1871.] DR. J. E. GRAY ON THI, - » DYK!»DIDJE. 439 



Bradypus gularis for what are now considered the males of more 

 than one species. 



Mr. Salvia, in June 1809, informed me that the series of four 

 specimens of A. griseus, which he obtained for the British Museum, 

 were all shot together, and formed one family, consisting of a male, 

 a female, and two young of different ages ; that the male had a yel- 

 low patch with a black central streak on the back, which was not 

 present in the female and young. This observation induced me to 

 examine the other specimens in the Museum which have the yellow 

 patch on their backs ; and I am satisfied that they belong to two 

 species, which agree in all the characters, except the patch, with 

 the two species that I had named Arctopithecus marmoratus and 

 Arctopithecus blainvillei ; and therefore I have come to the con- 

 clusion that they are the males of those species. One cannot be 

 certain, because the sex of the specimens cannot be determined in 

 the skins as they are in the Museum, and the travelling naturalists 

 wbo collected them have not taken the trouble to mark the sex to 

 which they belonged. I thiuk this idea is confirmed, that all the 

 young specimens which I have seen are like what are here regarded 

 as females, and perhaps the patch does not appear until the animal 

 reaches nearly adult age. The under-fur is generally abundant, very 

 soft. It is white or black, like the base of the longer hair. It seems 

 to be more abundant in the species with long flaccid hair, which 

 generally have grey tips to the hair, and shortest and least abundant 

 in A. cuculliger, which has shorter and more rigid hair, and is rather 

 sooty-coloured. 



Cuvier, in the ' Ossemens Fossiles,' v. t. 6, 7, figured the skeleton 

 and skull of this genus, A. problematicusl 



Blainville, in his ' Osteographie,' figures the skulls of two animals ; 

 one he calls B. tridactylus brasiliensis, and the other B. tridactylus 

 guianensis, differing in the hinder part of the lower jaw. 



In my paper in the ' Proceedings' 1849, I pointed out that the 

 hinder part of the lower jaw seemed to afford very good characters 

 for the separation of the species, and figured this part from several 

 specimens. 



The species may be arranged according to the skull thus (and I 

 have found them subject to little or no variation in general form, and 

 change little in growth) : — 



1. Skull: nose rather elongate, narrow; lower jaw elongate, shal- 



low, the hinder angle much produced. — A. cuculliger, A. mar- 

 moratus. 



2. Skull : nose rather elongate, narrow ; angle of lower jaw rather 



produced, broad. — A. problematicus. 



3. Skull: nose very short, broad; angle of lower jaw produced, 



broad. — A. boliviensis, A. flaccidus, A. griseus, A. castaneiceps. 



4. Skull: nose very short, broad; angle of the lower jaw scarcely 



produced, very broad. — A. blainvillei. 



In this and my other paper of the kind I have only paid attention 

 to the zoological characters of the skulls, and not preferred to 



