EXPLANATION OF THE PLATES. 
f)i)U 
Fig. 3. 
Fig. 4. 
Fig. 5. 
Fig. G. 
Fig. 7. 
Fig. 8. 
Fig. 10 
Fig. 11 
Skull of Didelphys el cyans ; 3 a and 3 b , other 
views of the same; 3 c, lower jaw; 3 tl, the 
same magnified, and viewed from the inner 
side. 
Molar tooth of the upper jaw of Thy!acinus 
cynoctphaltix ; -1 a, a true molar tooth of the 
lower jaw of the same. 
Molar tooth of a Dasv urns; 5 «, ditto of lower jaw. 
„ of Perameles myoturos . 
„ of Pcramelrs obrsula . 
„ of a species of Ilypsiprymnus. 
„ of Pholangieta Cookii . 
,, of Phalanyisla vulpine . 
,, of a species of Macropus. 
The above figures, from No. 4 to No. 11 inclusive, are more or 
less magnified representations of the penultimate true molar tooth 
of the left side of the upper jaw, ns found in the principal genera 
of the Marsupiata. 
The four principal cusps, or tubercles, observable on the crown 
of the more complicated of these teeth, are marked a, b, c, and n; 
the anterior pair, a and c, are partially joined, so as to form a 
slightly interrupted transverse ridge in the teeth, fig. 10, and a 
second similar ridge is formed by the junction of the posterior 
pair of principal cusps, u and n. The principal cusps are also 
similarly united in the tooth, fig. 8, but in Macropus (fig. 11), 
they are most perfectly united, and form the high transverse 
ridges observed in the molar teeth of the species of that genus. 
In the tooth, fig. 7, all the cusps are most evenly developed, and 
there are besides these, four smaller cusps, 1, 2,3, and 4, arranged 
in a line along the outer side of the tooth, and, if 1 am not mis¬ 
taken in my identification of the corresponding parts in these 
molars, they become very important portions of the tooth in the 
carnivorous type of dentition, fig. 4 ; here, it appears as if the 
cusps 2 and 3 were much developed, and bent inwards so ns to 
be united to the principal cusps, x and u 1 ; the cusp, n, is wanting. 
1 It appeared tome, upon first comparing the molar teeth of the TbyUcinu* 
with those of the Daiyttfiu. that the chief difference consisted in the absence 
of the small cusps, *2 nml :t, in the molars of the former animal; but observing 
r 
