the most difficult of all. Next 
to the difficulty of distinguishing them is that of determining the 
names which have been applied to them by different authors, and 
(what ought not to be the case) the determining of the figures, given 
by Spix and others, representing the species under consideration. 
This mainly arises from the great variation of colour that the 
specimens of the same species present. 
The difficulty has also been increased by the works of compilers 
like Lesson and Wagner, who depend on the descriptions of authors 
without having the opportunity of examining species to correct their 
theories, and yet venture to decide what are species and what varieties : 
and the result shows how dangerous it is for compilers to venture 
to go beyond the author from whom they copy. 
M. Isidore Geoffroy has shown that Cedz when in confinement, 
especially in a dark place, become bleached; and he believes that 
specimens so decolorated have often embarrassed zoologists and led 
them into error (Castelnau, ‘ L’Amér. du Sud, Mammiféres,’ p. 10, 
note). 
ide on 
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