A difference with H. roberti McLean: the spiral ridge between row of holes and suture.
On rocks at 20-30m deep, Bahia Isabel, isla Fernandina, Galapagos.
30mm. Picture © Franck Frydman.

Same spot. 31mm. Picture © Franck Frydman.

12m deep, around boulders, Isla isabella, Galapagos.
47mm. Picture © R. Kershaw.