. Central Asiatic Expeditions of the American Museum of Natural History, under the leadership of Roy Chapman Andrews : preliminary contributions in geology, palaeontology, and zoology. Central Asiatic Expeditions (1921-1930); Scientific expeditions; Natural history; Scientific expeditions; Natural history. 1923] NEW RODENTS FROM OLIGOCENE OF MONGOLIA 5 Selenomys mimicus, new genus and species Type.—No. 19085, an upper jaw. Paratypes.—Nos. 19086-19093, a series of upper and lower jaws. Horizon and Locality.—Hsanda Gol formation, near Loh, Mongolia. Diagnosis.—Three subequal molar teeth, no prem
. Central Asiatic Expeditions of the American Museum of Natural History, under the leadership of Roy Chapman Andrews : preliminary contributions in geology, palaeontology, and zoology. Central Asiatic Expeditions (1921-1930); Scientific expeditions; Natural history; Scientific expeditions; Natural history. 1923] NEW RODENTS FROM OLIGOCENE OF MONGOLIA 5 Selenomys mimicus, new genus and species Type.—No. 19085, an upper jaw. Paratypes.—Nos. 19086-19093, a series of upper and lower jaws. Horizon and Locality.—Hsanda Gol formation, near Loh, Mongolia. Diagnosis.—Three subequal molar teeth, no premolars. (There is some doubt about the absence of the upper premolar.) Crowns of molars moderately high, each composed of four inward-facing crescents, an anterior and a posterior pair, as in ruminant molars. The lower jaw in front of the molars is rather thick, not deep, moderately long; incisor not preserved. Angle only partly preserved, appears to be straight, as in Myomorpha Fig. 5. Selenomys mimicus, upper and lower teeth four diameters: A, upper teeth, right side; B, lower teeth, left side, crown view; Bl, external view of left ramus of lower jaw. All from the type specimen, No. 19085. We do not know of anything near to this peculiar genus. It is provisionally associated with Cricetops, which has some suggestion of approach in pattern, but the jaw proportions are quite different. Cteno- dactylus has a pattern which sugggests derivation from something of this type but it retains the premolar in upper and lower jaw which Selenomys has lost. So far as preserved, the character of the zygomatic arch accords with Cricetops; the genus is clearly not a myomorph and probably be- longs in the same group as Cricetops. ? Eomyidse Tataromys plicidens, new genus and species Type.—No. 19082, a palate with p'^m^ r. and 1. Paratypes.—Nos. 19081, , 19084, upper and lower jaws. Horizon and Locality.—Hsanda Go! formation, Loh, Mongolia. Diagnosis.—Premolar sm
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