rudist

 
Pronunciation: /ˈruːdɪst/
(also rudistid /ruːˈdɪstɪd/)

noun

  • a cone-shaped fossil bivalve mollusc which formed colonies resembling reefs in the Cretaceous period: [as modifier]: rudist bivalves
    • Superfamily Rudistacea, order Hippuritoida

Origin:

late 19th century: from modern Latin Rudista (former group name), from Latin rudis 'rude'; for the variant spelling see -id3