†FAMILY CHIONELASMATIDAE BUCKERIDGE, 1983

Diagnosis: Shell six plated, with single rostrum, carina, paired carinomarginals and rostromarginals. Shell with up to several rows of imbricating plates at base; imbricating plates including two pairs of dedicated latera. Sheath formed by rostrum, carina and carinomarginals only; rostromarginals do not enter sheath. Basis thin, calcareous.

† Chionelasmus Pilsbry, 1911 (Eocene–Recent) (two species)

Eochionelasmus Yamaguchi, 1990 (three species)