†FAMILY PACHYLASMATIDAE UTINOMI, 1968

Diagnosis: Shell wall comprises eight distinct compartmental plates, including rostrum, paired rostromarginals, marginals and carinomarginals, and carina. Shell with or without imbricating plates. Rostrum compound with rostromargin but not entering sheath, parietes solid and radii absent. Base membranous or solid calcareous, not interdigitated with shell wall.