ORDER MARSUPIALIA. 



I2«I 



the latter being known only by a single species. Remains of exist- 

 ing species of both genera occur very commonly in the Pleistocene 

 breccias of the Brazilian caves ; and to the type genus may also be 

 referred a large number of species from the Lower Miocene and 

 Upper Eocene of Europe, which by some writers are referred to 

 distinct genera under the names of Peratherium and Amphipera- 

 therium. Spalacodon, of the Eocene of Hordwell, is probably a 

 Didelphys. It was in Didelphys Cuvieri, of the Paris gypsum, that 



Ggg BMii^ Sa 



Fig. 1151. — Didelphys (?) fugax ', from the White-river Miocene of Colorado. Twice natural 

 size, a, b, Inferior and lateral views of skull ; c, d, Superior and lateral views of right man- 

 dibular ramus. (After Cope.) 



Cuvier demonstrated the existence of marsupial bones by a careful 

 clearing of the matrix. Other extinct forms from the Miocene of 

 North America (fig. 1151) may in all probability be referred to the 

 same genus. 



Suborder 2. Diprotodontia. — If we exclude the Multituber- 

 culata, which have been already mentioned, this suborder will be 

 confined to the Australian region, where it has been known since 

 the Pleistocene ; and with this limitation it may probably be re- 

 garded as an offset from the more generalised Polyprotodontia. In 

 all cases there is only a single pair of lower incisors, but in the upper 

 jaws there are usually three pairs of such teeth, although they are 

 reduced to one in the Wombats. 

 The lower incisors, and the first, 

 or innermost, pair of upper in- 

 cisors are always of large size and 

 adapted for cutting. The canines 

 are frequently absent, and when 

 present are of relatively small size. 

 The crowns of the true molars 

 are either tuberculate or have 

 transverse ridges ; and as a general 

 rule there are not more than two 

 premolars. Very frequently the last premolar has a long and narrow 

 crown, with a concave superior border adapted solely for cutting. 



Fig. 1 152. — Posterior reduced view of the 

 mandible of the Wombat (Phascolomys). 



