1886.] MR. O THOMAS ON LAGORCHIiSTES FASCIATUS. 54.) 



individual teeth are more or less as follows : — i' is tlie largest of the 

 three, boldly curved forwards, and descending below the level of the 

 other two, its tip sharp and gauge-shaped ; i'' and i'' 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 in 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, F and i^ are 

 each longer antero-posteriorly than i' and, when looked at externally, 

 have much the same appearance as those of Lac/orchestes, except 

 that i'' is longer than i^, while in Lagoi-chestes 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 surface of i" forms an even oblong, its breadth slightly 

 more tban half its length ; wbile the flatness of i^ is only modifitd 

 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 Macropodince, 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. 18li(>, p. 28. 

 Proc. Zool. Soc— 1886, No. XXXVI. 36 



