LOL bill not a clue I thought it was the same shape as CC variant in red cloissone on ysart glass , though it may be shape F it certainly isn't the the same shape as the coloured shape F but if you click on the shape f in Scotland glass there is a black and white photograph from the monart catalogue that looks similar, god knows ,

, pic below of surface decorated CC and black n white pic F from Ysartglass.com