On Neotropical Mammals. 161 



where custom docs not confine the feet in coverings, the 

 human foot retains a certain amount of its prehensile power. 

 In the ape the foot is far superior to tiie hand as a prehensile 

 organ, for not only is the hallux better developed than the 

 pollex, but it has much greater power to oppose the other 

 digits. Grasping and progression in animals of arboreal 

 habits are to some extent synonymous. In the human foot 

 the hallux is so bound up with the rest of the foot that it is 

 practically incapable of any independent action. 



References. 



[i] 'Anatomical Memoirs of John Goodsir.' Vol. I. Edited by W. 



Turner. 

 [2] ' Journal of Anatomy and Physiology,' 1893. 



EXPLANATION OF PLATE V. 



i^i'y. 1. A, hand, B, foot of Ilylohates ayilis, to show the arrangement of 

 the creases. Owing to the hook-like position of the hand, the 

 finger-tips are out of focus. 



Fig. 2. Skin from the palmar aspect of the fingers, to show the chevron- 

 like arrangement of the fine lines. 



XXVI. — On JSeotropical Mammals of the Genera Callicebus, 

 Keithrodontomys, Ctenomys, Dasypus, and Marmosa. By 

 Oldfield Thomas. 



Callicehus pallescens, sp. n. 



Allied to C. donacophilus, d'Orb., with which it shares the 

 greyish-white hands, feet, and tail, but the head and body are 

 almost of the same pale colour, so that the whole animal is 

 one of the palest and most uniformly coloured species of the 

 group. 



Size very small. Fur thick and soft; the longer hairs of 

 back about 60, the shorter 35 mm. in length. General 

 colour of body ])ale greyish, suffused with pinkish buff j the 

 long hairs indistinctly ringed with whitish and black, the 

 underfur pinkish buff for its terminal half, its ba.sul half dark 

 brown. Under surface and inner side of limbs rufous, rather 

 paler than in C. donacophilus. Head rather yellower than 

 back, owing to the hairs being tipped with yellow, but the 

 difference is not conspicuous. Aluzzle and lips whitish. 

 Hands and feet greyish white. Tail also greyish white, but 

 the hairs inconspicuously ringed with blackish. 



Anfi. cD Ma^. lY. IJiSt. Ser. 7. Vol. xx. 1 1 



