The Tarphyceratidae are tightly coiled, evolute Tarphycerida with ventral siphuncles. The dorsum is characteristically impressed where the whorl presses against the venter of the previous. The Tarphyceratidae are derived from Bassleroceras or possibly from some member of the Estonioceratidae. The Tarphyceratidae are known mainly from the Lower Ordovician (M-U Canad); gave rise to the Trocholitidae and provided the sources for the more advanced barrandeocerids