BEISTTAL CHARACTERS OF AUSTRALIAN RATS. 



595 



and the introduced forms K. rattus and R. norvegicus are identical. 

 Evidently the unknown rat which lives on Goat Island is akin, 

 as a compai"ison of text-figs. 1 k 7, B, will show. 



Leporillus Oldfield Thomas, 1906. 



The species examined is that recently named L. jonesi (Ann. & 

 Mag. Nat. Hist. ser. 9, vol. viii. p. 618, Dec. 1921). All the 

 examples come from Franklin Island in Nuyt's Archipelago, on 

 which island the type was taken. 



Upper Molars. 



The upper molar occlusal pattern is shown at text-iig. 8. The 

 molars are large and are deep set in the jaws. The alveolar 

 cavities show a rather noteworthy sinking of the whole tooth 

 into the alveolar area of the jaw ; the cavities for the indi- 

 vidual roots opeiiing from an area which is itself somewhat 

 below the general surface of the surrounding bone. (See text- 

 fig. 9.) 



Text-figure 8. 



Left VTpper molar series of Leporillus jonesi. Three specimens, A, B, and C, 

 showing the alteration of the occlusal pattern, with varying degrees of attrition. 



The first molar has 3 roots, each having a distinct socket in 

 the jaw. Of these three roots one is anterior and median, and 

 the other two are posterior lingual and labial ; the postero- 

 lingual root in some specimens shows a tendency to be bifid. 



The second molar also has 3 roots, but the lingual root is 

 further advanced in the jaw so as to be more truly lingual, and 

 not so postero-lingual in position. 



Proc. Zool. Soc— 1922, No. XLI. 41 



