Please help ID this plant

Please could anyone ID this plant, I believe a Coryphantha, purchased unnamed from a garden centre this spring. It has not been growing, although roots appear healthy.

Sorry, a beginner at navigating this image hosting system. It has come out in triplicate, although not a Trichocereus.

I think it is a Coryphantha, but which I do not know.

Today I received a suggestion that this might be Coryphantha cornifera "radians". It has the nickname "rhinocereus cactus", that fits very well with its central spines.

C. cornifera was my thought as well, either that or C. pallida. I find identification very difficult, although I have the Dicht and Luthy book. Interestingly, I have seen C. cornifera in habitat and it can be found growing with no central spines at all. A very confusing genus!
I also removed the triple entries, just to save space.