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Show 77 1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 2. Sciurus, Linnaeus, Syst. Nat. i. p. 86 t Limbs free, form agile, tail long, bushy. No * £ g ™ £ £ three or four pairs of teats. First upper premolar " J ™ " ™ lost Frontals ankylosed with parietals; postorbital processes moderate ; infraorbital opening in front of anterior root of zygoma. Palate broad, flat. 3. Xerus, Hemprich & Ehrenberg, Symbol. Phys., M a m m - g Ears very short or rudimentary, tail short, fur sparse, harsh with flattened spines. N o cheek-pouches, two pairs of teats Nasab and palate narrower, and postorbital processes much smaller than in Sciurus. 4. Tamias, Illiger, Prod. Syst. M a m m . p. 83 . . . . • (1811). Fars short fore feet with the fourth digit longest, limbs subequal, taifsnort Large internal cheek-pouches. First upper premolar soon lost! Skull slender; infraorbital opening in anterior root of zygoma, not in front of it. B ARCTOMYIN**. Incisors not compressed. Limbs free, form usually stout, tail short. Palaearctic and Nearctic. Recent genera : - 5 Spermophilus, F. Cuvier, Mem. du Mus. vi. p. 293 . (1822). Form somewhat slender; tail short or moderate. Claw of pollex rudimentary or absent. Large cheek-pouches Series of grinding-teeth nearly parallel. Skull with no marked ridges; postorbital processes slender, directed backwards. 6. Cynomys, Rafinesque, Amer. Monthly Mag. ii. p. 45 (1817). Form thickset, tail short, claws of fore feet long on all the digits, shallow cheek-pouches. Series of grinding-teeth strong y convergent behind. Skull short and broad ; postorbital processes long, directed backwards ; parietals narrow, parallelogrammatic. 7. Arctomys. Schreber, Saugethiere, iv. p. 721 (1792). Form thickset, tail short; pollex rudimentary, with a flat nail. Cheek-pouches rudimentary or absent. Series of grinding-teeth nearly parallel. Skull broad ; postorbital processes large triangular, standing out at right angles ; parietals narrow, parallelogram-maFossil genera. The following genera, characterized from details of dentition, seem to be referable to this family -.-Plesarctomys, Bravard, in Gervais's ' Zool. et Pal. Franc.' pl. xlvi. (1852), Eocene of France* Pseudosciurus, Hensel, Z. Deutsch. geol. bes. lSob, n 660 bone-beds of Wurttemberg ; Sciuravus, Marsh, A m . Journ. Sc 1871 P 120 Eocene of North America ; Paramys, Leidy, Geol. Survey, Montana! 1871, p. 363 (perhaps the same as the last) ; Gym-notrichus, Cope, Pal. Bulletin, i. p. 6 (1874), Miocene of North America. |