84 MR. E. R. ALSTON ON THE ORDER GLIRES. [Jan. 18, 



feet as in Mus ; tail long, scaly. Skull as in Mus ; the infraorbital 

 foramen lower and wider. Incisors plain. Molars like those of Hes- 

 peromys ; the first upper, when worn, with one internal and two 

 external indenting folds ; the first lower with one external and two 

 internal, the rest with one external and one internal fold. 



23. Brachytarsomys, Giinther, P. Z. S. 18/5, p. 79 . . (1875). 

 Upper lip grooved, not cleft ; eyes small ; ears short ; hind feet 



much shorter than the lower leg ; tail long, scaly. No supraorbital 

 ridges ; auditory bullae moderate. Incisors plain. Molars with two or 

 three indenting folds on each side, one of which in the upper molars 

 passes quite across the crown. 



24. Drymomys, Tschudi, Fauna Peruana, p. 1/8 . . (1844-6). 

 Form murine; muzzle pointed; upper lip cleft; ears large; tail long, 



scaly. Incisors furrowed on the sides. Molars small; the first with 

 three pairs of tubercles, the second with two, the third with one pair 

 only. 



25. Holochilus, Brandt, Mem. Ac. St.Petersb. (6 m e ser.) iii. p. 428 



(1835). 



Muzzle obtuse ; upper lip not fully cleft; fore feet small ; hind limbs 

 large and strong; tail long, sparsely haired. Skull short, strong; 

 supraorbital ridges well marked. Incisors broad, flat, plain. Molars 

 large, the third as large as the second, with tubercles arranged in 

 pairs, which soon wear awav, leaving the crown flat with indenting 

 folds. 



26. Hesperomys, Waterhouse, Zool. Voy. Beagle, i. p. 75 (1839). 

 Upper lip cleft ; ears large or moderate ; tail sparsely haired. Small 



internal cheek-pouches in a few species. Skull murine, with or with- 

 out marked supraorbital ridges. Incisors plain. Molars as in the 

 last geuus, but narrower ; the third smaller than the second, and the 

 first upper with three roots. 



27. Ochetodoa, Coues, Proc. Acad. Philad. 1874, p. 184 (1874). 

 As in the last genus ; tail moderate. Upper incisors grooved. 



First upper molar with four roots. 



28. Rdthrodon, Waterhouse, P. Z. S. 1837, p. 29 . . . (1837). 

 Profile arched; eyes large; ears hairy; hind feet with first and fifth 



digits very short ; tail moderate, hairy. Skull with nasal portion 

 large, supraorbital ridges well marked, posterior nares narrowed by 

 the approximation of the pterygoids. Upper incisors grooved. 

 Molars as in Hesperomys, their indenting folds deep. 



29. Sigmodon, Say & Ord, Journ. Acad. Philad. iv. p. 352 (1825). 

 Muzzle blunt ; upper lip partially cleft ; ears large, but nearly 



concealed in the long fur ; hind feet with first and filth digits very 

 short ; tail moderate, nearly naked. Skull with supraorbital ridges 

 sharp, perpendicular plate of zygoma emarginate iu front, incisive 



