Cardiff Blues pair James and Turnbull last played for Wales in 2010 and 2014 respectively, though James was part of Wales' 2015 Rugby World Cup training squad before withdrawing through injury.
The experienced squad includes 31 players who featured for Wales in the 2015 Rugby World Cup and will be led by Wales' most experienced captain Sam Warburton.
The front-row contingent is made up of props Gethin Jenkins, Paul James and Rob Evans, along with Samson Lee, Tomas Francis and Aaron Jarvis.
Scott Baldwin, Ken Owens and Kristian Dacey are named as the hookers.
Alun Wyn Jones, who today it was announced signed a new long-term National Dual Contract, is named along with Luke Charteris, Dominic Day, Bradley Davies, Jake Ball and Josh Turnbull.
Four British and Irish Lions are named in the back-row, captain Sam Warburton, Dan Lydiate, Justin Tipuric and Taulupe Faletau. They are joined by James King and Ross Moriarty.
Uncapped scrum half Aled Davies is joined by regional team-mate Gareth Davies and Lloyd Williams. Dan Biggar and Rhys Priestland are named as the fly-halves. Jonathan Davies, who missed the RWC through injury, returns alongside Jamie Roberts, Cory Allen and Tyler Morgan in the centres. The back three players include Tom James, Hallam Amos, George North, Alex Cuthbert, Gareth Anscombe, Matthew Morgan and Liam Williams.
"We have selected a squad that rewards players form as well as picking a lot of experience and that continuity is important to us," said Gatland.
"We have picked a larger squad than normal, we have a few injuries at the moment, those players aren't too far away from getting back on the field so we are happy with the mix.
"Aled (Davies) is someone who has been on the radar the last couple of years and his selection is reward for his form.
"Tom (James) is playing very well for the Blues and we have been impressed with Josh's (Turnbull) performances recently.
"It is always exciting when the Six Nations comes around and we are looking forward to meeting up next Monday."
Wales kick off their 2016 campaign away to reigning champions Ireland on Sunday February 7th before welcoming Scotland to Principality Stadium on Saturday February 13th.
WALES' 2016 RBS 6 NATIONS SQUAD: (37 Players)
Forwards:
Rob Evans (Scarlets), Paul James (Ospreys), Gethin Jenkins (Cardiff Blues), Tomas Francis (Exeter Chiefs), Aaron Jarvis (Ospreys), Samson Lee (Scarlets), Scott Baldwin (Ospreys), Kristian Dacey (Cardiff Blues), Ken Owens (Scarlets), Jake Ball (Scarlets), Luke Charteris (Racing 92), Bradley Davies (Wasps), Dominic Day (Bath Rugby), Alun Wyn Jones (Ospreys), Josh Turnbull (Cardiff Blues), Taulupe Faletau (Newport Gwent Dragons), James King (Ospreys), Dan Lydiate (Ospreys), Ross Moriarty (Gloucester Rugby), Justin Tipuric (Ospreys), Sam Warburton (CAPT) (Cardiff Blues).
Backs:
Aled Davies (Scarlets) *, Gareth Davies (Scarlets), Lloyd Williams (Cardiff Blues) Dan Biggar (Ospreys), Rhys Priestland (Bath Rugby), Cory Allen (Cardiff Blues), Jonathan Davies (Clermont Auvergne), Tyler Morgan (Newport Gwent Dragons), Jamie Roberts (Harlequins), Hallam Amos (Newport Gwent Dragons), Alex Cuthbert (Cardiff Blues), Tom James (Cardiff Blues), George North (Northampton Saints), Gareth Anscombe (Cardiff Blues), Matthew Morgan (Bristol Rugby), Liam Williams (Scarlets).
* Denotes uncapped player
