The English Lower Tertiary fossil Mya plana J. Sow. 1814, often referred to Erodona Bosc 1802, lacks the distinctive erodonid chondrophore and seems closer to Mya. It is, however, unlike other myids in having a pit or slot confluent with the resilifer in the beak of the right valve, which receives the beak of the left valve. This characteristic seems sufficient reason to retain the valid generic name Potamomya J. de C. Sow. 1835 for this fossil.