MARSUPIALIA. 
gressively increasing in length as they are 
placed forward. An interspace occurs between 
these and the canine, which is long, slender, 
sharp-pointed, and recurved. The first incisor 
is longer than the two behind, but is much 
shorter than the canine. In the lower jaw the 
true molars are preceded by two functional 
false ones, similar in size and shape to the 
three above the anterior false molar, and the 
canine are represented by minute rudimental 
simple teeth; the single incisor is long and 
procumbent as in the other Petaurists. 
With these differences of dentition approach- 
ing more or less to one or other of the modifi- 
cations of the dentition in the group of Phalan- 
gers, the Petaurists may nevertheless be readily 
discriminated from those Phalangers which 
_ they most resemble ; for example, the Petaurus 
Taguanoides may be distinguished from the 
_Phalangista Cookii by the greater relative 
length in the latter of the nasal and maxillary 
_ portion of the skull; while in most of the other 
ies of Petaurus, the facial part of the skull 
_ is relatively shorter than in the Pet. Tugua- 
 noides. 
Genus PHASCOLARCTUS. 
The absence of anomalous or functionless 
premolars and of inferior canines appears to be 
constant in the only known species of this 
genus. The dental formula in three examples 
of this species ( Phasc. fuscus, Desm.) is 
3—3 . int 
Gags INS omy 5... Premo- 
EE ———— “<_< — 
dd ee 
Incisors 
Sy... 1—1 4—4, ; 
; lars ei molars — 30. ( Fig. 95.) 
The true molars are larger in proportion than 
in the Phalangers; each is beset with four 
_ three-sided pyramids, the cusps of which wear 
down in age, the outer series in the upper teeth 
being the first to give way; those of the lower 
_ jaw are narrower than those of the upper. The 
“spurious molars are compressed and terminate 
in a cutting edge; in those of the upper jaw 
_ there is a small parallel ridge along the inner 
side of the base. The canines slightly exceed 
‘in size the posterior incisors; they terminate in 
an oblique cutting edge rather than a point ; 
their fang is closed at the extremity: they are 
situated as in the Phalangers close to the inter- 
maxillary suture. The lateral incisors of the 
upper jaw are small and obtuse; the two ante- 
rior or middle incisors are twice as long, broad, 
and thick as the posterior incisors; they are 
conical, slightly curved, sub-compressed, be- 
velled off obliquely to an anterior cutting edge, 
but differing essentially from the dentes scal- 
prari of the Rodentia in being closed at the 
extremity of the fang. The two incisors of the 
lower jaw resemble those of the upper, but are 
larger and more compressed; they are also 
formed by a temporary pulp, and its absorption 
is accompanied by a closure of the aperture of 
the pulp cavity, as in the upper incisors. The 
Koala, therefore, in regard to the number, kind, 
and conformation of its teeth, closely resembles 
the Phalangers, with which it also agrees in its 
long cecum and the general conformation of 
its digestive organs. It has also the extremities 
aa 
265 
similarly organised for prehension iftach is ter- 
minated by five digits; the hind feet are provided 
witha large thumb, and have the two contiguous 
digits enveloped in the same tegumentary fold ; 
the anterior digits are divided into two groups 
the thumb and index being opposed to the 
other three fingers. We have already noticed 
a structure approaching to this in some of the 
small Phalangers. The Koala, however, differs 
from the Phalangers and Petaurists in the ex- 
treme shortness of its tail, and in its more com- 
pact and heavy general form. It is only known 
to feed on the buds and leaves of the trees in 
which it habitually resides. 
Tribe IV. POEPHAGA. 
The present tribe includes the most strictly 
vegetable feeders; all the species have a com- 
plex sacculated stomach, and a long simple 
cecum. 
Genus HYPSIPRYMNUS. Potoroos. 
Guided by the modifications of the teeth 
we pass from the Koala to the Potoroos 
and Kangaroos—animals of widely different 
general form. The Potoroos, however, present 
Hypsiprymnus murinus. 
absolutely the same dentition as does the Koala, 
some slight modifications in the form of certain 
teeth excepted. The premolars in their longi- 
tudinal extent, compressed form, and cutting 
edge, would chiefly distinguish the dentition of 
the Potoroo; but the Koala evidently offers 
the transitional structure between the Phalangers 
and Potoroos in the condition of these teeth, of 
which one only is retained on each side of each 
Jaw in the Potoroos as in the Koala. 
The dental formula of Hypsiprymnus, the 
generic name of the Potoroos, is : 
Tncisors 
3 eee 
ot canines 
As molars — 30. 
—t1 
5% Premo- 
lars 
The two anterior incisors are longer and more 
curved, the lateral incisors relatively smaller 
than in the Koala. The pulps of the anterior 
incisors are persistent. The canines are larger 
than in the Koala; they always project from 
the line of the intermaxillary suture; and, 
while the fang is lodged in the maxillary bone, 
the crown projects almost wholly from the in- 
termaxillary. In the large Hypsiprymnus ursi- 
mus the canines are relatively smaller than in 
the other Potoroos, a structure which indicates 
the transition from the Potoroo to the Kangaroo 
genus. In the skeleton of this species in the 
