Here's an easy trick to remember which is which - STALACTITEs cling tight to the ceiling. That's what my father the geologist told me. I see now, that you could also think that the one with the C hangs from the Ceiling, and the one from the G grows from the Ground. So, take your pick, but know the difference, because this puzzle forces you to know one from the other! Either would fit in the spaces provided, and the crosses would still work. It's a "CLINTON/BOBDOLE light" situation. For 28A: Features of some front teeth, either CAPS or GAPS would be a correct answer. Same for 34A: Work hard (TOIL/MOIL), 44A: Undermine, as a government program (GUT/CUT), and 48A: Plural suffix with organ (ISMS/ISTS). I think the italics on those clues cheapen it a bit, but still - very nice.
Pop Quiz - What do you call it when they connect?
With that kind of a stunt, you end up with a few things like DOSO, ICUS, NEY, and SIRICA (Watergate judge... who knew?), but overall, there's way more good than bad in here. The long non-themers are all strong. COMEDYTEAM (39A: Sid Caesar and Imogene Coca, e.g.), DIRTSTAINS (32A: They're often found on baseball uniforms), CASTAWAY (17A: One sending a message in a bottle, maybe), and PAPERTHIN (50A: Like walls in a cheap motel, it seems), for example. The cluing, too, is quite good. 51D: Every family has one (TREE), 7D: Present time, informally (BDAY), and I even like things like VANILLA (36A: Ordinary), ADMITONE (15A: What a ticket may do), and VEST (3D: One of three pieces).
It's a little weird that TSE and TSETSE are both on the bottom there, and I don't love AMS or ENOL, but then you've got RANATAB, DITCH, MORASS, TACIT, CAMP, ICHABOD and more.
Very good Thursday.