168 MAMMALS. 



The species of tLese are all from the middle tertiaries of Europe or one or other of them, and 

 have been found in England, France, German3% Spain, and Italy. 



NesodontiDvE. The reader may here expect to find two peculiar animals, the Toxodon and 

 Hyrax, which are usually ranked among the Pac:hyderms. They appear to me to belong to the 

 Rodents, and I have placed tlicm as distinct families in that order. The grounds for doing so 

 will be found stated under the Rodents. During the expedition of the " Beagle " Mr. Darwin 

 discovered some remains at Bahia Blanca and on the banks of the Sarondis, a small stream entering 

 the Rio Negro about one hundred and twenty-one miles north-west of Monte Video, in South 

 America. Nothing but skulls, more or less imperfect, were found, but there were sufficient 

 remains of these to enable Professor Owen to characterise two genera, the first of which he 

 named Toxodon, with one species ; and the second, Nesodon, with four species. 



Professor Owen combined these two into an order which he called Toxodontid.e, but 

 Burmeister has detached the genus Nesodon from it, and proposes to establish it as a 

 separate order, and in a ditfcrent position in the arrangement. Tlie Toxodoxs as just men- 

 tioned I carry to the Rodents. The genus Nesodon I keep here. It has a very different dentition 

 from Toxodon, viz., three incisors and a small canine in each side of the jaw, and is considered 

 by Burmeister, who has lately published his views on the subject, as more akin to the genus 

 Macr.vuchexia. I have adopted his suggestion, but we know so little of them, that whatever 

 course we take regarding them is almost certain to be disavowed by Nature when we are at 

 last fortunate enough to hear her speak, that is, when more perfect remains of the sjjecies 

 arc discovered. This has been eminently the case with the Macrauchenia, mentioned be- 

 low, and will always be .so ^^•here we attemjit to supply a scarcity of facts by an abundance of 

 conjectures. 



Although four species of this genus have been described our knowledge of them is 

 almost entirely confined to the teeth. There is a small canine tooth, and three incisors, and seven 

 grinders on each side of each jaw. One species, N. imbricatus, appears to have been of the size of 

 a Lama ; another, N. Sullivani, of that of a Zebra ; N. ovinus, of that of a Sheep ; and N. 

 MAGNUS, of that of a Rhinoceros. Some of these dimensions, however, are calciJatcd from very 

 imj)erfect materials, the last for example, from a molar tooth. 



Macrauchenia. Professor Owen, who first described this animal from some vertebra; and other 

 fragmentary portions of a skeleton, obtained by Mr. Darwin at Port St. Julian, in Patagonia, re- 

 ferred it to the order Pachydermata, but he thought that its cervical vertebra; showed marked 

 affinities to the Ruminants, and especially the Camels.* M. Gervais, in tlie " Zoologie " of 

 Castelnau's expedition, did not see any resemblance to the Cajiei.id.e, but regarded it as a 

 Perissodactylian Pachyderm, the structure of the foot being nearly the same as that of the Rhino- 

 ceros and Tapir. Mr. Darwin himself partly adopted both views. He says that it is fully as large 

 as a Camel, and belongs to the same division of the Pachydermata as the Rhinoceros, Tapir, and 

 Palixiotherium ; but in the structure of the bones of its long neck shows a clear relation to the 

 Camel, or rather to the Guanaco and Llama. f 



Subsequently to this, remains of another species, consisting, however, of only two very imperfect 



t Owen, "Zoology of the Beagle." § Darwin's Journal, sccoud edition, p. 172. ISl."). 



