284 Wortman — Studies of Eocene Mammalia in the 



and concluded that "its nearest living ally is the Thylacyniis 

 cynocephalus of Tasmania." In opposition to this view, 

 Matthew observes* — " Clsenodon has, however, no marsupial 

 characters except such as may be considered an inheritance 

 from a common stock, which gave rise to both Marsupials and 

 Placentals. Its progressive characters are placental carnivore." 

 Just how this latter author explains the remarkable resem- 

 blances of foot structure in the two groups, including the 

 marked tendency towards opposability of pollex and hallux, or 

 what constitutes the so-called progressive characters of which 

 he speaks, other than these same marsupial characters, I am at 

 a loss to imagine. Jn my judgment Cope's position rests upon 

 very sound anatomical reasoning, the force of which is rendered 

 all the more patent by these later discoveries. 



As regards the third group, I am compelled to add that I 

 find myself unable to accept the definition as accurate, or the 

 grouping as natural. If by the term carnassial is meant the 

 most specialized cutting teeth of the series, then the definition 

 is fairly satisfactory, but the character would have been much 

 better and more clearly expressed, had it been stated what 

 teeth are sectorial. The character of the ungual phalanges, 

 and their supposed manner of articulation, I do not regard as 

 of any very great value in the classification of the major divis- 

 ions of this group, for the reason that within the limits of one 

 of the families, at least, their structure ranges from the com- 

 pressed, curved, and sharp-pointed variety, to the flattened, 

 depressed, and fissured type. 



The statement that the podials are tending toward an " Un- 

 gulate type" is such an extraordinary one, and is so at variance 

 with the facts, especially as regards the Oxyeenidae and Ilyeeno- 

 dontidse, that I can hardly believe that the author intended it 

 to apply to these families. It is true that the feet of the 

 Mesonychidae, in the later members, assumed a more or less 

 "Ungulate type," because of a highly developed running habit, 

 just as, among the living Carnassidents, the limbs of the mod- 

 ern Canidee have taken on a similar structure from a like cause. 

 But to suppose that there is even the faintest suggestion of 

 anything "Ungulate" in the foot structure of such forms as 

 Sinojpa, Limnocyon, Oxyama, Patriofelis* or Hycenodo?i i other 

 than the fissured claws in the last three genera, is certainly 

 quite beyond the facts. 



The association, moreover, of the Mesonychidae with the 

 OxyDenidee and Hysenodontidee is not very apt, since in point 

 of structure it is widely separated from these two families, and 

 constitutes one of the most distinct and separate groups of 



* Bull. Amer. Mus. Nat. Hist., 1901, p. 12. 



