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Show 86 MR. E. R. ALSTON ON THE ORDER GLIRES. [Jail. 18, that of the fifth digit being longer than the toe itself; tail short, hairy. Skull broader and more trunc ated behind than in Ellobius ; 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 family : -Cricetodon, Lartet, Notice, p. 20 (1851) ; Eumys, Leidy, Proc. Ac. Philad. 1856, p. 90; Heliscomys, Cope, New Vert. Colorado, p. 3 (1873), Miocene of North America; Mysojjs, Leidy, U.S. Geol. Surv. Terr. i. p. Ill (1873), Eocene of America. Family IV. SPALACIDE. 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 cylindrical ; eye and ear-conch very small, sometimes rudimentary; limbs short and stout; claws large; tail short or absent. Two subfamilies :- A. SPALACINE. 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). Palaearctic, Indian and Ethiopian. Recent genera:- 1. Spalax, 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 enamel- folds in youth only. 2. Rhizomys, Gray, P. Z. S. 1830, p. 95 (1830). Form robust; eyes very small; ears very short, naked; pollex rudimentary ; tail rather short, partially haired. Skull broad, occipital 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 Rhizomys, but broader, occipital plane more perpendicular, and infraorbital foramen larger. Dentition similar, but the upper molars with an external indenting fold only, the lower with one external and one internal fold. |