522 J. TIT. WILSON AND J. P. HILL. 
fore merely equivalent to that which later develops 
beside the third permanent premolar. 
It may be noted that in Phascolarctus p? appears to 
differentiate at a much earlier period than does the corre- 
sponding tooth in Perameles; for though the stage figured 
by Leche is considerably less advanced in its general develop- 
ment, and as regards the rest of its dentinal characters, than 
the present stage of Perameles, yet the Anlage of pz has 
attained a somewhat higher degree of organisation. 
Stage XIV.—P. nasuta: dried skull of a young adult 
about three quarters grown. (See figs. 78 and 79.) 
Skull length : 5 
Here (fig. 78) in the upper jaw the fourth molar is in course 
of eruption, and the premolar tooth-change is now almost 
completed. The third permanent premolar, p2, has broken 
through, and its crown has nearly attained the level of the 
anterior premolars. By the eruption of its posterior portion 
it is displacing the small dp®. On the right side the latter 
tooth is missing, but may have been accidentally lost. On the 
left side dp2 is still present, lodged in the slight hollow over 
the posterior end of p3. In the lower jaw (fig. 79) the erup- 
tion of pz is not so far advanced, but the relations are other- 
wise entirely similar to those on the upper jaw. The crown 
of dp? is worn and flattish or slightly hollowed. In this con- 
nection we may note that Flower (4, p. 635, and Pl. XXX, 
fig. 1) describes and figures the tooth-change in Perameles 
in an animal not quite full grown. His description of the 
condition is as follows :—‘‘ The permanent incisors, canines, 
and two anterior premolars are in place. Behind these in each 
jaw is a very minute, rather compressed tuberculated tooth, 
succeeded posteriorly by the true molars of the permanent 
series. In the alveolus above this minute tooth, which is the 
temporary or deciduous molar, is lodged the germ of the 
posterior permanent premolar, a tooth having a large com- 
pressed, pointed, triangular crown, with small anterior and 
posterior basal tubercles.” (PI. XXX, fig. 1.) 
70 mm. 
