The first lower molar, on the other hand, is as large in PhascoJomys Intifrons (PI. LI V. 

 fig. 1, d :i) as in Phascolomys 2)/(tti/rfiinus (PI. LIII. fig. 2, <1 8) ; it is consequently larger 

 in proportion to the size of the species, and in proportion to the other molar teeth ; it has 

 also a different form. In l'hascolomys platyrli'uius the transverse section and working 

 surface of d 3 is usually a full ellipse, with the long axis nearly parallel with that of the 

 jaw. In Phascolomys latifrons the section is subquadrate. The anterior surface usually 

 shows a feeble longitudinal groove ; the outer surface is rather narrower than the other 

 three. The enamel covering it extends a short way upon the front surface, and then, 

 after an interruption, is resumed upon the antero-internal angle: the outer enamel 

 extends uninterruptedly over two thirds of the hinder surface. The other bilobcd or 

 biprismatic molars show little more than the difference of size, the four (PI. L1V. d 4, 

 m 1,2,3, fig. 1) equalling in longitudinal extent three and a half of those in Phascolomys 

 platyrhinus (PI. LIII. fig. 2). In all the species the enamel is wanting on the inner side 

 of the tooth, which is nearly on a level with the inner wall of the alveolus ; the outer 

 wall is lower and exposes more of the tooth ; the curves of the positions of the prismatic 

 surfaces are reversed in the upper and lower molars. 



Mr. Waterhouse, in his instructive paper on the Dentition of the Flying Opossums 1 , 

 pointed out two subgenera as having four true molar teeth on each side of both jaws, and 

 a third subgenus as having three true molars on each side of both jaws ; but the obser- 

 vations on marsupial modifications of dentition were not extended further in that paper. 



In January 1839 I communicated to the Zoological Society of London a paper on 

 the classification of the Marsupialia', which contained the generalized expression of 

 observations on the dentition and other systems, carried out through all the materials 

 then at my command. This was chiefly in relation to the actual phase of Mammalian 

 taxonomy in reference to Cuvier's order " Marsupiaux " 3 . W. S. Macleay and others 

 opposed such ordinal group or union of the pouched quadrupeds. The learned Vice- 

 Secretary of the Zoological Society had published reasons for rejecting the Marsupialia 

 as a distinct group, and for distributing them among different placental orders accord- 

 ing to their supposed closer affinities. 4 The contrary views set forth by Cuvier and 

 De Blainville 5 were defective in that kind of evidence which could alone render them 

 convincing ; accordingly Mr. Bennett asks, in 1831, " What is there of importance in the 

 structure of the Wombat, except this solitary character of the marsupium, to separate it 

 from the Rodent order ? " 



1 Proc. Zool. Soc. 1838, p. 149. 3 Trans. Zool. Soc. vol. ii. p. 315. 



1 Begne Animal, vol. i. p. 172 (ed. 1829). 



4 'Gardens and Menagerie of the Zoological Society' (of London) 'delineated,' 2 vols. 8vo, 1831. By 

 Edward Bennett, Esq., F.B.S., &c. 



s Although De Blainville was able to anticipate the appearance of the concluding volume of the ' Begne 

 Animal,' by a few months, in the issue of his Tabular Sheets of Classification, the priority of the proposition of 

 a Marsupial series distinct from, but paralleling, the higher Mammalian orders, is due to Cuvier (" Preface 

 de la premiere edition, Octobre 1816'"). 



