AFFINITIE8 OF EXTINCT SPECIES. 357 



living or to the extinct species of the same class, the series 

 is far less perfect than if we combine both into one general 

 system. In the writings of Professor Owen we continually 

 meet with the expression of generalized forms, as applied 

 to extinct animals; and in the writings of Agassiz, of 

 prophetic or synthetic types; and these terms imply that 

 such forms are, in fact, intermediate or connecting links. 

 Another distinguished paleontologist, M. Gaudry, has 

 shown in the most striking manner that many of the fossil 

 mammals discovered by him in Attica serve to break down 

 the intervals between existing genera. Cuvier ranked the 

 Euminants and Pachyderms as two of the most distinct 

 orders of mammals; but so many fossil links have been dis- 

 entombed that Owen has had to alter the whole classifica- 

 tion, and has placed certain Pachyderms in the same 

 sub-order with ruminants; for example, he dissolves by 

 gradations the apparently wide interval between the pig 

 and the camel. The ITngulata or hoofed quadrupeds are 

 now divided into the even-toed or odd-toed divisions; but 

 the Macrauchenia of South America connects to a certain 

 extent these two grand divisions. No one will deny that 

 the Hipparion is intermediate between the existing horse 

 and certain other ungulate forms. What a wonderful con- 

 necting link in the chain of mammals is the Typotherium 

 from South America, as the name given to it by Professor 

 Gervais exjDresses, and which cannot be placed in any ex- 

 isting order. The Sirenia form a very distinct group of the 

 mammals, and one of the most remarkable peculiarities in 

 existing dngong and lamentin is the entire absence of hind 

 limbs, without even a rudiment being left; but the extinct 

 Halitherium had, according to Professor Flower, an ossified 

 thigh-bone "articulated to a well-defined acetabulum in 

 the pelvis," and it thus makes some approach to ordinary 

 hoofed quadrupeds, to which the Sirenia are in other re- 

 spects allied. The cetaceans or whales are widely different 

 from all other mammals, but the tertiary Zeuglodon and 

 Squalodon, which have been placed by some naturalists in 

 an order by themselves, are considered by Professor Huxley 

 to be undoubtedly cetaceans, "and to constitute connect- 

 ing links with the aquatic carnivora." 



Even the wide interval between birds and reptiles has 

 been shown by the naturalist [just quoted to be partially 



