Yapock

from The Collaborative International Dictionary of English v.0.48

Opossum \O*pos"sum\, n. [Of N. American Indian origin.] (Zool.)
   Any American marsupial of the genera {Didelphys} and
   {Chironectes}; called also {possum}. The common species of
   the United States is {Didelphys Virginiana}.
   [1913 Webster]

   Note: Several related species are found in South America. The
         water opossum of Brazil ({Chironectes variegatus}),
         which has the hind feet, webbed, is provided with a
         marsupial pouch and with cheek pouches. It is called
         also {yapock}.
         [1913 Webster]

   {Opossum mouse}. (Zool.) See {Flying mouse}, under {Flying}.
      

   {Opossum shrimp} (Zool.), any schizopod crustacean of the
      genus {Mysis} and allied genera. See {Schizopoda}.
      [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Yapock \Ya"pock\ (?; 277), n. [Probably from the river Oyapok,
   between French Guiana and Brazil.] (Zool.)
   A South American aquatic opossum ({Chironectes variegatus})
   found in Guiana and Brazil. Its hind feet are webbed, and its
   fore feet do not have an opposable thumb for climbing. Called
   also {water opossum}. [Written also {yapack}.]
   [1913 Webster]
   [1913 Webster]