AN ARRANGEMENT OF THE MAMMALIA. 73 



cations, may be derived from the general formula of 44 in the 

 two jaws. 



Palaeontology has gone far to show that the Eutheria have 

 all sprung from a common, general type, and il has been through 

 ages of gradual evolution and development that we now have 

 existing on the earth the remarkable variety of them that we 

 have. Fossil representatives of the Eutheria, however, fill in 

 many of the apparently wide gaps existing among the present- 

 day orders. 



Turning once more to the latter, we have besides the three 

 already enumerated above, the fourth in the series, or the Pro- 

 boscidea, now only in evidence through the two species of 

 Elephants left on the earth. In former ages of the world, how- 

 ever, the Prohoscidea was an elegant array of ponderous ani- 

 mals rich in species and vast in numbers. They included the 

 Mastodons, the Mammoths, and the Dinotheria, with their allies. 

 And, as hinted at above, we may add that undoubtedly through 

 the extinct Dinocerata, the elephant-forms are in a way, though 

 nevertheless really, linked with modern ungulate animals, such 

 as horses, pigs, tapirs, all the ruminants, and the rhinoceroses. 



Another somewhat isolated group is represented by a very 

 few and small Old World species known as Conies [Hyrax). 

 Some mammalogists consider them to form an order [Hyra- 

 coidea), while others relegate them to subordinal rank. 



As I have elsewhere said, the discovery of fossil mammals 

 both nearly and remotely related to the ungulate series [Ungulala] 

 is constantly tending toward a re-arrangement of these forms, 

 and it may be that in the future this order will be much 

 extended, and even possibly to include the Prohoscidea and the 

 Hyracoidea. 



Another great group is seen in the Rodentia, and one that 

 is more or less clearly differentiated from all the other orders. 

 As we know, it includes all the existing species of gnawing 

 mammals, or the Rodents, abundantly represented in the various 



