802 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [Juiie 2/, 



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. p^ati/rhinus is as 73 to 100 

 P. loomhat „ 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 5/ to 100 

 P. wombat ,, 57 to 100 



P. latifrons „ 58 to 100 



The mandible bears correspondence to the first of these propor- 

 tions ; in it the breadth is to the length in 



P. platyrhinus as 95 to 100 

 P. ioombat „ 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 rela- 

 tively a narrower skull than P. wombat at the hinder part of the zygo- 

 matic 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 differentia- 

 ting 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 fi'ontal. 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 seem- 

 ingly a great irregularity in the form of the nasals ; but these devia- 

 tions 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. ioombat (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 7^ to 100 

 P. wombat „ 08 to 100 



P. latifrons „ 112 to 100 



* Owen's type specimen, for a representation of which, of tlie natural size, see 

 ' Trans. Zool. Soc.' vol. iii. pi. 37. f. 4. 



