| OCR Text |
Show 130 MR. O. THOMAS ON A NEW GENUS OF MURID.E. L 4. On a new and interesting Annectant Genus of Muridce, with Remarks on the Relations of the Old- and New- World Members of the Family. By OLDFIELD THOMAS, Natural History Museum. [Received February 10, 1888.] (Plate V.) By the kindness of Prof. Alphonse Milne-Edwards I have been entrusted with the description of a specimen which has been in the Paris Museum for some years, where it has borne the unpublished name of " Malacomys ferrugineus," a name by which it has been incidentally referred to in print, and which therefore, so far as the species is concerned, I now retain in order to avoid confusion. The genus may be termed DEOMYS1, g. n. General external form as in Mus. Pollex with a narrow nail. Hind feet elongate. Infraorbital foramen triangular, not narrowed below, its external plate slender, not produced forwards. Upper incisors each with two minute, almost microscopic, grooves; lower incisors smooth. Anterior upper molars with seven distinct and prominent cusps, arranged 2-3-2, the extra one on the middle lamina2 placed quite internal to the general series. Second molars not placed obliquely ; with five cusps arranged 3-2, as in Mus, but the antero-internal cusp not pushed forwards in front of the others. Lower molars with the cusps biserially arranged as usual. All the cusps above and below unusually high and distinct, connected with one another by quite low and inconspicuous enamel ridges. DEOMYS FERRUGINEUS, sp. n. General colour of head and body a clear pale red or reddish fawn-colour, thickly grizzled along the centre of the back with black, but the reddish colour of the cheeks, shoulders, sides, and hips quite clear and unmixed. Face rather duller in general tone ; area round eyes black, not sharply defined. Ears very large, oval, rounded ; 1 dew, I link. 2 To avoid the too frequent use of such terms as the " anterior internal" cusp, or " central cusp of tho middle lamina," it would be useful to have a simple formula for the naming of each cusp. This might be done by calling the three lamina, of mi A, B, and C, and their respective cusps 1, 2, and 3, counting from outside inwards. Thus the cusps just quoted would be A 3 and B 2 respectively, while one would say of Beomys that the cusp-formula of its m1 was A 1, 2 ; B 1, 2, 3 ; C 1, 2, since it is without the A 3 present in Mus, and possesses the B 3 absent in the Criceti. The same formula is of course equally applicable to m2 o r a n y other tooth. The reason for numbering the cusps from the outside inwards is that Beomys shows that the third cusp has been added on the inner side, and therefore that the two cusps of Cricelus are homologous with the two outer cusps of Mus. |
