316 MAMMALIA: GLIRES. XLVIII. 



FAMILY CLXXX. DIDELPHIDID^J. (THE OPOSSUMS.) 



Marsupial mammals of small size, with the teeth i. f :f, c. \'.\, 

 pm. f I , m. | : |. Feet five-toed, plantigrade, the claws 5-4. Tail 

 usually very long, prehensile, nearly naked, covered by a scaly skin, 

 with a few scattered hairs. Genera 2, species about 15 ; all Ameri- 

 can and chiefly belonging to the tropics. The common opossum 

 is one of the largest of the group. All are sluggish animals, 

 arboreal (Didelphis) or aquatic (Chironectes'), and becoming very 

 fat. They feed on insects and other small animals, 

 a. Arboreal; feet not webbed DIDELPHIS, 536. 



536. DIDELPHIS Linnaeus. (S/s, two ; 5eX<vs, womb.) 

 1029. D. virginiana Kerr. COMMON OPOSSUM. Soiled yel- 

 lowish, with some darker hairs ; ears black, leathery ; legs dark. 

 L. 35. T. 15. N. Y. to Cal. and S. ; common. 



ORDER XLVIII. GLIRES. (THE RODENTS OR GNAWERS.) 



Mammals with the incisor teeth -| or -| in number, chisel-shaped, 

 adapted for gnawing ; no canine teeth, a toothless space in the 

 place of canines ; molar teeth adapted for grinding ; cerebrum 

 small, little convoluted ; intestinal canal elongate ; ears and eyes 

 usually well developed. Food chiefly vegetable. 



The Glires or Rodentia is the largest order of Mammals, and in 

 individuals by far more numerous than any other. Most of the 

 species are of small size, the Beaver -being one of the very largest 

 of the forms now living. 



" Though a feeble folk, comparatively insignificant in size and 

 strength, they hold their own in legions against a host of natural 

 enemies, rapacious beasts and birds, by their fecundity, their wari- 

 ness and cunning, their timidity and agility, their secretiveness, 

 each after the means by which it is provided for exercising its in- 

 stinct of self-preservation, among which insignificance itself is no 

 small factor." (Coues.) (Lat., glis, dormouse ; the Linnaean name 

 Glires is much older than Cuvier's Rodentia.) 



Families of Glires. 



a. Incisors f, the median upper incisors large, vertically grooved, the outer 

 small; teeth 28; tail very short; ears long; fibula united with the heel- 

 bone LEPORID^E, 181. 



a. Incisors f ; tail well developed. 



b. Fur with stiff spine-like bristles; tibia and fibula separate. 



ERETHIZONID.E, 182. 

 bb. Fur more or less soft, without spines. 

 c. Tibia and fibula united below. 



d. Tail and hind legs excessively elongated, the latter adapted for 

 leaping; molars on each side ZAPODID.-E, 183. 



