46 NILS GYLDENSTOLPE, THE SWEDISH ZOOLOGICAL EXPEDITIONS TO SIAM. 



Rattus sakeratensis sp. n. 



Plate VI. Fig. 6 & 9. 

 § Sakerat, Eastern Siarn, January 1912. — Head and body = 100 mm.; tail = 103 mm.; hindfoot = 26 inm. 



During my former Expedition to Siarn 1911—1912 I obtained 9 specimen of a 

 small rat which I referred to Mus concolor Blyth in my paper about the Mammals of 

 Siarn (Arkiv för zoologi, Band 8. N:o 23. 1914 p. 18). Since more material of typical 

 Rattus concolor has now been available I have foimd it necessary to describe the Sake- 

 rat-specimen as new. It is, however, related to Rattus concolor though it differs in sev- 

 eral particulars. 



Colour: General colouration above rufous umber intermixed with some black hairs 

 which are longer than the other hairs. Spines few in number and very feeble; sides of 

 the body creamy white; rest of the under surface white with dusky bases to the hairs. 

 The whole lower surface is faintly washed with cream colour. Feet light brown, clothed 

 with hairs; at the root of the claws a tuft of white hairs; hands påle brown washed with 

 cream colour and with a short tuft of white hairs at the root of the claws; tail blackish 

 brown throughout its whole length and clothed with short hairs; whiskers black trough- 

 out and rather long; muzzle dusky brown. 



Skull: The cranial differences between the new form and that one of Rattus con- 

 color are striking. The foramina incisiva are very short, measuring 4,i mm. agamst 5,5 

 mm. in typical concolor from the Malay Peninsula. The foramina are also much broader 

 measuring 1,8 mm. at about the middle against 1,3 mm. in concolor. The bulla? are very 

 small and much flattened and the distance between the bulla? greater. The breadth of 

 the palate is less measuring 1,8 mm. between the first molars against 2,i mm. in con- 

 color. The basioccipitale is also much broader anteriorly. The molars both in the upper 

 and in the lower jaw are broader. The nasals are greatly tapering off posteriorly. Fron- 

 tal ridges well developed. The supraoccipitale is of another form: 5,o mm. in length and 

 8,6 mm. in breadth while in concolor it is only 3,5 mm. in length and 8,5 mm. in breadth. 

 The bony palate does not extend as far backwards as in Rattus concolor and the foramen 

 magnum is somewhat wider. Brain case rather large, making the whole skull more ro- 

 bust that in concolor. Oompared with the skull of Rattus ephippium Jent. from Borneo 

 the following differences are to be noted. Bulla? much smaller and more flattened; fora- 

 mina incisiva longer and broader, measuring 4,i mm. in length and 1,8 mm. in combined 

 breadth against 3,o mm. and l,o mm. respectively in R. ephippium. Palatal length from 

 henselion =11,2 mm. against 12,6 mm. in R. ephippium. 



Remarks: From Rattus ephippium Jent. which it approaches in size, it may at a 

 glance be distinguished by the different colouration of the fur which in that species is 

 bright tawny. The underparts are creamy white and much paler than the abdomen in 

 R. ephippium. The feet are light brown with long white hairs covering the claws, while 

 in R. ephippium the feet are almost concolourous with the abdomen. The tail is blackish 

 brown for its whole length while in ephippium it is dark brown. One of the most noticable 

 differences is, however, the length of the hindfoot which in the new form measures 26,o 

 mm. against 22,5 mm. in Rattus ephippium and 23,5 mm. in Rattus concolor Blyth. 



