108 AFFINITIES OF EXTINCT SPECIES. [Chap. XL 



and certain older ungulate forms. What a wonderful 

 connecting link in the chain of mammals is the Typo- 

 therium from S. 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 dis- 

 tinct group of mammals, and one of the most remark- 

 able peculiarities in the existing dugong and lamentin 

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

 ment being left; but the extinct Hahtherium had, ac- 

 cording 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 natu- 

 rahsts in an order by themselves, are considered by Pro- 

 fessor Huxley to be undoubtedly cetaceans, " and to 

 constitute 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 Archeo- 

 pteryx, and on the other hand, by the Compsognathus, 

 one of the Dinosaurians — that group which includes 

 the most gigantic of all terrestrial reptiles. Turning to 

 the Invertebrata, Barrande asserts, and a higher author- 

 ity could not be named, that he is every day taught that, 

 although paleozoic animals can certainly be classed 

 under existing groups, yet that at this ancient period 

 the groups were not so distinctly separated from each 

 other as they now are. 



Some writers have objected to any extinct species, 



