NOTE: Jo Durrance: Ribbed Opal Rings, attributed to Northwood (probably) circa 1888 by Heacock. Reported produced in white, blue and cranberry. I've seen photos of a tumbler and a short tankard in cranberry (Heacock book 8 & Opalescent Glass A-Z, Heacock & Elmore), and it's reported in a covered sugar bowl, so a full table set is speculated.
NOTE: Sid Lethbridge 2020 - Basis: Several moulds including those for the tumbler and sugar shaker are identical to those used for Ribbed Coinspot.