The term possum is used mainly for members of certain marsupial in the Australasian region. The family Didelphidae, containing 11 Recent genera and 77 species, is found naturally from southeastern Canada through the eastern United States and Mexico and into South America to about 47 degrees S in Argentina. Opossums also occur on some of the islands in the Lesser Antilles. The members of this family are small to medium in size. The tail is usually long, scaly, very scantily haired, and prehensile, but in some forms it is short and rather hairy.
Some genera have long, projecting guard hairs in the pelage.
The muzzle is elongate, and the ears have well-developed conches. The limbs are short, with the hind limbs slightly longer. All four feet have five separate digits. The great toe is large, clawless, and opposable. A distinct marsupial pouch is present in Didelphis, Chironectes , and Philander .