PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS., 347 
foramen presents a somewhat trilobate or trefoil figure, as noticed in Phascolomys voin- 
batus, in my first memoir. 
Since the date of its communication specimens have come to hand which show that 
this character is not constant in either species, although the exceptions are rare. In 
fig. 5, Pl. L. is shown one of these exceptions in Phascolomys platyrhinus, and in fig. 6 
another in Phascolomys vombatus. The foramen magnum has always a greater trans- 
verse than vertical diameter; and the exceptions to the trefoil figure show it to be 
transversely elliptical, as in figs. 5 & 6. 
In Phascolomys latifrons this is the common form of the foramen magnum, with the 
ellipse more depressed, as in fig. 4. But of this species I have received the skull of 
a young, though nearly full-grown, animal, in which the sutures between the ex- and 
superoccipitals (Pl. L. fig. 7, 2,3) are not obliterated, and in which an unossified space 
or emargination exists between the exoccipitals below the superoccipital. In two 
skulls of Phascolomys latifrons the occipital part of the mastoid (8, 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 Phas- 
colomys 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 differences 
shown in this respect between the platyrhine (Pl. LI. fig. 1) and Tasmanian Wombats 
are less easily seized. In all the skulls I have yet seen of both species the temporal 
fossz (ib. fig. 1, 7,27) approach each other more nearly, absolutely as well as relatively, 
in the larger continental species” ; yet this character may be shown to be exceptionally 
affected in an aged male Tasmanian Wombat. Size, of course, is of itself a character of 
variety. The upper third of the fossa is formed by a longitudinal strip of parietal 
(Pl. LI. fig. 1 & Pl. LIL. 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 well-defined lacrymal 
tubercle (ib. 73) defining the fore and upper part of the orbit, are common to both the 
bare-nosed species, and distinguish them from Phascolomys latifrons. 
We come next to compare the nasal bones (PI. LI. figs. 1, 3, 4, 5, 15) in regard to 
shape, size, and connexions. 
' Compare Trans. Zool. Soc. vol. iii. pl. xxvii. fig. 1 (Phascolomys vombatus) and fig. 4 (Phascolomys latifrons) 
with fig. 1, Pl. LI. of the present paper. 
* Compare fig. 1, tom. cit. with fig. 1 in Pl. LI. of the present paper. 
3D2 
