CHAP. XIV.] THE NEOTROPICAL REGION. 7 



species, have the prehensile tail, the remainder having this organ 

 either short, or lax as in the Old World monkeys. Other dif- 

 ferences from Old World apes, are the possession of a broad nasal 

 septum, and a less opposable thumb ; and the absence of cheek- 

 pouches, ischial callosities, and a bony ear-tube. The Hapalidse, 

 or marmozets, agree with the Cebidse in all these characters, but 

 have others in addition which still more widely separate them from 

 the Simiidse ; such as an additional premolar tooth, acute claws, and 

 thumb not at all opposable ; so that the whole group of American 

 monkeys are radically different from the remainder of the order. 



The Procyonidse are a distinct family of Carnivora, which make 

 up for the scarcity of Mustelidse in South America. The Suidse 

 are represented by the very distinct genus Dicoti/les (Teccary) form- 

 ing a separate sub-family, and differing from all other genera in 

 their dentition, the absence of tail and of one of the toes of the 

 liind feet, the possession of a dorsal gland, and only two mammae. 

 The rodents are represented by the Chinchillidse and Caviidae, 

 the latter comprising the largest animals in the order. The 

 Edentata are almost wholly confined to this region ; and the three 

 families of the sloths (Brady podidse), armadillos (Dasypodidse), 

 and ant-eaters (Myrmecophagidse), are widely separated in struc- 

 ture from any Old World animals. Lastly, we have the opossums 

 (Didelphyidse), a family of marsupials, but having no close aflfi- 

 nity to any of the numerous Australian forms of that order. 

 We have already arrived at the conclusion that the presence of 

 marsupials in South America is not due to any direct transfer- 

 ence from Australia, but that their introduction is comparatively 

 recent, and that they came from the Old World by way of North 

 America (vol. i., p. 155). But the numerous and deep-seated 

 peculiarities of many other of its mammalia, would indicate a 

 very remote origin; and a long-continued isolation of South 

 America from the rest of the world is required, in order to account 

 for the preservation and development of so many distinct groups 

 of comparatively low-type quadrupeds. 



Distinctive Character's of Neotropical Birds. — The birds which 

 are especially characteristic of this region, present similar 

 distinctive features. In the enormous group of Passerine 



Vol. II.— 2 



