Lepidochitona cinerea valve v (lowest image), viewed from posterior. Boreochiton ruber valve iv (middle image ) & T. marmorea valve iv (upper image)
1: Tonicella marmorea, low arch-profile (height 20% of width) with pronounced keel (Orkney, April 1971).
2: upper slope flat or slightly convex.
3: hip half way down slope.
4: lower slope slightly concave.
5: B. ruber, low smoothly-convex arch-profile (height 23% of width) with moderate keel. (N.Yorks, Sept. 2014. leg. P. Lightfoot.)
6: Lepidochitona cinerea, moderately-high arch-profile (height 32% of width) with keel. (N.Yorks, Sept. 2014. leg. P. Lightfoot.)
7: upper slope slightly convex.
8. lower slope slightly concave.
Kaas & Van Belle in Schwabe define valve elevations (height/width) as low below 25%, moderate 25% – 45% and high greater than 45%.

KEY ID FEATURES and similar species at: 01 Lepidochitona cinerea