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Show 248 MR. O. THOMAS ON A NEW GENUS OF MURID.E. [May 7, dentition, as both the cranial and external characters of the genus are those of ordinary Muridae. 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 Hydromys, I propose to call it XEROMYS1, g. n. External form murine. Tip of muzzle as in Mus, not as in LLydromys. 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 musculus. Ears short (as compared to most members of Mus), 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 LLydromys. Fur very short, uniform in length. Whiskers 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. 5). Mammae 0 - 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 N. Australian Uromys 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 premaxillae. Interorbital region smoothly convex, the supraorbital 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. Bullae small, inflated, transparent. Teeth.-Upper incisors long, less curved than in Mus, and recalling in their general appearance those of the Voles. Their 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 1 £--/pi*s, dry; •>) Knpel, the dry laud. |
