1909.J R. K. Lloyd : The Races of Indian Rats. 9 



as Amritsar, Allahabad, Nowgong, Tellicherri and Calcutta, we 

 must conclude that they form one class throughout, although 

 great individual differences of colour, size and proportion can be 

 noticed among the rats of any one place, and in spite of the fact 

 that the rats of one place may collectively show certain peculiari- 

 ties of colour and sometimes of proportions. Until recently it was 

 thought that two varieties of the species were to be met with on 

 the plains of India, a large northern variety {alexandrinus) , 

 measuring about six inches in length, and a smaller southern variety 

 {riifescens). It seems that this idea should now be abandoned. 



Reference must be made to the skulls of the rats of this group. 

 It has been mentioned before that over ninet}" species of rats have 

 been described from the Oriental region which are, indisputably, 

 closely allied to Mus rattus. From the definitions of most of these 

 species one learns that each of them has its own peculiar t^^pe of 

 skull, the nasals are of a particular length or shape, the auditory 

 bullae are exceptionally small or unusually inflated, the infraorbital 

 foramen is more open below, the zygomatic plate may form a prom- 

 inent angle or it may not, the frontoparietal suture is in some a 

 widely open angle, in others it is less obtuse. However small they 

 may be, the skull of each species has its own peculiarities. 



But it seems to the writer that in most cases these differences 

 are such as can be readily found among any thousand skulls of 

 rats taken from any town in India. vSome of these specific types 

 of skulls have been carefully figured. A. comparison of these 

 figures with skulls selected from among large numbers of rats of any 

 district, confirms this opinion. There is, however, a considerable 

 range of variation. Small adult rats as well as young rats differ 

 considerably from large adults in the proportions of their skulls. 

 It will be shown that local groups of rats taken from a single house 

 may have skulls which are very closely alike, all agreeing in that 

 they are distant from the mean of the race to an approximately 

 equal extent. 



The differences between the skull types of most of the species 

 of Oriental rats fall within the range of variation exhibited by a 

 small number of rats from one town. This is proved by measure- 

 ments already published. 



For the sake of brevity the writer has dealt only with measure- 

 ments of the four most important features which are usually recor- 

 ded in ''types" of the species of Mus. These features are the 

 greatest or zygomatic breadth of the skull, the length of the nasal 

 bones, and the lengths of the palatine foramen and upper molar 

 series. The measurements have been expressed as percentages of 

 the greatest length of the skull. These features have been chosen 

 because it is in them that the more distinct forms, Mus mettada, 

 Mus decumanus, Gunomys, Nesokia and Bandicoia, differ from one 

 another and from the type of Mus rattus. 



A standard for comparison is afforded by Hossack's measure- 

 ments of forty-five skulls of Calcutta house rats of all sizes and of 

 the Mus rattus type. 



