154 RODENTIA— OCHOTONID^ 



DUPLICIDENTATA. 



These are rodents distinguished from all other members of 

 their order by the possession throughout life of four upper 

 incisors, in which the enamel extends round to the posterior 

 surface. Two of these are of the ordinary type, but large and 

 heavy ; the other two are minute, and, lying behind the larger 

 ones, are concealed from view ; a third outer pair is present at 

 birth, but persists for only a short time. The grinding teeth 

 are so arranged that the motion of the jaws in eating is from 

 side to side (see below, description of hares). The incisive 

 foramina are very large and posteriorly confluent, and the bony 

 palate is so reduced as to appear as at most a narrow bridge 

 lying between the premolars. 



There are two families, the Ochotonidce, the pikas, tailless- 

 or mouse-hares, and the LeporidcB, or hares and rabbits. 



[OCHOTONIDtE.^ 



PIKAS OR MOUSE-HARES. 



These are represented in Britain only by an extinct 

 species, Ochotona ° spelcea^ the bones of which occur in the latest 

 pleistocene cavern deposits. 



A member of the family, O. pusilla (Pallas), still inhabits 

 the Ural Mountains, and ranges from the Volga to Turkestan 

 and Western Siberia. Other forms are found through Asia 

 to the mountains of western North America. 



For our knowledge of the early history and evolution of 

 the Ochotonidce we are principally indebted to Forsyth Major's 

 paper, published in the Trans. Linnean Soc. (London), Zool., 

 Nov. 1899, 433-520. The group is first met with in the 

 lower miocene deposits of Western Europe, in which region 



1 Extinct in Britain. 



2 Of Link, 1795, antedating Lagomys, Cuvier, 1800. 



^ Lagomys spelaus, Owen, British Fossil Mammals, etc., 1846, 213, figs. 82-4. 



