Article: The dentition of the Durham Permian pelecypod Permophorus costatus (Brown)

The all-important Upper Magnesian Limestone specimens of Permophorus [formerly Pleurophorus] costatus (Brown) from Byers's Quarry, Durham, upon which King based his controversial diagnosis of the dentition of Pleurophorus King, have been located and re-examined. They confirm the belief of earlier authors that King's original description was erroneous and that there is only one cardinal tooth in each valve. Several other Upper Magnesian Limestone specimens of this species in the Kirkby Collection support these conclusions and have been figured. The essential characters of Pleurophorus King (renamed Permophorus by Chavan) are redefined in the light of these investigations.