It's an older one. The turlle's shell and the bottom of his foot are filled in, which is an older stamp. They are just outlined on the current stamps....current being from probably around 2000's onward. If I had to guess (and I do), I would say mid 80's to mid 90's.
A better question might be: what kind of bridge was on that thing? Those two screws holes on the outside, and the trace of some octagonal thingy. Hmmm....