810 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [Juue 27, 



lous among the Marsupials, by reason of its having fifteen ribs, in 

 coutradistinction to the other genera of its family, which have 

 thirteen, excepting the Petavxrists, where they are twelve in number. 

 The Phascolomys latifrons, however, reduces this anomalous cha- 

 racter to specific variety, for in it we have a return to the usual 

 Marsupial number of thirteen. This diminution in the number of 

 ribs may of itself be regarded as a marked character, fully justifying 

 and carrying out Prof. Owen's proof, from the skull, of the specific 

 distinctnness of the animal. 



This circumstance, however, is unfortunate for the Professor's rea- 

 soning upon the adaptive design of AVombats having fifteen pairs, as 

 opposed to other genera of the Marsu))iata. He remarks*, "The 

 pressure to which the trunk of the Wombat must occasionally be 

 subjected, in its subterranean burrowings, is probably the condition 

 of the development of the additional pairs of ribs in that species." 

 But in P. latifrons we have a doubtless burrowing Wombat wherein 

 no more than the usual development of ribs in the Marsupials is 

 found ; for Mr. G. F. Angas's observations -f lead to the belief that, 

 so far as scratching and burrowing are concerned, the Hairy-nosed 

 Wombat is a thorough adept in the art. 



The ribs in the Platyrhine Wombat bear a proportion to its much 

 more strongly built body ; and anteriorly the grooves for the attach- 

 ment of the intercostal muscles are well marked. Both the Common 

 and Hairj'-nosed species have rounder as well as weaker costse. In 

 all the species the first rib is the flattest and shortest one. 



Bones of the Fore Limb. 



Scapula. — There is a distinct and well-marked difference in the 

 form of this bone in the three species of Wombat, and such as would 

 not occur by mere growth from a younger towards an older condi- 

 tion — that is, supposing that P. wombat were but an immature stage 

 of the larger-sized P. platijrhimts. 



For example, the proportional breadth to length is in P. platij- 

 rliinus as 72 to 100, in P. wombat 53 to 100, and in P. latifrons 

 56 to 100, the preponderance of breadth to length, then, being 

 greatly in favour of the Platyrkine species. 



In P. platyrhinus the scapula approaches to a square form, and 

 is not oblong as in P. wombat, or irregularly oblong as in P. lati- 

 frons. The total length of the bone is more nearly aUke in the 

 three species ; but the relative breadth in the first named is almost 

 one-third greater. The entire bone in P. platyrhinus is immensely 

 strong and massive, and the free margin of the spine is unusually 

 broad for attachment of the muscles. 



In P. latifrons this bone does not conform to the remarkably 

 regular oblong quadrate figure which Prof. Owen has pointed out to 

 be characteristic of P. wombatX, where the superior and inferior costse 

 run nearly parallel the one to the other. 



* Trans. Zool. Soc. vol. ii. p. 396. t P- Z. S. 1861, p. 270. 



+ Trans. Zool. Soc. vol. ii. p. 399. 



