The outer horny or fibrous organic covering of the shell of a mollusc or brachiopod.
Origin
Mid 19th century; earliest use found in Philosophical Transactions of the Royal Society of London. From scientific Latin periostracum from peri- + ancient Greek ὄστρακον.
Definition of periostracum in US English:
periostracum
nounˌpɛrɪˈɒstrəkəm
Zoology
The outer horny or fibrous organic covering of the shell of a mollusc or brachiopod.
Origin
Mid 19th century; earliest use found in Philosophical Transactions of the Royal Society of London. From scientific Latin periostracum from peri- + ancient Greek ὄστρακον.