or THE AUSTEALIAX MAESUPIALTA. 103 



almost at the level of that of the trigonid, and partly that the cusps of both portions 

 have much the same characters. In tig. 9i is represented a tooth whicli had not yet 

 appeared above the bone, and in this the trigonid will bo seen to show indications of the 

 angularity characteristic of normal forms. This specimen is of great interest, not only 

 as iadicating the former presence of this condition in the lower molai's, but also as 

 implying a similar condition in the more highly modified upper teeth. In some cases it 

 is possible to recognize in the lower molars an anterior tubercle representing the antero- 

 extornal shelf characteristic of normal forms. 



The most peculiar feature of the lower teeth is, however, the marked differentiation 

 between the outer and inner cusps, the j)i"otoconid and hypoconid being reduced, while 

 the paraconid, metaconid, entoconid, and sometimes the hypoconulid are large and 

 elongated. These relations are exactly the reverse of those in tlie Dasyurinte. As 

 Leche has joointed out, the condition is partly attributable to mechanical wear. In the 

 anterior molars, which, heing older, have been in use for a longer time, the protoconid 

 and hypoconid are ibund in a much more advanced stage of redaction than in the newer 

 posterior teeth. In extreme cases, where the outer cusps have been worn down to their 

 bases, the teeth present a curious appearance ; when viewed internally in profile they 

 appear triconodont, or, in cases where the hypoconulid is well developed, quadri- 

 conodont, the cusps being arranged in a linear series from before backwards. The basal 

 ledge, which formerly supj)orted the two outer cusps, presents the appearance of a wide 

 external cingulura. The reduced condition of the protoconid and hypoconid is not, 

 however, wholly attributable to mechanical wear, since the same tendency is seen in the 

 unworn teeth, although naturally in a lesser degree. It apjiears as if the repeated 

 obliteration of the outer cusps by wear had produced a development in that direction. 



The first lower molar, believed by Winge to represent a formerly deciduous tooth, is 

 usually found in a much more reduced condition than the remaining teeth. Leche 

 regards this also as the result of use. In all of the older specimens which I have 

 examined, and also in the young specimen represented in PI. 6. fig. 9 <?, the tooth 

 shows three or four cusps arranged in a linear series. These apparently represent the 

 inner cusps of the posterior teeth, although apart from this their homologies are usually 

 obscure. In the young specimen represented in text-figure 3 (p. lOG) of the second pair of 

 molariform teeth, that of the left side shows one outer and two inner cusps of doubtful 

 homologies, while that of the right side shows all of the cusps characteristic of tlic 

 posterior teeth. It is probable that the same remark made for the posterior teeth is 

 true to a greater extent of the first, namely, that the reduction is partly a natural one 

 and partly the result of mechanical wear. 



Examples of the patterns of the upper molars are given in PI. 5. fig. 5. The cusp 

 designations, and also the descriptions here given, are based on a study of seven 

 specimens. As already intimated, these teeth present an infinite variety of minor 

 characters, but it is possible to recognize a ground-type apparently representing a, 

 moditication of the condition in normal forms. 



Taking the intermediate members of the molar series as more typical than the extreme 



