399 



predecessor, it must then be the tooth (p 3) which I suppose it to represent. In either 

 case the modification is rare, and, so far as I know, unique in the bilophodont section of 

 Macropodidw. assuming the foremost tooth to be 6,2, it repeats the condition and 

 formula of the molar series in Diprotodon and Nototherium. 



I shall not here carry further the account of the dental changes in living species of 

 Kangaroos; but there are modifications of the grinding- surface and crown of the molar 

 teeth which are useful in tracing out the affinities of extinct species. 



The premolar, like the foremost deciduous molar, has an antero-posteriorly extended 

 crown, with a more or less trenchant margin, supported by two roots. The margin 

 may be slightly thickened and obtuse posteriorly, with a still more feeble swelling 

 anteriorly, and the crown may not show any other modification ; such is the very small 

 lower premolar of Macropus (Osphranter) robustus, Gd. (ib. fig. 13, p 3). In the upper 

 jaw of this species the premolar (fig. 14', a, b), with an increase in antero-posterior and 

 transverse extent, shows none in the vertical direction ; but the thickened fore part 

 of the crown is divided by a notch from the rest of the trenchant border, and this by a 

 smaller notch from the hind swellings ; moreover the base of the crown is produced 

 inward, and this ridge swells out posteriorly. The fore-and-aft dimension of the upper 

 premolar does not, however, exceed that of the adjoining molar, d 4. 



In Macropus [Boriogale) magnus (fig. 12) the upper premolar, or its representative, 

 is not so long from before backward as the adjoining two-ridged molar. The anterior 

 thickening is not marked off by a notch ; it is connected by a basal rising with the hinder 

 thickening, and the intermediate rather depressed outer surface shows two faint vertical 

 ridges. An inner basal ridge swells into a small tubercle posteriorly. 



In the lower jaw (fig. 12 a) the still smaller homotype has the crown transversely 

 cleft to its base, and the hinder, somewhat larger lobe is thickest behind, with a feeble 

 internal tubercle. 



The upper premolar of Macropus erubescens (ib. figs. 1 & 2, p 3) is similarly cleft, 

 though not quite to the base ; it has an inner basal ridge swelling behind into a 

 tubercle, which abuts upon the hinder and larger division of the cleft crown. The 

 lower premolar, of smaller size (Plate LXXX. figs. 4 & 5,p 3), is cleft in a minor degree. 



In Macropus ualabatus the premolar exceeds the adjoining molar (^4) in antero- 

 posterior extent. In the upper jaw the trenchant border is slightly notched by a few 

 vertical grooves traversing the outer side of the crown ; and the inner basal ridge is 

 similarly but more deeply notched ; the entire crown is also broader than in the pre- 

 molars of the previously cited species. 



The modifications of the crown in the transversely two-ridged or " bilophodont " molars 

 add characters in the discrimination of fossils, and it is convenient to define and name 

 the parts affording them. The main 'lobes" (ib. figs. 29, 30, & Plate LXXXI. fig. 13, 

 m 3) are " front " (a) and " back " (b) ; a ridge along the fore part of the base of the 

 crown is " prebasal " (f) ; if, as is usual, there be one at the back part of the crown it 

 is " postbasal" (g, fig. 29, Plate LXXX. & Plate LXXXI. figs. 12 & 15, ni), Com- 



40* 



