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Show 1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 79 4. Castoroides, J. W. Forster, 2nd Rep. Geol. Ohio, p. 81 (1838). Parietals not parallelogrammatic ; interparietal very small; basioccipital concave. Incisors with numerous longitudinal grooves ; grinding-teeth with the enamel-folds extending quite across their crowns, completely separated and united only by cement; the last upper molar and lower premolar with four folds, the rest with three only. More doubtful fossil genera are:-Troyontherium, Fischer, M e m. Soc. Imp. Nat. Mosc. ii. p. 260 (1809) ; Palaomys, Kaup, Isis, 1832, p. 992 ; Chalicomys, Kaup, op. cit. p. 994 ; Chelodus, Kaup, op. cit. p. 995 ; Palaocaster, Leidy, Journ. Ac. Philad. vii. p. 338 (1869). Section II. Myomorpha. Premolars present or absent ; grinding-teeth rooted or rootless. No postorbital frontal processes ; infraorbital opening various. Zygomatic arch slender; the malar rarely extending far forward, and being usually supported below by a continuation of the maxillary zygomatic process. Incisive foramina usually long, and extending into the maxillaries. Outer walls of pterygoid fossae often obsolete, no inter-pterygoid fissure (except in Bathyergina). Angular portion of mandible springing from the lower edge of the bony covering of the lower incisor (except in Bathyergina). Clavicles perfect (except in Lophiomyida). Tibia and fibula completely ankylosed in the adult for at least their lower third. Upper lip usually cleft; muffle small and naked; nostrils comma-shaped, rounded above. Tail cylindrical, either hairy or covered with scales arranged in rings. Seven families:- Family I. M Y Q X I D . E. One premolar above and below, which is rather smaller than the molars ; all the grinding-teeth rooted, with transverse enamel-folds. Skull with frontals much contracted, clasped by the parietals ; interparietal broad, articulating with the squamosals. Infraorbital opening moderate, high, narrow. Mandible with the angle rounded or subquadrate, coronoid long and slender. No caecum. Form gracile; eyes and ears large ; fore limbs small; tail long, hairy. Palaearctic and Ethiopian. Recent genera :- 1. Myoxus, Schreber, Saugeth. iv. p. 824 (1/92), Tail bushy and distichous throughout. Stomach simple. Angular portion of mandible not perforate. Premolars small; molars large, with well-marked enamel-folds. 2. Muscardinus, Kaup, Entw. europ. Thierw. p. 139 . . (1829). Tail bushy and cylindrical throughout. Stomach complicated. Mandible not perforate. Grinding-teeth large ; their crown flat, with well-marked and numerous folds. 3. Eliomys, Wagner, Abhand. baierisch. Akad. iii. p. 179 (1843). Tail with short hairs at base, tufted and distichous towards its |