14 Memoirs of the Indian Museum. [Voi.. I, 



I feel that some apology is required for venturing on a subject that is still in such 

 a tangle of confusion as the varieties of Mus rattus (or alexandrinus as Thomas has 

 named it). Thomas's invaluable work in showing that the three varieties, alexandrinus , 

 rufescens and nitidus are intergrading varieties with no skull differences and separated 

 only by size, cleared up matters very considerably. One gathers, however, that there 

 is still considerable doubt as to what exactly is the typical Mus rattus of India and what 

 variations from the type are sufficiently distinct to warrant names, from the following 

 passage in the same author's review (1894) of the Bornean species of Mus : " I^astly 

 there remains to be considered the group to which the European house rats belong, a 

 group which has been the bane of workers on the Oriental Muridse, and which at 

 present owing to want of material is quite impossible to bring into any sort of order. 

 Fortunately, so far as the present paper is concerned, there is a Bornean name 

 available, and this I propose to use for the lowland rats of the group, without express- 

 ing any opinion as to their relationship with extra-Bornean species." The name is 

 not given, however, and no further mention is made of the group. Similar sentiments 

 are conveyed more tersely in a footnote to Miller's key to the rats of Trong, lyower 

 Siam, which simply states that Mus alexandrinus has been excluded. As to the 

 house rats of India generally, I have nothing to say ; but I have hopes that my com- 

 paratively extensive work on the house rats of Calcutta will afford material which, in 

 experienced hands, may aid in attacking the general question of the varieties of the 

 Oriental M. rattus, particularly in reducing vague varieties and sub- varieties to a 

 common denominator.^ For I shall try to demonstrate that M. rattus, as found 

 in Calcutta, shows the greatest possible variation in coat, colour and size; so much 

 so as to render it absurd to give a new name to every slight variation found in each 

 new locality investigated, as is the tendency at present. Thomas has already shown 

 that the presence or absence of spines is valueless as a mark of specific difference, 

 and that the length of the nasals is variable, though some doubt is cast on this latter 

 observation by the measurements I have collected. I shall try to estabhsh that 

 differences of size have to be regarded with great suspicion, while white-tipped tails 

 and white underparts and colour variations generally, and even, in the matter of 

 skulls, differences which at present are made to have specific value, are liable to 

 be nothing more than normal individual variations. The material which I have to 

 go upon consists of fresh measurements of over 90 specimens, skull measurements of 

 46 of these, and the rough examination of some 300, examined in the months of 

 February, March and April, with only a few in May. 



The first point to settle was whether there were two distinct size varieties, alex- 

 andrinus and rufescens. These Thomas describes as larger and smaller, but he gives 

 the measurements as follows : — 



Hind foot. 



^i-From spirit specimens. 



35 (A hill variety not found in Cal cutta . ) 



M. 



alexandrinus . . 



Body. 



• 15-6 



Tail. 

 17-5 



M. 



rufescens 



13-3 



i6-5 



M. 



nitidus 



i6-5 



167 



I vSee note on Millais' description of the rats of Great Britain at the end of this paper. 



