or THE AUSTRALIAN MARSUPIALIA. 119 



given, whicli have been taken from a specimen in which no signs of wearing are 

 apparent. 



Both the upper and lower molars are extremely simple ia structure. Each of the 

 upper teeth is composed of a high triangular pillar, to which is attached two small 

 external cusps and a large internal one. The apex of the triangular pillar forms a 

 large cusp, which ia the pointed character and the triangular section of its tip resembles 

 the paracone or metacone of a normal insectivorous tooth. Of the external cusps, one 

 is attached anteriorly to the tip of the triangiilar pillar, while the other occupies a 

 similar position posteriorly. The former shows indications of a composite structure. 

 The large internal cusp is crescentic in shape when viewed from the crown, and its tip 

 is placed at a much lower level than that of the median pillar. Each of the lower teeth 

 shows a triangular pillar similar to that of the upper teeth, but with the section-apex 

 reversed. The crown-surface bears three cusps, showing the same arrangement and 

 proportions as those of the trigonid in the Dasyuridse and primitive Peramelidfe. The 

 talonid, which in the latter forms is well developed, is, however, only represented by a 

 minute tubercle attached to the postero-internal angle of the trigonid in the first and 

 second molars. 



It will be observed that the molars of Isoloryctes present a less complicated condition 

 than is found in any of the other polyprotodont families ; and this raises the interesting 

 question, involving the origin not only of Notoryctes but that of all recent Marsupials, 

 as to whether the modification represents a more primitive phase or is the result of 

 special development proceeding from the type represented by the teeth of the Dasyuridie 

 and Peramelidae. 



Cope has called attention to the fact that there is an intimate resemblance between 

 the molars of Notoryctes and those of Chrysochloris, and has further stated tliat "the 

 tritubercular molars .... show Notoryctes to be a primitive type " ; while Winge, on the 

 other hand, has expressed the opinion that the teeth of Notoryctes have lost some of 

 their cusps, and has further compared them with those of the Centetidte. A similar 

 comparison with the Centetidse has been made by Forsyth Major. 



Whether the teeth of Notoryctes are primitive or specialized, one thing is apparent, 

 namely that there are no intermediate stages connecting them with those of any other 

 marsupial forms. Their relations can therefore only be surmised from the parallel case 

 of the Centetidae. The evolution of the teeth in the latter family has been carefullv 

 studied by Eorsyth Major (1897), and the following statement of the case is based to a 

 considerable extent upon tliis writer's views : — In certain of the Insectivora (Tal^jidte) 

 (<?/". text-fig. 5, p. 120) the upper molars show an arrangement of the cusps wliich is very 

 similar to that seen in the DidelpliyidtC, there being in each case a triangle of three 

 main cusps and an outer row of styles. In the Potamogalid;t tlie two outer cusps of 

 the triangle, the paracone and metacone, are partially fused together, while the 

 protocone and the external styles tend to retain their original characters. In all of 

 the Centetidae, and also in the Chrysochloridic and Solenodontidtc, the paracone and 

 metacone are completely fused together to form a median pillar, in which it is not 



