110 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



Brasiliensis, it may be concluded that the present fossil is equally distinct from 

 both. 



The portion of the right hind- foot of the Rodent figured at fig. 12, includes 

 the calcaneum, astragalus, cuboides, external and middle cuneiform bones, and the 

 metatarsals and proximal phalanges of the toes corresponding with the three 

 middle toes of five-toed quadrupeds. The metatarsals are chiefly remarkable for 

 the well-developed double-trochlear articular surface, and intermediate ridge. 

 These remains, as well as the jaws and teeth of the Ctenomys, were discovered 

 at Monte Hermoso in Bahia Blanca. 



In the same reddish earthy stratum of that locality, Mr. Darwin discovered the 

 decomposed molar of a Rodent, equalling in size, and closely resembling in the 

 disposition of its oblique component laminae, the hinder molar of the Capybara 

 (Hydrochcerus). The fossil differs, however, in the greater relative breadth of the 



component laminae. 



I have, lastly, to notice the head of a femur, and some fragments of pelvic 

 bones from the same formation which bear the same proportion to the tooth above 

 alluded to, as subsists between the teeth and bones of the Capybara, and which 

 are sufficient to prove that there once has existed in South America a species of 

 the family Caviidce, as large as the present Capybara, but now apparently 

 extinct. 



* 



This fact, together with the greater part of those which have been recorded in 

 the foregoing pages of the present work, establishes the correspondence, in regard 

 to the characteristic type, which exists between the present and extinct animals of 

 the South American Continent: we have abundant evidence likewise of the greater 

 number of generic and specific modifications of these fundamental types which the 

 animals of a former epoch exhibited, and also of the vastly superior size which 



* 



some of the species attained. 



At the same time it has been shewn that some of the present laws of the 

 geographical distribution of animals would not have been applicable to South 

 America, at the period when the Megatherioids, Toxodon, and Macrauchenia 

 existed: since the Horse, and according to M. Lund, the Antelope and the 

 Hyaena, were then associated with those more strictly South American forms. 

 The Horse, which, as regards the American continent, had once become extinct, 

 has again been introduced, and now ranges in countless troops over the pampas 

 and savannahs of the new world. If the small Opossums of South America 

 had been in like manner imported into Europe, and were now established like 

 the Squirrels and Dormice in the forests of France, an analogous case would 

 exist to that of the Horse in South America, as the fossil Didelphys of Mont- 

 martre proves. 



