510 



PLATE CXXIII. 



Diprotodon australis. 



Fig. 1 . Anconal surface of a distal phalanx of the left fore foot. 



Fig. 2. Thenal surface of the same. 



Pig. •">. Proximal end of the same. 



Fig. 4. Side view of the same. 



Fig. 5. Distal end of the same. 



All the figures are of the natural size. 



§ 4. Mandible and Teeth. — My friend Dr. Bennett, F.L.S., received from W. Gipps, 

 Esq., a considerable proportion of the right mandibular ramus of a Diprotodon which 

 was discovered by Mr. Gipps at "a place called Mandoona, near Wallarawang, New 

 South Wales," who kindly desired that it might be forwarded to me. 



The specimen arrived at the British Museum, with the instructive collection of 

 Australian fossils referred to at p. 507, which included the almost entire mandible of 

 a Diprotodon australis. Both specimens are of mature animals, with the teeth sym- 

 bolized as d 4, m i, m 2, m 3 in Plate XXIV.; and judging from the degree of wear of 

 these teeth in Dr. Bennett's specimen, and of the penultimate molar, the only tooth 

 sufficiently entire for comparison in Mr. Gipps's specimen, both are from aged indi- 

 viduals, but with some difference in that respect. 



The above molar series ranges along an extent of *i \ inches in both specimens ; and 

 as far as the mutilated condition of m 2, which is fractured and has lost much of its 

 enamel, will permit, the teeth are alike in size, shape, and proportions. 



It remains to be determined whether the following differences in the shape and pro- 

 portions of the jaw relate to age, or are sexual or specific. 



Assuming the latter, with a name for convenience of comparison, the horizontal 

 ramus in Diprotodon Bennettii is more slender in proportion to its length, and maintains 

 a more equable depth to the symphysial boss. The depth or vertical diameter at the 

 middle of the last molar is 4 inches 6 lines, in Diprotodon australis it is the same ; the 

 depth at the fore part of the socket of d 4 (first of the four molars in place) in Dipr. 

 Bennettii is 4 inches 6 lines, in Dipr. australis it is 5 inches 10 lines. From this 

 greater vertical extension of the fore part of the ramus the lower contour from the 

 symphysial boss to the antangular inflection is more concave in Dipr. australis. The 

 outer symphysial surface is continued from the boss more directly inward, more trans- 

 versely in Dipr. australis than in Dipr. Bennettii, in which it slopes more forward to 

 the median line of the fore part of the jaw. The outer alveolar wall of the molars, 

 especially of the first (d 4), is vertical and thin in Dipr. Bennettii, not swollen or pro- 

 tuberant as in Dipr. australis. The " foramen mentale " has the same relative position 

 to the boss in both species, but is midway between the upper and lower borders of the 



