OF THE MARSUPIALIA. 327 
family (Macropodide),—animals of widely different general form. The Potoroos, how- 
ever, in this group, present absolutely the same dentition as the Koala, some slight 
modifications in the form of certain teeth excepted. The spurious molars, in their 
longitudinal 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 re- 
tained on each side of each jaw, in both Phascolarctus and Hypsiprymnus. 
; minted t =o : | 
The dental formula of the genus Hypsiprymnus is: incisors = ; canines = ; pre- 
| 44 
molars Carte molars w= 30. 
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 in- 
termaxillary suture ; and while the fang is lodged in the maxillary bone, the crown 
projects almost wholly from the intermaxillary. In the large Hypsiprymnus ursinus 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 Leyden Museum the canines present a longitudinal groove on the outer side. 
The characteristic form of the trenchant spurious molar has just been alluded to ; its 
maximum of development is attained in the arboreal Potoroos of New Guinea (Hypsi- 
prymnus ursinus, and Hyps. dorcocephalus) ; in the latter of which its antero-posterior ex- 
tent nearly equals that of the three succeeding molar teeth. 
Tn all the Potoroos the trenchant spurious molar is sculptured, especially on the outer 
side and in young teeth, by many small vertical grooves. The true molares each pre- 
sent four three-sided pyramidal cusps, but the internal angles of the two opposite cusps 
are continued into each other across the tooth, forming two concave transverse ridges. 
In the old animal these cusps and ridges disappear, and the grinding surface is worn 
quite flat. 
In the genus Macropus the normal condition of the permanent teeth may be expressed 
Lp ede Saito 0=-0) iii 44 _., 
as follows :—incisors ici? canines 5— ; preemolars ee molars aS 28. 
The main difference, as compared with Hypsiprymnus, lies in the absence of the upper 
canines ; yet I have seen them present, but of very small size, and concealed by the 
gum, in an adult specimen’ of a small species of Kangaroo (Macropus rufiventer, Ogilby.). 
This, however, is a rare exception ; while the constant presence and conspicuous size of 
the canines will always serve to distinguish the Potoroo from the Kangaroo. But besides 
this, there are other differences in the form and proportions of certain teeth. 
The upper incisors of the Macropi have their cutting margins on the same line, the 
' I have found the germs of the canine teeth in the early mammary fwtus of the Great Kangaroo (Macropus 
major). 
