18/6.] MR. E. R. ALSTON ON THE ORDER GLIRE3. 93 



15. Dactylomys, Is. Geoffroy, Ana. Sc. Nat. (2 me ser.) x. p. 126 



(1838). 

 Ears short ; tail long, scaly ; fore feet with the pollex ohsolete, 

 and the third and fourth digits elongated, with short convex nails. 

 Skull with proportionally small orbits and high occiput. Incisors 

 flat. Grinding-teeeh (except the lower premolar) each divided into 

 two lobes, each of which has a single enamel-fold. 



16. Plagiodon ( = Plagiodontia), F. Cuvier, Ann. Sc. Nat. 

 (2 me ser.) vi. p. 347 (1836). 



Form stout; muzzle blunt; pollex rudimentary; outer hair coarse; 

 under-fur silky ; tail short, scaly. Grinding-teeth rootless, the 

 upper with a deep enamel-fold running diagonally forward from near 

 the internal posterior angle, and another running back from near the 

 outer anterior angle ; the lower with one external and two internal 

 folds. 



1 7. Capromys, Desmarest, Mem. Soc. d'Hist. Nat. i. p. 44 (1822). 

 External characters much as in Plagiodon ; fur long and harsh ; 



tail moderate or long, scaly, sparsely haired. Liver divided iuto 

 minute lobules. Skull elongate, with no marked crests ; malar 

 deep ; paroccipital process long. Incisors small, convex. Upper 

 grinding-teeth with one internal and two external folds ; the lower 

 similar but reversed. 



18. Aulacodus, Temminck, Monogr. de Mamm. i. p. 245 (1827). 

 Form stout ; muzzle blunt ; fur harsh ; tail moderate, sparsely 



haired ; fore feet with the pollex rudimentary and the filth digit very 

 short ; hind feet with four digits, of which the outer is rudimentary. 

 Skull with the facial portion much inflated; the brain-case small, with 

 strong sagittal and occipital crests ; parietals small ; infraorbital 

 opening with a separate canal for the nerve. Incisors very broad, 

 the upper with three deep grooves. Grinding-teeth rooted, with folds 

 arranged as in Capromys. 



Family II. Hystricid^e. 

 Grinding-teeth with external and internal enamel-folds. Skull 

 ovate, often greatly inflated by large air-sinuses in the bones ; facial 

 portion short and broad ; malar with no inferior angle ; occipital 

 plane perpendicular, with a median'ridge. Form robust ; limbs sub- 

 ecpial ; fur more or less modified into spines and hollow quills. Two 

 subfamilies : — 



A. Sphingurin^e. Grinding-teeth rooted. Skull short ; lachry- 

 mal bone not bounding the canal. Clavicles perfect. Upper lip 

 unfurrowed. Tail moderate or long, usually prehensile. Soles of 

 feet tuberculated. Four teats. Nearctic and Neotropical. Recent 

 genera : — 



1. Chcetomys, Gray, P. Z. S. 1843, p. 21 (1843). 



Head and body clad with stout wavy bristles ; feet with four 



