254 



HISTORICAL PALAEONTOLOGY. 



the latter is supposed to find its nearest living ally in the 

 Opossums (Didelphys) of America. Lastly, the Stereognathus 



Fig. 183. Lower jaw of A mf hither! nm (Thylacothermm) Prevostii. 

 Stonesfield Slate (Great Oolite.) 



of the Stonesfield Slate is in a dubious position. It may have 

 been a Marsupial ; but, upon the whole, Professor Owen is 

 inclined to believe that it must have been a hoofed and her- 

 bivorous Quadruped belonging to the series of the higher Mam- 

 mals (Placentalia). In the Middle Purbeck beds, near to the 

 close of the Oolitic period, we have also evidence of the exist- 

 ence of a number of small Mammals, all of which are probably 

 Marsupials. Fourteen species are known, all of small size, 

 the largest being no bigger than a Polecat or Hedgehog. The 

 genera to which these little quadrupeds have been referred are 

 Plagiaulax, Spalacotherium, Triconodon, and Galestes. The 

 first of these (fig. 184, 4) is believed by Professor Owen to 



Fig. 184. Oolitic Mammals. i, Lower jaw and teeth of Phascolotherium, Stonesfield 

 Slate ; 2, Lower jaw and teeth of Amphitherhim, Stonesfield Slate ; 3, Lower jaw and 

 teeth of Triconodon, Purbeck beds ; 4, Lower jaw and teeth of Plagiaidax, Purbeck 

 beds. All the figures are of the natural size. 



have been carnivorous in its habits; but other authorities 

 maintain that it was most nearly allied to the living Kangaroo- 

 rats (Hypsiprymnus) of Australia, and that it was essentially 

 herbivorous. The remaining three genera appear to have 

 been certainly insectivorous, and find their nearest living rep- 

 resentatives in the Australian Phalangers and the American 

 Opossums. 



Finally, it is interesting to notice in how many respects the 



