366 DR. F. A. JENTINK. MAMMALS. 



straight from the anterior molar on both sides. The interdental ridges are somewhat 

 complicated: they are interrupted, the anterior pair has a feeble curvature, the free 

 ends strongly bent backward ; the second pair shows on each side a sharply broken 

 angular ridge; the third pair of ridges is reduced to small thickened relicts rather close 

 to the fourth ridge, which is slightly interrupted, curved on the sides, nearly straight 

 in the middle; ail the three interdental ridges are more or less crenated, the small 

 relicts of the third pair not crenated. In thjs species the number of interdental palate- 

 ridges may be supposed to be three and a lialf. 



From the foregoing it appears that in the hitherto described Pogonomj/s-species the 

 tail constantly is much larger than head and body taken together, moreover that the number 

 of interdental ridges varies from three to four, at least in Ave among the eight described 

 species. 



The Humboldt Bay expédition has collected on the Sentani Lake two mice apparently 

 belonging to the Pogonomys-genus, but differing in many points from ail the known species; 

 both they hâve the tail shorter than head and body ; one has six interdental ridges, mean- 

 while the other one présents a much greater number! They certainly merit spécifie distinc- 

 tion as moreover will be évident from the following descriptions. 



9. Pogonomys sexplicatus n. sp. 



Plate 16. 



A single pregnant female in alcohol, collected April 2. 1903 on the Sentani Lake, Hum- 

 boldt Bay expédition. 



Measurements taken from the spécimen in the flesh, in millimeters: 



head and body 150 



tail 135 



hind foot 26 



ear 13 



Hairs very soft to the touch ; two thirds of each hair on back and sides of the body 

 colored like our common Mus rattus, the terminal third of a fine mahogany; hairs on head 

 shorter, colored like the back ; breast and belly with wholly pure white hairs. A blackish 

 ring round each eye. Whiskers like in the other Pogonoînys-species numerous and very long. 

 Ears normally rounded off above. Tail ringed, scales not overlapping; each scale with a single 

 very short hair, so that the tail looks as if bald ; towards the terminal part the underside of 

 the tail is clad with parallel plates, the top of the tail is bald. Hands with four clawed digits, 

 the fifth very small with a blunt nail; hind feet with five clawed toes. 



Upper incisors light brown, lower ones white. Molars 3 / 3 (fig. 3). The three anterior 

 palate-ridges undivided, the first one a trifolium, the other two feebly curved, in the middle 

 connected with one another and with the trifolium by a very small raised bridge. There are 

 six interdental ridges; the first one connects the proximal margin of the anterior molars by 

 an uninterrupted slightly curved ridge; the three following ones are slightly interrupted, almost 

 straightly run thèse half-ridges towards the middle of the palate in a forwardly direction; the 



