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Show 1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 87 B. BATHYERGINJE. Palate between the molars not broader than one of the alveoli; an interpterygoid fissure ; mandible hystricine in form (the angular portion springing from the side of the bony covering of the lower incisor). Ethiopian. Recent genera :- 4. Bathyergus, Illiger, Prod. Syst. Mamm. p. 86 ... (1811). Eyes small; no ear-conch; fore feet with very long claws ; hind feet with the third digit longest; tail short, hairy. Skull massive, occipital plane perpendicular ; nasals very narrow ; parietals very small; infraorbital foramen very small, subcircular; angle of mandible pointed. Upper incisors enormously large, broad, grooved. One premolar above and below. Molars with indenting enamel-folds in youth only. 5. Georychus, Illiger, Prod. Syst. Mamm. p. 87 .... (1811). Externally like Bathyergus, but the claws, especially of the fore feet, shorter and weaker, skull with the profile more arched, the occipital plane slightly sloped forward, and the angle of the mandible rounded. Upper incisors long, arched forwards, plain. Grinding-teeth as in Bathyergus. 6. Heliophobius, Peters, Monatsb. Ak. Berlin, 1846, p. 239 (1846). Differs externally from Georychus in the second digit of the hind feet being the longest. Skull with the infraorbital opening smaller, the bony palate shorter, and the coronoid process larger. Incisors plain. Three premolars above and below ; but sometimes two only are developed. Family V. G E O M V I D J E. One premolar above and below. Grinding-teeth rooted or rootless. Malar extending forward to the lachrymal. Squamosals extremely large. Angular portion of mandible strongly twisted. Large cheek-pouches, opening on the cheeks outside the mouth. Upper lip not cleft. Other external characters very variable. Nearctic and Neotropical. Two subfamilies :- A. GEOMYINE. Incisors broad. Skull massive; infraorbital opening very small; mastoid not appearing on the top of the skull; malar stout. Form thickset; eyes small; ear-conch rudimentary ; limbs short, subequal; fore claws very large. Recent genera:- 1. Geomys, Rafinesque, Am. Monthly Mag. ii. p. 45 . . (1817). Fore feet large, with very large compressed curved claws; tip of tail naked; cheek-pouches large. Skull very massive ; zygomatic arches stout. Upper incisors deeply grooved. Crowns of premolars divided into two subequal lobes. 2. Thomomys, Max. Prinz zu Wied, Nov. Act. Ac. Car. Leop. xix. i. p. 383 (1839). Fore feet comparatively small, with moderate claws ; cheek-pouches moderate. Skull less massive; zygoma more slender. Upper incisors plain, or with merely a fine groove near their inner edge. An- |