18/6.] MR. E. R. ALSTON ON THE ORDER GLIRES. 91 



B. Octodontin.'E. Grinding-teeth serairooted or rootless, with 

 short and simple enamel-folds. Fur soft. Tad usually short. Ethio- 

 pian and Neotropical. Recent genera : — 



3. Petromys, A. Smith, S.African Quart. Journ. ii. p. 2 (1831). 

 Ears short. Fur rather harsh. Pollex very short, with a small nail. 



Claws short. Tail moderate, rather bushy. Infraorbital opening with 

 a small groove for the nerve. Grinding-teeth semi rooted, with single 

 external and internal folds, which nearly meet in the middle. 



4. Ctenomys,De Blainville, Bull. Soc. Philomath. 1826, p. 62 



'(1826). 

 Eye and ear very small. Fur soft. Claws longer than the toes, 

 those of the hind feet with comblike bristles (as in Ctenodactylince). 

 Tail rather short, clad with short hairs. Skull and mandible very 

 massive ; auditory bullae long and pear-shaped ; malar with strong 

 superior and inferior angles ; infraorbital opening with no groove for 

 the nerve. Incisors very broad. Grinding-teeth rootless, with kidney- 

 shaped crowns ; the third molar above and below small and sub- 

 circular. 



5. Schizodon, Waterhouse, P. Z. S. 1841, p. 91 (1841). 



External characters much as in Ctenomys, but the ears larger and 



the claws, th ough strong, not longer than the digits themselves. Skull 

 less massive ; the superior and inferior angles of the malar weaker ; 

 infraorbital opening with a groove for the nerve. Incisors broad, 

 convex. Grinding-teeth placed transversely, with single external and 

 internal folds, which meet in the middle. 



6. Spalacopus, Wagler, Isis, 1832, p. 1219 (1832). 



Ear rudimentary ; tail short ; claws of fore feet shorter than the 



digits. Skull shorter than in Schizodon ; superior and inferior angles 

 of malar obsolete ; infraorbital opening smaller, with no separate 

 canal for the nerve. Incisors broad, the upper arched boldly for- 

 ward, the lower very long. Grinding-teeth like those of Schizodon ; 

 but the external and internal folds do not meet in the middle line. 



7. Octodon, Bennett, P. Z. S. 1832, p. 46 (1832). 



Ears rather large. Claws small, that of the pollex truncated. Tail 



long, hairy, bushy at the tip. Skull similar to that of Spalacopus, 

 but with a separate canal in the infraobital opening for the nerve. 

 Incisors narrow. Molars like those of Spalacopus, but placed diago- 

 nally, and the posterior lobe smaller than the anterior in the upper 

 teeth. 



8. Habrocoma (=-Abrocoma), Waterhouse, P. Z. S. 1837. p. 30 



(1837). 



Ears very. large. Fur very soft. Tail moderate, clad with short hairs, 



not tufted. Pollex obsolete. Skull with the facial portion elongated ; 



malar with moderate superior and inferior angles ; auditory bullae 



very large. Incisors narrow. Upper grinding-teeth with single exter- 



