igoy.] DR- Hossack : The Rats of Calcutta. 79 



NOTE. 



The relations of the Mus rattus of India to the Mus rattus of Great Britain. 



One difficult}- that lias caused me trouble in the writing of this paper is that, except for a couple 

 of skins of the English black rat preserved in the Indian Museum, both faded to a ruddy plum-colour, I 

 have had no opportunity of examining specimens of English rats. Indeed, I have not even been able 

 to find access to any full and reliable account of the rats of Great Britain, so that it has not been pos- 

 sible for me to come to anj^ definite conclusions as to the relationship of the British and Indian forms of 

 Mus. While the work was in the press, however, I have fortunately been able to consult Millais's recent 

 work on the Mammals of Great Britaia and Ireland in which the rals of Great Britain are treated very 

 full}'. Mus decumanus is apparently identical in both countries except that Millais agrees with Thomas 

 in making the tail uniformly brown as compared with the bi-coloured tail found in Calcutta and appa- 

 rently in India generally ; the skull and general body measurements appear to be the same in both 

 countries. 



The subject of Mus rattus is wrapped up in such confusion that before attempting to correlate the 

 findings of Millais and the result of my own investigations, it would be as well to clearly define the posi- 

 tion we both take up. 



With regard to the Mus rattus of India the distinction formerly drawn between Mus rattus var. rufes- 

 cens and Mus rattus var. alexandrinus, must be abandoned. Thomas has shown that for India gener- 

 ally the distinction is indeterminate, as the two varieties intergrade completely ; and the only conclu- 

 sion to be drawn from luj- investigation in Calcutta is that only one form has in reality to be dealt with, 

 a form with an extrem.- range of both size and colour ; and from this form two varieties have been arti- 

 ficially manufactured. Mus rattus var. nitidus is, I am inclined to think, a clearly marked Indian 

 hill variety distinguished by its short bi-coloured tail and long far, but the evidence on which I ha\'e 

 to rely is extremely incomplete. 



Millais describes three sub-species of Mus rattus found in Great Britain, as follows : — 



1. Mus rattus alexandrinus. — 



This is the original Alexandrine Rat of Geoft"roy, or southern type of Mus rattus. He descri1:)es it 

 as a long-tailed rat, but in the example he gives the respective measurements of the head and body and 

 tail are 9 in. and j\ ins. It is a light j-ellowish-brown above with white underparts, with a dividing line 

 of grey. He regards it as the parent race of Mus rattus rattus and recently imported into England. 



2. Mus rattus rattus. — 



This is the old English Black Rat, now practically extinct in England. He distinguishes it from the 

 next purely by the colour, which he describes as blue rather than black, bluish or purplish-black 

 above, and greyish-black below, with yellowish soles to the feet. His knowledge of this rat has been 

 gained apparently in main part from an examination of a hundred specimens collected from all parts of 

 Great Britain in the last fifty yeais. There is no doubt that the old English Black Rat existed as a 

 distinct northern variety ; but I maintain that to lay down from old faded specimens that the old English 

 rat was " blue " rather than black, is rather a courageous undertaking, considering what is known as to 

 the changes in colour in old specimens. 



3. Mus rattus ater.— 



This, the Black Alexandrine Rat, is separated from the two previous sub-species only by its colour, 

 and by the doubtful fact that its tail is not so thick at the base and is proportionately longer. The back 

 is a rich black with greenish lights ; the lower parts are blackish, as are the feet and soles. It is an im- 

 ported rat found mostly in seaports. I am afraid this differentiation into three sub-species cannot be 

 accepted, for it is one based practically entirely on shades of colour and is absolutely contradicted by 



