This is similar to published figures of Moerchiella dorbignyi, although color and slight differences in shape keep the ID tentative. The shell in the upper photo was occupied by a hermit crab and observed under a rock on a lagoon pinnacle in Enewetak Atoll.
The empty specimen below was on a lagoon beach in the northern Kwajalein Atoll.
Created 10 June 2019
Updated 11 October 2019