1886.] | MR.O THOMAS ON LAGORCHESTES FASCIATUS, 545 
individual teeth are more or less as follows :—i’ is the largest of the 
three, boldly curved forwards, and descending below the level of the 
other two, its tip sharp and gauge-shaped; i° andi’ are both much 
smaller than i', very narrow transversely, and provided with sharp 
cutting-edges ; of the two, i° is nearly invariably the larger. On 
. placing the mandible iv position, the large scalpriform lower incisors 
fit in naturally between the upper ones, not biting vertically upon 
their edges, but only upon the palate between them (fig. 9). The 
lower incisors themselves are very uniform in shape, and always 
provided with sharp cutting-edges along their inner margins (see the 
section fig. 10), the animals being able, owing to the looseness of the 
symphysial joint, to separate and approximate these cutting-edges’, 
and thus to utilize them as a pair of scissors with which to snip off 
leaves or grass, 
Turning, on the other hand, to Lagostrophus fasciatus, we find a 
very different state of things. First, the two series of upper 
incisors are close together, meeting at a sharp angle in front and 
diverging but little behind (fig. 2). Then as to the size of the 
teeth, i’, instead of being the largest, is the smallest of the three, 
at least in cross section, and even vertically it is but little longer 
than the others (figs. 2 and 6); in shape it is conical, scarcely curved 
forwards, and with a blunt, rounded or flattened tip. I? and i° are 
each longer antero-posteriorly than i* and, when looked at externally, 
have much the same appearance as those of Lagorchestes, except 
that i is longer than i*, while in Lagorchestes and in nearly all 
other Kangaroos the reverse in this case. But when looked at from 
below (fig. 2), there appears a very remarkable difference ; instead 
of being narrow and sharp-edged, they are broad and flat-topped, 
and are evidently not formed for cutting in the true sense at all. 
The palatal surtace of i forms an even oblong, its breadth slightly 
more than half its length ; while the flatness of i° is only modified 
by a broad shallow groove running along its centre, and terminating 
at its postero-external corner, where it forms a notch on the outer 
edge of the tooth evidently homologous with that found in a similar 
position in the other Wallabies. 
Trying now the same experiment as before of placing the lower 
jaw in position, we see at once what a difference the contraction of 
the incisor series must make in the manner of using them; for the 
lower incisors, instead of dropping down between the upper ones, 
come flat upon the top of them, so that there can only be a grinding- 
and not a cutting-action between the upper and lower teeth, 
An examination of the lower jaw of L. fasciatus seems to show 
that this species, and this alone of the Macropodine, is without the 
power of using the two rami independently, as the junction between 
them, instead of being loose and narrow, is broad, close, and firm, 
the vertical height at the symphysis being so great in proportion to 
the size of the jaw as to produce a distinct rounded prominence on 
1 See Murie and Bartlett, P. Z.S. 1866, p. 28. 
Proc. Zoon. Soc,—1886, No. XXXVI. 36 
