pro-ostracum
/(ˌ)prəʊˈɒstrək(ə)m/Palaeontology
noun
An anterior prolongation of the guard or rostrum of a belemnite or other fossil cephalopod, usually long and flat.
Origin
Mid 19th century; earliest use found in Thomas Huxley (1825–1895), biologist and science educationist. From pro- + ancient Greek ὄστρακον ostracon, with remodelling of the ending after Latin neuter nouns in -um.