Miniaceoliva miniacea (Röding, 1798)?
L x W: 81.3 x 34.1 mm
~50 ft. Dead, along edge of sand channel
Agat Bay, Guam.
19 Jan 2004.
Not a perfect specimen as noted by pitting in the nacre, but it is exceptionally large for Guam.
Note: The Miniaceoliva miniacea-efasciata-lamberti species complex is confusing, One can argue that Guam specimens are berti now considered a subspecies of efasciata, generally associated Marshall and Caroline Islands.