Something along
these lines. Not the same model or brand. I can't find any labels on mine so I don't know who actually made it. The reviews mention how surprisingly stable the mouse pad is, which is true of mine as well. It's just hanging on there at the end, but I can rest the weight of my arm on my wrist while using the mouse no problem. It's a little different, it's a bit below the keyboard bit and it rotates back and forth, which I've grown accustomed to over the years.
Edit: actually it's almost exactly
this model, except black and with a slightly different shape to the back of the keyboard tray.