148 PROCEEDINGS OF THE ACADEMY OF [1881. 



as those of the Hippopotamus. It is proper to mention, however, 

 that the same distinguished observer considers the teeth of the 

 Manatee and the Prorastomus^ another extinct Sirenean, to be 

 rather allied to those of the Tapir and Lophiodon, but this quali- 

 fication does not really invalidate the supposed affinities between 

 the Sirenea and the Hippopotamus. For the Artiodactyla and 

 Perisodactyla are probably offshoots of a common stock, and 

 hence we may expect to find in these two groups certain characters 

 common to both, inherited from their Lophiodon and Ooryphiodon- 

 like ancestors. The affinities of the teeth of the Manatee with 

 those of the Tapir — the first an embryonic Artiodactyle, the 

 second a generalized Perisodactyle — would be examples of the 

 above view. I do not mean to imply that the Manatee has neces- 

 sarily descended directly from the Hippopotamus, though extinct 

 intermediate forms may in the future show this to be so, for 

 possibly they may be the descendants of a common ancestor. To 

 many such speculations may appear mere waste of time, we being 

 unable, from the nature of the case, to experimentally prove or 

 disprove the truth of the hypothesis advanced. It seems to me, 

 however, that the only explanation of the structure of the living 

 forms and of the petrified remains of the animals referred to in 

 these observations is the hypothesis of there being some generic 

 connection between them. 



