1865.] DR. J. E. GRAY ON NEW SPECIES OF CEBUS. 825 
There are two good essays on this genus, both based upon the 
collection in the Jardin des Plantes at Paris, which contains the type 
specimens described by the older: French zoologists (viz. MM. I. 
Geoffroy, F. Prevost), and in Pucheran’s ‘ Catalogue Méthodique de la 
Collection des Mammiféres,’ Paris, 1851, and Dr. A. G. Dahlbom’s 
‘Studia Zoologica,’ vol. i. 1856. The latter gives comparative. de- 
scriptions of the species, drawn up in the form of tables. 
I have compared these with the large collection of specimens in the 
British Museum, and believe that the species I have here described 
are not contained in them. 
In stuffed specimens there is to be observed a considerable dif- 
ference in the length and slenderness or thickness of the fingers, and 
at one time I thought this might afford a good character; but I ob- 
served that the fingers of those that are short when adult appeared 
to be longer and more slender in younger specimens, and I am not 
satisfied that part of this difference may not depend on the art of 
the taxidermist. 
I believe that the manner in which the hair is distributed on the 
head is a good character; but this is one which requires careful exa- 
mination ; for the animal-preserver, by carelessness or by design, 
sometimes disfigures specimens in this respect. But the difference 
between natural distribution and disfigurement is easily discovered 
by careful study. 
The greater number of.species have a generic coloration ; that is to 
say, the side of the head, the chest, and the front of the fore legs, 
and often the shoulders and outside of the thighs, are paler-coloured 
than the rest of the body. A few of the species are at once known 
by the distribution of their colours, as C. leucocephalus by its white 
head, chest, and shoulders, all the rest of the body being dark in 
this species ; C. leucogenys, C. cirrifer and C. vellerosus are known 
by their uniform black colour, and C. flavescens by its nearly uniform 
pale yellow ; C. zanthocephalus is known from the others by the yel- 
lowness of the hinder part of the body before the thighs. 
The species in the British Museum may be thus arranged :— 
I. Hairs of the crown reflered, bent back round the face, forming a 
short, erect crest over each eyebrow. Colour uniform. 
1. C. LEUCOGENYs, sp. nov. (PI. XLV.) 
Fur blackish, soft, elongate, silky, with a thick underfur; hair of 
head short, of the circumference of the face reflexed ; cheek and tem- 
ple pale yellow. 
Hab. Brazil. 
Il. Hairs of the crown bent back; those on the sides of the dark 
crown-spot elongate, in the perfect state forming two more or 
less erect crests or tufts. 
2. C. APELLA, I. Geoff., is the hornless, and C. fatuellus, I. Geoff., 
the horned state. 
