‖ periostracum Zool.
(pɛrɪˈɒstrəkəm)
[mod.L., f. Gr. περί around + ὄστρακον shell of a mussel, etc.]
The outer horny covering of the shell of a mollusc or brachiopod. Hence periˈostracal a., pertaining to the periostracum.
| 1840 Penny Cycl. XVII. 452/1. 1841 Ibid. XXI. 373/1 The external coat or layer, Epidermis and Periostracum of authors, is of a somewhat horny or membranaceous character. 1870 Nicholson Man. Zool. 230 All living shells have an outer layer of animal matter, which is known as the ‘epidermis’, or ‘periostracum’. |