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Show 696 DR. C I. FORSYTH MAJOR O N T H E [June 1, group of muriform Rodents (Muriclce, auct.), of which they are the lowest of existing forms, having affinities with some of the least specialized of the family Dipodidae, as defined by Winge, viz. with Sminthus and Zapus." It was further pointed out that the African and Asiatic Rhlzomyes (Tachyoryctes and Bhizomys) present relations with the Malagasy Eodents, and that the affinity is especially close between Tachyoryctes and Brachyuromys raml-rohltra. In the present paper I propose to give a fuller description of the skull and dentition of the two species of Brachyuromys, and to compare them with those Eodents outside Madagascar with which, in m y opinion, they have affinities. The description of the other Malagasy Muridae must be postponed to a future paper; but I shall have to refer to them repeatedly in the following pages. Genus BRACHYUROMYS, Maj. Skull broad and massive. Upper profile of cerebral cranium flattened. Supraorbital crests rounded off. Incisors and rooted semibypselodont molars (3E3) large as compared to the size of the skull. Infraorbital foramen large, but on the whole with the shape characteristic of Muridse. Jugal large and approaching the lachrymal. Transverse diameter of incisors exceeding the longitudinall. Crowns of molars flattened, not tuberculate; unworn molars of species 2 half-tuberculate. In young specimens the crowns of the molars show three lobes of enamel, united by cement and obliquely disposed (inclining forwards with their outer portion), the posterior lobe in the upper, the anterior one in the lower molars being the smallest. These lobes soon unite together, producing various patterns, by which the different species may be easily distinguished. Tail shorter than usual in MuridaB. By their broad, moderately flattened, roundish beads and comparatively short tails these Eodents recall somewhat the Voles in outer appearance. 1. BRACHYUROMYS RAMIROHTTRA, Maj. (Plate XXXVII. fig. 2 and Plate X X X I X . figs. 1-3.) Ears large, oval. Coloration of upper parts brown, abuudantly mixed with black, on the sides less dark, the black hairs gradually diminishing. Lower parts fawn. Bases of hairs slate-coloured. Tail furnished above with black, beneath with grey hairs. Parietal crests diverging anteriorly. Interparietal short in transverse, but longer in antero-posterior diameter than in B. betsl-leoensis. Molars very large, all about of equal size and pattern, the third in both jaws generally slightly smaller than the other 1 (1) Where the incisors are wider than thick, the gnawing habit is feebly developed.-(2) Where the incisors are thicker than wide, the gnawing habit is greatly developed (Rvder, " The Significance of the Diameters of the Incisors in Rodents," Proc. Acad. Nat. Sci. Philadelphia, 1877, pp. 314-18). |
