636 
MR. W. H. FLOWER ON THE DEVELOPMENT AND 
XXX. fig. 4). The broad deciduous molar teeth were still in place (coloured red). On 
removing part of the alveolar wall, the calcified crowns of their successors (coloured blue) 
were seen, the upper one less advanced than the lower, and, as in the other genera 
described, placed rather anteriorly to the tooth it was destined to succeed. The form 
of the crowns of these reserve teeth was quite different from their molariform prede- 
cessors, being in fact that of the third premolars of the adult (Plate XXX. fig. 5). 
The true molars had begun to take their place in the jaw, two in the maxilla and 
four in the mandible on each side, having their crowns calcified. Except those men- 
tioned above no traces of reserve or successional teeth were seen. 
We thus find in this American family of Marsupials precisely the same peculiarity in 
the succession of the teeth as noticed in their Australian congeners. I have been careful 
to verify these observations upon several other members of the genus, being unable to 
reconcile them with the figure given by Professor Owen of the lower jaw of a Didelphys 
with two reserve premolar teeth, below the crowns of teeth, which, though showing the 
triangular pointed form of the permanent premolars, are indicated as the molar teeth of 
the deciduous series*. 
Family Dasyuridai. 
Genus Thylacinus . — In a young female Thylacine, very scantily covered with hair, 
Rnd the entire length of which was 13 inches, the head being 2*8 and the tail 4, the 
gums were entirely edentulous (see Plate XXX. fig. 6). There was no appearance even 
of teeth raising the mucous membrane, except a small sharp prominence rather behind 
the middle of each alveolar border. On raising the membrane this was seen to be 
caused by a small tooth which was just elevated above the level of the bone. This 
tooth is the deciduous or temporary molar (coloured red in the figure). In the upper 
jaw it had a trihedral obtusely pointed crown yg- inch in length from before backwards, 
flat externally, and having an angle projecting inwards. The fang is absent, being 
either not developed or absorbed ; the corresponding tooth of the mandible is slightly 
smaller and more compressed, also rootless. The crowns of these teeth, by their 
hardness and whiteness, contrast with those next to be described, which have all a 
brown colour, and are evidently the germs of the persistent teeth. Such parts as are 
calcified correspond precisely in size and form with those of the adult animal; they 
are consequently much crowded in the jaw. 
In the upper jaw the four incisors have their crowns calcified ; the second and fourth 
lie superficially, nearly concealing the first and third. The apex of the canine is calcified 
to the extent of *35 inch. The apices of the crowns of the three premolars are calcified. 
That of the third (coloured blue) is least developed in proportion to its ultimate size ; 
its apex is just above and rather in front of the minute deciduous molar. The crown of 
the first molar is in great part calcified, that of the seccnd to a less extent. The third 
could not be recognized. 
* Reade Lecture “ On the Classification and Geographical Distribution cf be Mammalia ” (1859), p. 18. 
