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THE ESSEX NATURALIST
What is the relationship of C. glaucum to C. edule? Eisma
(1965) regards C. glaucum (as C. lamarcki) as a variety of C. edule,
whilst Mars (1951) and Petersen (1958) consider the two cockles
as separate species; an opinion adopted here because of the
anatomical and ecological differences. C. edule is recognised as a
variable species, and some thirty-five varieties have been