Profile of valve v from posterior (upper image), and anterior. Animal 26mm long, 19mm wide. Dorset, England. April 2017.
When removed from the girdle, intermediate valves have a relatively elevated profile with a definite keel (1) and slightly curved side slopes (2).
The tegmentum (3) , visible on the live animal, is a dorsal, sculptured, coloured layer of organic chitinous material and inorganic aragonite permeated by canals.
The articulamentum (4), concealed on the live animal, is a ventral layer of white, nacreous aragonite, permeated by canals only in the jugal tract (5) which is often black.

KEY ID FEATURES : 01 Acanthochitona fascicularis