60 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVI. 



districts, could be induced to furnish us with corresponding data, 

 each dealing with say 100 fully adult rats from his own district 

 and carefully studied by himself, our knowledge of the geogra- 

 phical variation and its systematic value would very quickly be 

 placed upon a secure foundation. 



Key to Indian, Cinghalese, & Burmese members of the group 

 based principally upon external characters) : — 



I. Tail bi-coloured ... ... ... Rattus vicerex,'Bou\\ote. 



II. Tail unicoloured. 



A. Fur very fine ; lacking all trace of 



bristles. Nasal length exceeding 



40 per cent, of the condylo-basal 



length of skull. 



a. Tail longer, about 108 per 



cent, of length of head and 



body. Fur long and thick ; 



underparts silvery or hoary. Rattus nitidiis nitidus, 



Hodgson. 

 I>. Tail scarcely longer than head 

 and body. Fur short and 

 thin ; underparts not silvery, 



frequently with rusty tinge ... Rattus nitidus ohsoletus, 



Hinton. 



B. Fur coarser, usually with many 



bristles (though these vary in 

 strength). Nasals usually less 

 than 40 per cent, of the condylo- 

 basal length of the skull. 

 a. Ventral fvir white to bases ; 

 lateral line of demarcation 

 usually well defined. 

 a' Mammae normally 3-3=12. 

 a' Pectoral mammae not under- 

 going reduction. 

 a^ Tail relatively short, 

 averaging less than ] 20 

 per cent, of the head and 

 body length. 



«* Dorsal colour dull 

 greyish brown ; audital 



bullae very large ... R. rattus tatkonensis, 



Hinton. 

 7/ Dorsal colour with an 

 ochreous tinge; audital 

 bullfB medium sized... R. rattus l-Jiyensis, 



Hinton. 



