Wiktionary
rudist
n. Any of many box, tube or ring -shaped marine heterodont bivalves from the Jurassic and Cretaceous periods
Usage examples of "rudist".
Tethys Sea, Xanadu was a bubble of blue-green glass anchored and buttressed by rudist reefs that twenty-second-century biotechnicians had shaped and trained to their purposes.
Xanadu Station is to study the rudist clams that make up the reefs surrounding us.