20 
ramus; but the molares veri of the fossil differ from those of the Opos~ 
sum and Thylacothere 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 Phascolotherium, 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 similiarities 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 harmonié 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 
artery, and that the author possesses the jaw of a Didelphys Virgi- 
niana which exhibits a similar groove in the same place. Moreover, 
this groove in the Phascolothere does not occupy the same relative 
position as any of the contiguous margins of the opercular and den- 
tary pieces of a reptile’s jaw. The other impression in the jaw of 
the Phascolotherium is a deep groove continued from the anterior 
extremity of the fractured base of the inflected angle obliquely 
downwards to the broken surface of the anterior part of the jaw. 
Whether this line be due to a vascular impression, or an accidental 
fracture, is doubtful; but as the lower jaw of the Wombat presents an 
impression in the precisely corresponding situation, and which is 
undoubtedly due to the presence of an artery, Mr. Owen conceives 
that this impression is also natural in the Phascolothere, but equally 
