PEOFESSOR OAVEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



193 



and curves iminterruptedly to the underside, as in Phase. ])latyrlvinus and Phase, voirir 

 hatus. In size this fossil does not exceed the Tasmanian species. The antero-postcrior 

 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 DoAvns, Queensland, and was presented to the British 

 Museum by Sir William M*^Artiiur, Bart. 



§ 16. Mandibular fossil q/' Phascolomys platyrhinus, Ow. — The subject of figs, 3 & 4, 

 Plate XX., well exemplifies the differences by which I^hascolomys 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 (/) is repeated ; the formal characters of d z 

 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 Eiver, Queensland, by Edwaed 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 q/" Phascolomys parvus, Oiu. — 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, e. g., in the Tasmanian 

 Wombat, which is the smallest of the known existing species. The series of molars in 

 Plate XIX. fig. 6, contrasted with those in fig. 1, is implanted in a mandible of similar 

 small size (Plate XX. figs. 6 & 7). In the lower contour, the depth of the ectocrota- 

 phyte fossa (/"), 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. s.s*) ; it is long, but less deep relatively 

 than in Phascolomys Mitchelli (Plate XXI. fig. 6). 



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 3|- lines, the fore lobe of the first {d 4) and the hind lobe of the last {in 3) being 



