316 mammalia: glikks. — XLvni. 



Family CLXXX. DIDELPHIDID^. (The Opossums.) 



Marsupial inammals of small size, with the teeth i- f l|, c. ^: j, 

 pm. §:§, 111. |: J. Ft'L't five-toL'd, ])lantiyratk', the daws 5-4. Tail 

 usually very lon<i:, prehensile, nearl}' naked, eovered by a scaly skin, 

 with a few scattered hairs. Genera 2, sj)eeies aljout 15 ; all Ameri- 

 can and ehietly belonging to the tropics. The common opossum 

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

 arboreal (IJidelpJns) or aquatic (Chirotieclex), and becoming very 

 fat. 'J'hey feed on insects and other small animals. 

 a. Arboreal; feet not webhi-il Dideli-iiis, 536. 



536. DIDELPHIS Linnaeus. (Sty, two ; SeX0us, womb.) 

 102;). 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 XL VIII. 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 Rodenlia 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., ^//.s, dormouse ; the Linnawn name 

 Glires is much older than Cuvier's Rodenlia.') 



Families of Glires. 



a. Incisors j, the median upper incisors Inrfrc, vertically grooved, the outer 

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

 bone LEroKiD.i-T 181. 



aa. Incisors i ; tail well developed. 



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



ERKTITIZONTn.F., 182. 



bb. Fur more or less soft, without spines. 

 C. Tibia and fibula united below. 

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

 leaping; molars J on each side ZAi-ouiD.ii, 18.J. 



