RECORDS OF W.A. MUSEUM. 
[59 
The Balladonia specimens both show this polished surface ; in 
the younger tooth it has only just commenced, but on the inner 
surface of the other, one of the serrated ridges has quite disappeared 
— the action seems to commence at the point of the tooth and 
extend along the anterior edge, and then backwards towards the 
posterior border. The irregular area of the worn and polished 
surface is shown at b in figs. 4 and 6 of plate vm. 
The presence of these polished surfaces on the incisors of 
carnivorous or ossivorous animals is, I believe, unique. A carnivore 
would not require its lower median incisors to work against one 
another in a scissor-like manner, as do those of the phytivorous 
Kangaroo, and if traces of attrition are present an explanation must 
be sought in another direction. On examining the mandibles of 
the Dasyurida, among the marsupials, and of the Canidtz, which 
may be considered their Placental equivalents, it will be found that 
the two halves of the lower jaw are but loosely connected for a 
longer or shorter period of the animal’s existence. A number of 
these mandibles in the Museum Collection were carefully inspected, 
but no marks of attrition could be seen on the inner sides of the 
first incisors. It was, however, noted in these animals that during 
the process of crushing the food the upper cheek teeth are directly 
and alternately above the lower ones, hence any movement of the 
mandible due to the force used in crushing or masticating food 
would be outwards, that is to say, the two median incisors would 
be forced apart. 
In Thylacoleo, as restored by Prof. Owen, on the other hand, 
the relative positions of the large functional upper and lower 
premolars are such that the upper teeth pass outside the lower 
ones. The crushing of food between the cheek teeth would there- 
fore tend to press the lower mandibles together, and cause the 
incisors to rub against one another. In this way, flat surfaces 
might be worn on the inner sides of the two median incisors. 
It is to be hoped that more abundant remains of this animal 
will be found in the near future, for, could an almost perfect 
skeleton be examined, many points which are at present difficult 
to interpret would be made clear. 
At various dates, odd skeletal bones have been determined as 
probably belonging to Thylacoleo, and suggestions made concerning 
