xv 3 THE PIKA 505 
mountain. Externally it is something hke the Pikas, since it 
has no tail visible. The ears, too, are short, and the hind-legs 
comparatively short. The skull is very lke that of the Rabbit ; 
but in other osteological details it is aberrant. Thus the clavicle 
is quite complete, and only six ribs articulate with the sternum, 
instead of the seven that we find in the Rabbit. 
Fam. 2. Lagomyidae.—The animals of this family are smaller 
than the Hares and Rabbits; they have short Vole-like ears and 
no external tail. The limbs also appear to be shorter. As there 
is but a single genus, the characters of the family may be de- 
scribed in connexion with those of the genus, which is known as 
Lagomys (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 Rabbits, 
and has a well-marked backward process of the zygomatic arch. 
There are eighteen dorsal vertebrae. The molars and premolars 
are five. 
The 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 
L. roylei, the “ Himalayan Mouse Hare,’ is found at elevations 
as high as 16,000 feet; while Z. ladacensis 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 
todents are known from even the earlier strata of the Tertiary 
period. The Squirrels (and even the genus Sciwrus itself) occur in 
the Upper Eocene. So, too, do the genera Myoxus, and (in South 
America) Lagostomus. Spermophilus, Acomys, Hystrix, Lagomys, 
Lepus, Hesperomys are known from Miocene rocks. Rhizomys, 
Castor, Cricetus, Mus, Microtus, and some others appear to have 
originated so far as we know in the Pliocene, while a still 
larger series of existing genera are Pleistocene. It is interesting 
