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| per·i·os·tra·cum [ pèrree óstrəkəm ] (plural per·i·os·tra·ca [ pèrree óstrəkə ]) |
noun |
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| Definition: |
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shell's outer layer: the hard outer layer of the shell of some mollusks, especially freshwater mollusks
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| [Mid-19th century. < modern Latin< Greek peri "around" + ostrakon "shell"] |
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