122 Mr. 0. Thomas on new 



While tl>e first of tliese groups unquestionably deserves 

 distinction from Mits, the second is more or less intermediate 

 in its tooth-eliaracters; but .since it shows a distinct tendency 

 to the true T/iamnomt/s type of teeth, and has absolutely the 

 same external characteristics, 1 think it advisable to refer it 

 to the new genus rather than to leave it in Mus. 



In the typical venitstus-nitilans group all the supplementary 

 cusps of the teeth are highly developed, and the x cusp in 

 ])articular is a distinct separate cusp almost equalling in sizd 

 the other internal cusps in front of it, and there are con- 

 sequently nine well-marked cusps along tlie inner side of tiie 

 Uj»per tooth-row. 



On the other hand, in the doUchurus grou]i the x cusp is 

 but little developed, and in fact is usually represented by a 

 mere ridge runninii backwards from the liindcr ed";e of the 

 second internal cusp of ?«* and m^ and joining the inner side 

 of the median cusp of the hinder lamina of each tooth. 



In the lower jaw the postero-external supplementary cusp 

 of /»i is decidedly larger than in Mus, nearly as large in area 

 and at least half as high as the main posterior cusp against 

 ■which it lies. 



Externally, as already noted, tlie mice of the genus 

 Tliainnomijs are characterized by their terminally ])cncilled 

 tails, in the same way as the analogous forms Uhipidomya 

 and CEcomys in S. America. The feet are similarly modified 

 for climbing, with broad rounded sole-pads, and the fifth 

 hind toe reaches nearly to the end of the second phalanx of 

 the fourth, and is therefore nearly as long as the second. 



Thamnomys venustus, sp, n. 



Allied to T/t. rutUans, Peters, but larger and with much 

 longer lur. 



i'ur of back about 15 mm. in length. General colour 

 above dark rufous (in spirit), a brighter line along the sides ; 

 belly white, with a faint buffy sufi'usion, the basal halves of 

 the hairs slaty. Ears dull greyish. Upper surface of feet 

 buff, becoming whiter on the toes. Tail long, jjcncilled ter- 

 minally, uniformly dark brown, as in Th. rutdans. ]\Ian)nue 

 0—2 = 4. 



Skull decidedly larger than in Th. rutilans ; muzzle long, 

 parallel-sided; interorbital region narrow, the edges not so 

 widely expanded as in rutiJans ; palatine foramina loTig, not 

 expanded mesially, reaching back to the level of the front of 

 m' ; bullte rather larger than in rutilans. Molars large, 

 heavy, the series markedly larger than in rutilans. 



Dimensions of the type (measured on the spirit-specimen): — 



Head and body 125 mm.; tail 181; hind foot 25; ear 18. 



