18Gr.] DR. J. MURIK ON PHASCOLOMYS PLATYRHINUS. 803 



Towards the anterior ends of the nasals the breadth in proportion 

 to length is in p pjatyrhinus as 29 to 100 



P. wombat ,, 25 to 100 

 P. latifrons „ 52 to 100 



The relation of breadth to length in P. platyrhinns is manifested 

 most distinctly in the first and third forms. In tliese the fronto- 

 maxillar)' suture approaches nearer the orbits, and the width of the 

 nasals continues forward generally beyond their middles ; in the 

 first the nasals begin to narrow only at the anterior third. In the 

 pattern which most nearly approaches that of P. wombat (i. e. spear- 

 headed), the fronto-nasal articulation, from its angular setting, gives 

 the nasals a certain narrowness ; the naso-premaxillary sutures 

 also early (at the posterior one-third) run towards each other, and 

 continue narrowing forwards, so that the anterior two-thirds, com- 

 pared with the posterior one-third, is very narrow. 



It is this very far backward narrowing, therefore, wherein consists 

 any real difference between P. ivombat and P. platyrhinus ; so that 

 the breadth of the anterior half of the nasals, compared with the 

 corresponding adjoining premaxillaries, is in a series relatively greater 

 in P. platyi-hinus than in P. wombat. The reverse or greatest rela- 

 tive breadth at the top of the premaxillaries is in favour of P. 

 wombat. But this rule has occasional exceptions, which, however, 

 do not militate against the general correctness of the proposition. 



Third. — As to the moderately deep tympanic excavation in P. pla- 

 tyrhinus, this obtained, with modifications, in six of the seven skulls 

 of this species examined. The converse was observed in P. wombat, 

 where one out of nine alone possessed a tendency to deep and broad 

 excavation of the supratympanic region. 



Fourth. — The more triangular form of the posterior palatine fora- 

 mina. This character, as so expressed, requires modification, inas- 

 much as in the Platyrhine Wombat, although it is generally large 

 and has an elongated and somewhat triangular form, yet this is sub- 

 ject to variation. In the Common Wombat it is even more incon- 

 stant, more often, however, round and small. 



The Vertebral Column. 



The regional distribution of the vertebral column in the genus 

 Phascolomys is as in Marsupials generally ; but the total number of 

 vertebral elements in the dorsal, lumbar, and caudal regions varies 

 so far as P. latifrons is concerned. P. platyrhinus and P. wombat 

 agree, excepting in the former of these two possessing occasionally 

 an additional caudal ossicle. P. latifrons, on the contrary, seems 

 always to have two less dorsal vertebrae, which come to be reckoned 

 as additional lumbar ones, while the caudal vertebra may be said to 

 be more than either of the other mentioned species. 



The vertebral formula, according to my investigations, is repre- 

 sented as follows : — 



P. platyrhinus Cv. 7, D. 1 5, L. 4, S. 4, Cd. 12, =42. 



P. wombat .. Cv. 7, D. 15, L. 4, S. 4, Cd. lOto ll,=40or4I. 



P. latifrons . . Cv. 7, D. lo, L. 6, S. 4, Cd. 15 to 1(), = 45 or 46. 



