Are there any experts on Tridacnidae out there?

In 1966 Crozier described a 8mm bivalve from 805m depth in the far north of
New Zealand as Corculum inexpectatum nsp.

Bruce Marshall has pointed out to me that this is definitely NOT a
Corculum, but he was at a loss as to what it IS. He also told me that an
undescribed congener occurs in New Caledonia.

The shell does rather resemble some extinct tridacnids, and I suspect that
this may be where it belongs. I have not actually seen a specimen, and the
holotype may be unique, I'm not sure. Crozier's illustration, reproduced in
Powell 1979 "New Zealand Mollusca", does not adequately show the hinge, but
it does show a marked circular byssal opening.

Andrew