266 MAMMALIA. 



little expanded forwards. The enlarged anterior pair of upper incisors 

 have a closed root, and the lower incisors are less persistently growing 

 than those of Diprotodon. The humerus apparently belonging to this 

 genus has an entepicondylar foramen, and the ulna exhibits a well- 

 developed olecranon process. The feet are unknown. The typical species, 

 Nototherium mitckelli, occurs in Queensland, and there is evidence of one 

 or more additional species in the same region. Another form, N. victorice, 

 is found in South Australia. 



The extinct wombats or Phascolomyidae, found in the 

 superficial deposits of Australia, are closely similar to those 

 still existing. All except one relatively large animal (Phasco- 

 lonus) seem to belong to the recent genus Phascolomys. 



The extinct kangaroos or Macropodidae, also known only 

 from the superficial deposits of Australia, differ in few particulars 

 from the surviving types. The larger and more massive forms, 

 however, seem to have had the fore and hind limbs less dispro- 

 portionate in size than in the modern kangaroo. Procoptodon 

 exhibits the two rami of the mandible fused together at the 

 symphysis in the adult. The skull of Palorchestes azael must 

 have measured nearly 0'4 m. in length. 



Sub-Class 3. Eutheria. 



Of the truly placental (or Eutherian) mammals there still 

 remain two well-defined groups or orders concerning the origin 

 and relationships of which Palaeontology affords no information. 

 These are the marine mammalia grouped under the ordinal 

 names of Cetacea and Sirenia. There is also a third division 

 whose origin has only lately become a little less obscure, namely 

 that of the Edentata, from which an order termed Effodientia 

 is now sometimes separated by zoologists. With these excep- 

 tions, however, the main lines in the evolution of the Eutheria 

 can now be traced in a general way ; and, as already remarked 

 (p, 247), the chief modifications are to be noticed in the limbs 

 and teeth. 



Perhaps the most interesting feature is the regular and 

 orderly manner in which the crowns of the teeth become com- 

 plicated by the development of tubercles and ridges in the 

 various groups. It has long been admitted that within any 

 given restricted series these coronal prominences or cusps are 



