1865.] Sclateb on the Mammals of South America. 607 



remarked that the American Monkeys, are, without exception, ex- 

 clusively arboreal in their habits. Some of the Old World members 

 of the order, such as the Formosan Macaque (Macacus cyclopia, 

 Swinhoe),* and the Barbary Ape (Macacus Sylvanus), are rather rock- 

 climbers than tree-livers. But this is not the case with any species 

 of the two American families of Quadrumana, as far as has been 

 hitherto recorded. Commencing the series with these forms of the 

 Cebidae, wherein the possession of a fifth hand, in the shape of a 

 prehensile tail, shows a more especial adaptation to tree-life, we first 

 meet with the genera Mycetes,^ Lagothrix, Brachyteles, and Ateles. 

 In these forms the terminal vertebrae of the tail are dilated, and its 

 extremity is denuded of hair on the under side, so as to permit of a 

 firmer hold being taken by this organ, and to render it still more 

 available for locomotion. Of the Mijcetoz, or Howling Monkeys, so 

 remarkable for the terrific bellowings which they are enabled to 

 produce by a special modification of the hyoid bone and thyroid 

 cartilage, about six species are generally recognized by naturalists. 

 These range over nearly the whole of the limits within which the 

 American Quadrumana are distributed, at any rate from Guatemala 

 to Southern Brazil. Lagothrix, on the other hand, is a form confined 

 to the valley of the Upper Amazon. Though several species of this 

 genus have been described, it is probable that they may be all 

 referable to varieties of the Lagothrix Humboldtii.\ The genus Brachy- 

 teles of Spix ( = Eriodes of Isidore Geoffroy St. Hilaire) is another 

 monotypic form, peculiar to the forests of S.E. Brazil. Although nearly 

 allied to Ateles, it is distinguishable by " the peculiar position of the 

 nostrils, the equality in size of the incisors, the shortness of the 

 canines, and the globular form of the head." § Ateles, on the other 

 hand, is more numerous in species, and more widely diffused, the 

 most northern monkey hitherto recorded in the New World belonging 

 to this genus, || and the group being represented also in Southern 

 Brazil. About seven or eight species of Ateles appear to rest on good 

 authority, and are usually recognized. They are all remarkable for 

 their long slender bodies and elongated limbs, whence they have ob- 

 tained the appropriate name of Spider Monkeys. They are also dis- 

 tinguishable by the absence or imperfection of the thumb, a structure 

 which, singularly enough, likewise occurs in a genus of Simiidse 

 (Colobus) met with in the corresponding latitudes of the African 

 continent. 



* < Proc. Zool. Soc.,' 1812, p. 350. 



t Mycetes is usually arranged in this neighbourhood, but Mr. Flower has 

 recently shown (' P. Z. S.,' 1864, p. 338) that, as regards its brain-structure, it 

 departs widely from Cebus and the more highly-organized Platyrhines, and 

 appears to be more closely allied to Nyctopithecus. The structure of its sternum 

 is also abnormal. 



% Cf. Bates' ' Naturalist on the Amazon,' ii. p. 319 ; and Slack in ■ Journ. 

 Acad. Phil.,' 1862, p. 515. 



§ Slack, ' Proc. Acad. Phil.,' 1862, p. 513. 



|| See ' Nat. Hist. Rev.,' 1861, p. 508. 



