On the Classification of Mammalia. 175 



has not yet yielded all the data by which alone we delineate 

 the history of the pachyderms and allied groups from their 

 cradle up to our days. 



Amongst the living genera, we observe the following parti- 

 culars : The Manati, when young, have on the lower jaw 

 two small incisors directed forwards and downwards, remind- 

 ing us of the tusks in Dinotherium. The presence of tusks, 

 therefore, assigns to the latter a lower position. In Halicore, 

 tusks exist on the upper jaw, as in the elephant, w T ith which 

 the genus Rytina seems also related by its teeth, although 

 completely deprived of tusk of any kind. 



§ 5. The position of the Walrus is between Sirenidia and 

 Pachydermata ; they belong to the pachydermic order by 

 structural evidences, and bear only analogies to the seals. 

 They constitute a small group whose distinctive features 

 from Manati consist in the presence of four locomotive mem- 

 bers ; and from the other pachyderms, in having these four 

 locomotive members adapted for aquatic habits. 



§ 6. The order of Pachydermata is the least understood 

 of all, on the very ground that its history belongs chiefly to 

 the past ; and since Sirenidia and Trichechidae (walrus) are 

 referred to the same group, it becomes difficult to determine 

 the relationships between the living and the extinct repre- 

 sentatives in order to establish a graduated series. 



We are satisfied of the existence of two progressive series 

 in the pachydermic groups, in the following way : 



WITHOUT PROBOSCIS. PROBOSCIDIANS. 



EQUID^], ELEPHANTID^E, 



SUID-*], MASTODONTID^E, 



HYRACID.E, 

 RHINOCEROTID^E, 



RYTINID^E, 

 HALICHORID.E, 



HIPPOPOTAMUS, MANATID^E, 



TRICHECHIDAE, DINOTHERID^E, 



ANOPLOTHERID^E, 



PAL^OTHERID^E. 



At the bottom of the order, the extinct Palseotherium and 

 Anoplotherium : on one side the proboscidians, and on the 



