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Show 84 MR. E. R. ALSTON ON THE ORDER GLIRES. [Jan. 18, feet as in Mus ; tail long, scaly. Skull as in Mus ; the infraorbital foramen lower and wider. Incisors plain. Molars like those ot Hesperomys ; the first upper, when worn, with one internal and two external indenting folds; the first lower with one external and two internal, the rest with one external and one internal fold. 23. Brachytarsomys, Gunther, P. Z. S. 1875, p. 79 . . (1875). Upper lip grooved, not cleft; eyes small; ears short; hind feet much shorter than the lower leg ; tail long, scaly. No supraorbital ridges ; auditory bullae moderate. Incisors plain. Molars with two or three indenting folds on each side, one of which in the upper molars passes quite across the crown. 24. Drymomys, Tschudi, Fauna Peruana, p. 178 . . (1844-6). Form murine; muzzle pointed; upper lip cleft; ears large; tail long, scaly. Incisors furrowed on the sides. Molars small; the first with three pairs of tubercles, the second with two, the third with one pair only. 25. Holochilus, Brandt, M e m . Ac. St. Petersb. (6™ ser.) iii. p. 428 (1835). Muzzle obtuse; upper lip not fully cleft; fore feet small; hind limbs large and strong; tail long, sparsely haired. Skull short, strong ; supraorbital ridges well marked. Incisors broad, flat, plain. Molars large, the third as large as the second, with tubercles arranged in pairs, which soon wear away, leaving the crown flat with indenting folds. 26. Hesperomys, Waterhouse, Zool. Voy. Beagle, i. p. 75 (1839). Upper lip cleft; ears large or moderate; tail sparsely haired. Small internal cheek-pouches in a few species. Skull murine, with or without marked supraorbital ridges. Incisors plain. Molars as in the last genus, but narrower ; the third smaller than the second, and the first upper with three roots. 27. Ochetodon, Coues, Proc. Acad. Philad. 1874, p. 184 (1874). As in the last genus; tail moderate. Upper incisors grooved. First upper molar with four roots. 28. Reithrodon, Waterhouse, P. Z. S. 1837, p. 29 . . . (1837). Profile arched; eyes large; ears hairy; hind feet with first and fifth digits very short; tail moderate, hairy. Skull with nasal portion large, supraorbital ridges well marked, posterior nares narrowed by the approximation of the pterygoids. Upper incisors grooved. Molars as in Hesperomys, their indenting folds deep. 29. Sigmodon, Say & Ord, Journ. Acad. Philad. iv. p. 352 (1825). Muzzle blunt; upper lip partially cleft; ears large, but nearly concealed in the long fur; hind feet with first and fifth digits very short; tail moderate, nearly naked. Skull with supraorbital ridges sharp, perpendicular plate of zygoma emarginate in front, incisive |