578 PROF. OWEN ON HYPSIPRYMNODON. 



narrower than, in Potoroos. The palatal vacuities are bound behind by slender trans- 

 verse bars of the palatines, and extend forward to the interspace betweeen the premolar 

 and first molar teeth. Mr. Ramsay rightly notes of the posterior palatal openings 

 the character of the anterior margins meeting the exterior lateral at an acute angle *. 

 The breadth of the skull outside the zygomata is 1 inch 3 lines (32 millims.) ; the 

 vertical diameter of the zygoma at the back part of the orbit is 5 millims. It does not 

 increase posterior to this part, as in Kangaroos, but rather loses in that dimension as it 

 extends to the tympanic bone. 



The dental formula of Hypsiprymnoclon is that of the Potoroos, viz. i. j—^, c. ttzq, 



1 1 4 4 



p. j~p m. -r — -. — 30. The molar series in each jaw, according to characters of develop- 

 ment, include the teeth symbolized as p. 4, d. 3, m. 1, m. 2, m. 3f . In some Potoroos 

 {Hypsiprymnus Gilberti e. g.) the crown of the premolar deviates from the longitudinal line 

 of direction of the four following teeth by a slight turn outwards, and rather more so 

 in the mandible $ . A similar outward bend of the premolar is more marked in Hypsi- 

 prymnoclon §, in which the crown of the tooth, p. 3, presents the proportions shown in 

 H. Gilberti. In most Potoroos the fore-and-aft extent of the crown of the grooved and 

 trenchant premolar is relatively greater. The molars in Hypsiprymnoclon repeat the 

 proportions most common in the Potoroos, the last (m. 3) being the smallest, whilst in 

 H. Gilberti the first (cl. 4) is the smallest. 



The length of the forearm and hand from tip of elbow to the nail, inclusive, is 3 inches 

 2 lines (80 millims.), of leg and foot, 4 inches 9 lines (122 millims.), of fore foot, in- 

 cluding carpus, 1 inch 3 lines (30 millims.), of hind foot, including tarsus, 2 inches 5 lines 

 (61 millims.), of face from tip of nose to base of ear 2 inches 5 lines (61 millims.). 



The ulna and radius are in contact along their distal halves (PI. LXXII. fig. 5). The 

 radius is more slender and of more uniform breadth than in Hypsiprymnus Gilberti or 

 Bettongia penicillata (PI. LXXII. fig. 9). In these and other Potoroos the bone is pro- 

 duced ulnad at its distal lower two thirds as a sharp plate. The length of the radius is 

 1 inch 9 lines (45 millims.) in Hypsiprymnoclon moschatus, but is only 1 inch 6 lines 

 (40 millims.) in Bettongia penicillata,, with twice the breadth, viz. 5 millims. These 

 differences are notable for the exigencies of palaeontology in reference to detached bones 

 in caves, breccias, and drifts. The ulna of Hypsiprymnoclon is 2 inches 2 lines 

 (55 millims.). The metacarpal and phalanges are longer and more slender in Hypsi- 

 prymnoclon than in Hypsiprymnus, save the ungual phalanges of n, in, and iv, which are 

 both longer and stronger than in the Potoroos. 



The tibia and fibula, after their proximal coarticulation, keep -apart for more than 

 half their length distad ; in the rest of their course they are in close contact but not 

 ankylosed. In Bettongia penicillata the interosseous space occupies but one third of the 

 proximal portions of the shafts of the two leg-bones ; in the rest of their extent the tibia 

 and fibula are ankylosed, with a slight linear indication of their primitive distinctness. 



* Tom. cit. p. 34. t ' Odontography,' 1844 ; Proceedings of the Zoological Society, 1877, p. 358. 



X Plate LXXII. fig. 8. § lb. figs. 3 & 4. 



