ORDER MARSUPIALIA. 



I287 



are not anchylosed together, and the hind-limbs are much longer 

 than the front ones. A large number of fossil species occur in the 

 Australian Pleistocene, among which may be mentioned several 

 very large forms like M. brehus, which have the fourth premolar 

 longer than the first true molar, and are allied to the small existing 

 Wallaby, M. ualabatus (which also occurs in the Pleistocene). 



Fig. 1158. — Dentition of Potorous. z", Incisors; c, Canine; fim, Premolar; 711, Molars. 



Then, again, we have in the same deposits remains of the existing 

 Rock-Kangaroo, M. (Petrogale) penicillatus, and also of the larger 

 M. robustus, and some allied extinct forms. Another group, in 

 which the fourth premolar is very small and soon falls out, is repre- 

 sented by the existing M. giganteus, and the larger extinct M. titan 

 and M. ferragus. Sthenurus is an entirely extinct genus character- 

 ised by the presence of a distinct inner lobe to the fourth upper 

 premolar, and is represented by a single species of considerable 

 size. In Procoptodon, again, which is likewise extinct, the fourth 



Fig. 1159. — Macropus Bcnnctti. Lateral view of skull ; from Australia. Reduced. 



upper premolar is like that of Sthenurus, but the rami of the man- 

 dible become anchylosed together in the adult : more than one 

 species are known. Finally, the extinct Palorchestes, comprising 

 the largest known member of the family, is distinguished from the 

 last-named genus by the longer mandibular symphysis, and the 

 absence of an anterior talon in the upper true molars. The length 

 vol. 11. 2 c 



