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Show 1867.] DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. 803 Towards the anterior ends of the nasals the breadth in proportion to length is in p piatyrhinus as 29 to 100 P. wombat „ 25 to 100 P. latifrons „ 52 to 100 The relation of breadth to length in P. platyrhinus is manifested most distinctly in the first and third forms. In these the fronto-maxillary 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. spearheaded), 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, compared with the posterior one-third, is very narrow. It is this very far backward narrowing, therefore, wherein consists any real difference between P. wombat 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. platyrhinus than in P. wombat. The reverse or greatest relative 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. platyrhinus, 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 foramina. This character, as so expressed, requires modification, inasmuch as in the Platyrhine Wombat, although it is generally large and has an elongated and somewhat triangular form, yet this is subject to variation. In the Common Wombat it is even more inconstant, 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 represented 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. 10 to 11, = 40 or 41. P. latifrons . . Cv. 7, D. 13, L. 6, S. 4, Cd. 15 to 16, = 45 or 46. |