98 
MAMMALIA. 
Castor fiber .— The Beaver. 
Plate XVIII. fig. 1. 
Fur an uniform reddish-brown, consisting of two sorts; one 
coarse and brownish, the other fine and downy, of a gray colour. 
About two feet long. Inhabits North America and Europe. 
Genus 2 .— Fiber. — Cuvier. 
Generic Character. —Incisors no canines, grinders jj-3. 
total 16. Lower incisors sharp-pointed, and convex in front; 
grinders with flat crowns, furnished with scaly transverse zigzag 
laminae; fore feet with four toes, and the rudiments of a thumb ; 
hind feet with five toes, having the edges furnished with stiff 
hairs, used in swimming like the membrane of palmated feet; 
tail long, compressed laterally; both sexes secrete an odorifer¬ 
ous musky unguent. 
Fiber Zibethicus .— The Musk Rat, or Ondatra. 
Plate XVIII. fig. 2. 
Fur reddish-gray above, ash-coloured beneath. About the 
size of a rabbit. Inhabits Canada, and other parts of North 
America. 
Genus 3.—Arvicola. — Desmarest. 
Generic Character. —Incisory teeth |, no canines, grinders . 
total 16. Grinders are flat on the crowns, with angular plates 
of enamel; ears large; anterior toes with nails; tail round, 
covered with hair, and almost as long as the body. 
Arvicola amphibius .— The Water Rat. 
Plate XIX. fig. 4. 
Fur blackish gray, slightly tinged with yellow above, lighter 
underneath ; tail black. Somewhat larger than the common 
Norway rat. Inhabits Europe, Northern Asia, and North 
America. 
