CEEODONTA. 263 



Phylogeny. It is among the genera above enumerated that we are to look 

 for the ancestors of the existing Carnivora, excepting, perhaps, the seals, and 

 even these were probably contemporaries. The genera with developed 

 inner cusps and tubercles of the molars, are probably modifications of the 

 Leptictidce, which are also nearest to the Marsupialia. In those genera 

 without developed internal tubercles of the molars, we may look for the 

 ancestors of the Hycenodontido&, a family which early attained specialization 

 at the expense of strength of structure, and did not survive the Lower 

 Miocene period. Such genera may be found in the Mesonychidce as the 

 later, and the Amhlyctonidce as the earlier types. 



In distinguishing between the ancestors of the Felidce and Canidce, we 

 naturally seek to recognize in each an anticipation of the leading characters 

 in the dentition which distinguish those families to-day. This consists, in 

 the Felidce, in the successive abbreviation of the true molar series from 

 behind, so that ultimately two molars are lost, and the remaining or anterior 

 one becomes transverse ; also in the development of a preglenoid cross- 

 ridge which embraces the mandibular condyle in front. On the other 

 hand in the Canidce, firstly, the full number of true molars is retained in 

 some genera, as AmpJiicyon, and only one is lost in Canis. Secondly, the 

 tubercular character of the posterior molars in both jaws in the Canidce is 

 distinguished from their sectorial character in Felidce. Estimated by these 

 tests the Miacidce are clearly the forerunners of the Canidce, and the Oxyce- 

 nidce, of the Felidce. In Miacis we have in fact a near approach to the den- 

 tition of Canis, in the lower jaw; while in the same part of Didymictis, 

 posterior abbreviation has commenced, reminding one of Viverra. In the 

 Oxycenidce, one degree of posterior abbreviation is seen in Stypoloplms, where 

 the last superior molar is narrowed and turned at right angles to the others. 

 In Oxycena, the process had advanced a step, for there are but two superior 

 true molars, and the last of these is driven in, transversely. The first true 

 molar is functionally sectorial in this genus, while the last premolar is the 

 true sectorial of the superior series in existing Carnivora. In the inferior 

 series there are only two true molars in Oxycena, both primitive, or "tuber- 

 cular-sectorial" in character. In existing Felidce the second is lost, while 

 the first undergoes great changes in becoming a specialized sectorial. The 



