282 Wortman — Studies of JEocene Mammalia in the 



and if any of the molars and premolars are especially enlarged, 

 it is never exclusively the fourth premolar above and the first 

 molar below. The scaphoid, lunar, and centrale are very gen- 

 erally free ; but according to Cope,* they are united in some 

 French species of Hycenodon from the Miocene. In some 

 forms, such as certain of the Arctocyonid3e,f there may also be 

 union of the scaphoid and centrale, as in many carnivorous 

 Marsupials, and the pollex and hallux may be more or less 

 opposable. In some species, the ungual phalanges are rela- 

 tively broad, flattened, and fissured at their ends, while in 

 others they are laterally compressed, curved, and pointed. 



If we now contrast these characters with those of the Car- 

 nassidentia, we observe that in them the lachrymal is never 

 spread out on the side of the face, but is confined within the 

 orbit. :£ The nasals are not especially broad posteriorly ; the 

 posterior edge of the palate is not thickened ; the numerous 

 posterior palatal foramina are absent ; there is never a double 

 condyloid foramen, and it is always the anterior border of the 

 superior molars that is elongate, if either .§ If there is enlarge- 

 ment and specialization of any of the teeth it is always the 

 fourth superior premolar above and the first true molar below. 

 From the Upper Eocene stage onward, the scaphoid, lunar, and 

 centrale are always united, and there is never union of scaph- 

 oid and centrale alone. The bony claws are always curved, 

 compressed, and pointed. 



Present evidence points to the fact that the two groups 



probably arose side by side from the Mesozoic Marsupials,) 



although we do not know any true Carnassidents earlier than 



the Torrejon, while certain of the Creodonts come from the 



' Puerco. 



Quite recently, Matthewlf has classified the Creodonta as 

 follows : 



* Tertiary Vertebrata, p, 256. 



f See Matthew, Bull. Amer. Mus., Nat. Hist., Jan., 190 L, p. 14. 



\ The only exception to this statement with which I am acquainted is found 

 in the yiverrine Eupleres gondati, from Madagascar, which otherwise resembles 

 the Insectivores. 



§ An apparent exception to this is found in Palceonictis, in which the posterior 

 border of the first molar is slightly longer than the anterior. 



|| I here use the term Marsupials in its larger sense, or as equivalent to the 

 Metatheria of Huxley. It would appear to be more or less doubtful whether the 

 existing Marsupials furnish a stage of embryonic development immediately ante- 

 cedent to that of the appearance of a distinct allantoic placenta. Just how far 

 they may have departed from their Mesozoic ancestors in this respect we shall 

 never, perhaps, be able to ascertain, but there cannot be the slightest doubt of 

 the fact that a preplacental stage existed, from which the placental had its origin. 

 While it may not have been exactly like that seeu in the living Marsupials, it 

 must have, according to the very nature of the case, resembled it in a great many 

 important particulars. 



^[ Loc. cit., p. 7. 



