246 VERTEBRATE ANIMALS OF THE UNITED STATES 



mother in an abdominal pouch called the marsupiiim, in which the 

 nipples of the milk-glands are situated. The marsupium is supported 

 on each side by the marsupial bone which projects forward from the 

 pelvis and is present in both sexes. The uterus and vagina are double 

 and paired. 



The marsupials vary much in their general form and in the form of 

 their teeth, and the different groups are fitted to maintain themselves 

 in very diverse environments. About 150 species are known, grouped 

 in 2 suborders, all of which, with the exception of about two dozen 

 American species, inhabit Australia and the neighboring islands. 



Key to the Suborders of Marsupialia 



ai Prominent eye-teeth present; carnivorous species i. Polyprotodontia. 



a2 Eye-teeth small or wanting; herbivorous species (not present 



in America) 2. Diprotodontia. 



Suborder Polyprotodontia. — Carnivorous marsupials with 4 or 5 

 upper and 3 or 4 lower incisors, prominent canines and cuspidate 

 molars: 4 families, in the American and Australian regions, i in America. 



Family Didelphiidae.^ — Opossums. Body rather slender, tail long 

 and prehensile and scaly; legs of about equal length; feet pentadacty- 

 lous; first digit of hind foot nailless and opposable; dentition 5/4, i/i, 

 3/3, 4/4: 10 genera, all American, mostly tropical; arboreal or aquatic; 

 5 genera and 22 species in North and Central America; i genus in the 

 United States. 



Didelphis L. Marsupial pouch well developed; fur a mixture of 

 soft hairs and bristles: about 4 species, i in the United States. 



D. virginiana Kerr. Common opossum. Length 700 mm.; tail 

 300 mm.; color dirty white on the sides, gray on the back: eastern and 

 central States, from Long Island and the Great Lakes to the Gulf; 

 westward to Louisiana, Oklahoma and Nebraska; arboreal animals 

 which feed on birds, insects and reptiles, as well as on nuts, corn and 

 fruit. The young are often carried on the mother's back when they 

 are big enough to leave her pouch, clinging to her fur or holding on 

 by entwining their tails around hers as she holds it over her back. 

 The nest is usually in a hollow tree; the young number from 5 to 14 and 

 two or three litters are raised in a season. A new-born oppossum is 

 about 12 mm. long. 



Subspecies of D. virginiana 



D. V. texensis Allen. Color black or gray: southwestern Texas; 

 northward to San Antonio. 



