A standard 155, no lock, is what it looked like in the picture. I thought the "CO" was something different. Bear & Son's Cutlery's web site doesn't list the 155CO anymore, just the "L" in the 155. Evidently they don't make the "CO" now. That is pretty much what I was thinking, I will have one 155 with a lock and one without.
The 156 is the Super Bear Jaws, 4.5". They only seem to be making it in the "L" version too.