MAMMALIA. . 91 
The small number of extinct Chiroptera known, 7.e. a few genera belonging to the 
Hipposideride and Vespertilionide from Eocene and Oligocene deposits of Europe, 
throw no light upon the present distribution of the order. 
Order RODENTIA. 
In the number of species and genera inhabiting Central America, this order rivals, 
if it does not surpass, the Chiroptera, the four usually admitted suborders (Sciuro- 
morpha, Myomorpha, Hystricomorpha, and Lagomorpha *) being well represented. 
Suborder SCIUROMORPIIA., 
Two families of this suborder have to be considered, namely the Petauristide or 
flying Squirrels and the Sciuride or true Squirrels, Ground-Squirrels, and Marmots. 
The one American genus of Petauristide, Sciwrepterus, ranges from Europe and 
Asia into North America, where it extends from Alaska to Guatemala. Of 
the Sciuride, the Chipping Squirrel (Ewtamias) and the Souslik (Citel/us) have a 
distribution as extensive as that of Sciwropterus, whereas an allied form, Callospermo- 
philus, and the Prairie Marmot ( Cynonys) are restricted to the South and Western 
States of North America and North Mexico. ‘True arboreal Squirrels are represented 
by vast numbers of species and subspecies in North, Central, and South America, as 
well as in Europe, Asia, and Africa; but the genera and subgenera to which they have 
been referred require revision and re-definition before their mutual affinities can be 
accurately ascertained. Of the Central American genera, Sciurus (s. s.) appears to 
ve the only one that occurs in the Old World, where it ranges from Japan to Ireland. 
In America it is generally distributed throughout the States, occurs everywhere in 
Central America at high and low levels, and enters the northern countries of South 
America (Colombia, Ecuador). An allied form with many species, Guerlinguetus 
(Parasciurus), is credited with a range from the United States to Peru. Others that 
may be mentioned are Baiosciurus (extending from Mexico to Nicaragua), Syntheo- 
sciurus (known only from Chiriqui in Panama), and Mrcrosciurus (alleged to spread 
from Costa Rica to Peru f). 
Genera regarded as primitive Sciuromorphs were abundant in North America 
(Ischyromyide) and Europe (Pseudosciuride) during early Tertiary times (Hocene and 
Oligocene), extinct Marmots (Palearctomys) and the still existing Cynomys have been 
traced back to the Upper Miocene in North America, while Sciurus itself has survived 
in Europe and North America since the Upper Oligocene. Since no extinct forms are 
: * Apart from the Lagomorpha, these suborders are not perhaps susceptible of precise definition, They 
are here maintained for the sake of convenience. 
+ Beavers (Castoride) should perhaps be added to this section, since they range in North America at least 
as far south as Sonora. In the Old World, Beavers occur in Northern Asia and North and Central Europe. 
NZ 
