1867.] DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. 809 



truncation of the body or shield-like flattening so verj' remarkahle 

 in the living Platyrhine Wombat. 



P. lati/rons differs from the other species in having the transverse 

 processes of the sacral vertebrae shortening from the first to the 

 fourth ; in other words, the sacrum narrows behind, whereas in P. 

 platyrhinus and P. wombat it is as broad, if not broader posteriorly 

 than anteriorly. 



Caudal Vertebrx. — In all the species the first six have transverse 

 processes, the seventh vertebra in each presenting a rudimental one. 

 The processes generally of the remaining caudal vertebrae are very 

 obscure, and the last two or three are little better than tiny ossicles. 



In P. platyrhinus the great length and breadth of the backwardly 

 inflected transverse processes of the first three or four caudal verte- 

 brae is somewhat remarkable. These almost reach the tuber ischii, 

 so that the sacral and these anterior caudal vertebrae taken together 

 present a long, broad, and flat shield, which in the live animal (P. 

 niger of Gould) in the Gardens is very conspicuous. 



The Common Wombat, though very much resembling P, platy- 

 rhinus in its caudal elements, seems to have the transverse processes 

 relatively shorter, and consequently to present a greater interspace 

 between their tips and the inner border of the ischium. 



P. lati/rons is readily distinguished by the very much shorter and 

 pointed nature of the caudal transverse processes ; but these are, 

 moreover, comparatively broader antero-posteriorly at their roots 

 than in P. wombat and P. platyrhinus. 



From this shortening of the outstanding transverse processes, and 

 a more or less greater length in the vertebrae themselves, the caudal 

 region in P. lati/rons entirely wants the short truncated aspect pre- 

 sent in the other two species. 



In all the animals when alive the tail is very short, but it is more 

 perceptible in the Hairy-nosed Wombat than in Common and Pla- 

 tyrhine species. 



Sternum and Ribs. 



Sternum. — I have found the bones of the sternum of the specimens 

 of the Platyrhine and Hairy-nosed species, except in one instance, 

 four in number, as is the case in thejCommon Wombat. In the ex- 

 ceptional example (a' portion of a disarticulated skeleton of P. pla- 

 tyrhinus in the College of Surgeons, at present labelled P. wombat) 

 there are five bony pieces composing the sternum. This peculiarity 

 in the number of sternal elements is a reversion to what obtains in 

 the Petaurus taguanoides. 



The sternal bones of P. jilatyrhinus are altogether much the largest 

 of the three, but those of P. lati/rons are relatively the stoutest. 

 The hindermost bone, that to which the xiphoid cartilage is attached, 

 is broadened posteriorly in P. platyrhinus, the fifth rib-cartilages 

 abutting against the lateral protruding portions. In P. lati/rons 

 this bone is obtusely pointed, and in P. wombat more abruptly trun- 

 cated posteriorly. 



Ribs. — The Common Wombat has been regarded as very anoma- 

 Proc. Zool. Soc— 186/, No. LII. 



