AFFINITIES OF EXTINCT SPECIES. 335 



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 palaeontologist, M. Gaudry, has shown 

 in the most striking manner that many of the fossil mam- 

 mals discovered by him in Attica serve to break down the 

 intervals between existing genera. Cuvier ranked the Rumi- 

 nants and Pachyderms as two of the most distinct orders of 

 mammals; but so many fossil links have been disentombed 

 that Owen has had to alter the whole classification, and has 

 placed certain Pachyderms in the same sub-order with rumi- 

 nants ; for example, he dissolves by gradations the appar- 

 ently wide interval between the pig and the camel. The 

 Ungulata 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 inter- 

 mediate between the existing horse and certain other ungu- 

 late forms. What a wonderful connecting link in the chain 

 of mammals is the Typotherium from South America, as 

 the name given to it by Professor Gervais expresses, and 

 which cannot be placed in any existing order. The Sirenia 

 form a very distinct group of the mammals, and one of the 

 most remarkable peculiarities in existing dugong and lamen- 

 tin is the entire absence of hind limbs, without even a rudi- 

 ment 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 respects 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 con- 

 stitute connecting links with the aquatic carnivora." 



Even the wide interval between birds and reptiles has 

 been shown by the naturalist just quoted to be partially 

 bridged over in the most unexpected manner, on the one 

 hand, by the ostrich and extinct Archeopteryx, and on the 

 Other hand by the Compsognathus, one of the Dinosauriaas 



