The scarcity of shells in the Denbighshire Coalfield has been commented on by a number of observers, and though numerous Carbonicola and Naiadites are to be found at certain horizons Anthracomya is exceedingly rare, particularly in the lower part of the Middle Measures. This lack of molluscan remains has made the zoning of the Coal Measures in Denbighshire a matter of considerable difficulty and only one occurrence of A. phillipsi (Williamson) has hitherto been recorded, namely from the Coed-yr-allt Beds, the middle division of the Upper Coal Measures.