Petzvals: Which is Crown, which Flint?

[c.d.ewen]

I've been farting around with a Petzval for a while, and decided I'd better ask wiser folk than I about the rear elements, before I go and put my foot in my mouth and call one by the other's name.

Below is a photo of the rear elements: one thick, one thin. As shown, the thick one is mildly convex on the top, and pronouncedly concave on the bottom. The thin one is noticably convex on the top, and mildly convex on the bottom.

Who's who?

Charley