dux 'manta ray' chair? reupholstery?  

Latex foam is the one that hardens with age and crumbles to a fine, annoying dust.  And yes, that's what chairs like this have in them.  It's great for a few decades, then it deteriorates.  It has more reslilience than urethane foam but costs 3 or 4 times as much, unfortunately.
It can definitely be reupholstered.  It's different than conventional upholstery in that there's a lot more gluing involved and you have to be very careful to stretch the fabric over the frame just so or you'll end up with ripples and creases where you don't want them.  There might also be a fair amount of hand stitching unless they used some kind of tacking that I don't know about---it has a foam frame (probably styrofoam, maybe with a layer of fiberglass over it, maybe not) and you can't use conventional staples in it because they just come right back out.  I've seen very long staples, sometimes even nails.  I just do the Danish style ladder stitch by hand.  It's easier, in my opinion.
Fabric--Maharam/Kvadrat vintage wools like Hallingdale or Tonus would be great.  You need something with give to it to go around the compound curves.  You also need something that spray adhesive will NOT bleed through!  So thinner fabrics are out.  Kvadrat "Outback" has a lot of give but i'm pretty sure the adhesive would soak right through it.  There are other fabrics from other manufacturers similar to those two.  You can order swatches from a lot of places for free or for a nominal charge.
Oh, and the latex foam may be dry on the surface but there will be big areas that are still rubbery that will need to be scraped off the styrofoam shell.  This is messy, tedious work.  

Just got a latex mattress topper from foambymail and it was only a ew dollars more than custom cut squares and I got ten times more foam.  It is still expensive though. 

Yeah, I got a latex topper a few years ago but I wasn't happy with the quality.  It has a lot of air in it.  I'm sure that varies a lot by manufacturer though.  
I also don't like the holes.  They show through when the fabric is glued to directly to the foam, and if you glue batting to the foam to bridge the holes and then glue fabric to the batting, the fabric can delaminate (for lack of a better word) the fibers of the batting and it ends up being like it wasn't glued down at all.
Back in the old days the latex foam had holes in it because that's how they control the density---but one side was always solid.  Now that is usually not the case, maybe never the case, I don't know.  

Interesting. Parts of the topper I got don't have holes all the way through. The original Papa Bear cushion had enormous holes in the latex foam that went all the way through, and I've never seen show-through on one of them. Of course the fabric isn't stretched much on the cushion. 

Spanky, as usual your reponse was so thorough in helping the naive and uninformed (me) to understand the mysteries of the bones beneath and the way the skin of these pieces must be set.
 I also really appreciate the fabric recommendations as well...it seems that some of these chairs need such particular fabrics with specific characteristics and hand ....thank you for sharing your time and expertise.
It sounds like not an easy renewal so I would first like to try to discover more about the chair.  Anyone recognize this chair or have any comment regarding the dux 'manta ray' attribution?thanks

I believe it is the high-back version of the manta ray. And I imagine if you look long enough you can find a marked specimen.  You might need to find a Dux catalog to find the designer. And given the scarcity I would not be surprised to discover you need to have a catalog from a narrow year range. 

hmmm, OK, thanks for the comments and opinion Leif.  Let the search begin.....

It was designed by Björn Engö for Möre Stolfabrik in Norway.  

Leif,
I have been away from the forum for a short time. I just wanted to thank you for looking for and publishing a reference on this inquiry.