Ch.XIIL] extinct fossil mammalia. 163 



fio\ 132. Iii both these specimens part of the substance of the jaw has 

 been broken open, so as to show the permanent false molar (a, fig. 131) 

 concealed in the socket. From the fact of this molar not having been 

 cut, we learn that the individual was young, and had not shed its first 

 Fi°- 133 teeth. In fig. 133, a front tooth of the same species of 

 kangaroo, is represented. 



Whether the breccias, above alluded to, of the Wellington 

 Valley, appertain strictly to the Pliocene period cannot be 

 affirmed with certainty, until we are more thoroughly 

 acquainted, with the recent quadrupeds of the same dis- 

 trict, and until we learn what species of fossil land shells, 

 if any, are buried in the deposits -of the same caves. 



The reader will observe that all these extinct quadrupeds 

 of Australia belong to the marsupial family, or, in other 

 words, that they are referable to the same peculiar type of 

 organization which now distinguishes the Australian mam- 

 incisor of Ma- mana from those of other parts of the globe. This fact is 

 cropus. one f many pointing to a general law deducible from the 

 fossil vertebrate and invertebrate animals of the eras immediately ante- 

 cedent to the human, namely, that the present geographical distribution 

 of organic forms dates back to a period anterior to the creation of ex- 

 isting species ; in other words, the limitation of particular genera or 

 families of quadrupeds, mollusca, &c, to certain existing provinces of 

 land and sea, began before the species now contemporary with man had 

 been introduced into the earth. 



Mr. Owen, in his excellent " History of British Fossil Mammals," has 

 called attention to this law, remarking that the fossil quadrupeds of 

 Europe and Asia differ from those of Australia or. South America. We 

 do not find, for example, in the Europseo- Asiatic province fossil kangaroos 

 or armadillos, but the elephant, rhinoceros, horse, bear, hysena, beaver, 

 hare, mole, and others, which still characterize the same continent. 



In like manner in the Pampas of South America the skeletons of Me- 

 gatherium, Megalonyx, Glyptodon, Mylodon, Toxodon, Macrauchenia, 

 and other extinct forms, are analogous to the living sloth, armadillo, cavy, 

 capybara, and llama. The fossil quadrumana, also associated with some 

 of these forms in the Brazilian caves, belong to the Platyrrhine family of 

 monkeys, now peculiar to South America. That the extinct fauna of 

 Buenos Ayres and Brazil was very modern has been shown by its rela- 

 tion to deposits of marine shells, agreeing with those now inhabiting the 

 Atlantic; and when in Georgia in 1845,1 ascertained that the Mega- 

 therium, Mylodon, Harlanus americanus (Owen), Equus curvidens, and 

 other quadrupeds allied to the Pampean type, were posterior in date to 

 beds containing marine shells belonging to forty-five recent species of the 

 neighboring sea. 



There are indeed some cosmopolite genera, such as the Mastodon (a 

 genus of the elephant family), and the horse, which were simultaneously 

 represented by different fossil species in Europe, North America, and 



