Size and shape
- Large, up to 90mm in length
- Height up to 75mm
- Trigonal-ovate in shape
- Markedly inequilateral
- Anterior margin strongly convex
- Shallowly concave marginal carina runs from the back of the umbones to posterior extremity of the valves.
- Flanks ornamented with irregular concentric rows of strong tubercles, some of which, in particular towards the anterior margins form spines.
- Tubercles are much reduced and more regularly spaced posteriorly, however, ornamentation is highly variable.