_The_ Pensieve? or _A_ Pensieve?

[Eustace_Scrubb]

Something I've wondered about for a while...

Is the Pensieve that we've come to know and love the _only_ Pensieve?
 Is it a singular object or may there be more of them out there?

Harry is absolutely certain that the Pensieve he sees in Snape's
office is the same one he saw in Dumbledore's office a year earlier:
"Harry recognized it at once--it was Dumbledore's Pensieve." (OoP,
Canadian ed.,  p. 467)

But it would seem that Dumbledore might not be the only one who would
be happy to clear out a few unnecessary thoughts from time to time or
to examine some at their leisure.  I imagine Nicholas and Perenelle
Flamel would have found it particularly useful, as they had over 600
years worth of memories to deal with.

Anyway, I don't know as this will have any great impact on the outcome
of the series, but I'm curious.  Thoughts?

Cheers,

Eustace_Scrubb