Source : Webster's Revised Unabridged Dictionary (1913)
Marsupialia \Mar*su`pi*a"li*a\, n. pl. [NL., fr. L. marsupium a
pouch, bag, purse, Gr. ?, dim. of ?, ?.] (Zo["o]l.)
A subclass of Mammalia, including nearly all the mammals of
Australia and the adjacent islands, together with the
opossums of America. They differ from ordinary mammals in
having the corpus callosum very small, in being implacental,
and in having their young born while very immature. The
female generally carries the young for some time after birth
in an external pouch, or marsupium. Called also {Marsupiata}.