PEOFESSOE OWEN ON THE SPECIES OP PHASCOLOMTS. 34T 



foramen presents a somewhat trilobate or trefoil figure, as noticed in Phascolomys vom- 

 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, PI. L. is shown one of these exceptions in Phascolomys platyrhinus, and in fig. 6 

 another in Phascolomys vomhatus. 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 (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 platyrkinus (ib. fig. 2) and Phas- 

 colomys vomhatus (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 diflferentiate the platyrhine 

 as strongly as they do the Tasmanian Wombat from the latifront species' ; the differences 

 shown in this respect between the platyrhine (PI. LI. fig. 1) and Tasmanian Wombats 

 are less easily seized. In all the skulls I have yet seen of both species the temporal 

 fossae (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 

 (PI. LI. fig. 1 & PI. LII. fig. 1, 7 ), and this bends down from the temporal ridge more 

 abruptly in Phascolomys vomhatus than in Phascolomys platyrhinus; while in the latter 

 a slight rising or ridge is developed from the line of the paiieto-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 (PL LI. figs. 1, 3, 4, 5, 15) in regard to 

 shape, size, and connexions. 



' Compare Trans. Zool. Soc. vol. iii. pi. xxxvii. fig. 1 (Phascolomys vombaius) and fig. 4 (Phascolomys latifrons) 

 ■with. fig. 1, PI. LI. of the present paper. 



' Compare fig. 1, torn. cit. with fig. 1 in PI. LI. of the present paper. ; 



3d2 



