a group of extinct organisms. The taxonomic position of the Coniconchia is uncertain; they have conditionally been assigned to the phylum Mollusca. Their remains are known from deposits of the Cambrian to the Permian epochs. As a rule, they had conical shells, divided in the initial part into chambers by crosswise barriers. The shells measure from a few mm to 15 cm. Some scientists consider the Coniconchia a class with the superorders Tentaculitoidea and Hyolithoidea; others consider the last two to be independent classes. The genera and species of Coniconchia are important index forms for subdividing and comparing deposits of the Cambrian to Devonian epochs.