03 Lacuna crassior. North Yorkshire. September 2014

03 Lacuna crassior. North Yorkshire. September 2014

Shell heights 1: 3.7 mm, outline thinner and ribs smaller/stronger as periostracum dried and contracted. 2: 3.7 mm, fresh shell in water. 3: 5.2 mm, fresh shell in water. 4: pinkish-white shell 5: ribs formed by periostracum. 6: periostracum protrudes beyond aperture lip.

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