252 



PEOFESSOE OWEX OX THE FOSSIL MAMMALS OF AUSTEALIA. 



The subject of Plate XXXIX. figs. 1, 2, 3 was obtained from " a salt-lake, nearly 100 

 miles west of Melbourne," and was transmitted to me by Dr. Hobson*. It is the sym- 

 physial end of the mandible, with 4^ inches of the joint (s, s'), the obliteration of which 

 indicates the age of the individual ; it includes the implanted parts of the incisors {i'), 

 and of the three anterior molars of each ramus (fig. 1 ). The under part of the symphysis 

 (fig. 2, Plate XXXIX.) shows the pair of subsymphysial foramina (r) in the same relative 

 position as in the existing Wombats (ib. fig. 4, r). The prolongation of the attenuated 

 anterior end of the mandible shows a nearer resemblance in Phascolomys gigas to Phas- 

 coJomys laiifrons (Phil. Trans. 1872, Plate xxiii. fig, 3) and Phascolomys Krefftii (ib. 

 Plate XX. fig. 2) than to Phascolomys platyrkinus (ib. Plate xix. fig. 2) or to Phascolomys 

 vomhatus (ib. fig. 1). The upper surface of the specimen (Plate XXXIX. fig. 1) shows 

 the same concavity between the right and left anterior molars as in the more perfect 

 specimen of Phascolomys gigas (Plate XXXVIL). The hollow implanted ends of the 

 incisors (Plate XXXIX. figs. 1 & 3, exposed by fracture of the fossil, hold the same 

 relative position to the third molars [m i) as in the more complete mandible. The 

 anterior outlets (ib. fig. 1, v) of the dental canal are in the same position. 



The subject of fig. 5, Plate XL., shows a slight inferiority in the size of the molar 

 teeth as compared with that of figs. 1, 2, & 3, Plate XXXVI. The present fossil is a 

 portion of the left ramus with the last four molars in place. The longitudinal extent 

 of their grinding-surfaces is 3 inches 5 lines (Plate XL. fig. 5), as against 3 inches 6 lines 

 (Plate XXXVI. fig. 3); that of the first three molars is the same in both specimens, 

 and the difference is due to a smaller size of the last molar in the present (Plate XL. 

 fig. 5, m 3), the hind lobe of which also shows a longitudinal indent. I am unwilling to 

 regard this as signifying more than a variety of Phascolomys gigas. The features of the 

 mandible, such as the anterior origin of the ectocrotaphyte ridge (ib. fig. 6, A), and of the 

 ascending ramus (ib. fig. 6, q), as also the ectalveolar groove (ib. fig. 5, u) and postalveolar 

 ridge (ib. ib. t), so far as they are preserved, closely resemble those of the more com- 

 plete specimen of mandible of the present large species. 



The fourth example of Phascolomys gigas I know through a cast and photograph of 

 the original, now in the Australian Museum, Sydney, New South Wales. The cast was 

 prepared by direction of the Trustees of that Museum, and was transmitted as a donation 

 to the British Museum. A photograph of the natural size, showing the grinding-surface 

 of the molar teeth, was forwarded to me through the same liberality. The specimen is 

 a portion of the right ramus, including the scries of five molars and the entire incisor 

 (Plate XL. figs. 1-4), of which tooth a separate cast was prepared and transmitted. The 

 molars show a slight superiority of size over those in the subject of Plate XXXVI., as 

 may be seen by comparison of figs. 3 & 4 in that Plate ; but this I take to be within the 

 limits of individual or sexual range of size. The configuration of the ramus, so far as 

 the comparison can be made, closely resembles that of the more complete mandibles of 

 the present species (Plates XXXVI., XXXVIL, & XXXIX.): the portion of the 



* Letter from Dr. Hodson, March 3rd, 1844. 



