Number eight Taulupe Faletau, winger George North and flyhalf Rhys Priestland were selected despite being injured while flanker Ross Moriarty has also been called up after returning from a lengthy injury layoff this month.
"James's form over the last couple of years has been impressive, he's in a competitive area but we look forward to seeing what he can do," Gatland said. "For Josh it's a great opportunity, he's been on great form...
"We have included a couple of players who are carrying injuries... It's useful to have these experienced guys around camp and to have them included and to work with them.
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Alun Wyn Jones will captain the side but veterans Luke Charteris, Gethin Jenkins and Jamie Roberts missed out along with injured back-row forwards Sam Warburton and Dan Lydiate.
Wales won two of their four November internationals against Georgia and South Africa, losing to New Zealand and Australia.
Gatland's side face Scotland in their opening Six Nations campaign in Cardiff on Feb. 3.
Squad:
Backs
Aled Davies (Scarlets), Gareth Davies (Scarlets), Rhys Webb (Ospreys), Gareth Anscombe (Cardiff Blues), Dan Biggar (Ospreys), Rhys Patchell (Scarlets), Rhys Priestland (Bath),
Hadleigh Parkes (Scarlets), Owen Watkin (Ospreys), Owen Williams (Gloucester), Scott Williams (Scarlets), Josh Adams (Worcester Warriors), Hallam Amos (Dragons), Alex Cuthbert (Cardiff Blues),
Steff Evans (Scarlets), Leigh Halfpenny (Scarlets), George North (Northampton Saints), Liam Williams (Saracens)
Forwards
Rob Evans (Scarlets), Wyn Jones (Scarlets), Nicky Smith (Ospreys), Scott Baldwin (Ospreys), Elliot Dee (Dragons), Ken Owens (Scarlets), Tomas Francis (Exeter Chiefs), Samson Lee (Scarlets), Dillon Lewis (Cardiff Blues), Adam Beard (Ospreys), Bradley Davies (Ospreys), Seb Davies (Cardiff Blues, Cory Hill (Dragons), Alun Wyn Jones (captain, Ospreys), James Davies (Scarlets), Taulupe Faletau (Bath), Ellis Jenkins (Cardiff Blues), Ross Moriarty (Gloucester), Josh Navidi (Cardiff Blues), Aaron Shingler (Scarlets), Justin Tipuric (Ospreys)
(Reporting by Aditi Prakash in Bengaluru, editing by Ed Osmond)
