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Show 802 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [Julie 27, First.-As to the greater relative size of the cranium, the above average measurements bring out that the proportion of breadth (at the posterior part of the zygomatic arch) to the length in P. platyrhinus is as 73 to 100 P. wombat „ 76 to 100 P. latifrons „ 73 to 100 Again the proportion of breadth to length at the anterior part of the zygomatic arch in P. platyrhinus is as 57 to 100 P. wombat „ 57 to 100 P. latifrons „ 58 to 100 The mandible bears correspondence to the first of these proportions ; in it the breadth is to the length in P. platyrhinus as 95 to 100 P. wombat „ 104 to 100 P. latifrons „ 89 to 100 From these results, then, it would appear that, besides absolute greater length, P. platyrhinus and P. latifrons agree in having relatively a narrower skull than P. wombat at the hinder part of the zygomatic arch, while P. platyrhinus and P. wombat resemble each other, again, in the comparative narrowing at the front part of the zygoma. Second.-The shape and greater relative breadth of the nasal bones is a point which, if constant, would serve admirably as a differentiating characteristic. For instance, in six examples of P. latifrons, of various ages, the skulls of which I placed side by side, there was only one which exhibited a very slight perceptible difference in the nasals. It, as well as all the others, was of an extremely regular equilateral triangular form. The exceptional specimen (No. 1843, Osteological Series, College of Surgeons*) had a slight break in the basal line of the forehead, wherein was wedged a narrow sharp-pointed process of the frontal. In other respects the straightness of the contour basal line was not altered. A similar inspection of crania of P. platyrhinus does not, however, afford the same striking uniformity. At first sight there is seemingly a great irregularity in the form of the nasals ; but these deviations resolve themselves into three kinds: one of these approaches the equilateral triangular figure found in P. latifrons ; another merges into what is more commonly obtained in P. wombat (namely a kind of spear-headed pattern); and the third is of an inconstant and intermediate grade between these two extremes. The proportional breadth of the two nasal bones at their hinder ends is to their length in P. platyrhinus as 76 to 100 P. wombat ,, 68 to 100 P. latifrons „ 112 to 100 * Owen's type specimen, for a representation of which, of the natural size, see ' Trans. Zool. Soc' vol. iii. pl. 37. f. 4. |