68 Records of the Indian Museum. [Vol. Ill, 



measured under the supervision of Captain Kelsall, I.M.S. In 

 making these measurements no selection was made ; all adult rats if 

 caught alive and if of the long-tailed races were measured until 

 500 records were obtained. It was expected that b}' representing 

 the measurements graphically (in the manner described on page 17) 

 a double humped curve would be produced owing to the fact that 

 rats of 120 and of 150 mm. length would be in the majority. 

 This expectation was not realized^ for at the time of the experi- 

 ment the white-bellied rats were not frequentl}^ caught, and only 

 sixteen of them were included among the 500. The diagram, 

 however, clearly shows the separation of the two races, for these 

 white-bellied rats are not distributed irregularly among the 500, 

 but are crowded into the upper half of the series. There are, 

 however, two specimens measuring 115 and 120 mm. in length, 

 which are both white-bellied and small, and one specimen measur- 

 ing as much as 170 mm., which is dark-bellied. The races are 

 none the less separate because of these exceptions, for of 139 rats 

 which measured about 120 mm,, only one is white-bellied, while of 

 four which measured 150 mm., all are white-bellied. 



Rug. I, the small race long known as Mus concolor — 



This rat has been recognised by all writers to be a miniature 

 of the Mus rattus type. It forms at least 50 % of the total rats of 

 Rangoon and at least 75 % of the true house rats. The proportions 

 of the race are illustrated in the diagrams, text-fig. 8 and plate v. 

 In length they vary from about 100 to 140 mm., the mean of the race 

 being close to 120 mm. In tail length they are very variable, the tail 

 percentage varying from 100 to 135, with a mean of about 117. 

 The foot is about 20 per cent, of the length. In colour these small 

 rats show the same types as are met with among the larger 

 Mus rattus of India. Any thousand of them will show the fulvous, 

 the rufous, the melanotic, and white-bellied varieties. The follow- 

 ing types will be described : — 



Type A — The brown type. — Rats of this kind resemble in 

 colour the common brown type of Mus rattus found throughout 

 India. The hairs of the back are slate-grey in the basal half or two- 

 thirds, their apical portions being of some shade of brown, reddish 

 in some rats, yellowish in others. Those hairs which are longer 

 than the majority are not only grey and brown but have black 

 tips ; a few of the longest hairs — the bristles — are black in most of 

 their length. In addition to these are certain hairs which are 

 conspicuous because they are flattened and of a light grey colour ; 

 these may have brown or blackish tips ; these ' ' spines," as they 

 are technically called, are plentiful in some specimens, scarce or 

 absent in others. 



The brown colour produced by this mixture of hairs becomes 

 lighter on the sides and passes gradually into the light brown 

 colour of the ventral surface. The short hairs of this surface are 

 grey in the basal half, brown in the apical half, the brown being 

 often yellowish, sometimes reddish. 



