254 



HISTORICAL PALAEONTOLOGY. 



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

 Opossums {Didelp/iys) of America. Lastly, the Stereognathiis 



Fig. 183. 



-Lower jaw q{ A7nphithe7-ium {Thylacotheriion) Prevostii. 

 Stonesiield 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 [Flacentalia). In the IMiddle Purbeck beds, near to the 

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

 ence of a number of small Mamm.als, all of which are probably 

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

 the lars^est beinsj no bio-aer than a Polecat or Hedo:ehoo^. The 

 genera to which these little quadrupeds have been referred are 

 Plagiaiilax^ Spalacothermm^ Triconodon^ and Galesfes. The 

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



^|^<£(Xj& 



Fig. 184. Oolitic Mammals. — i, Lower jaw and te&thoi Phascoiotherhim, Stonesfield 

 Slate ; 2, Lower jaw and teeth of Amphitlie-rium, Stonesfield Slate ; 3, Lower jaw and 

 teeth of Triconodofi, Purbeck beds ; 4, Lower jaw and teeth of Plagiaulax, 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 {Hypsiprymjius) 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 



