No.42] THE AUSTRALIAN MARSUPIALIA. 253 
upper molars, a conversion of the paracone and metacone into 
cutting blades, and a reduction of the outer styles, which are 
here represented by very inconspicuous tubercles. In thelower 
teeth the progressive modification is a conversion of the para- 
conid, protoconid, and hypoconid into cutting blades, and a 
reduction of the metaconid, hypoconulid, and entoconid. 
Turning to the second stem, leading to the omnivorous and 
herbivorous modifications, we find the first stage represented in 
the teeth of the Peramelide. The upper molars of Perameles 
nasuta (Pl. I, Fig. e) show all the essential characters of those 
of Dasyurus, but in addition they show an incipient hypocone. 
In the third molar the hypocone is not very pronounced, and 
the tooth is triangular; but in the second molar the hypocone 
is well developed, and the tooth is now quadrate. Thomas 
(88, p. 220) describes the triangular and quadrate modifica- 
tions as characteristic of the family. The upper molars of the 
Peramelidz parallel, in a general way, those of the Condylar- 
thra above mentioned. The lower molars of Perameles nasuta 
(Pl. II, Fig. e) resemble still more closely those of Dasyurus, 
the omnivorous modification being only apparent in the posterior 
heel, where the hypoconulid is reduced. 
The completed omnivorous: modification is doubtless to be 
met with in the Phalangerida. Unfortunately, only two exam- 
ples of this family have been available to the writer, namely, 
Trichosurus vulpecula, which is highly specialized, and Petau- 
roides volans. The teeth of the latter animal are represented 
in Pls. I and II, Fig. f. Although they illustrate the com- 
pleted quadrituberculate condition, they are only approximately 
transitional ; the hypocone is completely formed in the upper 
molars, and the paraconid is reduced in the lower molars; but 
the antero-external shelf, which is prominent in the lower teeth 
of the Peramelidee and Dasyuride and‘ very conspicuous in 
those of the Macropodidze (Pl. II, Fig. ï), is here absent, and 
there are no traces of external styles in the upper teeth. 
The selenoid modification of the cusps, which is so widely 
represented in the artiodactyl Ungulata, appears to be confined 
to the single form Phascolarctos (Pls. I and II, Fig. /) among the 
marsupials, but the lophoid modification is widely represented 
