326 



the malar (ib. ib. us) on the left side, showing the malo-maxillary suture. To this help 

 in the determination of fossils of the marsupial genus under consideration I was led by 

 the following comparisons. 



In the largest of three skulls of Phascolomys vombatus available for the purpose, the 

 left upper molary series, taken as in the fossil, does not equal 2 inches ; it falls short by 

 m arly a line. In the specimen figured in my "Osteology of the Marsupialia'f , it is 

 1 inch 8 lines ; in the next in size it is 1 inch 10 lines ; in an evidently younger Wombat, 

 with all the molars in place and use, the series is 1 inch 7 lines. 



These five ever-growing teeth gain in fore-and-aft as in transverse diameter, until the 

 full size of the individual is attained ; they grow with the growth of the skull, though 

 in a minor ratio ; and I have no evidence of their exceeding in size the teeth requiring 

 the extent of alveoli noted in the largest of the cranial specimens of Phase, vombatus 

 before me. 



Now in this, as in the second-sized skull, the lower border of the malar process of the 

 maxillary bone is G lines above the margin of the outer wall of the alveolar opening of 

 m 2 ; in the younger and smaller skull it is 5 lines. In all the specimens the maxillary 

 contributes to the inner and lower part of the beginning, or anterior pier, of the zygoma, 

 speedily narrowing to a point as it passes backward on the outer side of the arch, where 

 it ends about 7 lines from the back part of the origin of the process ; the depth or ver- 

 tical diameter of the outer side of the base of the zygomatic process of the maxillary is 

 about 2 lines. 



In the skull of a Phascolomys latifrons with an upper molary series, taken at the 

 alveolar outlets, of 1 inch 10 lines in extent, the malar process of the maxillary rises 

 7^ lines above the issue of the second molar, there contributes 3£ lines in depth to the 

 under and fore part of the beginning of the zygoma, and narrows to a point 7 lines behind 

 its origin. In another skull of Phascolomys latifrons with a molary series of 1 inch 

 1 line in extent, the maxillary process rises 8 lines above the outlet of the second molar, 

 and contributes a similar small proportion to the under and fore part of the zygoma. 



In the skull of a Phascolomys platyrhinus with a molary series 2 inches 1 line in extent, 

 the malar process of the maxillary (Woodcut, fig. 5, «•) rises 6 lines above the outlet of 

 the second molar, and contributes 3^ lines to the vertical extent of the beginning of the 

 zygoma (26), which here has a total depth of 1 inch 4 lines ; the process («•) decreases to 

 a point at 9 lines from its origin. 



In the fossil (Plate LI. fig. 5) with a molary series of the same extent as in the 

 last skull, the malar process of the maxillary (21) rises 9 lines above the outlet of the 

 molar, and contributes 7 lines to the vertical extent of the fore part of the zygoma (26). 

 The different relation of the malo-maxillary suture to the premasseteric ridge (m) is 

 strongly marked between the fossil and any of the recent species of Wombat, the 

 interspace between the front pier of the zygomatic arch and the alveolar outlets being 

 much greater in the fossil. 



t Trans. Zool. Soc. vol. ii. (1838) plate lxxi. fig. 6. 



