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



that of the fifth digit being longer than the toe itself ; tail short, 

 hairy. Skull broader and more truncated behind than in EUobius ; 

 supraorbital ridges nearly parallel ; occipital crest sharp; infraorbital 

 foramen subtriangular. Upper incisors perpendicular. 



Fossil genera. The following genera will probably prove to be 

 referable to this imuXy -.—Cncetodon, Lartet, Notice, p. 20 (1851) ; 

 Eumys, Leidy, Proc. Ac. Philad. 1856, p. 90; Helisconnjs, Cope, New 

 Vert. Colorado, p. 3 (18/3), Miocene of North America; Mi/sops, 

 Leidy, U.S. Geol. Surv. Terr. i. p. Ill (1873), Eocene of America. 



Family IV. Spalacid^e. 



Incisors large ; premolars present or absent ; grinding-teeth 

 rooted, not tuberculate, with reentering enamel-folds. Infraorbital 

 opening moderate or small, with no perpendicular plate ; occipital 

 plane high, often sloped boldly forward ; palate n arrow. Form cylin- 

 drical ; eye and ear-conch very small, sometimes rudimentary; Hmbs 

 short and stout ; claws large ; tail short or absent. Two sub- 

 families : — 



A. Spalacin^. Palate between the molars broader than one of 

 the alveoli. No interpterygoid fissure. Mandible of normal myo- 

 morphine form (the angular portion springing from the edge of the 

 bony covering of the lower incisors). Palsearctic, Indian and Ethi- 

 opian. Recent genera : — 



1. Saalax, Giildenstadt, Nov. Comment. Petrop. xiv. i. p. 409 



(1770). 



Head broad, flat, with a ridge of long stiff hairs on each side ; 

 eyes rudimentary, covered by the skin ; no ear-conch or external 

 tail ; feet broad, claws short. Skull depressed, occipital plane high 

 and sloped boldly forward ; parietals and interparietal small and soon 

 ankylosed ; infraorbital opening moderate, suboval. Upper incisors 

 plain, nearly perpendicular. No premolars. Molars with curved ena- 

 mel-folds in youth only. 



2. Rhizomys, Gray, P. Z. S. 183(|), p. 95 (183(i). 



Form robust ; eyes very small ; ears very short, naked ; pollex 



rudimentary ; tail rather short, partially haired. Skull broad, occi- 

 pital plane only slightly sloped forward ; infraorbital opening small, 

 subtriangular. Upper incisors arched forward. No premolar. Upper 

 molars with one deep internal and two or more external enamel-folds ; 

 the lower molars reversed. 



3. Heterocephalus, Riippell, Mus. Senkenb. i. Saugeth. p. 99 



(1834). 



Eyes very small ; no ear-conch ; pollex short, not rudimentary ; tail 

 short; whole body almost hairless. Skull as in Rhhomys, but 

 broader, occipital plane more perpendicular, and infraorbital fora- 

 men larger. Dentition similar, but the upper molars with an exter- 

 nal indenting fold only, the lower with one external and one internal 

 fold. 



