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Show 1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 93 15. Dactylomys, Is. Geoffroy, Ann. Sc. Nat. (2me ser.) x. p. 126 (1838). Ears short; tail long, scaly ; fore feet with the pollex obsolete, and the third and fourth digits elongated, with short convex nails. Skull with proportionally small orbits and high occiput. Incisors flat. Grinding-teeeh (except the lower premolar) each divided into two lobes, each of which has a single enamel-fold. 16. Plagiodon ( = Plagiodontia), F. Cuvier, Ann. Sc. Nat. (2™ ser.) vi. p. 347 (1836). Form stout; muzzle blunt; pollex rudimentary; outer hair coarse; under-fur silky; tail short, scaly. Grinding-teeth rootless, the upper with a deep enamel-fold running diagonally forward from near the internal posterior angle, and another running back from near the outer anterior angle ; the lower with one external and two internal folds. 17. Capromys, Desmarest, Mem, Soc. d'Hist. Nat. i. p. 44 (1822). External characters much as in Plagiodon ; far long and harsh; tail moderate or long, scaly, sparsely haired. Liver divided into minute lobules. Skull elongate, with no marked crests ; malar deep; paroccipital process long. Incisors small, convex. Upper grinding-teeth with one internal and two external folds ; the lower similar but reversed. 18. Aulacodus, Temminck, Monogr. de Mamm. i. p. 245 (1827). Form stout; muzzle blunt; fur harsh ; tail moderate, sparsely haired ; fore feet with the pollex rudimentary and the fifth digit very short; hind feet with four digits, of which the outer is rudimentary. Skull with the facial portion much inflated; the brain-case small, with strong sagittal and occipital crests ; parietals small; infraorbital opening with a separate canal for the nerve. Incisors very broad, the upper with three deep grooves. Grinding-teeth rooted, with folds arranged as in Capromys. Family II. HYSTRICID^E. Grinding-teeth with external and internal enamel-folds. Skull ovate, often greatly inflated by large air-sinuses in the bones; facial portion short and broad ; malar with no inferior angle ; occipital plane perpendicular, with a median ridge. Form robust; limbs sub-equal ; fur more or less modified into spines and hollow quills. Two subfamilies :- A. SPHINGURIN^E. Grinding-teeth rooted. Skull short; lachrymal bone not bounding the canal. Clavicles perfect. Upper lip unfurrowed. Tail moderate or long, usually prehensile. Soles of feet tuberculated. Four teats. Nearctic and Neotropical. Recent genera:- 1. Chatomys, Gray, P. Z. S. 1843, p. 21 (1843). Head and body clad with stout wavy bristles ; feet with four |