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Suborder DIPROTODONTI A . 



Family FOSSORIA. 

 Genus Phascolomys. 



Osteology of the existing Species. 



§ 1. The Skull— The occiput (PI. XLVL fig. 1, 2, 3, & fig. 2) rises vertically from 

 the foramen magnum at the median line, but curves a little backward laterally, where 

 it forms the sides of the broad superoccipital (ib. fig 2, 3). The lower and lateral parts 

 of the occiput are formed by the exoccipitals (ib. fig. 2, 2), the mastoids ( 8 ), and 

 squamosals (27). The occiput is higher in proportion to its basal breadth than in 

 Phascolomys vombatus (ib. fig. 3) ; it is more quadrate in form ; it does not curve upward 

 and inward so regularly from the mastoid processes (s) to the summit, as in Phasco- 

 lomys latifrons (ib. fig. 4). 



The basioccipital (PI. XLVHL fig. 1, 1) contributes about half an inch of the thick 

 lower border of the foramen magnum. The exoccipitals (PI. XLYL fig. 2, 2) form the 

 lateral borders, developing there the condyles ; and the superoccipital completes the 

 middle of the upper border, which is sharp ; and as ossification of the latter element 

 does not usually extend so low down as to fill up the whole interspace left by the 

 exoccipitals, the foramen presents a somewhat trilobate or trefoil figure. The foramen 

 magnum has always a greater transverse than vertical diameter ; and the exceptions to 

 the trefoil figure show it to be transversely elliptical, as in figs. 5 & 6. 



In two skulls of Phascolomys latifrons the occipital part of the mastoid (s, fig. 7) 

 ascends above the process (8'), of nearly uniform breadth, to the superoccipital (3), and 

 separates the exoccipital ( 2 ) from the squamosal (27). In a third this character obtains 

 on one side ; on the other side it is obscure. In Phascolomys platyrhinus (ib. fig. 2) and 

 Phascolomys vombatus (ib. fig. 6) the upper part of the exoccipital ( 2) usually articulates 

 more extensively with the squamosal (27). 



The characters afforded by the upper surface of the skull differentiate the platyrhine 

 as strongly as they do the Tasmanian Wombat from the latifront species. The temporal 

 fossae (ib. fig. 1, 7, 27) approach each other more nearly, absolutely as well as relatively, 

 in the larger continental species than in the Tasmanian "Wombat. The upper third of 

 the fossa is formed by a longitudinal strip of parietal (PI. XLVII. fig. 1, & PI. XLVIII. 

 fig. 1,7); and this bends down from the temporal ridge more abruptly in Phascolomys 

 vombatus than in Phascolomys platyrhinus, while in the latter a slight rising or ridge is 

 developed from the line of the parieto-squamosal suture. In Phascolomys latifrons the 

 temporal ridges are less marked, and the parietals incline therefrom more outwardly to 

 join the squamosals. The feeble indication of the postorbital process (ib. 12), and the 



