The small shell looks like a badly worn 'tridacna' (those very
bivalves.) There are a few choices for names. The very long one
is a 'watering pot shell' which also is a bivalve, but the original
pair of shells are very small, incorporated into the base of the
shell. Most of the shell would be buried while alive. Again there
a few genera/species; someone will probably come up with the right
one. ...Allen A.
looks very much like a worn shall of a giant clam (genus Tridacna),
and the shape looks closest to T. derasa, found in southeast Asia
and Indonesia usually. Not sure of any clams of that genus found
in Africa, but possibly a fossil species? Batt R.