(Whoops! I broke the teeth off in trying to open the valves).

Hi David,

I think the above statement provides the answer to the question.  Only a
Spondylus hinge would have such interlocking teeth, preventing the shell
valves from being separated, except by breaking the hinge.  If it were
not for that fact, there are a couple of other species I might suggest,
such as Hyotissa hyotis.  But a hinge like that says SPONDYLUS!  A few
Spondylus species are virtually spineless, and even other species may
become spineless through erosion.  The specimen you described sounds
pretty eroded.

Regards,
Paul M.