This important Coal-measure zonal Lamellibranch has already been recorded from the Yorkshire and Nottingham Coalfield (Cadeby and Gedling Colliery respectively), the Lancashire Coal-field (Ardwick, Manchester), the North Staffordshire Coalfield generally, the Forest of Dean and Bristol Coalfields, the South Wales Coalfield; and in all these widely separated districts it is found at the top of that portion of the Coal-measures characterised by the presence of the most valuable seams of coal.