CHARACTERS OF THE SOUTH AMERICAN MONKEYS. 97 



and the ridge of the antihelix being well developed, (Text-fig. 3, 

 G, H.) 



In Lagothrix the ear shows similar suppression of the lower 

 half of the margin of the pinna ; but the upper portion is also 

 i-educed and stands away from the head to a comparatively small 

 extent, being fleshy and thickly covered with hairs. (Text- 

 fig. 3, I.) 



By the structure of the ear, therefore, the genera of Cebidse 

 fall into two groups: — (1) comprising Ateles and Lagothrix, in 

 which the inferior portion of the pinna has no freely projecting 

 laminate margin ; (2) comprising Alouatta, Cacujao, Saimiris, 

 Callicebics, Cebus, and Callimico, in which the free laminate 

 margin extends right round the pinna inferiorly to a point below 

 the intertragal notch. 



Dr. Boas (Ohrknorpel etc. der Siiug. 1912, pp. 199-206, pi. 23) 

 describes and figures the ears of several species of Cebus, of 

 Alouatta, Ateles, Samiiris, Mystax,_ and HajKile. So far as my 

 observations on these genera extend, they agree completely with 

 those of Dr. Boas. 



The Hands and Feet. 



In a paper upon the genera of Hapalidse or Marmozets (Ann. 

 Mag. Nat. Hist. (8) xx. p. 249) I pointed out that the hands 

 and feet of Leontdcehus difl;er from those of Hapale, Mystax, and 

 (Edipomidas in the elongation of the palm and sole, and that the 

 hand further diflfers in the presence of webs tying the second 

 digit to the third, and the third to the fourth, the latter web 

 being of considerable depth, so that the two digits in question are 

 only separable from a distance a little on the proximal side of the 

 joint between the first and second phalanges. 



I have since found that this chaiacter does not always hold, for 

 in an example of Mystax mystax, subsequently examined, I found 

 the third and fourth fingers of the right hand webbed almost to 

 the same extent as in Leontocebus ; while the left hand hardly 

 difl[ered in that respect from the hands of examples of other 

 species of Mystax, and of all specimens of Hapale and of (Edipo- 

 midas examined. In this connection it is interesting to recall 

 that W. A. Forbes recorded in the case of Pithecia satanas a 

 similar abnormal instance of intei'digital webbing, the third and 

 fourth digits of both hands being tightly tied together to the 

 bases of the claws (P. Z. S. 1882, p. 442). 



The hands and feet of the HapaJidte differ from those of all the 

 other South American Monkeys, except Callimico, in two partic- 

 ulars : — (1) The hallux is extremely reduced in size, so that when 

 it is turned forwards its apex falls short of the distal margin of 

 the plantar pad ; (2) the nails of all the digits, except the hallux, 

 are converted into strongly compressed, curved, pointed claws like 

 those of a Squirrel. The capacity of these claws for maintaining 

 a secure hold on the rough bark of trees compensates for the loss 

 of grasping power in the foot, due to the feeble development of 

 Proc. Zool. Soc— 1920, No. VII. 7 



