Pleurotomariacea
The name Pleurotomariacea is based on Swainson , 1840 ( Pleurotomariae ) and was described in 1960 in the Treatise on Invertebrate Paleontology , ( I197 ) The taxon was established for mostly conispiral , but also discoidal and auriform ( ear-like ) shells which have a nacreous , aragonite , inner layer . 
<triplet> Pleurotomariacea <subj> taxon <obj> instance of