OF THE AU8TKALIAN MAESUPIALIA. 187 



nearer that shown by the Pcramelitke (PL 5. fig- 8)- Style c does not become greatly 

 enlarg'ed as in the DasyuriuiB, but retains more the proportions seen in Peratherium 

 and the Peramelidae. Pinally, there is a greater tendency towards the retention of the 

 intermediate styles fij and c^. 



The following additional cliaracters of resemblance between the Didelphyidse, including 

 Feratherium, and the Dasyurinas and Peramelidte may be noticed. The tirst molai- is 

 always more laterally compressed than the second, while the reverse is trne of the 

 tliird. In the latter also the external styles are poorly developed. The fouith molar 

 is in every case reduced. 



Passing to the lower molar patterns, we note the fact that the smaller Dasyurinae 

 present prototypal relations which are exactly duplicated in the Didelphyidte. The 

 jjattern figured for Sminthopsis leiicopus (PI. 6. fig. 2) will be seen to be practically 

 identical with that of Teratherium (fig. 1) and Iletachirus (fig. 32). An exception will 

 be noticed in the absence of the entoconid in Sminthopsis, but, as already mentioned in 

 connection with the Dasyurinae, the condition in this form and other species of 

 Sminthopsis is not typical of the subfamily. It is interesting to note that, notwith- 

 standing the increase in size of the body in the advanced members of the Didelphyidae, 

 the primitive molar type is for the most part retained, while in the similarly advanced 

 members of the Dasyurime carnivorovis modifications begin to appear. 



As noticed above, the first lower molar in the Dasyuriute shows a series of I'eductions 

 of the paraconid and meiaconid, beginning with a type like that figured for Sminthopsis 

 crassicaudafa (PI. 6. fig. 0), in w^hich these cusps are fairly well developed. In the 

 primitive; Peramelidae, in Peratherium, and all of the existing Didelphyidae (af. PI. 6. 

 fig. 33) we find prototypal relations, these elements being well developed tiiroughout. 



In the fourth lower molar of the Dasyurime there is a marked tendency towards the 

 reduction of the talonid. The same tendency is seen in a somewhat lesser degree in 

 the existing Didelphyidae. Pive specimens of Peratherium in the' British Museum 

 Collection show the characters of these teeth, and in three of them the talonid is fairly 

 developed, and all of the three cusps are recognizable, while in two others the talonid is 

 reduced*. 



Incisors. — On account of the lack of information concerning the incisors of Pera- 

 therium the following comparisons include only the existing Didclphyidte. In the 

 Australian series, and apart from the incisor formula, the smaller Dasyurinae are the 

 only forms showing prototypal characters. In these we find no less than five points of 

 resemblance with the Didelphyidae. The median upper teeth are procumbent and sub- 

 caniniform. The upper lateral teeth, when unworn, have triangular tips. The median 

 lower incisors are unmodified. Like the lower lateral teeth their tips are rounded. 

 The insertion of the three anterior lower teeth is arranged so tliat the root of the second 



* These specimens are P. arvernennis (I'lij-df-Dome, M. 27700), an uudetcrmined sjiecies from Auvcrgno 

 (M. 27811), an undetermined species from Hordwoll, Hants (M. 30350), K Lamandini (Cayliix, M. 2;Wh (/), ;iud 

 J', ajinis (Tarn-et-Garoune, 51. 238!? a). Cf. Lydekker (1887). 



SECOND SERIES. — ZOOLOGY, VOL. IX. 20 



