1. DIBELPHTS. 317 



Size varying from that of a large cat to that of a mouse. Ears 

 generally large and weU developed, with several supplementary 

 folds of skin around and in front of their bases ; their inner margins 

 frequently produced forwards into a prominent pointed projection 

 (see PI. XXVI. fig. 1). Hind feet short, modified for grasping ; 

 with a widely opposable clawless haUiix, and broad rounded pads. 

 Tail in most of the species longer than the head and body, practi- 

 cally naked, except at its base, and distinctly prehensile ; in one 

 species hairy throughout, and in several (subgenus Peramys) shorter 

 than the head and body, and doubtfully prehensile. Pouch only 

 present in the larger species, generally rudimentary or absent. 

 Mammae uneven in number, varying from about 7 to 25, arranged 

 not in two parallel rows, as in the Basyuridce, but in two series — an 

 inner and an outer, the outer consisting of a variable number of 

 symmetrical pairs, the inner generally of one single mamma placed 

 in the middle line posteriorly, but sometimes of three or five, the 

 odd one in each case placed mesiaUy (see PI. XXVIJI. figs. 3 and 6). 



SJcull stout and strongly built, with, at least in the larger species, 

 well-developed ridges and crests. Nasals long, almost always 

 widely and abruptly expanded behind. Anterior palatine foramina 

 short. Palate generally slightly imperfect behind. Bullse rudi- 

 mentary, often almost obsolete. 



Dentition as described above. 



Eange. That of the family. 



The systematic arrangement of the Opossums has formed the 

 subject of an unusually large number of memoirs, of which the best 

 have been written by Temminck, Waterhouse, and Burmeister. 

 These and all other authors appear, however, to have erred in the 

 admission of by far too great a number of species, formed on the 

 most trivial characters of colour and size, and therefore a large re- 

 duction has been found to be necessary in the present work. With 

 the exception of the Short-tailed Opossums (subgenus Peramys), the 

 series available for examination in the European Museums seems to 

 be fairly complete, but in the case of these more specimens are 

 urgently needed before the species can be at aU satisfactorily worked 

 out ; and the present arrangement of that, the most difficidt, group 

 must be looked upon as merely tentative in its nature. 



In this genus alone of the Marsupials I have found it necessary 

 to use subgenerio names, since the groups are so natural in them- 

 selves, and at the same time pass so gradually into one another, that 

 it is impossible either, on the one hand, to ignore them altogether, or, 

 on the other, to give them each fuU generic rank. 



Owing to the shortness of the hind feet in this genus it has been 

 found inadvisable to use their length as a standard of size, and 

 therefore, as in the Phalangeridae, the length of the lower leg has 

 been^used as the chief guide to the general size. 



