A study of a non-marine lamellibranch succession in the Anthraconaia lenisulcata zone of the Yorkshire coal measures

Abstract
Previous investigation has shown that the non-marine lamellibranchs of the Lenisulcata zone vary to an exceptional degree. In Yorkshire, where the Lenisulcata zone was fust defined (Wray & Trueman 1931, 1934), most of the material studied has hitherto been derived from borings so that few shells have been available for study. In Lancashire, however, much material was collected from open sections by W. B. Wright, who first demonstrated some of the variational trends of certain Lenisulcata zone faunas and created several new species (Wright 1934 a,b ). Wright made a special study of the fauna above the Bassy Mine at two localities where he found shells on several horizons. For purposes of describing the variation he mixed all his material together and added to it a few specimens from various levels above the Bassy Mine at other localities. Wright concluded that most of these forms were merely variants of his two species, Carbonicola fallax and C. protea , which were very abundant and appeared to function as norms.

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