PHALANGtEKED*. 



127 



Upper premolars two or three in number (one in Phaseolarctince) ; the 

 last one, p.'', generally sharp-edged and cutting, but not so much so 



Kg. 4. 



Dactylopsila irivirgata. — Front of jaw, showing diprotodont dentition. 



as in the Macropodidce. Molars either with sharp cutting-crests or 

 bluntly tuberculate, usually four in number, but the last is some- 

 times absent. Lower posterior incisors and anterior premolars 

 minute, probably nearly funotionless, very variable in number. 



Tooth-change as a rule in a very much aborted state ; the milk- 

 premolar generally very small and early deciduous, and in many 

 cases apparently quite functionless. So far as is yet known, 

 Phalanger and Trichosurus alone have their milk-premolars per- 

 sistent long enough to be of service, 



Raruje. Austro-Malayan, Papuan, and Australian subregions, 

 from Celebes to Tasmania. 



This family, among the Diprotodonts, corresponds to the 

 Basyuridm among the Polyprotodonts, as being the most generalized, 

 and therefore probably containing the most ancient forms now exist- 

 ing of the Suborder." In their general external form and the charac- 

 ters of their limbs its members are fairly closely related to each 

 other, but their teeth are exceedingly diverse, and present a very 

 considerable range of variability. On this account the homologies 

 of the teeth and the best way of formulating them for descriptive 

 purposes are here matters of very considerable difflbulty. Of the 

 upper teeth the incisors, canine, and molars are of course homo- 

 logized easily enough; but in the case -of the premolars it is very^ 

 difficult to determine which of the full series of four has disappeared 

 to leave the common number of three. Among the Polyprotodonts 

 it has been shown (PhiL Trans, clxxviii. p. 446, 1887), that p.'' is the 

 one lost ; and a consideration of the present j^amUy convinces me that 

 the same tooth, although quite independently, has probably disap- 



