Very thick periostracum conceals markings and ridges (1). Periostracum eroded revealing white shell (2) and brown marks (3). Remnants of eroded periostracum (4).
Mature shell with well developed, continuous, basally flared, white peristome around the aperture (5), which contrasts with thick dark periostracum.
Adapical angle of aperture 60º (6).
Menai Strait, Wales, March 2012 & July 2013 (left & centre) and Lleyn, Wales, September 2009 (right).
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