1909.] R. E. Lloyd : The Races of Indian Rats. y 



Confusion of nomenclature among the group is increasing at 

 the present Ao-y. Two new species, Mus listoni and Mus combcri, 

 have been recently added to the list of Indian rats [6]. In the 

 words of their discoverer '' There is little to distinguish listoni from 

 mcttada except the difference in the size of the molars, but this 

 difference is quite constant and easil}^ appreciable even b}' the 

 naked eye." It seems to be noteworthy that specific difference;^ in 

 an animal so large as a rat should be appreciable even by the naked 

 eye. Mus combcri was discovered among eight rats collected at 

 Nasik, four of which were identified as Mus mettada, the remaining 

 four being regarded as of the new species. The measurement of the 

 molar series of these specimens is given in millimetres as 56, 5*7, 

 57, 57; 6, 6, 6"i,6"2. Those with molar series measuring 5 -6 — 57 

 formed the new species Mus comber i. Those from 6 — 6*2 were re- 

 garded as Mus mettada. As regards these dimensions, the difference 

 between the largest and smallest in mettada is "2 mm. The difference 

 between the smallest in mettada and the largest in comberi is "3 mm. 

 There is no other difference between the two species, which live 

 together in Nasik. Anyone who accepts the separation of these two 

 species must suppose that among an}- thousand '' Mettads " from 

 the Nasik district, a very small proportion will possess molar series 

 measuring 5*8 and 5"9 mm. ; he must further suppose that a 

 " Mettad" with molar series measuring 57 mm. will recognise and 

 refuse to mate with one whose series measures 6 mm., lest mongrel 

 offspring with series of 5"8 and 5'9 be born. After reflecting on 

 the smallness of the dimension represented b}^ "i mm., and the 

 impossibility of measuring it b)^ means of ordinary appliances, it 

 is difficult to regard these two suppositions as well founded. 



il/ws listoni was defined from five specimens from the Konkan; 

 it is separated from mettada for the same reason that Mus comberi 

 was separated, because the teeth are some three-tenths of a milli- 

 metre less than in mettada. 



Mus listoni and conibcri are separated because the latter is 

 " distinctly smaller " and for no other reason. The author of these 

 new species gives the dimensions as follows : — 



Head and body length in millimetres. 



Mwscomim (4 adult females) . .. 118 | 119 120 125 



Mus mettada (3 , , , , ) • • 

 Mus listoni (2 ) . . 



The same author continues : ' ' The specific separation of comberi 

 and listoni, however, must depend on the non-existence of inter- 

 mediates {i.e., in size) ; from my knowledge of the country I argue 

 that the discovery of such is most unlikely, and I have not 

 hesitated, therefore, to rank them both as species." 



