18/6.] 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 ; basi- 

 occipital 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: — Trogontherium, Fiscber, Mem. 

 Soc. Imp. Nat. Mosc. ii. p. 2G0 (1809) ; Pakeomys, Kaup, Isis, 1832, 

 p. 992 ; Chalicomys, Kaup, op. cit. p. 994 ; Chelodus, Kaup, op. cit. 

 p. 99o ; Palceocaster, Leidy, Journ. Ac. Pbilad. vii. p. 338 (1869). 



Section II. Myomorpha. 



Premolars present or absent ; grinding-teeth rooted or rootless. 

 No postorbital frontal processes ; infraorbital opening various. Zygo- 

 matic 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 

 inaxiilaries. Outer walls of pterygoid fossce often obsolete, no inter- 

 pterygoid fissure (except in Bathyergince). Angular portion of 

 mandible springing from the lower edge of the bony covering of the 

 lower incisor (except in Bathyergince). Clavicles perfect (except in 

 Lophiomyidce). 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. Myoxid^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 ; inter- 

 parietal broad, articulating with the squamosals. Infraorbital opening 

 moderate, high, narrow. Mandible with the angle rounded or sub- 

 quadrate, coronoid long and slender. No CEecum. Form gracile ; 

 eyes and ears large ; fore limbs small ; tail long, hairy. Palsearctic 

 and Ethiopian. Recent genera : — 



1. Myoxus, Schreber, Saugeth. iv. p. 824 (1792), 



Tail bushy and distichous throughout. Stomach simple. An- 

 gular 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 



