18/6.] MR. E. R. ALSTON ON THE ORDER GLIRES. 95 



Fore limbs small; hind limbs elongate, with four or five toes. Fur very 

 soft. Tail moderate or long, bushy. Neotropical. Recent genera : — 



1. Chinchilla, Bennett, Gardens &c. Zool. Soc. pt. i. p. 1 (1829). 



Ears broad, not elongated. Fore feet with five digits ; the pollex 

 very small, but bearing a claw ; hind feet with four digits. Tail long, 

 bushy. Skull with the auditory bullae enormous, appearing on the 

 top of the skull between the supraoccipital, interparietal, and squa- 

 mosals. Grinding-teeth rootless, with their enamel-folds nearly 

 straight, each with three laminse; the two anterior laminae of the 

 lower premolar imperfectly separated. 



2. Lagidium, Meyer, Nov. Act. Acad. Nat. -Cur. xvi. p. 576 



(1833). 



Ears elongated. Both fore and hind feet with four digits. Skull 

 as in Chinchilla, but the auditory bullae more moderate, articulating 

 on the top of the skull with the supraoccipital and squamosals only. 

 Grinding-teeth similar, but their folds curved ; all three laminse of 

 the lower premolar perfectly separated. 



3. Lagostomus, Brooks, Tr. Linn. Soc. xvi. p. 102 . . . (1828). 



Ears moderate. Fore feet with four digits, and hind feet with 

 three ; the tarsus elongated. Tail moderate, bushy, tufted. Skull more 

 massive than in the other genera, with well-marked sagittal and occi- 

 pital crests ; auditory bullae smaller, not appearing on the top of the 

 skull ; infraorbital opening with a separate canal for the nerve. 

 Grinding-teeth with two laminae, except the last upper molar, which 

 has three. 



Fossil genera : — 



4. Amhlyrhiza, Cope, Proc Amer. Phil. Soc. xi. p. 183 . (1869). 

 Grinding-teeth semirooted, each with either four or five laminae. 



5. Loxomylus, Cope, op. cit. p. 187 (1869). 



Grinding-teeth as in Amhlyrhiza, but each with three laminae 

 only, their crowns obliquely sloped both longitudinally and laterally. 



Family IV. Dasyproctid^. 



Incisors long. Grinding-teeth semirooted, with external and inter- 

 nal enamel-folds. Milk-teeth long retained. Optic foramina sepa- 

 rate ; palate broad ; incisive foramina short ; mandible with the masse- 

 teric ridge obsolete. Clavicles rudimentary. Form somewhat slender, 

 limbs moderate ; upper lip entire ; ears short ; tail short and naked 

 or rudimentary. Fore feet with five digits ; hind feet with five or 

 three ; claws short and hoof-like. Neotropical. Recent genera : — 



1. Dasyprocta, Illiger, Prod. Syst. Mamm. p. 93 . . . . (1811). 



Form compact ; limbs long ; hind feet with three digits only ; tail 

 either obsolete or short and subnaked. Skull elongate, smooth ; 

 infraorbital opening with no separate canal ; malar simple ; parocci- 



