466 ZOOLOGY. 
The Murina were represented in the fauna of the tertiary epoch by 
species belonging to the genera Mus (rats) and Cricetus (hamsters), and 
were very abundant during the diluvial period, at least in Europe. 
Sub-fam. 6. Ctenodactylina, is the smallest section among Muridee, there 
being only one species known, and therefore constituting one genus, the 
genus Otenodactylus (the hairy-focted jerboa), belonging to Barbary, in 
northern Africa. The head is more compressed than in any of its 
congeners. There are only three toes to the hind feet, as in the jerboa 
(Dipus), but they are more hairy. 
Sub-fam. 7. Dipodina, are those murines in which the hind legs are 
much longer than the fore ones, the consequence of which is that they 
jump instead of run on the ground. -In general appearance they have 
some resemblance to the kangaroos. The species are distributed into four 
genera, three of which belong to the old hemisphere and one to North 
America. The latter is the genus Meriones, with but one species, I. 
americanus (the jumping mouse). ‘The upper incisors are grooved, and a 
very small tooth is observed in advance of the upper molars. The tail is 
very long and nearly naked. A very active animal, that shuts itself up m 
its burrow and passes the winter in a state of lethargy. : 
In the genus Dzpus (jerboas) the tail is long and tufted at its extremity ; 
the head is large; the eyes also are large and prominent. The ancients 
called these animals the biped rats, from the enormous disproportion of 
their posterior limbs. ‘They seldom move otherwise than by great leaps 
on their hind feet. There are five toes to each of the fore feet, and in 
certain species, besides the three great toes to the hind feet, there are small 
lateral ones. They live in burrows, and become torpid during the winter. - 
Six species are contained in this genus, all of them inhabiting the old 
hemisphere. 
The genus Alactaga contains eight species also inhabiting the old hemi- 
sphere. They are distinguished from the jerboas (Dipus) by much longer 
ears. ‘They also possess two small lateral toes. 
The genus Pedetes has a large and flattish head, a thick snout, and long 
ears. ‘T’he anterior limbs have five toes armed with very long claws; the 
posterior legs, very long, have but four toes. The tail is long and bushy. 
The molars are simple, four above and four below on each side. A single 
species, P. capensis or Helamys caffer (pl. 118, fig. 5), is known from the 
Cape of Good Hope. 
A fossil species of Dipodina (Dipus dipoides) has been discovered in cen- 
tral Europe. ~ 
Sub-fam. 8. Myoxina, are excluded from the new world. The genus 
Myoxus or dormice, characterized by the presence of four molars above 
and below on each side; a very long tail, sometimes well clothed with hair 
and round, sometimes depressed, and sometimes tufted at the extremity 
only. The fur is very soft and fine. There are five toes behind, four and 
the vestiges of a fifth in front. Dormice are pretty little animals with 
lively eyes, living on trees like squirrels, and feed on fruits. They become 
torpid in winter. This genus is composed of ten species, seventeen of 
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