96 MR. R. I. POCOCK ON THE EXTERNAL 



supratragus. The upper edge of the pinna is always folded ; 

 but the posterior edge may be unfolded, partly folded, or folded 

 throughout its extent. In the latter case the fossa behind the 

 antihelix is especially well defined. Sometimes the upper edge 

 of the pinna shows an angular projection, sometimes it is evenly 

 rounded ; but I have not worked at the variation of the ears 

 with a view to their possible systematic value in the determination 

 of species. (Text-fig. 3, A,) 



The ear of a specimen of Alouaita resembles that of Cebus, 

 except that the antitragus is less well developed and the semi- 

 circular fossa behind the ridge of the antihelix does not extend 

 so fa,r beneath the antitragus. The entire edge of the pinna is 

 folded. (Text-fig. 3, F.) 



In a specimen of Aotus the shape of the pinna recalls that of 

 Mystax. The antero-superior portion of the edge is the only 

 part that is folded. There is no definite fossa behind the ridge 

 of the antihelix except iuferiorly behind the massive antitragal 

 thickening. The posterior edge is convex below, concave above. 

 At the summit of the concavity it runs out into a short, obtusely 

 angular point, above which the edge extends obliquely upwards 

 and backwards to the rounded top of the ear. (Text-fig. 3, B.) 



In Cacajao the ear is very like that of Cehus, but the inferior 

 portion of the submarginal fossa does not extend so far foi'wards 

 below the antitragus. The posterior and infeiior edges of the 

 pinna are unfolded. 



There is nothing in the ear of Gcdlimico that calls for particular 

 notice. The tragus is hardl}^ developed, but the antitragus is 

 massive ; the superior edge of the pinna is folded to a slight 

 extent, the posterior edge being flat, and the postero-inferior 

 portion is not so prominently rounded as in typical members of 

 the Cebida?. (Text-fig. 3, E.) 



In Callicehus and Saimiris the postero-infei-ior portion of the 

 pinna is somewhat reduced, its free margin ceasing at a point 

 below the notch defining the posterior margin of the antitragus, 

 and the fossa behind the antihelix, which is very shallow in 

 Saimiris, falls short of the antiti'agus infeviorly in both genera,. 

 This partial suppression of the free margin of the pinna inferiorly 

 foreshadows, in a measure, the condition seen in the two genera 

 to be considered next. (Text-fig. 3, 0, D.) 



The above-mentioned geneia have normally formed and nor- 

 mally developed pithecoid ears; but in Ateles f\-nd Lagothrix 

 the ear is modified in a manner similar to that of CEdijwmidas 

 in the Hapalidje. In Ateles the upper portion of the pinna is as 

 well developed as in Cebus, with the anterior edge folded and the 

 upper and posterior edge folded or flat ; but the inferior portion 

 of the pinna has no free margin below a point approximately on 

 a level with a line half-way between the supratragus and the 

 antitragus, there being no postero-inferior laminate lobe and no 

 fossa impressing the antitragus or the area just behind it. For 

 the rest, the ear is normal, the tragus, antiti'agus, supratragus, 



