[ S3 ] 



III. On the Ecolutlon of tlte Australian llaf^supialia ; with Remarks on the Helation- 

 ships of the Marsupials in general. By B. Arthur Benslet, B.A. {Tor.), 

 Ph.D. {Columbia), TJniversity of Toronto, Canada. {Communicated by Prof. G. B. 

 Howes, D.Sc., LL.D., F.B.S., See.L.S.) 



(Plates 5-7.) 



Eead 7th May, 1903. 



Contents. 



Page 

 Introduction bii 



The Adaptive Modifications of the Dentition in the Australian Marsupials 88 



The Adaptive Modifications of the Foot-structure in the Australian Marsupials 1(52 



The Identification of the Stem-Form of the Australian Marsupials 1 7'-* 



The Phylogenetic Arrangement of the Australian Marsupials 1<J2 



The Question of the Time and Mode of Origin of the Australian Kadiation 204 



The Major Classification of the Marsupials in general ,. . 207 



The Systematic Arrangement of tlie Australian Families 210 



Bibliography 211 



Explanation of the Plates 214 



Introduction. 



On reviewing the general progress of opinion in mammalian phylogeny, we note 

 the fact that the discussions bearing on the affinities of the Marsupials have largely 

 centred around the broader question of the relationships of these animals with the 

 Placentals, and that in respect to the latter there has been a gradual change from an 

 older view, by which the Marsnpials were assigned an ancestral position, on the 

 assumption that they represent a lower grade of organization, to a newer one, by which 

 they are regarded as a collateral or even a derived group. 



The three groups into which the existing Mammalia are divisible have been commonly 

 recognized as representing, to a certain extent, three grades of organization — the 

 Placentalia, mainly distinguished by their vascular nutritive allantois, standing highest 

 in the scale ; the Mouotreniata, in virtue of their sauropsidan characters, especially their 

 oviparity, lowest; while the Marsupialia occujiy a somewhat intermediate position, 

 especially in respect to their combination of a non- vascular allantois, which they possess 

 in common with lower oviparous forms, with the actual viviparity of the Placentalia. 

 following the evolutionary princii)le, the tendency has been to connect these groups 



SECOND SERIES. — ZOOLOGY, VOL. IX. 13 



