| OCR Text |
Show 88 MR. E. R. ALSTON ON THE ORDER GLIRES. [Jan. 18, terior lobes of premolars small. A third upper molar small, sub-circular. B. HETEROMYIN;E. Incisors narrow. Skull more delicate, with the mastoid appearing largely on its top ; infraorbital opening not defined, through the non-development of the lower root of the maxillary zygomatic process ; malar slender. Cervical vertebrae sometimes ankylosed (as in Dipodina). Form slender; hind limbs and tail elongated ; eye and ear moderate or large. Recent genera :- 3. Dipodomys, Gray, Ann. & Mag. Nat. Hist. vii. p. 521 (1840). Ear large, rounded ; tail long, densely haired, tufted ; soles hairy ; pollex very small, with a small claw. Cheek-pouches large. Skull with nasals produced in front; upper part of zygoma produced into a flat plate articulating with the frontals ; interparietal very small, narrow; auditory bullae enormous, projecting far beyond the occipital plane. Incisors plain. Grinding-teeth rootless, at first with slight indenting enamel-folds, afterwards simple. 4. Perognathus, Max. Prinz zu Wied, Nov. Act. Ac. Car. Leop. xix. i. p. 369 (1839). Ears shorter ; tail thinly haired ; soles more or less naked; pollex with a flat nail. Skull less modified ; nasals not so much produced ; zygoma not developed into a flat plate ; interparietal broad ; auditory bullae not projecting behind the occipital plane. Incisors grooved. Grinding-teeth rooted, tuberculate in youth, afterwards with isolated enamel-loops. 5. Heteromys, Desmarest, Mammalogie, p. 313 (1820). Like Perognathus, but the fur bristly, mixed with flattened spines ; tail shorter, clad with large scales and scattered hairs. Skull with sharp supraorbital ridges; interparietal very broad. Upper incisors plain. Grinding-teeth as in Perognathus. Family VI. THERIDOMYID.E. One premolar present above and below. Grinding-teeth rooted or rootless, not tuberculate, with more or fewer transverse enamel-folds. Infraorbital opening large, suboval. Palate somewhat contracted in front and emarginate behind. Eocene and Miocene of Europe. Fossil genera:- I. Theridomys, Jourdan, Compt. Rend. Ac. Paris, v. p. 483 (1837). Grinding-teeth rooted, with three or four reentering enamel-folds, which become isolated enamel-loops in the worn teeth. 2. Archceomys, De Laizer et De Parieu, C. R. Ac. Paris, viii. p. 206 (1839). Grinding-teeth rootless, the enamel-folds continued diagonally across the crowns, which are thus divided into laminae, of which the anterior is the largest above, while they are subequal below. |
