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periostracum |
1 definition found From Webster's Revised Unabridged Dictionary (1913) [web1913]: Periostracum \Per`i*os"tra*cum\, n.; pl {Periostraca}. [NL., fr Gr ? around + ? shell of a testacean.] (Zo["o]l.) A chitinous membrane covering the exterior of many shells; -- called also {epidermis}.