680 MR. R. I. roCOCK A REVISION OF [June 18, 



jnaaiy cases to leave unsatisfactorily settled, is tlie decision as to the 

 status, whether specific or subspecific, that sliould be given to 

 certain forms. This is an extremely difficult point, and one about 

 which probably no two authors will agree. I suspect that most of 

 my present day colleagues w^ill think that I have been too lavish 

 witli subspecies, and will consider that the higher rank should 

 liave been assigned to them in most cases. Personally, I doul)t if 

 in all instances I have gone c|uite far enough in reducing species 

 to subspecific level. These, however, are relatively unimportant 

 points which futui-e investigation alone can settle. 



An interesting phenomenon connected with the coloration of 

 the species of this genus is the frequency of the interchange of the 

 three colours white, red, and black. For example, in C. erythro- 

 gaster the nose is said to change from black to white cUu-ing 

 growth. In C. patas I have reason to think that the lips, and in 

 some cases the nose, turn from black to white and the limbs from 

 red to white a,s age advances. In C. sdaterl the nose-spot is white; 

 in C. erythrotis it is red. In C. hurnetti the belly is white ; but 

 in the closely related C. grayi it is j^ellowish red. In C. petaurista 

 a,lso it is white, but in C. erythrogaster it is red. In C. kandti 

 the underside is red ; in C. le%iccmvpyx it is black. In C. diana 

 the thighs are rusty-red inside ; in C. roloway they are white or 

 yellow. In C. cepluis the tail may be red or coloured like the back. 

 Similar phenomena may be observed in the coloui- of the hairs on 

 the eai' in closely related species ; and the brow-band similai'ly 

 may be black, white, or red. 



The material I have had at my disposal has been the skins in 

 the collection of the Society and the examples living in the Gardens 

 during the past four years, most of which were deposited for 

 scientific work of this kind by the Hon. Walter Rothschild. I 

 cannot overestimate the help these specimens have been to me ; 

 ;t,nd my thanks are due to Mr. Rothschild for allowing me to make 

 full use of them. I am also greatly indebted to Sir Ray Lankester 

 and Mr. Oldfield Thomas for lending me the invaluable collection 

 of skins in the British Museum, and especially to Mr. Thomas for 

 giving me the freest possible access at all times to the collection 

 under his charge. Without this privilege and help my under- 

 taking would have been ten times more difiicult, perhaps indeed 

 quite impossible. 



The two most recent monogiuphs of this genus were those 

 by Dr. P. L. Sclater in the ' Proceedings' of this Society for 1893, 

 pp. 243-258, and by Dr. H. O. Forbes in Allen's Nat. Libr., 

 Monkeys, ii. pp. 41-83, 1894. Since that date a, considerable 

 number of species have been added, principally by Dr, Matschie, 

 Dr. Neumann, and Mr. Oldfield Thomas. References to the 

 literature relating to these will be found incorporated in the text 

 that follows. 



