Mike Wilks's 1935 Standard 10 features an arrangement called Tri-comfy seating. This was an optional fitment to the Standard 10/12/16/20 range during the 1934/5 season, but this is the first surviving example that your webmaster has seen

briefly speaking there is a large armrest in the centre of the rear seat that moves forward, along with the seat itself to create a third seat "in the centre" of the car.

Quite frankly, as Mike admits, in the 10 the arrangement is so small that he can hardly see any benefit, but when re-trimming his car he has preserved the mechanism, so we can all see it today. 

My guess is that the arrangement would have been somewhat more useful in the 16 or 20 models which had a wider seat and it is that model that is illustrated in the advertising literature that I have also shown below.

The three stage process that is required to convert from the "conventional" configuration to the "Tricomfy" arrangement is excellently illustrated by my photos below: