30b' PALEONTOLOGY 



these two kinds of teeth can only be determined by their order 

 of development and succession, the Phascolothere may well 

 have had three premolars and four true molars. 



The difference between these teeth in the lower jaw of 

 Didclphys is shown by the addition, in the true molars, of a 

 pointed tubercle on the inner side of the middle cone. In 

 Phascolothcrium a mere basal ridge or cingulum extends along 

 the inner side of the middle cone. Such a ridge is present in 

 the last molar of Sarcophilus, but not in the other molars ; but 

 in these there are two small hind cusps on the same transverse 

 line, whilst that cusp appears to be single in Phascolothcrium. 

 The cingulum, moreover, in the second to the penultimate of 

 the molar series of this fossil, extends so far as to form a small 

 talon at the fore and back part of the crown ; thus making five 

 points, which are very distinct in the third to the penultimate 

 tooth inclusive ; and by' this character the dentition of Phasco- 

 lotherium differs materially from any existing Marsupial, and 

 repeats the type of molar which, as yet, would seem to be 

 peculiar to the Insectivora of the oolitic epoch. There is a 

 feeble indication of this structure in the antepenultimate and 

 penultimate molars of Thylacinus, but the hinder division of 

 the crown shows two small cusps on the same transverse line, 

 besides the rudimental hindmost one ; and there is no cin- 

 gulum. Upon the whole, it would seem that, though the 

 affinity may not be close, Phascolothcrium most resembles 

 Thylacinus amongst existing Mammals ; but Thylacinus is now 

 confined to Tasmania, and is there fast verging to extinction. 



The resemblance shown by the lower jaw and its teeth of 

 the Ampliithere and Phascolothere to marsupial genera now 

 confined to Australia and Tasmania, leads one to reflect on the 

 interesting correspondence between other organic remains of 

 the Oxfordshire oolite and other existing forms now confined 

 to the Australian continent and surrounding sea. Here, for 

 example, swims the Cestracion, or Port-Jackson shark, which 



