18/6.] MR. E. R. ALSTON ON THE ORDER GLIRES. 85 



foramina large. Incisors plain. Molars never tuberculate, the in- 

 denting folds deep and closed, those of the second and third lower 

 molars sigmoid. 



30. Neotoma, Say & Ord, Journ. Acad. Philad. iv. p. 346 (1825). 



Ears large, nearly naked ; tail long, either sparsely haired or 

 bushy. Upper incisors broad, plain. Molars never tuberculate, with 

 open angular indenting folds, giving them a very arvicoline appear- 

 ance. 



(/3. Molars semirooted or rootless.) 



I. Arvicoline. Molars composed of triangular prisms placed 

 alternately. Skull with brain-case rhomboidal, frontals much con- 

 tracted, infraorbital opening typical. Limbs moderate ; tail mode- 

 rate or short, hairy. Palsearctic and Nearctic. Recent genera : — 



31. Fiber, G. Cuvier, Legons d' Anatomic (1800). 



Form thickset ; muzzle blunt ; limbs short, subequal ; hind feet 



fringed with long stiff hairs ; tail moderate, compressed, clad with 

 scales and short hairs; supraorbital ridges united in a sagittal 

 crest. Palate and lower surface of maxillaries minutely perforated. 

 Incisors plain. Molars semirooted, separated into prisms, which are 

 placed alternately. 



32. Arvicola, Lacepede, Tableau (1803). 



Muzzle blunt ; fore feet small, with short claws, soles naked ; tail 



longer than the hind foot, clad with short hairs. Skull as in Fiber ; 

 but the supraorbital ridges diverge after meeting, and converge again 

 on the interparietal ; palate not perforated. Incisors plain. Molars 

 as in Fiber, rootless (rarely semirooted). 



33. Myodes, Pallas, Zoogr. Rosso-Asiat. i. p. 173 . . . (1811). 

 Muzzle blunt ; fore feet moderate, with strong hooked claws ; soles 



hairy ; tail not longer than hind foot, hairy. Skull as in Arvicola, 

 but the brain-case broader and the zygomatic arches stronger. 

 Molars rootless, as in Arvicola, bmt the prisms of the posterior teeth 

 usually compressed and twisted. 



K, SiPHNEiNE. Molars as in the Arvicolince ; infraorbital open- 

 ing small and subtriangular. Form cyHndrical ; ear-conch rudimen- 

 tary ; limbs and tail very short. Paloearctic. Recent genera : — 



34. Ellobius, Fischer, Zoognosia, iii. p. 72 (1814). 



Body subcylindrical ; limbs very short, upper lip cleft ; eyes small ; 

 no external ear-conch ; fore feet with short claws, but stronger than 

 the hind feet ; tail very short. Skull as in Arvicola, but the profile 

 more arched and the facial portion shorter. Upper incisors arched 

 forward. 



35. Siphneus, Brants, Het Geslact der Muizen, p. 20 . . (1827). 

 Eyes small ; ears rudimentary ; fore feet with long, strong claws. 



