\Sheath"bill`\, n. (Zo["o]l.)
Either one of two species of birds composing the genus
{Chionis}, and family {Chionid[ae]}, native of the islands of
the Antarctic seas.
Note: They are related to the gulls and the plovers, but more
      nearly to the latter. The base of the bill is covered
      with a saddle-shaped horny sheath, and the toes are
      only slightly webbed. The plumage of both species is
      white.