OF THE AUSTRALIAN MAESUPIALIA. 93 



Of the remaining- upper molars, the Qrst differs from the second in being less com- 

 pressed antero-posteriorly, while the reverse is the case with the third. In the latter, 

 also, tlie styles are not so well developed, this being especially the case with style c. 

 ThQ fourth tooth is greatly reduced through the lack of development of the metacoue, 

 there being no lower teeth situate behind it, against wliich it might shear. The cusps 

 represented are the protocone, paracone, and style ab. The paracone is trencliaat 

 anteriorly. 



The third lower molar (PI. 6. fig. 2) shows the following characters: — The crown is 

 relatively short and broad, and presents the tuberculo-sectorial pattern, being composed 

 of an anterior triangular pillar (trigonid) and a posterior heel (talonid). The sectional 

 area of the trigonid is slightly greater than that of the talonid. The former bears three 

 cu.sps, of which the externally placed protoconid [pi-''.) is best developed, while of the 

 two internally placed cusps the posterior raetaconid {me''.) is smaller and the anterior 

 paraconid {pa''.) still more so. The antero-external side of the trigonid, formed by 

 the combined edges of the paraconid and protoconid, is treucliant and shears against the 

 metacoue-spur of the preceding upper molar. The trigonid also bears a small antero- 

 external shelf {a.e.s.). 



The talonid is basin-shaped, and its edge bears one outer and two inner cusps, repre- 

 senting respectively the hypoconid (%'^.), hypoconulid {hi'.), and entoconid {ell^'.). Tlie 

 last-named cusp is, however, vestigial. 



Of the remaining lower molars, the second repeats the characters of the third. The 

 first tooth {cf. PI. 6. fig. G, Sminthopsis crassicaudatu) presents the appearance of 

 transverse compression, the paraconid and metaconid being partially reduced. As 

 pointed out below, this tootli shows an interesting evolution connected Avith a gradual 

 change to a premolariform condition, in which the condition in the present species 

 represents the initial stage. The fourtli molar shows a reduction of the talonid by 

 lateral compression, the whole structure having the form of a spur attadied to the 

 posterior border of the trigonid. 



Among the smaller Dasyurinse the departures from the type just described are few and 

 imimportant. There are certain minor variations in the characters of the external styles 

 to which reference will be made in a subsequent section. The relative pruportioos of 

 the sectional areas of triiironid and talonid differ sliglitlyin different cases. Tlie vesti""ial 

 character of tlie entoconid seen in Smintliopsis leuooptas is a2)parently common to all of 

 the species of that genus except S. crassicaudata, in which this cusp is well developed. 

 It is also found in Fhasnogale minitflssima and in Antechinomys laniyer. In tlie casi; 

 of Sminthopsis and Atitechinonnjs the apparently vestigial condition of tlu' entoconid 

 may in reality he due to mechanical wear, the animals being ground-feeding types. 

 The cause of the reduction in the case of Phascogale minntis.'iinia is seen in the reduced 

 character of the talonid, the latter structure being possibly in process of reduction 

 in this form. The small size of the entoconid is, in any case, a secondary character, 

 this element being well developed in all of the larger forms, as in S. crassicaudata, as it 

 is in the primitive Peramelidse and all of the Didelphyidio. 



On examining the molar modifications of the larger species of Phascogale, we find 



11* 



