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Show MAMMALIA. hcilnodtheerd p worittiho nh.a irs, aud the tarsus is covered with hair beneath,-ut least the C.·anium .-Thc skulls of the species of the present genus differ fmm those of the species of Mus in being proportionately shorter and broader, and m01·e arched; the facial portion of the skull is larger, compared with the cranial, the space between the orhits is narrower, and the orbits are larger; the palate is narrower and the incisive foramina are more elongated and larger. The pte•·ygoids approximate anteriorly, so that the posterior,.,.,_, are greatly contracted. As in the genus Mus the anterior root of the zygomatic arch is directed upwards from the plane of the palate, and forwards in the form of a thin plate, protecting an opening behind, which leads into the nasal cavity, and also forming the outer boundary both of the ant-orbital foramen, and a second opening whose outlet is directed upwards. This tl1in plate, however, is narrower than is usually found in the genus Mus. The most striking dif:. ferences observable in the lower jaw consist in the srnalle1· size of the coronoid process, and its being curved ontwar·ds ; the condyloid pmcess is narrower, and the angle of the jaw, or descending ramus, approaches more nearly to a quadrate form·-the posterior edge of the jaw is more deeply emarginated. 69 Dentitz'on.-The incisors are narrow and compressed as in the genus Mus, bnt they are less de ep from front to back; those of the upper jaw (Plate 33. fig ~. b.) have each a distinct longitudinal groove, which is situated nearer to the oute1· than to the inner edge of the tooth. Close to the inner edge of each of these teeth an indistinct second longitudinal groove may be seen by means of a lens. The lower incisors are nearly equal in width to the upper. The crowns of the molar teeth in the young Reitltrodon are higher tl1an in Mus, and they are rootless; in the adult animal, however, they possess distinct roots. The folds of enamel form sigmoid flexures, are closely approximated to each other, and those of the opposite sides of the tooth meet. 1. REITHRODON CUNICULO'iDES. PLATE xxvr RoitlJrodon cuniculoldes, 1-Vate~·lt., Proceedings of the Zoological Society of London for February 1837, p. 30. R. supra griseus, jlavo-lavatus, pitis nigris intermix tis; ahdomine guldque pallide flavis; natibus albis; pedibus albis; aw·ibus mediocribus, inlus }Jilt's .flavz·s, e:r:tus pilis pallide jlavis, obsitis; pone aures, notd magnd albescentijiava; caudd corpore h1·eviore, supra pallidefuscd, subtz'ts alblt. DEscniPTioN.- Head rather large and arched; ears moderate; tail nearly as long |