OOLITIC FORMATIONS. 17 



Of the three incisors present in the fossil, only the inner and hinder parts of the 

 somewhat mutilated crown are seen, not the entire breadth of the crown, so that these 

 teeth appear to be narrower and farther apart than they really were. Nevertheless, they 

 could not have been so closely in contact as in SarcopJdlus or Thylacinus, nor have 

 occupied so short a relative extent of the alveolar tract, nor a situation turned inward at 

 such an angle from the line of the rest of the teeth. In all these characters the incisors of 

 Phascolotherium more resemble those of Myrmecohius. The canine, also, in its proportion 

 to the incisors and molars much more resembles that tooth in the above existing insecti- 

 vorous Marsupial (fig. 24, c) than the canine in the carnivorous genera of recent Marsupials. 



In the proportions of the molars, Phascolotherium resembles Myrmecohius more than 

 it does Bidelphys, Sarcophilus, or Thylacinus; but the hinder grinders decrease more 

 gradually, and the last two in a greater degree, than in Myrmecohius. In the form of the 

 crown the molars of Phascolotherium resemble those of Thylacinus more than those in 

 Myrmecohius or other existing Marsupials. There is, however, a well-marked distinction 

 in the molar type of the present Mesozoic fossil. A principal cone rises from the middle 

 of the crown, but there is no small cusp on the inner side of this, as in the true molars 

 of Bidelphys and Phascogale. 



Herein Phascolotherium resembles Sarcophilus and Thylacinus ; but it differs in the 

 presence of a basal ridge or ' cingulum,' shown along the inner side of the tooth in the 

 specimen described, which ridge projects as a ' talon ' beyond both the anterior and the 

 posterior subordinate cones, giving the quinquecuspid character of the crown of the tooth 

 in the second to the sixth of the series inclusive (fig. 26a). The molars increase in size 

 from the first to the third, and decrease from the fifth to the seventh, but in slight and 

 gradual way. 



In this series there is no distinction, by way of form, between false and true molars. 

 The character given by the successional premolar in existing Marsupials would be 

 arbitrarily applied to mark off" the first three from the last four of the molary series of 

 Phascolotherium. The distinction, by way of specialisation of form, between the (three) 

 false and (four) true molars is much more strongly established in the modern Opossums 

 and Dasyures, as it is in a minor degree in Sarcophilus and Thylacinus. 



Phascolotherium shows a closer affinity in the molar type, and in the gradual assump- 

 tion of that type as the teeth gain in size, to its contemporary Amphithcria ; from which, 

 however, it difi^ers in the reduction of the number of the molary series to the prevaihng 

 formula in existing Marsupials. 



Phascolotherium differs from the extinct and recent ' multidentate ' Marsupials, and 



resembles the Sarcophilus and Thylacinus, in the direct and broad inbending of the 



mandible below the mandibular condyle, and in the low position of the latter. It is entire 



in the present specimen {b), and stands out in bold relief from the matrix. It presents the 



same convexity from before backward as iu Sarcophilus and Thylacinus, but is relatively 



less extended transversely, and is rather more convex in that direction. The inflected 



3 



