If it has to be a Schlumbergera, then I guess it must be S. x exotica. Sure
took me long enough to find it - I'd been searching for weeks. I sure didn't
know there existed any Christmas cactus with stems other than "flattened".
Blossom-wise, it's turning out to be a much more difficult plant than my
truncata. It has a couple more teensy tiny little pink buds forming, and if
it drops them again just because I breathed in the same zip code I think
it'll wind up in the compost heap before long.

Anyway, thanks for all the help.