208 Geological Society, 



cially the small Bize of the hindermost molar; the Phascolothere resem- 

 bles the Myrmecobius more than it does the Opossum, Dasyurus or 

 Thylacynus ; but in the form of the erown, the molars of the fossil re- 

 semble the Thy lacy mis more closely than any other genus of marsupials. 

 In the number of the grinders the Phascolothere resembles the OpGssum 

 and Thylacine, having four true and three false in each maxillary 

 ramus ; but the molarcs vert of the fossil differ from those of the Opos- 

 sum and Tliylaeothcrc in wanting a pointed tubercle on the inner side 

 of the middle large tubercle, and in the same transverse line with it, 

 the place being occupied by a ridge which extends along the inner 

 side of the base of the crown of the true molars, and projects a little 

 beyond the anterior and posterior smaller cusps, giving the quin- 

 quecuspid appearance to the crown of the tooth. This ridge, 

 which, in Phascolotherlum, represents the inner cusps of the true 

 molars in Didelphys and Thylacotherium, is wanting in Thylacynus, 

 in which the true molars are more simple than in the Phascolo- 

 there, though hardly less distinguishable from the false molars. 

 In the second true molar of the Phascolothere, the internal ridge is 

 also obsolete at the base of the middle cusp, and this tooth presents 

 a close resemblance to the corresponding tooth in the Thylacine ; 

 but in the Thylacine the two posterior molars increase in size, 

 while in the Phascolothere they progressively diminish, as in the 

 Myrmecobius. As the outer sides of the grinders in the jaw of the 

 Phascolothere are imbedded in the matrix, we cannot be sure that 

 there is not a smaller cuspidated ridge sloping down towards that 

 side, as in the crowns of the teeth of the Myrmecobius. But, 

 assuming that all the cusps of the teeth of the Phascolothere are 

 exhibited in the fossil, still the crowns of these teeth resemble 

 those of the Thylacine more than they do those of any placental 

 Insectivora or Phoca, if even the form of the jaw permitted a com- 

 parison of it with that of any of the seal tribe. Connecting then the 

 close resemblance which the molar teeth of the Phascolotherium bear to 

 those of the Thylacynus with the similarities of the ascending ramus 

 of the jaw, Mr. Owen is of opinion that the Stonesfield fossil was 

 nearly allied to Thylacynus, and that its position in the marsupial 

 series is between Thylacynus and Didelphys. With respect to the 

 supposed compound structure of the jaw of the Phascolotherium, 

 Mr. Owen is of opinion that, of the two linear impressions which have 

 been mistaken for harmonics or toothless sutures, one, a faint shallow 

 linear impression continued from between the antepenultimate and 

 penultimate molars obliquely downwards and backwards to the 

 foramen of the dental artery, is due to the pressure of a small 



