248 MR. O. THOMAS ON A NEW GENUS OF MURID^. [May 7, 



dentition, as both the cranial and external characters of the new 

 genus are those of ordinary ;Murid^e. The new form, by its structure, 

 is obviously a land- and not a water-animal, and on this account, 

 in contradistinction to its aquatic ally Hydronujs, I propose to call it 



Xeromys\ g. n. 



External form murine. Tip of muzzle as in Mus, not as in 

 Hijdromys. Toes unwebbed. Tail scaly, very finely haired. Skull 

 as in Mus, except that the supraorbital edges are rounded. Teeth 

 both in number and structure as in Hydromys. 



XeROMYS MYOIDES, sp. n. 



External appearance exactly like that of an ordinary Mus. Size 

 about twice that of Mus viusculus. Ears short (as compared to most 

 members of 3Ivs), rounded, laid forward they only reach to within 

 about 3 or 4 millim. of the posterior canthus of the eye ; their anterior 

 edge without the little supplementary flap found in Hydromys. 

 Fur very short, uniform in length. AA'hiskers as in Mus, fewer and 

 slenderer than in Hydromys. General colour above dark slaty grey, 

 below white, the line of demarcation not sharply defined. Ears 

 grey. Arms and legs like back ; hands and feet very thinly haired, 

 almost naked terminally, white. Palms and soles (Plate XXIX. 

 fig. 9) naked, the former with five and the latter with six pads, the 

 last hind pad elongate. Pollex with a short broad nail, all the other 

 digits with claws ; fifth digit on each foot, without claw, reaching 

 just to the base of the fourth. Tail about the length of the body 

 without the head, slender, scaly, the scales rather irregularly disposed, 

 very small, averaging about 20 to 22 to the centimetre, the whole 

 tail very thinly covered with fine white hairs ; its substance pale 

 flesh-colour above and below. Palate-ridges exactly as in Hydromys, 

 i. e. three predental, the third notched in its centre, three interrupted 

 interdental ridges, and one posterior uninterrupted (see Plate XXIX. 

 fig. b). INIammse — 2 = 4, as in Hydromys. 



Skull (Plate XXIX. figs. 1-4), in its general form, not unlike that 

 of a small Rat, say of the common X. Australian Vromys cervinipes, 

 Gould. Nasals reaching much further forwards than in Hydromys, 

 but not so far as in Mus, just falling short of the level of the front 

 of the premaxillse. Interorbital region smoothly convex, the supra- 

 orbital edges rounded, not ridged or beaded. Interparietal very 

 broad transversely, and narrow antero-posteriorly. Infraorbital 

 foramen typically murine in character, the outer wall broad and 

 slightly projecting forwards (fig. 6). Anterior palatine foramina 

 short, not equalling the combined length of the two upper molars. 

 Bullse small, inflated, transparent. 



Teeth. — Upper incisors long, less curved than in Mus, and recalling 

 in their general appearance those of the Voles. Tlieir front surfaces 

 smooth, ungrooved, orange in colour. Molars (Plate XXIX. fig. 10) 

 as in Hydromys chrysogaster, except that the lateral ends of the 

 lobes are shorter and rounder, and that the inner wall of the second 

 ' ^'ipds, dry; jy ^t]pa, the dry laud. 



