604 Mr. 0. Thomas on the Australian Murines 



earlier than Epimys, and until a reason could be shown for its 

 separation from the latter, the proper generic name of all 

 true rats from Mus rattus downwards would remain in 

 doubt. 



I have not as yet been able to make any observations on 

 the characters and synonymy of the species, but have simply 

 taken all the types and authentic specimens in the Museum 

 and grouped them in genera. So rich, however, is the 

 Museum collection in types that this method allocates the 

 great majority of the described species without introducing 

 any element of doubt as to the correct determination of 

 species of which we do not possess typical examples. 



Certain groups of Australian Muridae have already been 

 dealt with *, namely those with elongate feet and those with 

 a postero-internal cusp on the upper molars, and there now 

 only remain the ordinary rat- and mouse-like forms without 

 the extra cusp on the molars. 



A careful examination of these shows that none of them, 

 except the introduced M. musculus, are referable to true Mus, 

 that about half may be retained in Epimys, the genus of 

 which " Mus rattus " is typical, and that the other half may 

 be referred to the specially Australian genus Pseudomys, 

 which may itself be divided into four subgenera. 



The characters and included species of these groups are as 

 follows :— 



Epimys, Trouess. 



Size uniformly large; all Australian species being "rats " 

 and not " mice. - " Pectoral mammae believed to be always 

 present, the formula, where known, varying from 1 — 2 = 6 to 

 3—3 = 12. 



Skull strongly built, with well-marked supraorbital ridges, 

 which generally extend back to the outer coiners of the 

 interparietal. Front edge of zygomatic plate always convex. 

 Pterygoids as in E. rattus, the parapterygoid fossa deep and 

 well defined. 



Molars normal, the laminre never specially tilted up ; no 

 cingular cusp on in 1 . 



Range. Whole of Old World, except Madagascar and the 

 far north. 



Type. E. rattus, L. 



* Ann. & Mag. Nat. Hist. (7) xvii. p. 81 (1906) ; op. cit. (8) iii. p. 37? 

 (1909). 



