Nigel suggested that I contact Linda and Stuart Smithson - and now had couple of phone conversations with them (was hoping they might email back, but not received yet). Their conclusions regarding my bowl agree with John's view that - despite looking unlike the one in the book - this can only be FT242, in view of the size. I understand that the original drawing for FT242 does in fact show a design with more elongated 'fingers' than the image shown in the book, although I don't know whether in practise pieces are more spikey like mine, or whether in general they look nearer to the book example. I look forward to finding my next piece of 242, for comparison.
So, sincere thanks to all for straightening me out, and special thanks to Linda and Stuart Smithson for their time and trouble.
Might be interesting to see pix of a range of these centrifuge pieces, in order to guage the extent of variation.
NOTE: Request to Mods..............grateful if the subject heading is amended to now read........"Variation in Dartington Centrifuge Design".