PEOFESSOE OWEN ON THE EOSSIL MAMMALS OF AUSTEALIA. 
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and curves uninterruptedly to the underside, as in Phase, platyrhinus and Phase, vom - 
batus. In size this fossil does not exceed the Tasmanian species. The antero-posterior 
extent of the working-surfaces of the five molars is the same, viz. 1 inch 11 lines; but 
the teeth are rather narrower transversely, and the last molar, especially its hinder lobe, 
shows a greater decrease, as in the Hairy-nosed Wombat. 
I indicate this modification of Phascolomys, from which the present fossil has been 
derived, by the name of the late estimable Professor of Geology in the Sydney University, 
New South Wales, Alex. M. Thomson, D.Sc. The specimen is from a lacustrine 
deposit at Gowrie, Darling Downs, Queensland, and was presented to the British 
Museum by Sir William M c Artiiur, Bart. 
§ 16. Mandibular fossil of Phascolomys platyrhinus, Ow. — The subject of figs. 3&4, 
Plate XX., well exemplifies the differences by which Phascolomys platyrhinus differs 
from Phascolomys Thomsoni. The symphysis has the same backward extent and relative 
position to the molar series as in the recent specimen (Plate XIX. fig. 2) ; the character 
of the upper surface of the diastemal tract (l) is repeated; the formal characters of d 3 
and of i in the fossil are precisely those in the recent continental bare-nosed Wombat: 
in size the fossil equals the largest living specimen of that species. The antero-posterior 
extent of the molar series is 2 inches 2-| lines. The shape and proportions of the molars 
characteristic of Phascolomys platyrhinus are closely preserved in the fossil. It was 
obtained from the bed of a tributary of the Condamine River, Queensland, by Edward S. 
Hill, Esq., and shows that the characters of the actual Platyrhine species were esta- 
blished at a period coeval with the existence of Diprotodon and Thylacoleo. 
§ 17. Mandibular and lower molary characters of Phascolomys parvus, Ow. — With 
present evidence of the constancy of size of the molar series of teeth in existing and 
extinct species of Wombat, such series fully in place and well worn, having a longitudinal 
extent of 1 inch 5 lines, cannot be referred to a species with a longitudinal extent of 
molars never less than 1 inch 9 lines, and usually more : as, c. g., in the Tasmanian 
Wombat, which is the smallest of the known existing species. The series of molars in 
Plate XIX. fig. G, contrasted with those in fig. 1, is implanted in a mandible of similar 
small size (Plate XX. figs. G & 7). In the lower contour, the depth of the ectocrota- 
phyte fossa (f), the breadth of the ectalveolar groove, the shape and size of the incisor, 
and the shape of the grinding-surface of the anterior molar (d 3 ) this fossil agrees with 
Phascolomys platyrhinus. But the symphysis (Plate XX. fig. 7, 3 ) does not extend so far 
back ; it ends there below the interspace between the second (d 4 ) and third ( m 1 ) molars. 
The hind contour of the symphysis is subbilobed (ib. ; it is long, but less deep relatively 
than in Phascolomys Mitchell i (Plate XXI. fig. G). 
The grinding-surface of the anterior molar (Plate XIX. fig. 6, d 3 ) is subelliptic, with 
the long axis nearly parallel with that of the jaw, 2 lines and 1 line in the two diameters, 
showing the usual disposition of the incomplete coat of enamel. The succeeding molars 
have the normal bilobed or biprismatic shape; their grinding-surfaces do not exceed 
severally 3tj? lines, the fore lobe of the first (d 4 ) and the hind lobe of the last (m 3 ) being 
