Size and shape

  • Large, up to 90mm in length
  • Height up to 75mm
  • Trigonal-ovate in shape
  • Markedly inequilateral
  • Anterior margin strongly convex

Umbones opisthogyrate

  • 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.