Thank you for the suggestion regarding them being for grapefruit. It felt like the plate part at the bottom would have a purpose of it's own. And now I feel a little foolish as I just searched on Whitefriars.org and sure enough, there it is, pattern number M94, in the 1957 catalogue (and 1964, 1966) described as Sundae Ribbed d4.1/8" 1960 Grapefruit. I blame being a mother of two young children for the lack of brain cells! Thank you John, for helping me to arrive at the obvious!