Redescription of the genus Anomalosaepia shows that the anomalous characters reported as defining the genus are partly preservational artifacts resulting from dissolution of aragonite from a skeleton composed of both calcite and aragonite. Thus, the presence of a slit-shaped opening and canal-like cavity in the skeleton is not supported. The skeleton of Anomalosaepia is composed of subequal amounts of aragonite and calcite, with an inner layer composed of radial-prismatic and fan-radial aragonite and an outer layer of elongate, non-prismatic calcite crystals secreted by the animal. The calcite microstructure has not been previously described. A new family, Anomalosaepiidae, is established and one new species, A. parmula, described. The species A. mariettani and A. andreanae are synonomized with A. alleni. The species A. jeletzkyi is valid and A. vernei is probably valid, but needs more documentation. Examination of North American and European specimens reveals that a bimineralic composition is a characteristic feature of species in the families Anomalosaepiidae and Belosaepiidae and implies that, in general, sepioids have a bimineralic skeleton with some calcite.