A further group of 12 sweep (single oar) rowers have been named to form the men's eight, pair and two reserves.
Pete Reed and Andrew Triggs Hodge, who won gold medals at Beijing 2008 and London 2012, have been named in the group.
Katherine Copeland, who won the women's double scull with Sophie Hosking four years ago, will seek to defend her title with Charlotte Taylor.
British Rowing performance director Sir David Tanner said: "We did some testing at the beginning of this week to see whether or not the double of Katherine Grainger and Vicky Thornley could, at their request, make a slot for themselves in the women's eight. That was not to be.
"It's my confident intention to announce very soon those two back in their double and racing for Team GB at the Olympic Games."
