Miller. — Seven JVew Rats collected in Siam. 143 



the ba-sal straight iMjrliDii directed slightly fonrard. Audital bullae smaller 

 than in Mm bowersi, though nearly double as large as in M. vociferans, 

 subcircular in outline when viewed from the side. 



Teeth.— The teeth are broader than in the other large rats from Trong, 

 but the toothrow as a whole is not correspondingly lengthened. Enamel 

 pattern of first upper molar as in Mas decumanus. In the second tooth a 

 small but distinct antero-external tubercle is added to the number nor- 

 mally present.* Occasionally this tubercle is connected with that of op- 

 posite side, so that the enamel pattern consists of three transverse folds 

 as in the first tooth. Third molar like second, though smaller, and the 

 elements of the tooth less distinct. This tooth is therefore of more com- 

 plicated structure than that of Mus decumanus, owing to the addition of 

 an anterior outer tubercle, and the normal division of the posterior cres- 

 cent into two transverse loops. 



Jlfmst<rCT7ie?.<s.— External measurements of type: total length, .521; head 

 and body, 254; tail vertebrae, 2(57; hind foot, 49 (46); ear from meatus, 

 20.6; ear from crown, 16; width of ear, 16. Another specimen, also a 

 male: total length, 515; head and body, 248; tail vertebrte, 267; hind 

 foot, 52 (49). 



Cranial measurements of type: greatest length, 55; basal length, 48.6; 

 basilar length, 45.6; palatal length, 26; least width of palate between 

 anterior molars, 5; diastema, 14.6; length of incisive foramen, 9: com- 

 bined breadth of incisive foramina, 3.6; length of nasals, 22.6; combined 

 breadth of nasals, 6.2; zygomatic breadth, 28; interorbital breadth, 8; 

 mastoid breadth, 19; breadth of braincase above roots of zygoma, 20; 

 depth of braincase at anterior border of basioccipital, 15; fron to-palatal 

 depth at posterior extremity of nasals, 13.4; least depth of rostrum im- 

 mediately behind incisors, 10; -maxillary toothrow (alveoli), 11; width of 

 front upper molars, 3; mandible, 31; mandibular toothrow (alveoli), 10. 



Specimens examined.— Two, both from the type locality. 



Remarks.— Though this rat bears a strong superficial resemblance to 

 il/t(s 6o?('em its skull and teeth show that there is no very close relation- 

 ship between the two animals. Probably the Siamese animal is more 

 nearly related to the Bornean Mus infraluteus Thomas. This species, 

 which is slightly larger than 3/hs caZttZu-s, and with actually as well as 

 relatively shorter tail, differs from it further in darker general color, and 

 in the dark undcrfur of the ventral surface. The skull is shorter and 

 apparently lu'oader, and the incisive foramina do not extend back to line 

 of front of molars. The palate is said to be 32 mm. in length, while in 

 M. validvs it is only 26 mm. In the original description of Mus infraluteus 

 the enamel pattern is not mentioned. It is therefore presumably normal 

 and quite ditt'erent from that of 31. mlidus. 



*A trace of this tubercle is usually visible close to the cingulum in 

 Mus decumanus, but forming no part of the triturating surface of the 

 crown. 



