XV THE PIKA 505 



mountain. Externally it is something like the Pikas, since it 

 has no tail visible. The ears, too, are short, and the hind-legs 

 comparatively short. The skull is very like that of the Eabbit ; 

 but in other osteological details it is al^errant. Thus the clavicle 

 is quite complete, and only six ribs articulate with the sternum, 

 instead of the seven that we find in the Eabbit. 



Fam. 2, Lagomyidae. — The animals of this family are smaller 

 than the Hares and Eabbits ; they have short Vole-like ears and 

 no external tail. The limbs also appear to be shorter. As there 

 is l:)ut a single genus, the characters of the family may be de- 

 scribed in connexion with those of the genus, which is known as 

 Layomys (apparently more correctly Ochotona). Of this genus 

 there are about sixteen species, which are mainly Asiatic ; one 

 species extends its range into Eastern Europe, and three are 

 North American. 



The skull has not the supra-orbital grooves of the Eabbits, 

 and has a well-marked backward process of the zygomatic arch. 

 There are eighteen dorsal vertebrae. The molars and premolars 

 are five. 



Tlie vernacular names of " Pika " and " Piping Hares " have 

 been applied to the members of this genus, the latter on account of 

 their peculiar call. They live among rocks in companies and they 

 burrow. They are usually found at considerable altitudes : thus 

 Z. roylei, the " Himalayan Mouse Hare," is found at elevations 

 as high as 16,000 feet; while L. ladaccnsis gets even higher, 

 19,000 feet having been recorded. With the habits of a Marmot, 

 so far as concerns living in burrows and at great altitudes, the 

 animals of this genus, with their squat form and short ears, are 

 not unlike those animals. In the past this genus occurred more 

 generally over Europe. Species from Miocene beds have been 

 met with in England, France, Germany, and Italy. 



Fossil Rodents. — Quite a large number of existing genera of 

 Eodents are known from even the earlier strata of the Tertiary 

 period. The Squirrels (and even the genus Sciurus itself) occur in 

 the Upper Eocene. So, too, do the genera Myoxus, and (in South 

 America) Lagostomus. Spermojihilus, Acomys, Hystrix, Lagomys, 

 Lepus, Hesperomys are known from Miocene rocks. Rhizomys, 

 Castor, Cricetu!^, Mus, Microtus, and some others appear to have 

 orisjinated so far as w^e know in the Pliocene, while a still 

 lareer series of existing genera are Pleistocene. It is interesting 



