When I was a kid, mellorine* was always in square (actually rectangular)
cartons, and I think ice cream came in round cartons. I don't remember
the ice cream all that much because we couldn't afford it very often so
we usually had mellorine instead.

I haven't noticed anything labeled "mellorine" in at least 30 years.
Ice cream in square cartons is still usually much cheaper than ice cream
sold in round cartons; I wonder if that's a holdover from the mellorine
days?

Best regards,
Bob

*Mellorine is a frozen dessert that resembles ice cream, but contains
vegetable oil or animal fat instead of much of the butterfat. Imagine
"ice milk" fortified with shortening.