94 MR. R. I. rOCOCK ON THE EXTERNAL 



of either. According to H. 0. Forbes's account, tlie nostrils of 

 Brachyteles seem to resemble those of Alouatta. (Text-fig. 2, 



The nostrils also vary in shape in a very interesting manner. 

 In Callicehus they are practically circular, and nearly so in 

 Gacajao. In Cebus they are longitudinally ovate. In Ateles the 

 upper edge has an ' S '-like curve, the posterior portion of the 

 orifice being a, narrow slit, owing to the presence of the down- 

 wardly projecting lobe which constricts the nostril behind. This 

 lobe is also present in Alouaita, but it is relatively larger in 

 Aot'iis than in any member of the Cebidae. In that genus, indeed, 

 the nostrils with their comparatively nari'ow septum and w ell- 

 developed posterior lobe are of a more primitive type, and more 

 resemble the nostrils of the Strepsirhine Primates (Lemurs) than 

 do those of any genus of the TIaplorhine Primates, including 

 even Tarsius. 



To sum up — the nostrils are typically platyrhine in Hapalidse, 

 CalUmico, Callicehus, Saiiniris, Cebus, Cacajao, Lagothrix, Ateles; 

 and stenorhine in Aotus, Alouatta, and, it is alleged, in Brachy- 

 tdes. 



The Ears. 



In my paper on the genera, of Hapalidaa, the ears of Hapale, 

 Mystax*, Leontocelms, and (Edi pomidas were described, and it 

 Avas pointed out that CEdipomidas may be distinguished by the 

 suppression of the free edge of the pinna from a point just below 

 the level of the upper portion of the antitragal thickening. 



In the Cebidpe the pinna of the ear generally resembles that 

 of the Hapalida?, showing variations in suppression analogous to 

 those of tha,t family. In the majority of cases (J oi»6-, C«ZZ^ce6^^s, 

 Alouatta, Cacajao, Cebus, and Gallimico) the pinna is pi'ovided 

 with a freely projecting laminate margin, which terminates 

 inferiorly just beneath the a-ntitrngal thickening as in all the 

 Hapalida^ except CEdipomidas. 



In the ear of Cebus, which will serve as well as another as 

 typical of the group, the intertragal notch is bordered in front 

 by a comparatively small tragus and behind by a,n enlarged, 

 prominent antitragus, which has a well-developed ridge on its 

 inner surface and is defined behind by a notch from the stiong 

 ridge of the antihelix, which curves upwards and forwards, 

 dividing above into two branches — one, less well-defined, passing 

 forwards and upwards to\va,rds the upper edge of the pinna in 

 front, the other, which runs horizontally forwards, constituting 

 the well-defined and shelf-like supratragus {plica principalis). 

 The anterior end of the supi'atragus is overlapped and concealed 

 by the backwardly folded edge of the antei-o-superior portion of 

 the pinna ; but this backwardly folded e(\ge is cai-ried only a 



* The only example of Hapalidse examined by me since that paper was written 

 was a specimen of Mystax mystax. In this the ear resembles that of M. midas. 



