I have found out that there are basically three different cases for the Omega Memomatic wristalarm. The Omega Memomatic uses a caliber 980 movement which is Lemania based. The designer of this watch is the man in the photo below:
(Source: I do not recall where I got this picture from, it has been on my laptop for a while. If you are the owner of the copyright, please let me know)
Here you see examples of the cushion cases of the Memomatic:
Some call this case the “pilot case”:
And this is a goldplated model, as you can see, this is the third kind of cushion case: