r^ 



404 



SCIENTIFIC RESULTS FROM THE MAMMAL SURVEY, 



No. XIII. 



A. — On MuRiDiE FROM Darjiling and the Chin Hills. 



By Oldfield Thomas. 



(^Published hy permission of the Trustees of the British Museum.) 



1. — A NEW Genus of Giant Rat from Sikkim. 



Among the collections recentty made in British Sikkim by- 

 Mr. N. A. Baptista for the Bombaj^ Survey with the active help and 

 interest of Mr. R. S. Lister and Mr. H. Stevens are three Giant rats 

 belonging to two species, both much larger than any other strictly 

 Indian species of ^pm^/s, and rivalling Bandicoots in size. One of 

 them, represented hj a single specimen, is clearly an Eimnys, and is 

 dealt with under the next heading below. 



The other, like as it is to a true rat externally, proves on stud}^ 

 of its skull to show such dental characters as to necessitate the 

 formation of a new genus for its reception. This may be called : — 



Dacnomys, g. n. 



External characters and qualit}- of h\r as in JEpimys. Mammge 

 of genotype 2-2 = 8. 



Skull with prominent overhanging supraorbital ridges, more 

 developed than in most T^pimys, less than in Lenomys and Lenothrix ; 

 the shape ot the crown between the ridges abou.t as in Lenothrix. 

 Anterior plate of zj^goma very slightly projected forward, about as 

 in Bi'plothrix,^' rather more than in Lenothrix ; less than in Lenomys, 

 much less than in Mpimys. Bullae quite small. 



Teeth. — Incisors normal. Molars very large, broad and heavy as 

 compared with all forms of Ejjimys, nearly equalling those of 

 Lenomys, the length of the series more than half the distance from 

 the back of M^ to the condylion ; breadth of palate between first 

 molars rather greater than the breadth of a molar. 



In structure, owing to their size and angularity, the teeth have 

 a strong superficial resemblance to those of Lenomys. But in detail 



* G. n. Genotype Diplotlirix legata {Lenothrix legata, Thos. Ann. Mag. N. H. (7) 

 XVII, p. 88, 1906) from the Lin Kin Islands. 



A further study of these Murines convinces me that the Liu Kiu Lenothrix 

 legata oug-ht to be genetically distinguished from its Sumatran ally L. cana, 

 Miller. The great breadth of the crown area between the parietal ridges, which is 

 broader than long, and gives quite a different aspect to the upper view of the 

 skull, the greater projection forward of the zygomatic plate, and certain detailed 

 differences in the molars, described in the original account, are my chief reasons 

 for this separation, which is also in accord with the geographical distribution of 

 the two forms. I may further note that in Diplothrix the posterior lamina of M' 

 consist of two elements, an internal and a median cusp, not of a single cusp only 

 as Mr. Miller says is the case in Lenothrix cana. M^ and M^ practically without 

 antero-external stipplementary cusps. 



