Miller. Seven New Rats collected in Siam. 141 



Skull. The skull of Mus ferreocanus (Pis. Ill and IV, Fig. 2) though of 

 the same general size as that of the other large rats of Trong, is easily 

 recognizable by its shallow, weak rostrum and tapering form as well as 

 by various details in structure. The zygomata are strongly convergent 

 anteriorly, their anterior roots relatively light and little spreading. An- 

 tiorbital foramina small, b-ut less contracted below than in the other 

 species. The plate forming its outer wall is faintly concave on the outer 

 surface, its anterior border slightly convex from below middle, the 

 straight portion at base sharing distinctly backward. Pterygoids long and 

 straight to the extreme tip, the interpterygoid space narrowing gradually 

 and continuously from behind forward. Audital bullae much larger than 

 in Mus voci/erans, but not peculiar in form. Interorbital region narrow. 

 Supraorbital ridges low and little developed, much as in Mus bowersi, but 

 traceable along sides of braincase to lambdoid ridge. 



Teeth. Molars slightly narrower than in Mus vocijerans, the enamel 

 folds relatively broader, but not essentially different in form. The pos 

 terior limb of the terminal crescent in the third upper molar is normally 

 divided from the anterior, even in unworn teeth. Lower molars differ 

 ing in much the same manner as the upper. Incisors relatively weak, 

 their anterior face yellowish white. 



Measurements. External measurements of type specimen: total length, 

 489; head and body, 238; tail vertebrae, 251; hind foot, 56 (53); ear from 

 meatus, 27; ear from crown, 21; width of ear, 17. A second adult 

 specimen: total length, 501; head and body, 241; tail vertebrae, 260; 

 hind foot, 56 (53). 



Cranial measurements of type: greatest length, 53.6; basal length 

 48; basilar length, 45; palatal length, 25; least width of palate between 

 anterior molars, 5; dias,tema, 15.8; length of incisive foramen, 9.4; com 

 bined breadth of incisive foramina, 3.8; length of nasals, 22.6; combined 

 breadth of nasals, 5.2; zygomatic breadth, 25.4; interorbital breadth, 8; 

 mastoid breadth, 20.2; breadth of braincase above roots of zygomata, 

 20; depth of braincase at anterior extremity of basioccipital, 14.6; fron- 

 topalatal depth at posterior extremity of nasals, 12; least depth of ros 

 trum immediately behind incisors, 8; maxillary toothrow (alveoli), 9.4; 

 width of front upper molar, 2.8; mandible, 30; mandibular toothrow 

 (alveoli), 9. 

 Specimens examined. Three, all from the type locality. 



Remarks. This species is not closely related to the other rats of the 

 Malay Peninsula; and I am unable to find any description of an animal 

 at all resembling it among the forms occurring in the East Indian Ar 

 chipelago. 



Mus validus sp. nov. 



Type adult male (skin and skull) No. 86,741 United States National 

 Museum, collected in the mountains of Trong, Lower Siam, at about 

 1000 ft, altitude, February 18, 1899. 



Characters. A large robust animal in size and general appearance re 

 sembling Mus bowersi Anderson from Burmah. Fur coarse, but essen- 



