372 Mr. 0. Thomas on the N. Australian Rats 



XLIX. — On the iV. Australian Bats referred to the Genus 

 Mesembriomys. By Oldfield Thomas. 



While working out a very distinct new rat from Kimberley, 

 N. Australia, sent to the British Museum by Mr, B. H. 

 Woodward, of Perth, I have had occasion to examine all the 

 species referred by me in 1906 to the genus Ammomys *, 

 whose name, being preoccupied, has since been altered to 

 Mesembriomys. 



Apart from the group-characters then described tliese 

 species are of a very heterogeneous .nature, and I am now 

 convinced that they should be further divided into three 

 genera, whose differential characters would be as follows : — 



I. Mesembriomys. 



Aynmomys, Tho3. /. c. {nee Raf.). Type Mus hirsutus, Gould. 



Size very large. Form normal ; feet narrow, fairly long. 

 Tail very long, jerboa-like, heavily tufted terminally. 



[Skull large and stout, peculiarly high and heavy in the 

 anterior frontal region, its highest point at or in front of the 

 front edge of m^, and its upper profile strongly bowed at this 

 point. 



Molars comparatively normal in structure, not Sj)ecially 

 laminate; inner cusp of anterior lamina of m^ situated, as is 

 usual, behind the level of the middle cusp, opposite tiie gap 

 between the latter and the middle cusp of the second lamina. 

 Lower molars (wj and wjj) each with a well-maiked re-entrant 

 concavity behind, in which a distinct median supplementary 

 cusp is placed. 



Species. M. hirsutus {Mus hirsutus, Gould) and M. ma- 

 crurus {Hapalotis macrura, Peters). 



II. Zyzomys. 



Genus novum. Type Mus argurus, Tbos. 



Size quite small. Form delicate. Tail slender or thick- 

 ened, lightly pencilled terminally, not heavily haired. 



Skull light and delicate, not bowed in the frontal region, 

 its highest point above ni^. 



* Ann. & Mag. Nat. Hist. (7) xvi. p. 84 (1906). I may take this 

 op}iortunity of drau-ing attention to an important lapsus calami in this 

 paper. On p. 83, bottom line, for Co)Hltirus read ^oiomys. 



