OF THE AUSTRALIAN MARSUPIALIA. 



159 



of small nodules arising from the sides of the main cusps. Apart from the obvious 

 quadrituberculatc grouud-pattei-n,the presence of these structures gives the teeth an almost 

 multituberculate appearance. This development appears to be unique among the 

 Marsupials. 



The lower teeth also present a quadrituberculatc pattern similar to that in Trichosurus 

 (PI. 6. fig. 19). As in the latter, the protoconid and hypoconid take part in the formation 

 of an external band enclosing tbe external anterior and posterior portions of the teeth. 

 The entoconid and metaconid are massive. The development of accessory nodules is 

 again in evidence. The appearance of these elements is well illustrated in the internal 

 profile view of the second lower molar given in PI. 6. fig. 30 h. 



A conspicuous feature of the unworn molars is the small sectional area of the crowns. 

 The crown-surface of the second vipper molar of an adult Phascolomys may be twice as 

 long as in the young and more than twice as broad; and similar proportions are 

 observable in the remaining molars. In the young the upper teeth decrease in size 

 backwards from the second ; tlie lower teeth increase in size from the first to the third. 



Incisors. — i\s in the Rodentia, with the exception of the Duplicidentata, the incisors 

 are limited to one on either side of the jaw above and below. They are greatly enlarged, 

 arched, and open-rooted. In the vmvvorn condition (PI. 5. fig. 41) they are pointed at the 

 tips, and thus resemble those of the Phalangerinse ; while in the worn condition they 

 are scalpriform, as in the larger Rodentia. The scalpriform modification is, however, 

 incomplete, the reason being that the teeth meet at such a narrow angle (10^) that the 

 wear falls obliquely on their tips rather than on their posterior sides. The degree 

 of differentiation of the enamel bands appears to vary in different individuals ; while 

 always thicker on the anterior sides of the teeth than anywhere else, the enamel sometimes 

 extends to their sides or even all the way round to their posterior surfaces. 



Posterior Premolars. — With the exception of the incisors, these are the only members 

 of the antemolar series present in the genus. Like the molars they are elongated, curved, 

 and open-rooted, but unlike them are not definitely bilobed. In the unworn lower teeth 

 there are indications of three cusps, including a somewhat larger anterior element and 

 two smaller posterior ones ; the latter arc connected by a small transverse ridge. The 

 lower teeth bear a certain resemblance to those of Nototherlum and Diprotodon. The 

 upper teeth are bifid at the tip, and resemble somewliat those of Dromicla. 



DIPROTODONTID/E. 



The available evidence concerning the dental derivation of this family points to a 

 connection with the Plialangerinae, in part through the Phascolomyidae. Notothermm 

 appears to represent one of the ancestral types leading towards Biprolodon. 



Molars. — Apart from their comparatively huge size, the molars of Diprotodon resemble 

 closely those of the Macropodime in having the opposite cusps completely connected by 



