Periostracum

1 definition found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Periostracum \Per`i*os"tra*cum\, n.; pl. {Periostraca}. [NL.,
     fr. Gr. peri` around + ? shell of a testacean.] (Zool.)
     A chitinous membrane covering the exterior of many shells; --
     called also {epidermis}.
     [1913 Webster]