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XXIII. On the Fossil Mammals of Australia . — Part IX. Family Magropodid^e ; Genera 
Macropus, Pachysiagon, Leptosiagon, Procoptodon, and Palorchestes. By Pro- 
fessor Owen, F.R.S. & c . 
Received April 19, — Read June 19, 1873. 
§ 1. Macropus Titan. — In illustration of certain fossils from the freshwater beds of the 
Queensland province, showing the hindmost mandibular molars with characters of the 
general type of those' of the Macropus Titan , but with modifications indicative of specific 
difference, it appears requisite to premise figures and descriptions of the corresponding 
molars at a similar stage of wear and age, which are plainly referable to Macropus Titan. 
In the subjects of figs. 13 & 15, Plate xxn. of a former Part*, the last mandibular 
molar had but recently come into use ; the edges of the two main lobes showed the 
backwardly oblique abrasion of the enamel, but not carried so far as to expose the 
dentine ; the links were entire from their origin at the fore and outer angles of the two 
lobes ; the hind surface of the second lobe showed the whole of the angular fossa on its 
inner half, and the small faint vertical notch external thereto. 
In the subjects of Plate LXXVI. figs. 2, 4, the direction of wear against the upper 
molar from above downward and backward has extended the abrasion from the second 
lobe to its hind basal surface, where the bottom of the hind fossa (g) alone remains ; 
with the edges of the wedge-shaped lobes the origins of the link (r) are gone, and only 
the lower antero-posterior ends remain, dividing the valley into a smaller outer and 
a larger inner depression. The prebasal ridge ( f ) is correspondingly reduced in fore- 
and-aft extent. 
That these changes or modifications of working-surface of m 2 and m 3 are due to age 
and wear will be clear to any one comparing these teeth in Plate LXXVI. figs. 2 & 4, 
with those before quoted of large full-grown individuals of Macropus Titan , described 
and figured in Part VIII., and with m 3 of fig. 1, Plate LXXVI. 
The size and form of the portions of mandible preserved closely agree with those of 
the corresponding parts of the more entire mandibles of Macropus Titan, figured in 
Plate xxii. figs. 13 & 15 and Plate xxvi, figs. 11 & 13 of Part VIII. And I here 
subjoin a view from above (Plate LXXVI. fig. 1), not before given, of the subject 
of the last-cited figure, to illustrate the correspondence in the breadth and direction of 
the “ectalveolar groove” (u) and in the thickness of the mandible, including the fore 
part of the base of the coronoid, with corresponding parts of the bone from the more 
aged animals that have afforded the subjects of figures 2 & 4, Plate LXXVI. 
* Part VIII., Philosophical Transactions, 1874, p. 256. 
5 N 
MDCCCLXXIV. 
