MAESUPIALIA. 1 67 



Glenoid cavity and mandibular condyle transverse ; anterior 



limbs constructed for flight Chiroptera. 



Glenoid cavity and mandibular condyle transverse; anterior 



limbs ambulatory Bunotheria. 



II. Ungual phalanges hoofs (ungulata). 

 a Os magnum supporting the lunar and not articulating with the 



scaphoid. 

 The astragalus articulating with the navicular only, and the 



cuboid with the calcaneum only Taxeopoda. 



(The astragalus articulating with the navicular only; cuboid 



articulating with distal faces of calcaneum and navicular. Prohoscidia.*) 

 The astragalus articulating with the cuboid and navicular.. Amhlypoda. 

 aa Os magnum supporting the scaphoid, and more or less of the 



lunar. 

 Astragalus articulating with both cuboid and navicular Biplaethra. 



MARSUPIALIA. 



Although many of the Mammalia of the Lower Eocene formation re- 

 semble the Marsupialia, few of them present chai'acters which are unques- 

 tionably those of that order. They appear in many instances to possess 

 characters of the Insectivorous and Carnivorous orders as well, so that it 

 has been thought best to refer them to a single order in combination with 

 the Insedivora, the Bunotheria. A few species, however, present the mar- 

 supial facies so decidedly, as to leaye no alternative but to refer them to 

 that order, until further evidence shall confirm or set aside such a conclusion. 



The two genera now to be treated of are not very nearly related to 

 any existing form of Marsupials. The nearest ally of one of them at least 

 is characteristic of the Jurassic age, and has been referred by Professor 

 Marsh to a distinct order under the name of the Allotheria. As Professor 

 Mai'sh does not offer any characters by which this group can be distin- 

 guished as an order from either the Marsupialia or the Bunotheria, I have 

 not been able to adopt it. As Falconer has suggested, their nearest ally is 

 perhaps Hypsiprymnus among the existing Marsupials, and Thylacoleo has 

 perhaps an equal affinity. As the only part of the structure of these genera 

 which is well known is the dentition, I define them as follows. The family 

 of the Plagiaulacidce differs from that of the MacropocUdce in the possession 

 of but two inferior true molars. Most of the genera have the fourth pre- 



* Not known a8 Eocene. 



