STONESFIELD SPECIES. 123 



Zeuglodon. The correctness of Cuvier's original determi- 

 nation was thus in the end triumphantly sustained, and 

 the existence of Jurassic mammals became henceforth an 

 established fact in geology, although the suggestion that 

 these fossils belonged to opossums was, of course, 

 unfounded. 



Passing on to the consideration of the specimens them- 

 selves, we find that the great peculiarity of the jaws of 

 these Stonesfield mammals (for one of which De Blainville 

 proposed the name of amphithere) is the excessive 

 number of their cheek-teeth, a feature now paralleled 

 only in the little banded anteater of Australia. This 

 multiplicity of teeth is well shown in the jaw represented 

 in Jb'ig. 38, which is preserved in the museum at York, 

 and shows upwards of nine cheek-teeth still remaining, 

 whereas in practically all existing mammals with complex 

 teeth, except the banded anteater, the number does not 

 exceed seven. Other jaws were, however, subsequently 

 discovered in Stonesfield, in which the number of 

 cheek-teeth was considerably less ; but one of these 

 later specimens (described as the phascolothere) revealed 

 the important fact that there were four pairs of front or 

 incisor teeth in the lower jaw. Now since it is only 

 among the pouched mammals, or marsupials, that more 

 than three pairs of incisor teeth are found, while the 

 banded anteater, with its numerous cheek-teeth, is a 

 member of the same group, it became a very natural 

 conclusion that the Stonesfield mammals were likewise 

 marsupials. Support was lent to this conclusion by the 

 circumstance that, with the exception of the egg-laying 

 mammals, or monotremes, the marsupials are the lowest 

 of all living mammals. And indirectly some further 

 support to this view is afforded by the fact that Australia 

 still retains other forms of animal life allied to those which 

 were living in Europe during the period of the Stonesfield 

 slate. For instance, it is in the Australian seas alone 

 that there still survives the solitary representative of the 

 beautiful genus of bivalve shells known as Trigonia, which 

 were so especially abundant in the oolites ; while it is also 

 there alone that swims the Port Jackson shark, whose 



